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An analytic investigation of the steam blocking in low pressure heating channels was conducted. In this paper, the dynamic model of the vapor-liquid interface is established through the basic conservation equations, and the rupture time of the vapor-liquid interface is predicted based on the Rayleigh-Taylor instability. Subsequently, the steam blocking model considering the steam accumulation and the vapor-liquid interface rupture in geysering flow is established. On these bases, the relative volume and relative pressure of the accumulated steam, the relative acceleration and perturbation intensity of the vapor-liquid interface, the time-varying behavior of the ratio of resistance and buoyancy are obtained. It is found that the accumulated steam basically increases linearly with the time going; The oscillation of the pressure and velocity, which is very large at the beginning time of the steam accumulation, decreases gradually with the continuous steam accumulation; The Reynolds number of the liquid within the rising section is very small at the stagnation state since there is no forced circulation flow, and finally a blockage is engendered in the pipeline with the steam accumulated. The theoretical results are in good agreements with the results obtained by a small-scale experiment. The mechanism model is able to predict the steam blocking property during the geysering flow in heating channels well, and can also establish a theoretical basis for the later analysis of the steam blocking elimination.Copyright © 2013 by ASME

This paper provides an extension of the previously described [1] formulation of a one-dimensional model for steady, compressible flow inside a channel, to the steam turbine application. The major challenge faced in the network simulation of the steam turbine secondary system is the prediction of the condensation that occurs during the engine start-up on the cold parts that are below the saturation temperature. Neglecting condensation effects may result in large errors in the engine temperatures since they are calculated based on the boundary conditions (heat transfer coefficient and bulk temperature) which depend on the solution of the network analysis. This paper provides a detailed formulation of a one-dimensional model for steady, compressible flow inside a channel which is based on the solution of two equations for a coupled system of mass, momentum and energy equations with wall condensation. The model also accounts for channel area variation, inclination with respect to the engine axis, rotation, wall friction and external heating. The formulation was first validated against existing 1D correlation for an idealized case. The wall condensation is modeled using the best-suited film condensation models for pressure and heat transfer coefficient available in the literature and has been validated against the experimental data with satisfactory predictions.

In Lurgi-Thyssen dedusting system of steelmaking converter, the evaporative cooler represents a crucial operating unit, in which the hot dust-laden flue gas has to be cooled by saturation with water. The cooling process of the gas consists of gas-liquid two phase flow and interphase heat and mass transfer. In this paper, k-epsilon standard equations and Lagrange discrete phase model are employed to describe the gas turbulent flow and the heat/mass transfer with droplet evaporation individually. The computational fluid dynamics (CFD) simulation for practical engineering project shows that the large-flux cooling gas is commonly constructed in a non-uniform flow caused by the sharp turnings at the inlet and outlet channels. The unevenness of velocity distribution and the effective cooling height are defined in this paper to evaluate the cooling flow process. A series of newly designed structures with guide plate are investigated by CFD method to eliminate the problems with the non-uniformity. The results of numerical simulation show that optimal designed guide ring plate could improve the flow uniformity and the heat transfer. The investigations have been used to guide the engineering application.Copyright © 2013 by ASME

A method for calculating the stress intensity factor for linear elastic fracture mechanics based flaw evaluation is provided in Appendix A-3000 of ASME Section XI. In the 2010 Edition of ASME Section XI, the calculation of stress intensity factor for a surface crack is based on characterization of stress field with a cubic equation and use of influence coefficients. The influence coefficients are currently only provided for flat plate geometry in tabular format. The ASME Section XI Working Group on Flaw Evaluation is in the process of rewriting Appendix A-3000. Proposed major updates include the implementation of explicit use of Universal Weight Function Method for calculation of the stress intensity factor for a surface flaw and the inclusion of closed-form influence coefficients for cylinder geometry. The explicit use of weight function method eliminates the need for fitting polynomial equations to the actual through-thickness stress distributions at crack location. In this paper, the proposed Appendix A procedure is applied to calculate the stress intensity factors in closed-form for an axial ID surface flaw in a cylinder subjected to a set of nonlinear hoop weld residual stress profiles. The calculated stress intensity factor results are compared with the results calculated based on the current method in Appendix A using cubic equations to represent the stress distribution. Three-dimensional finite element analyses were performed to verify the accuracy of the stress intensity factor results calculated based on the current and proposed Appendix A procedures. The results in this paper support the implementation of the proposed stress intensity factor calculation procedure into ASME Code.Copyright © 2013 by ASME

The dynamic stability of a flexible plate subjected to a parallel flow is investigated when it moves in a flowing fluid. As the flexible flat plates, the papers in a high speed printing machine, the papers discharged by a paper machine, and the thin plastic and metal films, the fluttering flag and the oscillating doom roof caused by wind are enumerated. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. The fluid-structure coupled equation of motion of a flexible flat plate supported simply at the both ends is derived into consideration with the added mass, added damping and added stiffness of a fluid, respectively. In addition, the effect of tension acting on a flexible plate, the influence of velocity of a moving plate and that of a fluid velocity, are also included into the coupled equation of motion respectively. The eigenvalue analysis is performed for the dynamic stability analysis. Changing the velocities of a plate and a fluid, and the specifications of a plate as parameter studies, the influences of these parameters on the dynamic stability of a plate are clarified. It is made clear that the plate moving in a still fluid becomes unstable at slightly lower velocity than the stationary plate subjected to a parallel flow. Moreover, it is found that the present solution shows a good agreement with the already reported experiments in which the flexible flat plate was a paper.Copyright © 2013 by ASME

The previous paper ASME PVP2012[1] reported application of Gurson model to the fracture test results using pipe models with part-through wall cracks on the dissimilar metal (DM) welds. The predicted maximum loads and the crack behaviors after penetration did not agree well. These results may originate from improper parameter values of Gurson model. This paper revised these parameters and improved the estimated fracture behaviors of the pipe models. A suitable fitting process of Gurson parameters was also proposed.Copyright © 2013 by ASME

Within the highly competitive electricity market, companies often reduce costs by using aging equipment and by overloading their transformers. These conditions substantially increase the risk of transformer explosions. These incidents are caused by electrical arcs occurring within oil filled transformers. The arc, within milliseconds, vaporizes the surrounding oil and the generated gas is pressurized because the liquid inertia prevents its expansion. The pressure difference between the gas bubble and the surrounding liquid oil generates a dynamic pressure peak, which interacts with the transformer. The reflections generate pressure waves that lead to transformer rupture since transformers are not designed to withstand these pressures. This results in dangerous explosions, expensive damages and possible environmental pollution. Despite all these risks, and contrary to usual pressure vessels, no specific standard has been set to protect sealed transformer tanks subjected to large dynamic overpressures. In order to study transformer rupture and its prevention, experiments have been performed on transformers. However, safely carrying out live tests is difficult and expensive. In order to limit the costs, to reduce the risks and to gain insight on these phenomena numerical simulation tools are necessary. First a computational fluid dynamics solver was developed; it is based on an unsteady compressible two-phase flow model, the equations parameterizing the system are solved using a 3D finite volume method. Previous papers showed the ability of the hydrodynamic tool to study in detail (1) dynamic pressure wave propagation inside transformer oil that leads to transformer rupture and (2) depressurization induced by efficient protection means. Later, the hydrodynamic numerical tool has been one-way coupled with Code_ASTER, a dynamic structural analysis package, to create a fluid structure interaction (FSI). Preliminary results were shown and this strategy has been applied to the study of more complex electrical equipment. The present paper’s goal is to illustrate the development and application of a two-way coupling for the aforementioned fluid structure interaction strategy. The methodology for the enhanced coupling is explained and the simulation results about the structural behavior caused by these dynamic pressures are presented.

When containment vessels are subjected to internal blast loading, not only the breathing mode, but also the other vibration modes may be excited. Therefore, it is very important to understand the vibration modes in spherical containment vessels. In this paper, we present experimental results of modal analysis of a spherical containment vessel, in which the mode frequency and mode shapes are given. We also conduct the frequency analysis on dynamic responses of the spherical containment vessel subjected to three different blast loadings, in which the vibration modes excited in the dynamic vibration are found. The current study may provide further understanding on dynamic responses of containment vessels.Copyright © 2013 by ASME

This paper addresses a practical problem: “Under which coverage of buoyancy modules, would the Vortex Induced Vibration (VIV) excitation on buoyant segments dominate the response?” This paper explores the excitation competition between bare and buoyant segments of a 38 meter long model riser. The source of data is a recent model test, conducted by SHELL Exploration and Production at the MARINTEK Ocean Basin in Trondheim Norway. A pipe model with five buoyancy configurations was tested. The results of these tests show that (1) the excitation on the bare and buoyant regions could be identified by frequency, because the bare and buoyant regions are associated with two different frequencies due to the different diameters; (2) a new phenomenon was observed; A third frequency in the spectrum is found not to be a multiple of the frequency associated with either bare or buoyancy regions, but the sum of the frequency associated with bare region and twice of the frequency associated with buoyancy region; (3) the contribution of the response at this third frequency to the total amplitude is small; (4) the power dissipated by damping at each excitation frequency is the metric used to determine the winner of excitation competition. For most buoyancy configurations, the excitation on buoyancy regions dominates the VIV response; (5) a formula is proposed to predict the winner of the excitation competition between bare and buoyant segments for a given buoyancy coverage.

In this paper the computational problem examined is the impulsive start of a two-dimensional flat-plate hydrofoil at a fixed angle of attack. The method applied is an equally-spaced lumped-vortex panel method. The results from a lumped-vortex wake model and a shed-vortex sheet wake model are reported. Comparisons with the linear theory of Wagner (1925), the theoretical results associated with the single lumped-vortex wake model and the full wake model are presented. In addition, it is shown that the computational predictions are consistent with results reported by Katz and Plotkin (2001); they applied a distribution of vortices to model the wake. In the present paper the importance of resolving the chordwise pressure distribution in unsteady hydrofoil problems is elucidated. New predictions of both the evolution of lift and induced drag are reported for the instantaneously started flat plate. The computational predictions are compared with theorecticalpredictions also discussed in this paper.Copyright © 2013 by ASME

This paper presents model-scale measurements and numerical models of a floating oscillating water column (OWC) system, consisting of an air cavity coupled with a Wells-type turbine energy extraction device. As waves travel through the OWC, air pressure cycles are generated. The oscillating water column captures the resulting pneumatic energy by directing the chamber pressure and air flow through the Wells turbine. A special feature of the system is a shuttering device that momentarily interrupts turbine air flow. The shuttering device is used to control the cavity pressure for optimum turbine performance. Shuttering in this manner can be shown to improve overall system efficiency up to 20% pressure. Physical scale models of the OWC system were tested in a wave tank at Maine Maritime Academy (MMA) at 1/30th scale as well as elastomeric diaphragm testing at 1/15th scale, under various conditions. Data from these tests, including cavity pressure response, turbine flow rate, and computed fluid power are discussed. In addition, numerical models of the system were developed using a parametric spring-mass-dashpot methodology and as well as a potential flow model derived for cavity geometry in a global wave field (see section 3). This paper describes the OWC system with adaptive shutter; comparison of experimental measurements to numerical model predictions; numerical model implementation and measurements of energy absorption/resonant effects within the chamber; and a potential flow derivation.

This paper describes a method in order to improve the performance of the primary conversion of wave power take-off. A corresponding wave energy convertor (WEC) is an oscillating water column (OWC) type. The method of the improvement has been proposed and its usefulness has been confirmed in past researches. In the method, projecting walls were attached onto front of inlet-outlet of OWC. The prediction method of hydrodynamic behaviors for the projecting walls installed OWC type WEC is explained in the paper. The boundary element method with the Green’s function is applied and influence of air pressure and free surface within every an air-chamber was directly taken into consideration in the prediction method based on a linear potential theory. Validity of the prediction method was proved comparing with results of model experiments. Series calculations are performed with the prediction method. Behaviors of air pressure, water elevation and the efficiency of primary conversion of wave power are investigated. From the calculations, length of the projecting walls was shown to affect the efficiency of primary conversion. It was available to equip the projecting walls for the improvement in oblique waves to beam sea condition as well as head sea condition. As well as only the projecting walls, application and effects of the end walls with the slit were investigated in the paper. The end walls were very useful to improve the efficiency.

This paper presents some predictions of ice ridge loads on a vertical cylinder, based on model experiments, analytical methods, and numerical simulations. The experiment program involved the interaction of a vertical cylinder with two unconsolidated ice ridges. Each ridge was nominally 1.9 m wide with a keel 0.5 m deep. The nominal scale used for the experiment was 1:30. The analytical methods included Dolgopolov, Mellor, Croasdale & Cammaert, and ISO19906. The numerical simulations were carried out using a discrete element computer code, named DECICE. The paper compared the results of model experiments, analytical methods and numerical simulations.Copyright © 2013 by ASME

This paper numerically investigates the transitional flow on a LPT (low pressure turbine) blade with fluctuating downstream potential field. A linear T106 cascade is subjected to an oscillating potential field generated by downstream moving bars. Previous experimental results in open literature showed that the unsteady downstream potential field has an obvious influence on the transitional boundary layer of LPT blade. For the numerical simulations in this paper, the unsteady Reynolds-Averaged Navier-Stokes equations are solved using the commercial software FLUENT. The transition model used in this paper is the γ-Reθ model, which has been validated against a number of transitional flows previously, including the influence of upstream wakes on the transitional boundary layer of T106 turbine blade. The simulation results are first compared to the experimental results in open literature to validate the numerical methods. Two different FSTI (free stream turbulence intensity), 1.6% and 4.0% are investigated with axial spacing between the blade and the downstream bar varying from 50% axial chord to 25% axial chord. To investigate the influence of flow compressibility, two different inlet Mach numbers, 0.02 and 0.2 are simulated. Results show that decreasing the axial spacing has an influence on the unsteady boundary layer separation and transition and the influence is enhanced at elevated inlet Mach number.Copyright © 2013 by ASME

This paper numerically investigates the aerodynamics and film cooling effectiveness of high pressure turbine blade tips. Two different rotor blade tip configurations have been studied: the plane tip with tip hole cooling and the squealer tip with tip hole cooling. The geometry of the blades is determined based on the blade profiles within the three-stage multi-purpose turbine research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. Seven perpendicular holes along the camber line are used for the tip hole cooling. The clearance between the blade tip and casing is 1.0% of the blade span. For each blade tip configuration, the coolant is ejected through the cooling holes under blowing ratios of M = 0.5, 1.0 and 1.5. In this paper, a comparison between the plane tip and the squealer tip has been presented. The detailed flow structures and film cooling effectiveness are discussed.

Effusion cooling technology has been assessed in past years as one of the most efficient methods to maintain allowable working temperature of combustor liners. Despite many efforts reported in literature to characterize the cooling performances of those devices, detailed analysis of the mixing process between coolant and hot gas are difficult to perform especially in case superposition and density ratio effects become important. Furthermore, recent investigations on the acoustic properties of these perforations pointed out the challenge to maintain optimal cooling performance also with orthogonal holes which showed higher sound absorption. This paper performs a CFD analysis of the flow and thermal field associated with adiabatic wall conditions to compute the cooling effectiveness. The geometry consists of an effusion cooling plate drilled with 18 holes and fed separately with a cold and hot gas flow. Two types of perforations equivalent in porosity and pitches are investigated to assess the influence of the drilling angle between 30 and 90 deg. The reference conditions considered in this work comprehend an effective blowing ratio ranging between 1 and 3 at isothermal conditions (reaching a maximum hole Reynolds number of 10000) and high inlet turbulence intensity (17%). This set of conditions was exploited to perform a validation of the numerical procedure against detailed experimental data presented in another paper. Inlet turbulence effects highlighted by measurements for the slanted perforation were also investigated simulating a low turbulence condition corresponding to 1.6% of intensity. Furthermore the nominal DR = 1.0 was increased up to 1.7 to expand the available data set towards typical working conditions for aero-engines. Steady state RANS calculations were performed with the commercial code ANSYS® CFX, modeling turbulence by means of the k — ω SST. In order to include anisotropic diffusion effects due to turbulence damping in the near wall region, the turbulence model is corrected considering a tensorial definition of the eddy viscosity with an algebraic correction to dope its stream-span components. Computational grids were finely clustered close to the main plate and inside the holes to obtain y+ < 1, to maximize solver accuracy according to previous similar analysis.

In this paper, detailed experimental results of total pressure loss and secondary flow field are presented for a high turning (127°) airfoil passage in presence of an upstream purge slot (with and without coolant injection). The experiments were performed at Virginia Tech’s quasi 2D linear turbine cascade operating at transonic conditions. Measurements were made at design exit Mach number 0.88 and design incidence angle. The selected coolant to mainstream mass flow ratio (MFR) was set at 1.0%. In order to match engine representative inlet/exit blade loading, a diverging endwall was utilized where the span increased from the inlet to the exit at a 13 degree angle. A 5-hole probe traverse was used to measure exit total pressure. Pressure loss coefficients were calculated both along pitchwise and spanwise directions at 0.1 axial chord downstream of the blade trailing edge. CFD studies were conducted to compliment the experimental results. The backward facing step present with the upstream slot affects the approaching boundary layer and influences the passage horse-shoe vortex strength. The addition of coolant from the purge slot further increased the aerodynamic losses. However, the backward facing step of the upstream slot seems to be the predominant factor in affecting pressure losses when compared to with or without blowing cases. These results provide further understanding of the passage secondary flow characteristics and aid towards improved design of endwall passages. The heat transfer experiments, designed to find the heat transfer coefficient and the film cooling effectiveness are described in detail in part II of this paper [1].Copyright © 2013 by Siemens Energy, Inc.

Improvement of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount in internal cooling channels with enhanced convective cooling. Nowadays the state of the art internal cooling technology for thermally high-loaded gas turbine blades consists of multiple serpentine-shaped cooling channels with angled ribs. Besides, huge effort is put on the development of more advanced internal cooling configurations with further internal heat transfer enhancements. Swirl chamber flow configurations, in which air is flowing through a pipe with a swirling motion generated by tangential jet inlet, have a potential for application as such advanced technology. This paper presents the validation of numerical results for a standard swirl chamber, which has been investigated experimentally in a reference publication. The numerical results obtained with application of the SST k-ω model show the best agreement with the experiment data in compare with other turbulence models. It has been found at the inlet region that the augmentation of the heat transfer is nearly seven times larger than the fully developed non-swirl flow. Within the further numerical study, another cooling configuration named Double Swirl Chambers (DSC) has been obtained and investigated. The numerical results are compared to the reference case. With the same boundary conditions and Reynolds number, the heat transfer coefficients are higher for the DSC configuration than for the reference configuration. In particular at the inlet region, the DSC configuration has even higher circumferentially averaged heat transfer enhancement in one section by approximately 41%. The globally-averaged heat transfer enhancement in DSC configuration is 34.5% higher than the value in the reference SC configuration. This paper presents the configuration of the DSC as an alternative internal cooling technology and explains its major physical phenomena, which are the reasons for the improvement of internal heat transfer.Copyright © 2013 by ASME

The experimental investigation of the unsteady flow field in a highly loaded single stage low pressure axial compressor, also called a booster, is presented in this paper. The compressor design is representative of an advanced direct drive turbofan booster. Tests were performed on different speed lines at choke, design, and near stall, in the VKI-R4 closed loop compressor test rig. The rotor casing was instrumented with fast response pressure transducers to perform a detailed survey of the tip flow features. Simultaneous time-resolved measurements with fast response aerodynamic pressure probes were performed by radial and circumferential traverses to map the unsteady flow field at rotor and stator exit. The originality of this paper also resides in the fact that unsteady flow angle data are presented as the probe was used in a virtual 3-hole mode. The casing measurements allow to map the direction and extension of the tip leakage vortex. The flow path measurements show its extension at the exit of the rotor blade passage and its evolution as throttling is increased towards the compressor stability limit. The results are presented in terms of periodic and random fluctuations. These experimental results are combined to provide a three-dimensional view of the experimental flow field. They are discussed and compared to CFD simulations, showing that, in some regions, important features are not captured by the numerical model. In particular, the presence of a second wake has been observed in the unsteady yaw angle map at rotor exit. This uncommon feature is currently under further investigation.Copyright © 2013 by ASME

Recent experimental work characterized the performance of a unique cross-flow heat exchanger design for application of cooling compressor bleed air using liquid jet fuel before it is consumed in the gas turbine combustor. The proposed design has micro-channels for liquid fuel and cools air flowing in passages created using rows of intermittent fins. The design appears well suited for aircraft applications because it is compact and light-weight. A theoretical model is reported to be in good agreement with experimental measurements using air and water, thus providing a design tool to evaluate variations in the heat exchanger dimensions. This paper presents an evaluation of the heat exchanger performance with consideration of uncertainties in both model parameters and predicted results. The evaluation of the design is proposed to be reproduced by students in a thermal-fluids design class. The heat exchanger performance is reevaluated using the effectiveness–NTU approach and shown to be consistent with the method reported in the original papers. Results show that the effectiveness is low and in the range of 20 to 30% as well as the NTU which ranges from 0.25 to 0.50 when the heat capacity ratio is near unity. The thermal resistance is dominated by the hot gas convective resistance. The uncertainties attributed to fluid properties, physical dimensions, gas pressure, and cold fluid flow rate are less significant when compared to uncertainties associated with hot fluid flow rate, hot fluid inlet temperature, cold fluid inlet temperature, and convective correlation for gas over a finned surface. The model shows which heat transfer mechanisms are most important in the performance of the heat exchanger.

The effect of blade row interaction and hub leakage flow on the performance of moderately loaded NASA transonic hybrid compressor stage (Rotor 35 / Stator 37) is investigated through three-dimensional steady state and time-accurate, Navier Stokes calculations of the stage using the ANSYS CFX code at peak efficiency and near stall operating conditions. Understanding unsteady flow phenomena in compressor stages requires the use of time-accurate CFD simulations. Due to the inherent differences in blade counts between adjacent blade rows, the flow conditions at any given instant in adjacent blade rows differ. Depending on the blade counts, it may be necessary to model the entire annulus of the stage; however, this requires considerable computational time and memory resources. Several methods for modeling the transient flow in turbo machinery stages which require a minimal number of blade passages per row, and therefore reduced computational demands, have been presented in the literature. Recently, some of these methods have become available in commercial CFD solvers. The paper describes the steady and the unsteady CFD approaches used for investigating the ability to predict the measured performance of the NASA transonic axial stage design known as the hybrid stage, which consists of the axial Rotor35 and the axial stator 37. The steady approach employs the mixing-plane while the unsteady approaches are URANS with one based on full annulus simulation for the stage and the second enables simulations for the stage using reduced computational model, with a single passage from each blade row based on the time-tilting or the time-transformation technique. The above methods are evaluated and compared in terms of computational efficiency and comparison is made to steady stage simulations. Comparisons to overall performance data and two-dimensional Laser Doppler Velocimeter measurements of the velocity field are used to assess the predictive capabilities of the methods. Computed flow features are examined, and compared with reported measurements. This paper presents validation and calibration of methods used for determining blade row interactions and the respective predictive capabilities against the full annulus and the experimental test data.

The accident scenario resulting from blockages due to the retention of dust in the coolant gas or from the rupture of one or more fuel particles used in the High Temperature Gas Cooled (Pebble Bed) Nuclear Reactors considered for the next generation of Advanced High Temperature Reactors (AHTR), for nuclear power production, and for high-temperature hydrogen production using nuclear reactors to reduce the carbon footprint is examined in this paper. Blockages can cause local variations in flow and heat transfer that may lead to hot spots within the bed that could compromise reactor safety. Therefore, it is important to know the void fraction distribution and the interstitial velocity field in the packed bed. The blockage for this numerical study simulated a region with significantly lower void than that in the rest of the bed. Finite difference technique solved the simplified continuity, momentum, and energy equations. Any meaningful outcome of the solution depended largely upon the validity of the boundary conditions. Among them, the inlet and outlet velocity profiles required special attention. Thus, a close approximation to these profiles obtained from an experimental set-up established the boundary conditions. This paper presents the development of the elliptic-partial differential equation for a bed of pebbles, and the solution procedure. The paper also discusses velocity and temperature profiles obtained from both numerical and experimental setup, with and without effect of blockage. In addition, the paper compares the results obtained from the experimental set-up with numerical simulation using a commercially available code that uses finite element techniques.

This paper presents experimental investigations of the Heat Transfer Coefficient (HTC) performance of a Micro-Tangential-Jet (MTJ) Film cooling scheme on a gas turbine vane using transient Thermochromic Liquid Crystal (TLC) technique. In part I of this paper, the film cooling effectiveness performance of the MTJ scheme was presented. The MTJ scheme is a micro-shaped scheme designed so that the secondary jet is supplied parallel to the vane surface. In order to supply the jet in a direction parallel to the vane surface, extra material was added on both pressure and suction sides. The added material is expected to produce more turbulence and hence increase the HTC values. The investigations showed that the increase in the HTC due to the presence of the MTJ scheme is very close to that resulting from the presence of normal traditional shaped schemes on the pressure side. Meanwhile, reduction in the HTC is recorded on the suction side. Such performance is attributed to the small overall height of the scheme which helped keeping the resulting turbulence at minimum. Moreover, the HTC distribution downstream the MTJ scheme is uniform in the lateral directions, which helps minimize the thermal stresses. To judge the overall performance of the MTJ scheme, the Net Heat Flux Reduction (NHFR) parameter is used. The NHFR represents a combination of the effects of both the cooling effectiveness and the HTC. Great enhancement in the NHFR performance of the MTJ was observed compared to traditional shaped schemes. The investigation showed that a blowing ratio close to unity, based on the scheme exit area, could be considered optimal for the MTJ scheme.Copyright © 2012 by ASME

This paper analytically predicts the existence, stability, and changes due to parameter variations on the different oscillations of a bistable piezoelectric generator. Existing work on this type of system has assumed linear piezoelectric behavior and linear damping and has been confined to numerical studies and experimental explorations. This paper improves upon the previous work by incorporating nonlinear dissipation and cubic softening influences in the electroelastic laminates prior to analytical analysis. This analysis provides a framework for theoretical prediction of a variety of empirical observations including potential well escape and optimum impedance loading.Copyright © 2012 by ASME

Severe limitations of the use of three-dimensional computational fluid dynamics codes (CFD) arise when trying to simulate multiphase flow in long pipes due to time constraints. 1D codes for two-phase flow, based on two-fluid models, are fast but are known to be accurate only when the velocities are within the Kelvin-Helmholtz inviscid limit [1]. An alternative is to carry out a two-dimensional CFD simulation of a channel based on the Volume of Fluid (VOF) model. 2D CFD has a wider applicability range compared to 1D, it does not have the issue of ill-posedness and it also has better turbulence models built in. Again compared to 1D the 2D VOF model has a better interface description and wall treatment. In this paper a novel method is introduced that allows swift simulations of pipeline two-phase flow in the stratified and slug flow regime, by approximating the pipe as a channel and with a methodology that solves the problem of the interfacial velocity differences, inherent in the volume of fluid model. An initial validation using the wave growth problem has already been carried out [2]. Here a set consisting of 92 experimental cases in the slug flow regime has been simulated with 2D CFD, and the simulation results showed a good agreement with experimental results. Discussions in the paper include also the question of the range of applicability for 2D CFD, and the advantages and disadvantages compared to 3D CFD and also to 1D code based on the two-fluid model. Shear stresses are then extracted from the 2D CFD simulations and used to recalibrate the friction factors [3] used in the 1D code.Copyright © 2012 by ASME

Current manufacturing technology for large diameter pipe, such as the UOE process, is known to result in pipe with reduced collapse pressure compared to a seamless one of the same steel grade and D/t. It has recently been demonstrated [1,2] that such deficient performance can be alleviated by finishing longitudinally welded pipe by compression. A newly developed cold sizing press, called Impander®, is used to produce pipe with reduced ovality, reduced residual stresses and increased compressive yield strength. The combination of these factors can lead to a significant increase in the collapse pressure of the pipe. The paper will review experimental and analytical results that demonstrate the improved collapse pressure of pipes manufactured by it. This improved performance was confirmed in a full-scale collapse experiment on a pipe finished by impansion of 1.1%. The test showed perfect agreement with the modelling. The collapse pressure was 37% higher than current design codes allow. Additional work has been performed aimed at evaluating the effect of low temperature heat treatment on the collapse pressure. A full-scale collapse test on impanded and heat-treated pipe has shown that a significant additional enhancement in collapse pressure results from the heat treatment. The paper will discuss the thermomechanical causes of these enhancements of the collapse pressure.Copyright © 2012 by ASME

The Eckert number emerges as an important non-dimensional parameter, in addition to the Reynolds number and the Prandtl number, in problems involving heat transfer in compressible flows. The Eckert number is considered to represent a ratio of the flow kinetic energy at the wall and the specific enthalpy difference between the wall and the fluid, and is important when viscous dissipation is significant. This paper investigates the role played by the Eckert number during rapid decompression of high pressure gas pipelines. During such processes, the gas temperature attains very low values corresponding to sonic flow at the vent location, and it is often assumed that the pipeline material is also cooled to a comparable degree (‘Low Temperature Excursions’). This has often led to over-specification of the properties required of the pipeline material. In this paper, it is shown using Computational Fluid Dynamics (CFD) simulations that the highly complex flow during rapid decompression of high-pressure gas pipelines leads to significant frictional dissipation (heating) adjacent to the pipe wall. This prevents the pipeline from attaining excessively low temperatures. It is shown that frictional heating may sometimes lead to a heat transfer reversal. This finding may help pipeline designers in making appropriate recommendations regarding the properties required of the pipeline materials. The paper also describes a preliminary experiment designed carried out to validate the CFD simulations. More detailed experiments are under way.Copyright © 2012 by ASME

This paper is devoted to critically analyse the simulation validity of flow regimes in large rooms and enclosed spaces using commercially available computational fluid dynamics code. This assessment is carried out through detailed comparisons between previous experimental and numerical data as well as present numerical data. Governing equations of mass, momentum, energy and species are solved numerically to predict the air flow patterns and thermal behaviour in rooms and healthcare facilities. The present paper is divided to several sections that review the previous research in open literature and briefly describe the governing equations, boundary and inlet conditions, as well as modelling assumptions. The turbulence characteristics of the flow is represented through the two equation turbulence model that solves the transport equations for the kinetic energy of turbulence k and its dissipation rate ε in full three dimensional domain under steady state conditions. Energy efficiency improvement in air-conditioned buildings applications was found to depend mainly on the design configurations and operating parameters. The room airside design is one of the essential factors that strongly influence the HVAC airflow pattern and consequently the air quality and comfort inside special rooms. After comparing measured and predicted flow regimes in different spaces, a brief summary of conclusions with some recommendations to facilitate the development of optimum energy efficient design are presented.

This paper deals with the numerical bifurcation analysis of the contact loss between a pantograph and an overhead rigid conductor line in a railway current collection system. In the previous study, we modeled this problem as impact oscillations of an intermediate spring-supported beam excited by an oscillating plate. We have already derived the modal interaction relationship equations that describe the velocities immediately after an impact as functions of the velocities before impact for each vibration mode. A numerical calculation using these relationship equations was performed to clarify the impact oscillations with multiple vibration modes. In this paper, we propose a numerical technique based on maps that transform the state of the system at the impact to the subsequent state at the next impact. This numerical method produces stability analyses of the fixed points of the map that describes an impact oscillation with multiple modes. These results can differ surprisingly from the expectations based on a single-mode solution. These results are compared with experiments undertaken in our laboratory, utilizing a thin stainless steel beam. The typical features of impact oscillations, which were theoretically predicted, were confirmed qualitatively.Copyright © 2012 by ASME

For Boiling Water Reactors (BWR) and steam generators, the water level is a safety-relevant process variable. The most commonly applied measuring method is based on the calculation of the liquid level from geodetic pressure differences to a reference column of defined height and density. However, transition processes occurring under operational and accident conditions may lead to dynamic changes in the reference level and therefore to fluctuations in the differential pressure signal. This paper presents experiments and numerical simulations on the steady-state and transient behavior of gas/liquid phase boundaries in “Zero Chamber Level Vessels” (ZCLV). In these slightly inclined miniature tubes, the constant reference level is provided by surface tension forces and the capillary effect, respectively. To investigate the basic topology of gas/liquid interfaces under simplified conditions (environmental parameters, no heat transfer), a test facility with optical access was developed. The construction allows for variations of the inner tube diameter, inclination angle and liquid mass flow rate, respectively. By this means, experiments on phase boundaries were carried out for ethanol/air and water/air. The results provide information about the impact of geometry parameters and their interactions on the interface topology. In addition, the dynamic draining of excess liquid mass at the free end of the tube and at artificial weld seams, which is supposed to be the reason for temperature fluctuations observed in ZCLV during power operation of BWR, was experimentally analyzed. The measurements represent the basis for an experimental validation and optimizations of the numerical flow code ANSYS CFX 12.0. In the next step, water/vapor phase boundaries at 286 °C and 70 bar will be investigated by applying x-ray radiography to a scale model. The results will be discussed in context with the hydrostatic level measurement in BWR.

Many graphite blocks in the core of the HTR-PM serve as the construction material, the neutron reflector and the flow paths of the helium. A small part of helium gas may flow in widely distributed gaps among graphite blocks and enter the hot plenum at low temperature. In our previous paper, a simple flow network combined with CFD simulations of complex flow paths was established to analyze the bypass flow in HTR-PM. In the present paper, the flow network was detailed by assigning more inner nodes and links in the pebble bed. In all kinds of bypass flow paths, only the bypass flow from cold plenum to hot plenum (P-P) was considered. Horizontal flow between the core and the P-P bypass flow path was also added into the flow network in various heights from the top to the bottom. The existence of the horizontal flow enhanced the helium exchange between the core and the bypass flow to different extent in different position, and finally changed the P-P bypass flow ratio. Moreover, gaps in larger sizes had more significant effects on the P-P bypass flows.Copyright © 2012 by ASME

The heat transfer principle of power maximization in power plants with heat transfer irreversibilities was cleverly extended by Bejan [1] to fluid flow, by obtaining that the energy conversion efficiency at maximum power is ηmax = 1/2(1 − P2/P1). This result is analog to the efficiency at maximum power for power plants, ηmax = 1 − (T2/T1)1/2 which was deduced by Curzon and Ahlborn [2]. In this paper, the analysis to obtain maximum power output delivered from a piston between two pressure reservoir across linear flow resistance is generalized by considering the piston cylinder friction, by obtaining relations of maximum power output and optimal speed of the piston in terms of first law efficiency. Expressions to relate the power output, cross sectional area of the chamber and first law efficiency, were deduced in order to evaluate the influence of the overall size constraints and fluid regime in the performance of the piston cylinder system. Flow in circular ducts and developed laminar flow between parallel plates, are considered to demonstrate that when two pressure reservoirs oriented in counterflow, with different and arbitrary cross sectional area, must have the same area in order to maximize the power output of the system. These results introduce some modifications to the results obtained by Bejan [1] and Chen [3]. This paper extends the Bejan and Chen’s work by estimating under turbulent regime the lost available work rate associated with the degree of irreversibilities caused by the flow resistances of the system. This analysis is equivalent to evaluate the irreversibilities in an endoirreversible Carnot heat engine model caused by the heat resistance loss between the engine and its surrounding heat reservoirs. This paper concludes with an application to illustrate the practical applications by estimating the lost available work of an actual steady-flow turbine and the layout pipes upstream and downstream of the same device.Copyright © 2012 by ASME

The present paper attempts to predict ratchet boundary for 90-degree mitred and smooth pipe bends subjected to sustained pressure and cyclic in-plane bending. The methodology utilizes a recently published technique known as the “Uniform Modified Yielding” (UMY) technique, which relies on generation of a virtual structure with inhomogeneous reduced yield strength, whose magnitude and distribution depend on the elastic stress field due to the cyclic load. The collapse load of this virtual structure determines the threshold steady load necessary for commencement of “incremental collapse”. The technique is applied first to predict ratchet boundaries for two benchmark problems possessing analytical descriptions of ratchet boundary and uni-axial states of stress; the two-bar structure problem and the Bree cylinder. Predicted ratchet boundaries exactly coincided with the corresponding published analytical descriptions, and reasons for this correlation were discussed in this paper. The technique was then applied to three 90-degree pipe bends with similar geometries as follows: smooth pipe bend (SPB), single mitred pipe bend (SMPB), and three weld mitred pipe bend (3WMPB). Certain assumptions are adopted to enable treatment of the problem as a quasi-uniaxial one. Conservative estimates are obtained for ratchet boundaries in pipe bends that correlates well with elastic shakedown/ratchet boundary of the same problems as predicted by a recently developed non-cyclic direct technique.Copyright © 2012 by ASME

This paper proposes a simple expression for calculating the restoring and damping forces of an air spring equipped with a small tube. Air springs are commonly used in railway vehicles, automobiles, and various vibration isolators. The air spring used in this study consists of two tanks connected by a long tube. Using a tube instead of an orifice enables flexibility in the arrangement of the two tanks. In addition, this makes it possible to manufacture a thin air spring. The oscillating system, which consists of a single mass supported by this type of air spring, is a single-degree-of-freedom (SDOF) system. However, it has two resonance points for a reason that had been unknown for a long period of time. In this paper, we explain why the SDOF system has two resonance points. After that, assuming that the vibration is small and the flow through the tube is laminar, we derive the spring constant and damping coefficient of an air spring subjected to a simple harmonic motion. Then, we calculate the frequency response curves for the system and compare the calculated results with the experimental values. According to the experiment, there is a remarkable amplitude dependency in this type of air spring, so the frequency response curves for the system change with the magnitude of the input amplitude. It becomes clear that the calculation results are in agreement with the limit value when the input amplitude approaches zero.Copyright © 2012 by ASME

Building upon a companion paper, the present paper addresses additional mechanisms of the tidal bore, including channel taper and friction; building, maximum height, variation, and dissipation of the bore; and standing waves. Early studies of these mechanisms are cited and discussed in historical context. Relationships developed to investigate the effects of horizontal channel taper, vertical channel taper, and channel friction agree qualitatively with and explain field observations. Building of the bore is explained, with favorable comparison of methodology with flume observations. The maximum height that the bore is capable of achieving is one of its most interesting features; this is explained in terms agreeing with experimental observation. The two forms of the jump, undular and wall-like, are discussed. The variation of the bore height as it moves into regions of greater or lesser depth is described from field observations and flume observation, and relationships derived which explain such variation. Frictional dissipation of the bore is discussed. Standing waves that occur after the tidal bore has passed are explained as a separate phenomenon.Copyright © 2012 by ASME

This paper describes experimental approaches for ensuring high heat-flux annular flow boiling and flow condensation under conditions for which shear and pressure forces dominate buoyancy effects. The paper also describes fundamental predictive tools for such flows. For annular flows, the liquid phase flows in the form of a wavy film (often micro-meter scale thin) that continuously irrigates the heat-exchange surface inside millimeter scale ducts. Controlled attainments of these annular flow configurations (which experience only second order effects of surface-tension forces) are essential to integration of functional boilers and condensers for certain space-based as well as micro-scale thermal systems. The experiments deal with flow condensation of FC-72 in a 2 mm gap horizontal channel of 1 m length and flow boiling of FC-72 in a 1.6 mm gap horizontal channel of 0.74 m length. For both boiling and condensing flow experiments, annularity of the respective flows is ensured by choice of an appropriate rate of through flow of vapor that does not actively participate in phase-change and has a flow rate which lies within a well defined range. The through flow of vapor is shown to ensure stability, annularity (by effectively suppressing nucleation in the case of flow boiling), and predictability. This fact is demonstrated by relevant flow visualization videos whose schematic and still pictures are included here. Two sets of annular condensing flow simulation results (one based on a full computational fluid dynamics based steady/unsteady simulations and another based on a quasi 1-D steady simulations) are compared against experimental heat-flux measurements obtained for annular shear driven condensing flows of FC-72 vapor. For quasi-steady annular boiling, only the quasi 1-D steady simulations approach is used for comparisons with experimental heat load measurements. The reasonableness of the proposed 1-D predictive engineering tool, with proper understanding of its scope and limitations, enables one to generate useful results for more sophisticated simulations. Furthermore the tool readily yields results/estimates for other working fluids, channel dimensions, and flow conditions.

In this paper, the use of computational fluid dynamics is evaluated as a design tool to investigate the indoor climate of a confined greenhouse. The finite volume method using polyhedral cells is used to solve the governing mass, momentum and energy equations. Natural convection in a cavity corresponding to a mono-span venlo-type greenhouse is numerically investigated using Computational Fluid Dynamics. The CFD model is designed so as to simulate the climate above a plant canopy in an actual multi-span greenhouse heated by solar radiation. The aim of this paper is to investigate the influence of various design parameters such as pitch angle and roof asymmetry and on the velocity and temperature patterns inside a confined single span greenhouse heated from below. In the study reported in this paper a two-dimensional CFD model was generated for the mono-span venlo-type greenhouse, and a mesh sensitivity analysis was conducted to determine the mesh independence of the solution. Similar two-dimensional flow patterns were observed in the obtained CFD results as the experimental results reported by Lamrani et al [2]. The CFD model was then modified and used to explore the effect of roof pitch angle and roof asymmetry at floor level on the development of the flow and temperature patterns inside the cavity for various Rayleigh numbers. Results are presented in the form of vector and contour plots. It was found that considerable temperature and velocity gradients were observed in the centre of the greenhouse for each case in the first 40mm above the ground, as well as in the last 24mm close to the roof. Results also indicated that the Rayleigh number did not have a significant impact on the flow and temperature patterns inside the greenhouse, although roof angle and asymmetry did. The current results demonstrate the importance of CFD as a design tool in the case of greenhouse design.Copyright © 2012 by ASME

Model tests are usually used for the traditional seakeeping predictions (transfer functions of ship motions and loads in regular waves). Experience shows that numerical solution of Reynolds-averaged Navier-Stokes equations (RANSE) can provide accurate results for this task, however, such computations require too much computational time for the required large number of the loading conditions, ship speeds and wave directions and periods. Traditionally, potential flow methods are used for such computations at early design stages. Although potential flow methods can produce results very quickly for large number of conditions, viscosity effects (most important for the roll motion) have to be taken into account using measurements or RANSE computations. Rankine source method, applied to seakeeping problems perhaps for the first time by Yeung [1] to oscillating ship sections, is increasingly used in practical seakeeping analysis. This paper presents a three-dimensional Rankine source code GL Rankine. Patch method is used instead of the usual collocation method to satisfy boundary conditions on the solid body surface. Periodic flow due to waves is linearized with respect to wave and motion amplitude, taking into account interactions between the nonlinear steady flow and periodic flow due to waves and ship motions. The steady flow solution accounts for the nonlinear free-surface conditions, ship wave and dynamic squat. The paper shows results of the method for ship motions in waves in comparison with model measurements and RANSE simulations.

This paper describes the performance of wave power conversion. A large scale floating system on which oscillating water column type wave energy convertors installed is proposed and the efficiency of primary conversion of wave power is estimated. In this paper, a boundary condition due to OWC is theoretically modeled in order to consider influence of wave energy absorption to hydrodynamic forces on the floating structure into the three-dimensional singular point distribution method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and variation of water elevation within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement. The damper effect of OWC devices is taken into account. The validity of the prediction method proposed is proven by comparing with experimental results. There are three types of large scale wave energy platform which is a pontoon type in the paper. Each performance of the efficiency of primary conversion of wave power is estimated. It is shown that the performance is very good.

The present paper concerns an OWC spar-buoy, possibly the simplest concept for a floating oscillating-water-column (OWC) wave energy converter. It is an axisymmetric device (and so insensitive to wave direction) consisting basically of a (relatively long) submerged vertical tail tube open at both ends, fixed to a floater that moves essentially in heave. The length of the tube determines the resonance frequency of the inner water column. The oscillating motion of the internal free surface relative to the buoy, produced by the incident waves, makes the air flow through a turbine that drives an electrical generator. It is well known that the frequency response of point absorbers like the spar buoy is relatively narrow, which implies that their performance in irregular waves is relatively poor. Phase control has been proposed to improve this situation. The present paper presents a theoretical investigation of phase control by latching of an OWC spar-buoy in which the compressibility of air in the chamber plays an important role (the latching is performed by fast closing and opening an air valve in series with the turbine). In particular such compressibility may remove the constraint of latching threshold having to coincide with an instant of zero relative velocity between the two bodies (in the case under consideration, between the floater and the OWC). The modelling is performed in the time domain for a given device geometry, and includes the numerical optimization of the air turbine rotational speed, chamber volume and latching parameters. Results are obtained for regular waves.Copyright © 2012 by ASME

This paper reports a theoretical study of the power performance and environmental footprint of high-speed vessels in calm deep water, paying particular attention to a high-speed catamaran cargo vessel Faltinsen [1]. The power analysis uses a modified version of the method of Doctors and Day [2]. One modification to their approach is that the wave resistance and free surface wave profiles, have been numerically predicted using two different linear potential flow field theories; Michell thin-ship theory (Yeung and Wan [3]) and the 3D Rankine panel method (Hess and Smith [4]), respectively. We have based the latter method on the combination of the Dawson [5] upstream finite difference operator and the ‘staggered grid’ technique (Jensen et al. [6]). In addition, this paper shows how the viscosity effects modeled on the free surface layer influence the behavior of the wave resistance curves as predicted by Michell’s thin ship theory. This was done by adopting the approaches described by Tuck [7] and Lazauskas [8]. The wave resistance models were verified and validated using the examples of Wigley monohull (Lazauskas [8], Tarafder and Suzuki [9]) and catamaran (Yeung and Wan [3], Tarafder and Suzuki [10]) analytical forms, as well as on the Tuck parabolic strut (Tuck [7]). Furthermore, the resistance models were extended using free surface profile estimates at selected Froude numbers and applied to the case of a high-speed catamaran cargo vessel. The numerical results obtained were compared with published results and their accuracy and application feasibility is discussed from the perspective of preliminary high-speed vessel design. Based on the discussion above, suitable wave resistance models were selected and combined with the modified Doctors and Day [2] method giving the total resistance of the high-speed catamaran cargo vessel in the interval of Froude numbers. Having the estimates of total resistance, enables the effective power to be found. The results were compared with known results and were found to be in good agreement. Through combination of the effective power and propulsion factors, the brake power of the generic propulsion system is predicted. Taking into account the type of vessel being analyzed, the most common type of the propulsion diesel engine was selected. Finally, knowing the indicative environmental footprint of the selected engine, emission levels of Green House Gases (GHG) and solid particles were obtained. The emission results are further discussed in an ecologically friendly high-speed vessel design perspective (IMO [11, 19]).

This paper presents initial results from the following-up study of the ‘inverse’ or ‘green water concept’ for wave energy conversion. Initially presented in 2009, the ‘inverse concept’ was developed by MARIN as a vehicle for open discussion and exchange of ideas in the field of wave energy conversion. Pilot model tests presented in 2010 showed the great potential of the concept, but also revealed the challenges associated with Power Take Off design. The present study aims to further optimize the inverse concept. A new PTO system has been incorporated, based on robustness and effective use of the structure’s (de)optimized hull. The resulting renewed concept combines maximized vessel motions with OWC-type of wave energy conversion. This paper focuses on the motion response of the renewed concept. Frequency domain calculations show the response of the concept with water columns (moonpools) at the bow and stern. Remarkably, the already maximized motions of the hull become even more extreme when moonpools are incorporated. Special attention is given to the relative motions of the water inside the moonpools, as these give an indication of the wave energy conversion potential of the concept. The relative water motions inside the moonpools show a large response that is characterized by multiple peaks. This indicates the concept’s ability to convert energy in a wide range of sea states. Results from additional diffraction analysis show that through proper tuning, the water columns inside the moonpools can be modeled as solid water-bodies. This allows for a future numerical modeling of the hydrodynamic interaction between structure, water columns, entrapped air and PTO damping in the time domain.

The development of new methods in the field of numerical aeroacoustics is one of the current research interests. For this kind of approaches, highly efficient methods are necessary. Aerodynamic noise prediction codes in use today are typically based on Lighthill analogies. In this paper an alternative approach is developed and implemented in a three dimensional CFD finite volume code. The method is based on the Expansion about Incompressible Flow (EIF) technique, which was proposed first by Hardin and Pope in 1994. Based on the solution of the incompressible flow, acoustic radiation is obtained in a compressible, inviscid fluid. The advantage of this technique, as compared to unsteady RANS simulations, is that small acoustic perturbations can easily be separated from the fluctuations of the pressure field of the bulk flow, which are some orders of magnitude greater. In comparison to the acoustic analogy approach, the method extends the region of applications towards the moderate Mach numbers (up to Ma = 0.6). Moreover, the flow and acoustic effects are resolved on different length scales. This makes the computations more efficient. The EIF method accounts both for the sound radiation and scattering. In the presented paper a further development towards three dimensional simulations and numerical implementation for centrifugal pumps is presented.Copyright © 2012 by ASME

In an earlier paper of the authors, the occurrence of the so called Kelvin-Helmholtz instabilities (KHI) near the rim cavity of a 1.5 stage gas turbine has been examined by the use of CFD methods. It is shown that the KHI’s occur, when the swirl component of the hot gas flow is very strong. Due to the fact, that a high swirl is produced by the guide vanes of the first stage, this matter concerns most common gas turbines. A further paper validated the CFD methods used and derived KHI parameters (vortex appearance, vortex periodicity and vortex velocity) of a splitter plate model. In the current study, essential parameters revealed by the analysis of a gas turbine rim cavity model are compared to the parameters extracted from the investigation of the splitter plate model and the potential linear theory of Turner. The rim cavity model is derived from a test rig of a 1.5 stage gas turbine. The blades and vanes have been removed from the computations. As main flow boundary conditions, surface averaged parameters are used. It is shown that a description of KHI developing in a rim cavity model is partly possible using splitter plate KHI characteristics and the potential linear theory of Turner as well. A mathematical approach is formulated, which can predict the vortex velocity of KHI’s in turbine rim cavities.

This paper explores the conjugate heat transfer (CHT) numerical simulation approach to calculate the metal temperature for the gas turbine cooled stator. ANSYS CFX12.1 code was selected to be the computational fluid dynamic (CFD) tool to perform the CHT simulation. The 2-equation RNG k-ε turbulence model with scalable modified wall function was employed. A full engine test with thermocouple measurement was performed and used to validate the CHT results. Metal temperatures calculated with the CHT model were compared to engine test data. The results demonstrated good agreement between test data and airfoil metal temperatures and cooling flow temperatures using the CHT model. However, the CHT calculations in the outer end wall had a discrepancy compared to the measured temperatures, which was due to the fact that the CHT model assumed an adiabatic wall as a boundary condition. This paper presents a process to calculate convection heat transfer coefficient (HTC) for cooling passages and airfoil surfaces using CHT results. This process is possible because local wall heat flux and fluid temperatures are known. This approach assists in calibrating an in-house conduction thermal model for steady state and transient thermal analyses.

The co-generative micro-power plant with the HFE7100 as a working medium was designed and built for experimental investigations. The heat output of the plant was assumed equal to 20 kW, while the electric output amounted to about 3kW. In the paper a multi-stage micro-turbine with partial admission of all the stages is described in detail and the results of the particular experimental investigations and numerical calculations are shown, followed by an appropriate discussion and conclusions. The flow calculations were performed using ANSYS package and finally the axial multistage turbine was chosen. This allowed to apply typical nozzle and blade profiles. The turbine consists of 5 similar (almost identical) stages with constant section blades, the only difference being the increase of the admission arc (number of nozzles) in the successive stages. The rotor speed was assumed equal to 8000 rpm, mean rotor diameter −100 mm and blade height −10 mm. The stream lines, pressure and temperature distribution in the nominal and off-design conditions are presented and discussed in the paper. The micro-turbine was built and tested experimentally. The turbine performance was calculated for HFE7100 but also for air and nitrogen as a working medium for testing purposes. In the first stage of experiments the turbine behaviour was checked using these gases and the results were compared with the calculation data. The results of the experiments correspond very well with the appropriate CFD calculation data.

The flow field in High-Work Single-Stage (HWSS) turbines differs from traditional turbine flow fields. Operating at increased pressure ratios, wakes and trailing edge shocks at the exit of the vane are more likely to cause a vibratory response in the rotating blade. This flow field can produce increased excitation at harmonics that correspond to the vane passing frequency and harmonics higher than the vane passing frequency. In this paper, blade vibratory stresses in a HWSS gas turbine stage are predicted using unsteady pressures from two Rolls-Royce in-house flow codes that employ different phase lagged unsteady approaches. Hydra uses a harmonic storage approach, and the Vane/Blade Interaction (VBI) code uses a direct storage approach. Harmonic storage reduces memory requirements considerably. The predicted stress for four modes at two engine speeds are presented and are compared with rig test strain gauge data to assess and validate the predictive capability of the codes for forced response. Strain gauge data showed the need to consider harmonics higher than the fundamental vane passing frequency for the max power shaft speed and operating at the conditions. Because of this, it was a good case for validation and for comparing the two codes. Overall, it was found that, stress predictions using the Hydra flow code compare better with data. To the best of the authors’ knowledge, this paper is a first in comparing two different phase lagged unsteady approaches, in the context of forced response, to engine rig data for a High-Work Single Stage turbine.Copyright © 2012 by Rolls-Royce Corporation

This paper describes investigations into unsteady flow phenomena in a high turning linear cascade with a nominal steady flow. A fast response five hole probe was used to obtain time-accurate measurements. Since a single probe was used to traverse an entire measurement plane, the results were obtained as discrete points and were not synchronous. One method used to address this issue is to traverse the measurement plane point by point and record the signal of a reference probe simultaneously. Synchronization can be performed during post processing by analyzing the reference signal for a common periodic component and phase-shifting all signals with respect to the reference phase of that flow feature. This paper presents results from the application this unsteady reconstruction technique to the so-called Durham Cascade 28% downstream of the trailing edge in order to provide insight into the nature of the dominant unsteady mode. It was found that there was significant temporal variation in the strength of the passage vortex but the position of the vortex remains fixed.

Many Alstom heavy-duty gas turbines with a silo combustor are in service and moreover undergoing upgrades for performance augmentation, lifetime extension, and emission reduction. Several structural parts of the combustor are exposed to high gas temperatures, and therefore their lifetime depends mainly on the metal temperatures, which must be kept within the acceptable limits. This paper describes methodology based on the state of the art methods of 3D CFD and finite element (FE) computations, which are combined into the computational process for the reliable silo combustor thermal analyses. In the first part of the paper the computational model of the silo combustor is discussed. The model comprises CFD models simulating the hot gas path and the cooling air supply system, as well as the FE model of the structural parts. The CFD models predict the gas temperatures and heat transfer coefficients that are used by the FE model for calculating the metal temperatures. In the second part of the paper the computational results are presented and several 3D flow phenomena are analysed in details. One effect is the interaction of dilution jets in swirled cross flow. At different operation conditions, pairing of those jets occurs, which generates the periodic metal temperature distribution, as recorded in the field. This analysis also revealed factors, which influence on the temperature distribution. The combustor simulation delivers an insight into non-homogeneous temperature profiles in front of the turbine behind the transition channel of the silo-combustor. Finally, by adding leakages into the flow model, the interesting example of the non-homogeneous leakage of cold air, which can lead to local increase of material temperature, was simulated. All these simulations led to reliable silo-combustor upgrades.

The standard design process for the Siemens Industrial Turbomachinery, Lincoln, Dry Low Emissions combustion systems has adopted the Eddy Dissipation Model with Finite Rate Chemistry for reacting computational fluid dynamics simulations. The major drawbacks of this model have been the over-prediction of temperature and lack of species data limiting the applicability of the model. A novel combustion model referred to as the Scalar Dissipation Rate Model has been developed recently based on a flamelet type assumption. Previous attempts to adopt the flamelet philosophy with alternative closure models have failed, with the prediction of unphysical phenomenon. The Scalar Dissipation Rate Model (SDRM) was developed from a physical understanding of scalar dissipation rate, signifying the rate of mixing of hot and cold fluids at scales relevant to sustain combustion, in flames and was validated using direct numerical simulations data and experimental measurements. This paper reports on the first industrial application of the SDRM to SITL DLE combustion system. Previous applications have considered ideally premixed laboratory scale flames. The industrial application differs significantly in the complexity of the geometry, unmixedness and operating pressures. The model was implemented into ANSYS-CFX using their inbuilt command language. Simulations were run transiently using Scale Adaptive Simulation turbulence model, which switches between Large Eddy Simulation and Unsteady Reynolds Averaged Navier Stokes using a blending function. The model was validated in a research SITL DLE combustion system prior to being applied to the actual industrial geometry at real operating conditions. This system consists of the SGT-100 burner with a glass square-sectioned combustor allowing for detailed diagnostics. This paper shows the successful validation of the SDRM against time averaged temperature and velocity within measurement errors. The successful validation allowed application of the SDRM to the SGT-100 twin shaft at the relevant full load conditions. Limited validation data was available due to the complexity of measurement in the real geometry. Comparison of surface temperatures and combustor exit temperature profiles showed an improvement compared to EDM/FRC model. Furthermore, no unphysical phenomena were predicted. This paper presents the successful application of the SDRM to the industrial combustion system. The model shows a marked improvement in the prediction of temperature over the EDM/FRC model previously used. This is of significant importance in the future applications of combustion CFD for understanding of hardware mechanical integrity, combustion emissions and dynamics of the flame.