Search

The exergy analysis has already proved to be of interest for aerospace applications, with the possibility to analyze new types of configurations. It is of particular interest when a pertinent thrust/drag breakdown is not possible and when significant thermal exchanges take place in the control volume. In addition, this method allows to link the different contributions of the exergy terms to physical phenomena in the flow, improving the understanding of the sources of losses degrading the performance of the system under study. The applications and results obtained in a fixed frame of reference have thus motivated the improvement and extension of the exergy balance to more complex flows. This paper aims at presenting an extension of the exergy balance to rotating frames of reference for the analysis of rotating components of the propulsion system (e.g. propeller, turbomachine or helicopter rotor blades). The newly developed theoretical development is summarized, and an application to a numerical simulation of a propeller is presented. Results are discussed in terms of both physical interpretation and numerical accuracy. [ABSTRACT FROM AUTHOR]

For fans of a variable-cycle engine, a good aerodynamic performance over a wide range of rotating speeds is essential. However, when supersonic cascades designed for a high upstream Mach number operate under a low upstream Mach number, a starting problem may occur, which significantly decreases the aerodynamic performance of fan blades. As a result, the operating range of the supersonic cascades is severely limited. To solve the starting problem caused by the mismatch between geometry of supersonic cascades and upstream Mach number, a morphing supersonic cascade is developed. Thus, this study mainly focuses on the effect of the static deformation of supersonic cascades driven by smart materials on aerodynamic characteristics under a low upstream Mach number. To investigate this issue, numerous simulations are conducted on an S-type cascade by finite element method and computational fluid dynamics. As demonstrated by flow structure analysis, the morphing cascades are started under certain morphing configurations while the original cascade operates at nonstarted state. The results show that the deformation driven by smart materials alters the shock wave structures under a low upstream Mach number by adjusting key cascade geometric parameters. Specifically, the morphing cascades achieve 80% reduction of detached shock loss compared with the original cascades. [ABSTRACT FROM AUTHOR]

Multidisciplinary design optimization has great potential to support the turbomachinery development process by improving designs at reduced time and cost. As part of the industrial compressor design process, we seek for a rotor blade geometry that minimizes stresses without impairing the aerodynamic performance. However, the presence of structural mechanics, aerodynamics, and their interdisciplinary coupling poses challenges concerning computational effort and organizational integration. In order to reduce both computation times and the required exchange between disciplinary design teams, we propose an inter- instead of multidisciplinary design optimization approach tailored to the studied optimization problem. This involves a distinction between main and side discipline. The main discipline, structural mechanics, is computed by accurate high-fidelity finite element models. The side discipline, aerodynamics, is represented by efficient low-fidelity models, using Kriging and proper-orthogonal decomposition to approximate constraints and the gas load field as coupling variable. The proposed approach is shown to yield a valid blade design with reasonable computational effort for training the aerodynamic low-fidelity models and significantly reduced optimization times compared to a high-fidelity multidisciplinary design optimization. Especially for expensive side disciplines like aerodynamics, the multi-fidelity interdisciplinary design optimization has the potential to consider the effects of all involved disciplines at little additional cost and organizational complexity, while keeping the focus on the main discipline. [ABSTRACT FROM AUTHOR]

Centrifugal pumps are turbomachines that have wide industrial applications and could perform in different ways such as pump and turbine mode. The maintenance of this equipment is mostly carried out using invasive methods that are expensive, time-consuming, and even complicated. The application of non-invasive methods is sought since they offer the advantage of real-time monitoring without stopping the process, reducing component assembly and disassembly times and providing a faster response. The aim of this work is done an experimental investigation that shows evidence about how the information on the hydraulic variables can be obtained if the electrical variables are monitored for the modes of operation such as pump and turbine. This work is divided into two parts, the first part is based on a statistical analysis to perform a multivariate adjustment through copulas and probability distributions. The second part focuses on the graphical analysis of the power density spectra for the hydraulic variables, the torque, and the defined electrical variables. The amplitude peaks of each variable and which peaks are common between them are determined. A statistically significant fit for Tawn type 2 copula is obtained with the indicator variable of pressure fluctuation and a multivariate transformation of the three-phase network currents. In the spectra analysis, common amplitude peaks are observed between the spectra that indicate the information flow on the phenomena between the hydraulic variables and the electrical variables. [ABSTRACT FROM AUTHOR]

This article reports a procedure to implement as well as to validate non‐reflecting boundary conditions applied for turbomachinery simulations, using Navier–Stokes characteristic boundary conditions in a compressible lattice Boltzmann solver. The implementation of both an inlet condition imposing total pressure, total temperature, and flow angles, as well as an outlet condition imposing a static pressure profile that allows the simulation to reach a simplified radial equilibrium, is described within the context of a lattice Boltzmann approach. The treatment at the boundaries relies on the characteristic methodology to derive conditions which are non‐reflecting in terms of acoustics and is also compatible with turbulence injection at the inlet. These properties are evaluated on test cases of increasing complexity, ranging from a simple 2D periodic domain to an S‐duct stage with turbulence injection. [ABSTRACT FROM AUTHOR]

In recent years, CFD has proven to be a very useful asset to help with predicting complex flows in a wide range of situations, including multiphase and gas-particle flows. On this track, numerical modelling of particle-laden flows in multistage turbomachinery has become an important step in helping to analyse the behaviour of a discrete phase in gas turbines. Furthermore, unsteady effects due, for example, to rotor–stator interaction may have an effect on trajectories and capture efficiencies of the discrete phase. Unfortunately, computational times for transient simulations can be exceedingly high, especially if a discrete-phase needs also to be simulated. For this reason, this work reports a new method for the efficient and accurate simulation of particle-laden flows in gas turbine engines components. The Harmonic Balance Method is exploited to gain orders of magnitude speedup exploiting the idea that once the flow field has been embedded in the spectral basis, it can be reconstructed at any desired time. In this way, not only can the computational time needed to reach convergence of the flow field be dramatically reduced, but there is also no need to keep simulating the flow field during particle tracking. On the contrary, the continuous phase field can be retrieved at any desired time through flow reconstruction. This technique is conceptually simple, but, to the authors' knowledge, has never been applied so far in particle-laden flow simulations and represents a novelty in the field. First, the implementation of the method is described, and details are given on how phase-lagged boundary conditions can be applied to flow and particles to further speed up the calculation. Then, some relevant case studies are presented to highlight the performance of the method. [ABSTRACT FROM AUTHOR]

Blade tip-timing is an extensively used technique for measuring blade vibrations in turbine and compressor stages; it is one of the preferred techniques used for characterizing their dynamic behaviors using non-contact probes. Typically, arrival time signals are acquired and processed by a dedicated measurement system. Performing a sensitivity analysis on the data processing parameters is essential for the proper design of tip-timing test campaigns. This study proposes a mathematical model for generating synthetic tip-timing signals, descriptive of specific test conditions. The generated signals were used as the controlled input for a thorough characterization of post-processing software for tip-timing analysis. This work represents the first step in quantifying the uncertainty introduced by tip-timing analysis software into user measurements. The proposed methodology can also offer essential information for further sensitivity studies on parameters that influence the accuracy of data analysis during testing. [ABSTRACT FROM AUTHOR]

An integrated nonlinear dynamic model of rigid shaft motion, unsteady gas film, and deformations of foil structure is established in order to investigate the impact of external mechanical factors such as sinusoidal and broad-band random vibration of the rotor. The model was verified by experimental data. A notable agreement is demonstrated between the calculation results and experimental data. [ABSTRACT FROM AUTHOR]

Turbomachinery brush seals are used for achieving close clearance control with the aid of flexible bristles. Frictional forces between bristle tips and rotor surfaces induce counter torque, power loss, and heat generation during turbomachinery transients; all of these determine the overall efficiency, operation life, and stability of turbomachinery application. As a result of manufacturing tolerances, rotor dynamics-induced shaft deflections, and additional gyroscopic loads in aviation engines, eccentric rotor rub occurs toward brush seals in transients, causing partial rotor–seal contact with nonlinear radial interference and uneven tip force distribution. There is an inherent error in the current power loss and frictional heat rate analyses, as well as in counter torque methodologies, since they do not account for the uneven tip force distribution. In this study, a nonlinear radial interference profile of eccentric rotor contact conditions has been derived and its effect on contact angle has been examined with a comparative analysis with concentric rotor expansion. The methodology for counter torque, power loss, and generated frictional heat rate analyses has been detailed, and eccentric condition formulations have been derived with the surface integration of dynamic bristle tip force functions adopted from brush seal dynamic stiffness tests. Analysis of nonlinear interference and uneven contact force profiles has been conducted based on the combined effects of assembly conditions and eccentricity levels. Results obtained using the developed closed-form equations for eccentric rotor contact are compared with concentric rotor expansion and simple eccentric rotor rub analyses, which do not account for uneven tip forces. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To develop turbomachinery blades with high reliability, it is indispensable to verify the natural frequency, damping, resonant stress, etc. under operating condition, and utilize these data in the mechanical design of a new blade. BTT (Blade Tip Timing) and the telemetry system have been widely used to measure the modal parameters of turbomachinery blades. In measurement of the modal parameters of blades under rotation, it is pointed out that the mistuning phenomena make the identification of modal parameters difficult. Namely, because, in a mistuned bladed disk, responses of many vibration modes are superposed, it becomes difficult to correctly identify the natural frequency and damping of an individual blade. This is one of the critical issues to be overcome for developing blades with high reliability. In this study, a novel identification method of modal parameters of a mistuned system is proposed, where the modal parameters of a mistuned bladed disk are identified using the frequency responses consisting of many vibration modes. To verify the validity of the identification method proposed, typical mistuned systems of a turbocharger are analyzed, and the modal parameters are identified. The effect of the noise included in the measured frequency response on the accuracy of the identification is examined in detail.

In this work, an experimental investigation into vibration damping of elastomer filled open-pore metal foams and their effectiveness as a bearing support in turbomachinery is presented. The polyurethane fillers known for their high-energy absorption capacity were chosen to enhance the damping performance of the metal skeleton. Aluminum (Al), copper (Cu) and nickel-chromium foams (NiCr), with different relative density and pore size were tested dynamically using a dedicated device based on a single degree-of-freedom model. The results indicate that the storage modulus and the loss factor for foam-polymer composites were greater than the combined contribution of both phases taken separately. Foam morphology plays an important role in this effect and it is shown that the increase in performance was more significant for higher specific surface area. Fillers with different properties were also considered. The optimal combination of foam and polymer was selected and tested on a rotor kit test bench. Annular shaped samples were placed between the external race of the ball bearing and the housing. The tests were carried out using a flexible rotor configuration where the vibration amplitudes of the rotor were monitored for foam and foam-polyurethane composites for rotational speeds up to 100 Hz while hammer impact tests were performed using a semi-rigid shaft configuration due to higher resonance frequencies. In the first case, no significant difference was observed between the foam, foam composite and the bearings-only set-up. In the second case, the foam composite resulted with the highest energy dissipation capacity.

Hydrogen fuel-cell systems are one of the alternatives for the decarbonization of the transportation sector. In such systems, the usage of O2-enriched air has the potential to improve fuel cell performance as well as to reduce degradation phenomena linked to local O2 starvation. However, the production of an O2-enriched air stream implies energy consumption that needs to be evaluated in the overall system efficiency. In this study, the potential of a system including polymeric membranes for O2-N2 separation to produce O2-enriched air was evaluated theoretically. First, the balance of plant, including the O2-N2 separation membrane and a two-stage boosting system, was considered. Two sources of energy recovery were identified: a high-pressure H2 stream and retentate flow (N2-rich) at the outlet of the separation membrane. Then, the efficiency of the system was evaluated for different levels of O2 enrichment, with sensitivities to the main operational and design parameters, i.e., cathode excess O2 ratio, turbomachinery efficiency, essure ratios. The results show the potential for an O2-enriched system if the energy recovered reaches approximately 25% of the additional power consumption induced by the separation membrane.

A turbine vane frame is a special type of intermediate turbine duct, and is one option to improve the efficiency and reduce the length and weight of an aero-engine. However, due to its geometry, it features a complex flow field, and therefore in-depth aerodynamic investigations are necessary. Especially for aviation, every component needs to function reliably during all operating points. To perform this study at the Institute for Thermal Turbomachinery at the Graz University of Technology, the Subsonic Test Turbine Facility for Aerodynamic, Aeroacoustic and Aeroelastic Investigations was equipped with a turbine vane frame and a low-pressure turbine located downstream. Measurements were taken with aerodynamic five-hole probes for three operating points, and were compared with steady-state and transient simulations as well as analytic solutions for the pressure drop in the TVF. Finally, the most important loss mechanisms are described.

Non-destructive testing for structural health monitoring is becoming progressively important for gas turbine manufacturers. As several techniques for diagnostics and condition-based maintenance have been developed over the years, the tip-timing approach is one of the preferred approaches for characterizing the dynamic behavior of turbine blades using non-contact probes. This experimental work investigates the uncertainty of the time-of-arrival of a Blade Tip-Timing measurement system, a fundamental requirement for numerical and aeromechanical modeling validation. The study is applied to both the measurement setup and the data processing procedure of a generic commercial measurement system. The influence of electronic components and signal processing on the tip-timing uncertainty is determined under different operating conditions. [ABSTRACT FROM AUTHOR]

In hydraulic turbines, either Francis or axial turbines, a high swirling flow is generated at PL conditions at the inlet of the draft tube resulting in the formation of a rotating vortex rope (RVR). This leads to pressure fluctuations which limit the operating range of single regulated turbines. In the present study, an axial hydraulic turbine has been numerically simulated by the k − ϵ and SST-based Scale-Adaptive Simulation model (SST SAS) turbulent models to capture helical RVR. Considering the formation of the RVR as the result of a global instability, linear global stability analysis of the time-averaged turbulent flow field has been conducted. For the first time in axial hydraulic turbines, how boundary conditions affect the unstable mode and which frequency, plunging or rotating, is related to the vortex rope instability have been studied. It is found that the flow inside the draft tube is sensitive to the asymmetrical disturbances with a frequency close to the rotational component. [ABSTRACT FROM AUTHOR]

This paper presents a first investigation into the aerodynamics and performance breakdown of a distributed aft-fuselage boundary layer ingesting (BLI) tube-and-wing aircraft using fully coupled Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations that resolve the complete fan and installation geometries. Through the URANS simulations, the interaction between the turbulence from the fuselage boundary layer (BL) and the BLI propulsor is identified as an area that warrants further research. Using the URANS approach, the ingested turbulence leads to a 4.5% reduction in the propulsor stage total–total isentropic efficiency. A mechanical power balance has been drawn up to compare the power sources and sinks throughout the installation and propulsor for two test cases with different thicknesses of ingested BL. The test case with a thinner BL was found to generate significantly more dissipation in the BL development upstream of the propulsor, the flow separation over the outer cowl, and the interaction between the reversed flow over the cowl and the propulsor exhaust jet. Due to this increase in dissipation, the case with thinner ingested BL consumes 7% more power relative to a baseline case with thicker BL, representative of the upstream fuselage at cruise. This demonstrates the importance of matching the installation with the incoming fuselage BL. [ABSTRACT FROM AUTHOR]

This paper proposes an approach that combines manual differentiation (MD) and automatic differentiation (AD) to develop an efficient and accurate multi-row discrete adjoint solver. In this approach, the structures of adjoint codes generated using an AD tool are first analyzed. Then, the AD-generated codes are manually adjusted to reduce memory and CPU time consumption. This manual adjustment is performed by replacing the automatically generated low-efficient differentiated codes with manually developed ones. To demonstrate the effectiveness of the proposed approach, the single-stage transonic compressor–NASA Stage 35 and the 1.5-stage Aachen turbine–are used. The solution information exchange at a rotor-stator/stator-rotor interface is achieved by a conservative, non-reflective, and robust discrete adjoint mixing plane method. The results show that the discrete adjoint solver developed by hybrid automatic and manual differentiation is more economical in computational cost than that developed purely by an AD tool and has higher sensitivity accuracy than the adjoint solver with the constant eddy viscosity (CEV) assumption. Moreover, the multi-row turbomachinery design optimizations can be efficiently performed by the discrete adjoint solver developed by the hybrid automatic and manual differentiation. [ABSTRACT FROM AUTHOR]

An aircraft engine's performance depends largely on the compressors' aerodynamic design, which aims to achieve higher stage pressure, efficiency, and an acceptable stall margin. Existing design methods require substantial prior knowledge and different optimization algorithms to determine the 2D and 3D features of the blades, in which the design policy needs to be more readily systematized. With the development of artificial intelligence (AI), deep reinforcement learning (RL) has been successfully applied to complex design problems in different domains and provides a feasible method for compressor design. In addition, the applications of AI methods in compressor research have progressively developed. This paper described a combined artificial-intelligence aerodynamic design method based on a modified deep deterministic policy gradient algorithm and a genetic algorithm (GA) and integrated the GA into the RL framework. The trained agent learned the design policy and used it to improve the GA optimization result of a single-stage transonic compressor rotor. Consequently, the rotor exhibited a higher pressure ratio and efficiency owing to the sweep feature, lean feature, and 2D airfoil angle changes. The separation near the tip and the secondary flow decreased after the GA process, and at the same time, the shockwave was weakened, providing improved efficiency. Most of these beneficial flow field features remained after agent modification to improve the pressure ratio, showing that the policy learned by the agent was generally universal. The combination of RL and other design optimization methods is expected to benefit the future development of compressor designs by merging the advantages of different methods. [ABSTRACT FROM AUTHOR]

Modern approaches dedicated to controlling the operation of gas foil bearings require advanced measurement techniques to comprehensively investigate the bearings' thermal and thermomechanical properties. Their successful long-term maintenance with constant operational characteristics may be feasible only when the allowed thermal and mechanical regimes are rigorously kept. Hence, an adequate acquisition of experimental readings for the critical physical quantities should be conducted to track the actual condition of the bearing. The above-stated demand has motivated the authors of this present work to perform the thermomechanical characterization of the prototype installation of a gas foil bearing, applying a specialized sensing foil. This so-called top foil is a component of the structural part of the bearing's supporting layer and composed of a superalloy, Inconel 625. The strain and temperature distributions were identified based on the readings from the strain gauges and integrated thermocouples mounted on the top foil. The measurements' results were obtained for the experiments that represent the arbitrarily selected operational conditions of the tested bearing. Specifically, the considered measurement scenario relates to the operation at a nominal rotational speed, i.e., during the stable process, as well as to the run-up and run-out stages. The main objectives of the work are: (a) experimental proof for the described functionalities of the designed and manufactured specialized sensing foil that allow for the application of a novel approach to the bearing's characterization, and (b) qualitative investigation of the relation between the mechanical and thermal properties of the tested bearing, using the measurements conducted with the newly proposed technical solution. [ABSTRACT FROM AUTHOR]

A fast computational method of the aerodynamic characteristics of fan and booster with inlet distortion is developed in this paper. This method is based on a time-marching throughflow model, and the governing equations are circumferentially averaged Navier-Stokes equations. A model of distributed inviscid blade force and viscid blade force is adopted to reproduce the flow deflection and loss. The deviation angle and loss parameters are interpolated from a database which is extracted from 3-D simulation results of compressor with uniform inlet. After a validation case is performed, the aerodynamical performances of a multistage fan and booster with inlet radial and circumferential distortion are computed. The results show the predictive ability of this method, and the acceptable computational time cost indicates the future application potential of this method during the design stage of a new turbomachinery. [ABSTRACT FROM AUTHOR]

Time-series forecasting is the core of the prognostics and health management (PHM) of turbomachinery. However, missing data often occurs due to several reasons, such as the failure of sensors. These partially missing and irregular data greatly affect the quality of time-series modeling and prediction as most time-series models assume that the data are sampled uniformly over time. Meanwhile, the training process of models requires a large number of samples and time. Due to various reasons, it is difficult to obtain a significant amount of monitoring data, and the PHM of turbomachinery has high timeliness and accuracy requirements. To fix these problems, we propose a multi-task Gaussian process (MTGP)-based data imputation method that leverages knowledge transfer across multiple sensors and even equipment. Thereafter, we adopt long short-term memory (LSTM) neural networks to build time-series forecasting models based on the imputed data. In addition, the model integrates the methods of denoising and dimensionality reduction. The superiority of this integrated time-series forecasting framework, termed MT-LSTM, has been verified in various data imputation scenarios of a synthetic dataset and a real turbomachinery case. [ABSTRACT FROM AUTHOR]

The transcritical CO2 (T-CO2) power cycle using low temperature waste heat is a promising technique for energy saving and environmental protection. However, according to the literature, there is no commercialized unit in service yet. This study provides developers a reference to shorten the design phase of the T-CO2 cycle commercialization process. A sensitivity analysis of the system performance, i.e., thermal efficiency and net power output, regarding the isentropic efficiencies of pump ( η p ) and expander ( η e ) and the heat source temperature ( T h , i n ) has been carried out using MATLAB and NIST REFPROP database. Simple and recuperative configurations are investigated based on their own optimal working pressures. The results show that the enhancement of η e has a greater influence on improving the system performance, but the improvement will diminish as η p , η e , and T h , i n increase. Although better system performance can be achieved with higher η p , η e , and T h , i n , the cost of the system equipment will also increase due to the higher optimal working pressure. In addition, increasing η p and η e will negatively affect the effectiveness of the recuperator. Therefore, the turbomachinery efficiencies and the heat source temperature should be considered simultaneously for the most cost-effective system design. [ABSTRACT FROM AUTHOR]

This paper focuses on the design, construction, and the experimental testing of an anode recirculation blower (ARB) based on a turbocompressor for PEM-FCs. The blower presented consists of a high-speed centrifugal compressor, driven by a so-called media-gap motor. Additionally, it includes a droplet separator to eliminate liquid water from the anode loop. The aerodynamic design is based on one-dimensional-correlations and three-dimensional-numerical CFD simulations. Different gas compositions of hydrogen, nitrogen, and water vapor are considered in the design, depending on the operating points of a PEM-FC. The gas composition has a significant influence on the achievable pressure ratio at constant compressor speeds, depending mainly on the specific heat capacity of the gas. Performance maps for different gas compositions are calculated using CFD for the designed ARB. A prototype is built and tested. The results validate the CFD predictions and show that the operating range of a PEM fuel cell can be covered with the present blower. In addition, it could be shown that an enthalpy-based approach using common characteristic numbers of turbomachines, allows converting performance maps--acquired with different gas compositions--into one another. This allows the performance map prediction for different gas compositions based on existing performance maps. This approach is illustrated by numerical and experimental results. [ABSTRACT FROM AUTHOR]

Hybrid RANS-LES is a promising method for analyzing the complex flow structure in turbomachinery due to its excellent compromise between accuracy and computational cost. However, it is challenging to employ the existing URANS and LES grid resolution evaluation approaches in a hybrid RANS-LES simulation, thus commonly the required grid resolution is unknown, increasing the risk that LES relies on overly coarse grids and leading to unreliable predictions. Hence, spurred by this deficiency and driven by the aspects of coupling grid resolution evaluation with the interest quantity during turbomachinery design and mechanism analysis, this work proposes a novel grid resolution evaluation method suitable for both LES and URANS. The suggested technique considers three grid resolution criteria: no effects on the time-averaged flow field, major unsteadiness, and minor unsteadiness. The developed method is verified employing a classic scenario, i.e. Pitz-Daily backward-facing step. Furthermore, we demonstrate our method's applicability through a T106A turbine cascade example, confirming the feasibility and reliability of the proposed scheme. When applied to hybrid RANS-LES turbomachinery simulations, the research results highlight our method's capability to reduce uncertainty and improve reliability during gridding. [ABSTRACT FROM AUTHOR]

During the operation of supercritical CO 2 (sCO 2 ) turbomachineries, large pressure ratios, supersonic conditions and non-ideal gas fluid dynamic phenomenon may happen, which will decrease the whole cycle efficiencies. Hence non-standard designs for the turbomachineries geometry are needed. Successfully simulations in capturing non-ideal gas fluid dynamics and coupled with optimization algorithm are hard and currently not available in any commercial CFD software. Therefore, the problem of optimizing sCO 2 turbomachinery is difficult to solve, which has become a major obstacle to obtain compact and high-efficiency sCO 2 turbomachineries. In this study, a modularized geometry optimizer is developed to obtain the non-standard geometric designs for sCO 2 turbomachineries. Multiple techniques are applied to this optimizer, include the Nelder–Mead algorithm, Mahalanobis distance and stochastic algorithm. The newly developed optimizer can successfully find the optimum satisfying the objective function under given weighting factors. The computational cost can be reduced through a stochastic algorithm. To validate the optimizer, a convergent–divergent nozzle for air with a target Mach number equal to 2.4 is optimized. Different starting points and combinations of weighting factors are used to create a Pareto front. Adjust the weighting factors for different terms of the objective function leading the optimizer to go to different directions in n-dimensional spaces. Three optimized cases, one is Mach number optimized, one is outlet flow uniformity optimized and the other is compromised case, are picked out and analyzed. The results show that the optimizer can successfully find optimized geometry than the reference case and potentially save computational cost. Due to the modularized characteristics, the components of this optimizer can be replaced with any available techniques, which mean the optimizer can be applied to solve different types of optimization problems. [ABSTRACT FROM AUTHOR]

Modal parameter identification can be a valuable tool in mechanical engineering to predict vibrational behaviour and avoid machine damage during operation. Operational modal analysis is an output-only identification tool motivated by the structural identification of civil engineering structures, which are excited by ambient conditions. This technique is increasingly applied in mechanical engineering in order to characterise the system behaviour during operation as modal parameters can vary under operating conditions. The following study investigates the application of operational modal analysis on an axial compressor under operating conditions. Since the modal parameters of the system change depending on the life history and during the operation of the system, a corresponding data analysis might allow us to identify the present status of the system. Eigenfrequencies and eigenvectors are studied for the use of structural health monitoring approaches. According to the analysis, eigenfrequencies represent robust parameters for the studied purpose. Eigenvectors are sensitive to damages but need further investigation, especially for rotating machinery. This study will help the user to set up a virtual model, which describes the system behaviour for different boundary conditions. This in turn, will provide an accurate prediction of the vibrational behaviour in order to assure a safe operation.

• Hybrid approach using standard and finite-volume lattice Boltzmann methods. • Efficient aeroacoustic simulation for low-speed turbomachines. • Computations on Cartesian and body-fitted grids with the direct forcing method. • The hybrid method simulated flow and acoustic fields around a crossflow fan. In this study, we developed a hybrid approach using the lattice Boltzmann method (LBM) and finite-volume lattice Boltzmann method (FVLBM) to perform efficient aeroacoustic simulations with moving boundaries. An entire domain, including the flow and acoustic fields, was computed using the standard LBM with a Cartesian grid. Local domains around the moving objects were computed using the FVLBM with body-fitted grids. These simulations were coupled using the direct forcing method to consider moving boundaries. The hybrid method was validated for several problems including turbulent flows and flow-induced sounds under low-Mach-number conditions. These validation problems covered flows with Reynolds numbers up to 2.0 × 10 5 and Mach numbers less than 0.2. In the simulations of the aeolian tone generated from stationary and rotating cylinders, the hybrid method results were consistent with those of the conventional methods. In the simulation of the turbulent flow and broadband sound of the isolated airfoil, the hybrid method was 15 times faster than the standard LBM and produced results consistent with the experimental results. Furthermore, the application of a cross-flow fan demonstrated that the hybrid method successfully simulated the flow and acoustic fields around the rotor. [ABSTRACT FROM AUTHOR]

This paper considers the interaction between a rotating bladed-disc and static casing, specifically a synchronisation phenomenon called wave speed coincidence. Through tip rub, travelling waves in the bladed-disc and casing can interact and cause large amplitudes of vibration. Previous work has analysed this phenomenon using time integration methods, but these are often too computationally expensive for early design stages, especially if a large number of designs and conditions need to be considered. Frequency domain approaches such as the harmonic balance method have also been used but they required simplification in the periodicity of the problem which limits the usefulness of such methods. This paper demonstrates the use of a power method and consideration of periodicity over a contact cycle. This allows the problem to still be considered as a periodic behaviour, but without the loss of generality associated with conditional harmonic balance methods. The method is intended to act as a preliminary screening tool, to down-select cases with potential risks of instability due to wave speed coincidence. The smaller number of cases can then be checked using time integration methods. While the current power method is limited in capturing the bladed-disc dynamics, the results demonstrate its use and potential to be developed into a screening method for preliminary design stages. [ABSTRACT FROM AUTHOR]

Cross-Flow Fans (CFFs) have been widely applied in the automotive and domestic air conditioning industries in recent decades. They are high-pressure coefficient turbomachines compacted diametrically, and thus, the complex interactions of these fans require thorough evaluation. Their innovation has opened up new directions in turbomachinery, and both academic research and industry have seen numerous efforts to develop these types of fans. Despite extensive work, optimizing and improving their performance remains a challenge. Enhancing their efficiency necessitates improvements in structural characteristics, aerodynamic features, and acoustic properties. In this review, we aim to demonstrate the essential aspects of CFFs by introducing their fundamentals and primary characteristics. Furthermore, we delve into a discussion on the acoustic performance of these fans. We also summarize the flow characteristics and different flow-field patterns in CFFs and their impact on aeroacoustic behavior. The main objective of this review paper is to provide an overview of the research in this field, summarizing the critical factors that play a significant role in studying CFFs’ performance.

Numerical optimization methods are widely used for designing turbomachinery components due to the cost and time savings they can provide. In the available literature, the shape optimization of radial compressors mainly focuses on improving the impeller alone. However, it is well-established knowledge that the volute plays a key role in the overall performance of the compressor. The aim of the present paper is to perform an adjoint-based optimization of a volute that is designed for the SRV2-O compressor. The CAD model was first created by using the parametrization of 33 design parameters. Then, a butterfly topology was applied to mesh the computational domain with a multi-block structured grid, and an elliptic smoothing procedure was used to improve the quality of the fluid grid. A steady-state RANS CFD solver with a Spalart-Allmaras turbulence model was used to solve the Navier–Stokes equations, and then the flow sensitivities were computed with an adjoint solver. The objective function consists of minimizing the loss coefficient of the volute. The optimization is performed to obtain an improved design with a 14% loss reduction. A detailed flow and design analysis is carried out to highlight the loss reduction mechanisms, followed by the optimizer. Finally, the compressor map of the full stage is compared between the baseline and the optimized volute from the CFD simulations using a mixing plane interface. This research demonstrates the successful use of a gradient-based optimization technique to improve the volute of a radial compressor and opens the door towards simultaneously optimizing the wheel and the volute.

This paper presents the development of high-specific-speed mixed flow/centrifugal compressor vaned diffusers. Specifically, the design of a test rig that will make the visualization of shock waves on diffuser vanes manageable is addressed in the current study. In this particular case, linearization of an existing state-of-the-art compressor stage was used. For the computational modeling, a series of RANS analyses were conducted to examine the flow characteristics of the two cases explored: a complete transonic cascade and an idealized periodic passage. The distinct behavior exhibited by each vane passage within the entire cascade offers the opportunity to analyze the shockwave structures across a mass flow range of ±9% around the design point. Overall, the pressure coefficient distributions and flow field patterns appear to align with the single-passage conditions, although there are some minor lateral wall influences, particularly in the first passage close to the suction lateral wall. However, because of the nature of the flow, which is characterized by high velocity and density differences near the vanes, the equivalent mass flow per individual passage was difficult to estimate. This may also be attributed to the small endwall axial vortices; nonetheless, for the purposes of this paper, this was of little consequence.

The present work provides a detailed numerical investigation of a turbopump for waterjet applications in cavitating conditions. In particular, the study focuses on the complexities of cavitation modelling, serving as a pivotal reference for future computational research, especially in off-design hydro-jet scenarios, and it aims to extend current model assessments of the existing methods, by disputing their standard formulations. Thus, a computational domain of a single rotor-stator blade passage is solved using steady-state Reynolds-Averaged Navier–Stokes equations, coupled with one-, two-, and four-equation turbulence models, and compared with available measurements, encompassing both nominal and thrust breakdown conditions. Through grid dependency analysis, a medium refinement with the Shear Stress Transport turbulence model is chosen as the optimal configuration, reducing either computational time and relative error in breakdown efficiency to 1%. This arrangement is coupled with a systematic study of the Zwart cavitation model parameters through multipliers ranging from 10−2 to 102. Results reveal that properly tuning these values allows for a more accurate reconstruction of the initial phases of cavitation up to breakdown. Notably, increasing the nucleation radius reduces the difference between the estimated head rise and experimental values near breakdown, reducing the maximum error by 4%. This variation constrains vapour concentration, promoting cavitation volume extension in the passage. A similar observation occurs when modifying the condensation coefficient, whereas altering the vaporization coefficient yields opposite effects.

We present a speed line calculation model using physics-based surge point identification. When using surrogate model-based design of experiment (DOE) techniques, the large number of computations demands an automated, unsupervised process to calculate the speed line and to identify its significant points. A high-fidelity CAE workflow is used to calculate the machine design, create the CAD geometry, generate a mesh, and prepare a CFD setup. The choke point, the surge point and the peak efficiency point are sequentially identified using sophisticated identifiers and optimization algorithms. The model was used to calculate the speed line of 50 different centrifugal compressor designs with 50 geometry variations each. From these 2,500 designs, 2,449 speed lines were calculated successfully, without specific settings having been assigned to individual designs. This proves that the model enables the stable, reproducible, reliable and effective CFD calculation of the speed line of centrifugal compressors.

The vibration characteristics of a bladed disk with the continuous ring type structure have been studied extensively, and the vibration response analyses considering the friction damping between adjacent shrouds have been performed in the blade design. The effect of the friction damping on the self-excited vibration also has been studied by several researchers. However, because the most of these studies have been performed using the simple macroslip model, the damping characteristics of bladed disks with the friction damping are not yet clarified sufficiently. Moreover, few studies have focused on the transient response of a blade with the friction damping. In this paper, the damping characteristics of bladed disks with the continuous ring type structure is studied using the conventional macroslip model and the sophisticated microslip model for the transient response when passing through the resonance, and the results calculated by both models are compared. From the analysis results, it is concluded that, in the transient response when passing through the resonance, the damping characteristics predicted by both models are qualitatively the same if the excitation force is extremely large or small. However, when the excitation force is medium, the damping characteristics predicted by both models are quantitatively different. Therefore, it is recommended that the microslip model with appropriate parameters is used to improve the accuracy of the prediction of the damping characteristics.

This work presents the development and application of a machine learning model to predict the unsteady performance of a turbocharger radial turbine subject to on-engine pulsating flow conditions. The model proposed, based on a fully connected neural network, predicts the instantaneous turbine torque and circumferentially-averaged relative inflow angle when given, as only inputs, the total pressure and temperature pulses and the time derivative of the total pressure pulse upstream of the turbine.The training data set for the model is obtained from an experimentally-validated Reynolds-averaged Navier–Stokes model and consists of various operating conditions characterized by different pulse amplitudes and frequencies. Heat transfer effects are neglected by the use of adiabatic boundary conditions while the rotational speed of the rotor is otherwise maintained fixed. Based on the results obtained, the model is shown capable of accurately predicting the turbine torque and local properties of the flow, such as the relative inflow angle, with a high degree of accuracy (coefficient of determination larger than 0.98). At first, the model is tested for both interpolation and extrapolation conditions. Given a training data set constituted by only three pulses characterized by different amplitudes, the model accurately predicts the turbine performance both for conditions inside and outside the range of amplitudes of the training data set. Lastly, the model is trained with a larger data set, including both variations of the pulse amplitude and frequency, in order to predict the performance of the turbine subject to a more general pulse shape. The error indicators show an improvement with respect to the extrapolation case due to the larger size of the training data set, showing also a great capability of the model to predict the unsteady performance of the turbine for a more general pulse shape. The model represents a fast and efficient approach for predicting the unsteady turbine performance as compared to more complex experimental set-ups and time-consuming 3D numerical simulations and a valid alternative to the more common 0D-1D models.

The manufacturing process of blade-integrated disks (blisks) represents one of the most challenging tasks in turbomachinery manufacturing. The requirement is to machine complex, thin-walled blade geometries with high aspect ratios made of difficult-to-cut materials. In addition, extremely tight tolerances are required, since the smallest deviations can lead to a reduction in efficiency of the blisk in the later use. Nowadays, the ramp-up phase for the manufacturing of a new blisk is time and cost-intensive. To find a suitable manufacturing process that meets the required tolerances of the blisk, many experimental tests with different process parameters and strategies are necessary. The used approach is often trial and error, which offers limited testing opportunities, is time-consuming and waste of resources. Therefore, the objective of this paper is to develop a knowledge-based process design optimization in blisk manufacturing. For this purpose, this paper picks up the results from our previous work. Based on these results, an experimental validation of the two process design tasks "number of blocks" and "block transition" is conducted. As part of the validation, the results of machining tests on a demonstrator blisk made of Inconel 718 are presented and discussed. [ABSTRACT FROM AUTHOR]

With increasing design demands of turbomachinery, stochastic flutter behavior has become more prominent and even appears a hazard to reliability and safety. Stochastic flutter assessment is an effective measure to quantify the failure risk and improve aeroelastic stability. However, for complex turbomachinery with multiple dynamic influencing factors (i.e., aeroengine compressor with time-variant loads), the stochastic flutter assessment is hard to be achieved effectively, since large deviations and inefficient computing will be incurred no matter considering influencing factors at a certain instant or the whole time domain. To improve the assessing efficiency and accuracy of stochastic flutter behavior, a dynamic meta-modeling approach (termed BA-DWTR) is presented with the integration of bat algorithm (BA) and dynamic wavelet tube regression (DWTR). The stochastic flutter assessment of a typical compressor blade is considered as one case to evaluate the proposed approach with respect to condition variabilities and load fluctuations. The evaluation results reveal that the compressor blade has 0.95% probability to induce flutter failure when operating 100% rotative rate at t=170 s. The total temperature at rotor inlet and dynamic operating loads (vibrating frequency and rotative rate) are the primary sensitive parameters on flutter failure probability. Bymethod comparisons, the presented approach is validated to possess high-accuracy and highefficiency in assessing the stochastic flutter behavior for turbomachinery. [ABSTRACT FROM AUTHOR]

Boundary-layer flow separation is a common flow feature in many engineering applications. The consequences of flow separation in turbomachinery can be disastrous in terms of performance, stability and noise. In this context, flow separation is particularly difficult to understand because of its three-dimensional and confined aspects. Analyzing the skin friction lines is one key point to understanding and controlling this phenomenon. In the case of separation, the flow at the wall agglutinates around a manifold while the fluid from the boundary layer is ejected toward the flow away from the wall. The analysis of a three-dimensional separation zone based on topology is well addressed for a simple geometry. This paper aims at providing simple rules and methods, with a clear vocabulary based on mathematical background, to conduct a similar analysis with complex turbomachinery geometry (to understand a surface with a high genus). Such an analysis relies on physical principles that help in understanding the mechanisms of flow separation on complex geometries. This paper includes numerous typical turbomachinery surfaces: the stator row, vaneless diffuser, vaned diffuser, axial rotor and shrouded and unshrouded centrifugal impeller. Thanks to surface homeomorphisms, the generic examples presented can easily be converted into realistic shapes. Furthermore, classical turbomachinery problems are also addressed, such as periodicity or rotor clearance. In the last section, the proposed methodology is conducted on a radial diffuser of an industrial compressor. The flow at the wall is extracted from LES computations. This study presents the different closed separation zones in a high-efficiency operating condition. [ABSTRACT FROM AUTHOR]

Copyright of Dokuz Eylul University Muhendislik Faculty of Engineering Journal of Science & Engineering / Dokuz Eylül Üniversitesi Mühendislik Fakültesi Fen ve Mühendislik Dergisi is the property of Dokuz Eylul Universitesi Muhendislik Fakultesi Fen ve Muhendislik Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Currently, software products for numerical simulation of fluid dynamics processes (Ansys, Star CCM+, Comsol) are widely used in the power engineering industry when designing new equipment. However, computer simulation methods embedded in proprietary software products make specialists choose grid settings, boundary conditions, and a solver providing the minimal deviation from experimental data with the maximal calculation speed. This paper analyzes the influence of the main grid settings and boundary conditions in the Ansys software package on the error in the computer simulation of flows in standard elements of power equipment and gives recommendations for their optimal choice. As standard elements were considered blade turbine channels formed by C-90-22 A profiles. [ABSTRACT FROM AUTHOR]

Designing blades for efficient energy transfer by turning the flow and angular momentum change is both an art and iterative multidisciplinary engineering process. A robust parametric design tool with few inputs to create 3D blades for turbomachinery and rotating or non-rotating energy converters is described in this paper. The parameters include axial–radial coordinates of the leading/trailing edges, construction lines (streamlines), metal angles, thickness-to-chord ratio, standard, and user-defined airfoil type among others. Using these, 2D airfoils are created, conformally mapped to 3D stream surfaces, stacked radially with multiple options, and they are transformed to a 3D Cartesian coordinate system. Smooth changes in blade curvature are essential to ensure a smooth pressure distribution and attached flow. B-splines are used to control meanline curvature, thickness, leading edge shape, sweep-lean, and other parameters chordwise and spanwise, making the design iteration quick and easy. C2 curve continuity is achieved through parametric segments of cubic and quartic B-splines and is better than G2. New geometries using an efficient parametric scheme and minimal CAD interaction create watertight solid bodies and optional fluid domains. Several examples of ducted axial and radial turbomachinery with special airfoil shapes or otherwise, unducted rotors including propellers and wind and hydrokinetic turbines are presented to demonstrate versatility and robustness of the tool and can be easily tied to any automation chain and optimizer. [ABSTRACT FROM AUTHOR]