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THE NUMERICAL AND EXPERIMENTAL INVESTIGATION of boundary layer tripping using steps on the suction side of a transonic compressor rotor has been presented in this paper. The presented research corresponds to an EU project known as TFAST (Transition Location Effects on Shock Wave Boundary Layer Interaction). A representative single passage test section has been designed to investigate the SBLI (Shock wave Boundary Layer Interaction) effects on the rotor profile. The geometrical and inflow boundary conditions have been defined by the project partner RRD (Rolls-Royce Deutschland). Two locations of step (x=c = 0:16 and x=c = 0:02) were chosen upstream of the shock location to investigate the boundary layer tripping effects and are compared with configuration without tripping setup. The numerical simulations were carried out on the test section model using the steady-state Reynolds Averaged Navier-Stokes (RANS) model with Explicit Algebraic Reynolds Stress Model (EARSM) turbulence model with transition effects included. The chosen turbulence model could accurately predict the shock location on the suction side of the lower profile in the test section and had a good agreement with wall pressure measurements using pressure taps. A detailed shock structure was captured using the schlieren technique and compared for different tripping configurations. To estimate the effectiveness of the tripping setup losses have been estimated using LDA (Laser Doppler Anemometry) along the traverse downstream the blade passage. To understand the tripping effect on the boundary layer a detailed investigation has been carried out at ten selected traverse locations from leading edge to trailing edge of the rotor profile. Based on the experimental validation of the defined numerical model for tripping setup, a few more step heights were compared at selected tripping locations numerically. To analyse the effect of step heights, the isentropic Mach number and wall shear stress are compared with without tripping configuration. The wake and stagnation pressure losses downstream of the profile have been compared to investigate the sensitivity of location and geometrical definition of the boundary layer tripping setup on the aerodynamic losses. [ABSTRACT FROM AUTHOR]

This paper outlines the update of a turbomachinery course to cover three-dimensional (3D) aerodynamics using a Reynolds-Averaged Navier Stokes solver. Prior to the activities outlined in this paper, the course was taught in a conventional way with a series of lectures and a timed, written, open book examination in a formal exam setting. Students were equipped with a calculator and set of notes including correlations from Howell and Soderberg. The students had around 1 h to answer the turbomachinery question, which was revealed to them only when they opened the paper at the start of the exam. This limited the depth of any aerodynamic problem they could get through and so they were restricted to simple design or analysis exercises. The genesis of the course update was the release in 2017 of "MULTALL OPEN" (Denton, J. D., 2017, "Multall: An Open Source, Computational Fluid Dynamics Based, Turbomachinery Design System," ASME J. Turbomach., 139(12), p. 121001), a freely available turbomachinery design system, and this was adopted as the course software--although other software choices were considered. Students now produce two turbomachinery designs during the course. These are both based on the J85 turbojet--largely to keep cycle calculations to a minimum but it was also important to ensure that students recognize that they were completing a real engineering task. The first task was a 3D aerodynamic design of multistage turbine, which includes compressible flow, tip clearance, and stacking techniques such as lean or sweep. The second task was a midspan (two-dimensional) compressor design. The exact cycle conditions were varied each year to explore design scenarios such as an increase in firing temperature. Assessment was by means of a short report where the best students report on their design choices, provide critical analysis of the design using appropriate postprocessing techniques, and compare their designs to the state of the art in the wider literature. As well as describing the successes and challenges of the update to 3D design methods the paper provides some guidance for educators thinking about adopting a similar approach. [ABSTRACT FROM AUTHOR]

The use of film cooling is crucial to avoid high metal temperatures in gas turbine applications, thus ensuring a high lifetime for vanes and blades. The complex turbulent mixing process between the coolant and the main flow requires an accurate numerical prediction to correctly estimate the impact of ejection conditions on the cooling performance. Recent developments in numerical models aim at using hybrid approaches that combine high precision with low computational cost. This paper is focused on the numerical simulation of a cylindrical film cooling hole that operates at a unitary blowing ratio, with a hot gas Mach number of Ma m = 0.6, while the coolant is characterized by plenum conditions ( Ma c = 0). The adopted numerical approach is the Stress-Blended Eddy Simulation model (SBES), which is a blend between a Reynolds-Averaged Navier–Stokes approach and a modeled Large Eddy Simulation based on the local flow and mesh characteristics. The purpose of this paper is to investigate the ability of the hybrid model to capture the complex mixing between the coolant and the main flow. The cooling performance of the hole is quantified through the film cooling effectiveness, the Net Heat Flux Reduction (NHFR), and the discharge coefficient C D calculation. Numerical results are compared both with the experimental data obtained by the University of Karlsruhe during the EU-funded TATEF2 project and with a Scale Adaptive Simulation (SAS) run on the same computational grid. The use of λ 2 profiles extracted from the flow field allows for isolating the main vortical structures such as horseshoe vortices, counter-rotating vortex pairs (e.g., kidney vortices), Kelvin–Helmholtz instabilities, and hairpin vortices. Eventually, the contribution of the unsteady phenomena occurring at the hole exit section is quantified through Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition methods (SPOD). [ABSTRACT FROM AUTHOR]

When it comes to modern design of turbomachinery, one of the most critical objectives is to achieve higher efficiency and performance by reducing weight, fuel consumption, and noise emissions. This implies the need for reducing the mass and number of the components, by designing thinner, lighter, and more loaded blades. These choices may lead to mechanical issues caused by the fluid–structure interaction, such as flutter and forced response. Due to the periodic aerodynamic loading in rotating components, preventing or predicting resonances is essential to avoid or limit the dangerous vibration of the blades; thus, simulation methods are crucial to study such conditions during the machine design. The purpose of this paper is to assess a numerical approach based on a topology optimization method for the innovative design of a compressor rotor. A fluid-structural optimization process has been applied to a rotor blisk which belongs to a one-and-a-half-stage aeronautical compressor including static and dynamic loads coming from blade rotation and fluid flow interaction. The fluid forcing is computed by some CFD TRAF code, and it is processed via time and space discrete Fourier transform to extract the pressure fluctuation components in a cyclic-symmetry environment. Finally, a topological optimization of the disk is performed, and the encouraging results are presented and discussed. The remarkable mass reduction in the component (≈32%), the mode-shape frequency shift from a fluid forcing frequency, and an overall relevant reduction in the dynamic response around Campbell's crossing confirm the efficacy of the presented methodology. [ABSTRACT FROM AUTHOR]

This paper deals with the reactivation of three test benches of high, medium and low power electric generators for hydraulic energy conversion in the University of Carabobo Hydraulic Laboratory. The method involves three stages: i) Description of three high, medium and low power electric generators for hydraulic energy conversion, ii) Rehabilitation of three high, medium and low power electric generators for hydraulic energy conversion and iii) Evaluation of performance indexes of high, medium and low power electric generators for hydraulic conversion. The results indicate that for the low power electric generator, the position angle of the distributor blades is an experimental factor that has a significant effect on the response variables studied. With respect to the medium and high power electric generators, the most influential factor on operation and power generation is the flow supplied. [ABSTRACT FROM AUTHOR]

Pressure gain combustors (PGCs) have demonstrated significant advantages over conventional combustors in gas turbine engines by increasing the thermal efficiency and reducing the pollution emission level. PGCs use shock waves to transfer energy which contributes to the increase in outlet total pressure. One of the major obstacles in the actual implementation of PGCs in the gas turbine cycle is the exploitation of the highly unsteady flow of the combustor outlet with the downstream turbine. Because of the higher outlet temperature from the PGCs, the turbine blade cooling becomes essential. Due to the highly fluctuating unsteady flow of PGCs, 3D CFD simulation of turbines becomes very expensive. In this work, an alternative approach of using a 1D unsteady Euler model for the turbine is proposed. One of the novel aspects of this paper is to implement the turbine blade cooling in the unsteady 1D Euler model. The main parameters required for the turbine blade cooling are the cooling air mass flow rate, temperature, and pressure. Due to the introduction of coolant flow, the blades are no longer adiabatic and the mass flow rate across the turbine is not constant. Comparing the 1D Euler results against zero-dimensional calculation and 3D CFD approach showed a very good match for both steady and unsteady simulations confirming the applicability of the 1D method. [ABSTRACT FROM AUTHOR]

When rotating noise sources, such as turbomachinery, are investigated using phased microphone array measurements and beamforming, sidelobes appear on the resulting beamforming maps. Sidelobes can be decreased by increasing the number of microphones. However, if the investigated phenomenon is steady, then there is a cost-effective alternative: performing asynchronous measurements using phased arrays having a limited number of microphones. The single beamforming maps can be combined in order to arrive at results that are superior in resolution and sidelobe levels. This technique has been investigated in the literature, but according to the authors' best knowledge, has not yet been applied to turbomachinery. This article introduces a means for applying the asynchronous measurement technique and the combination methods for rotating noise sources. The combination methods are demonstrated on two rotating point sources (both in simulations and measurements), and then on an axial flow fan test case. In the case of the two rotating point sources, the achievable improvement in resolution, average-, and maximum sidelobe levels are shown as compared to the single results. In the case of the axial flow fan, it is demonstrated that the combination methods provide more reliable noise source locations and reveal further noise sources. [ABSTRACT FROM AUTHOR]

Vortex breakdown occurs in highly swirling flows in various engineering applications, such as hydraulic turbines working in either high-load or part-load conditions, leading to pressure pulsations and performance degradation. In the present study, the formation of a helical vortex breakdown having rotational and plunging components (axial oscillation) in a straight diffuser is investigated with transient simulation from its columnar state to a helical vortex breakdown state. It is similar to the helical precessing vortex rope occurring in hydraulic turbines operating at part-load condition. In addition, considering vortex breakdown as a global instability, a linear global stability analysis of the time-averaged turbulent flow field is conducted for different flow states. The main objective is to understand the role of plunging mode in vortex rope formation in straight draft tubes and identify its differences with the one observed in hydraulic turbines with elbow draft tubes operating at part-load condition. Results showed that in contrast to the elbow draft tubes where the plunging mode appears earlier than the rotating mode, the transient simulation showed that the plunging mode appears after several vortex rope rotations in the straight draft tube. This is confirmed by the stability analysis showing that the flow is unstable to the asymmetrical disturbances with a frequency close to the rotating frequency not the plunging ones. Finally, the stability analysis showed a higher critical flow rate than the one obtained from the contour of local swirl number and time history of pressure and velocity. [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. [ABSTRACT FROM AUTHOR]

Over the past few years, stringent environmental requirements and the need for increased overall efficiency have forced designers to bring turbomachine components closer to their operating limits. To address lifespan issues, costly redesign operations are thus unavoidable. These operations face many roadblocks, especially when they are triggered by nonlinear phenomena for which there exists no design guidelines. For aircraft engine blades, the handling of nonlinear structural interactions is a major challenge. This works proposes a proof of concept for the redesign of compressor blades undergoing structural contact interactions at the blade-tip/casing interface. The redesign process involves the modeling of an existing input blade, followed by a shape update based on an iterative optimization algorithm. A two-way modeling method is proposed to parameterize the input blade and generate a computer-aided design model from blade parameters describing several conical blade sections. The fidelity of the parameterized blade with respect to the input blade is assessed for the NASA blades rotor 37 and rotor 67. A high fidelity is observed with respect to geometric and dynamic characteristics. The modeling method is fully compatible with an iterative redesign process: it is applied to the redesign of rotor 37 to increase its robustness to contact interactions. [ABSTRACT FROM AUTHOR]

There has been an extensive amount of work developing reduced-order models (ROMs) for bladed disks using single-sector models and a cyclic analysis. Several ROMs currently exist to accurately model a bladed disk with under-platform dampers. To better predict the complex nonlinear response of a system with under-platform dampers, this work demonstrates how two linear models can determine bounds for the nonlinear response. The two cases explored are where the under-platform damper is completely stuck and also where the damper slides without friction. This work utilizes the component mode mistuning method to model small mistuning and a parametric ROM method to capture changes in properties due to rotational speed effects. Previously, these ROM methodologies have modeled freestanding bladed disk systems. To evaluate the ROM in predicting the bounds, blade tip amplitudes from the models are compared with high-speed rotating experiments conducted in a large, evacuated vacuum tank. The experimental data were collected during testing using strain gauges and laser blade tip timing probes. The blade amplitudes of the tip timing data, strain gauge data, and computational simulations are compared to determine the effectiveness of the simplified linear analysis in bounding the nonlinear response of the physical system. [ABSTRACT FROM AUTHOR]

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 10 2 . 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. [ABSTRACT FROM AUTHOR]

In recent years, the usage of open-source computational fluid dynamics tools is on a rise both in industry and academia. SU2 is one of these open-source tools. Unlike other open-source alternatives, SU2 is equipped with boundary condition types, solvers and methods that are especially developed for the analysis and design of turbomachinery. The aim of this work is to explore and investigate the capabilities of SU2 in the prediction of performance parameters of radial compressors. Two different single stage shrouded compressor geometries, one with a vaneless diffuser and the other with a vaned diffuser have been investigated with steady state CFD. The compressors were designed by MAN Energy Solutions Schweiz AG. Computational results with SU2 showed a satisfactory agreement with both the experimental data and reference CFD solutions obtained with Fidelity Flow, which is formerly known as Numeca Fine TURBO. Only at the relatively higher mass flow rates the difference between references and SU2 were higher compared to other operating points. After performance parameters were successfully calculated with SU2, the optimization tools that come with SU2 were also used. A 2D adjoint optimization study on the vane of the vaned diffuser was carried out. The study was carried out at a single operating point that is close to choke conditions. The loss generated by the large separated flow region at the suction side of the diffuser vane was reduced by 0.55 % in the optimized geometry using minimal modifications on the existing vane geometry to keep the performance of the compressor intact at other operating points. However, the resulting modification increased the total pressure loss by 0.86 % at one of the design operating points. This performance penalty could be due to the discontinuity in the vane geometry generated by the optimizer. Overall, the study shows that SU2 has the basic numerical schemes and models that are required for the analysis of radial turbomachinery flows and geometry optimization. [ABSTRACT FROM AUTHOR]

Designing turbomachines requires in many applications to find a suitable compromise between different disciplines, such as aerodynamics, vibration analysis, and structural mechanics. The optimization of such components requires, thus, the concurrent inclusion of all relevant disciplines. This paper presents an efficient gradient-based approach that allows to reach efficiently a compromise when different disciplines are involved. The use of a gradient-based technique guarantees a low computational effort to reach an optimal solution, but faces the challenge of computing the gradients of different disciplines and projecting them on a unified parameter space. This is especially challenging when the solid and fluid domains are governed by different numerical solvers and use different numerical grids. In the present framework, a CAD-based parametrization is used as an intermediate layer that is indifferent to the numerical grid used. This allows to combine sensitivities from different disciplines and grids onto a single set of parameters, and ensures at the same time that at the fluid–solid interface, no overlaps or voids are created between the different numerical grids. The approach is illustrated on the optimization of the SRV2-O radial compressor where concurrently the aerodynamic performance at two different operating points, the impeller moment of inertia, the maximum stress inside the material, and the vibration response of the compressor wheel are considered. Although 112 design variables are used, a 3.5% improvement in efficiency was achieved within less than 25 major iterations, while satisfying all mechanical and aerodynamic constraints. This demonstrates the cost effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Attempting to predict the physical response of a complex system under realistic conditions is extremely challenging. In this work, a parametric reduced-order model (PROM) of a bladed disk is briefly presented that allows for the quick and efficient modeling of rotational speed effects and mistuning effects in bladed disks. This computational model is tuned to match experimental data. The tuned PROM is then investigated through a parametric study. Three internal parameters investigated are i) forcing magnitude, ii) mistuning value magnitude, and iii) damping magnitude, and four external parameters are iv) forcing location, v) forcing radius, vi) probe placement error, and vii) arrival time error. These parameters are common in the structural analysis of turbomachines. Each internal parameter is increased and decreased by 10, 20, and 50%, while external parameters are changed by varying amounts due to geometric and practical limitations. The model is time integrated to simulate the conditions present in the experimental test rig. The maximum blade amplitudes are then compared to the baseline case and analyzed. The damping, followed by the forcing, is shown to cause the greatest impact on the final system response. This indicates a greater need to accurately measure the damping compared to other parameters. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

• 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]

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]

Maintenance of adequate thermal properties is critical for correct operation of a gas foil bearing. In this work, the authors present the results of the experimentally conducted thermal characterization of a prototype installation of the bearing. A novel method of temperature identification, based on integrated thermocouples readings, has been employed to determine the thermal properties of the specialized sensing top foil mounted in the tested bearing. Two measurement campaigns have been subsequently completed, applying freely-suspended and two-node support configurations, to gather complementary knowledge regarding the bearing's operation. Apart from the rotational speed and temperature field measurements, the authors have also studied the friction torque and the shaft's journal trajectories based on its radial displacements. The temporal courses for the above-mentioned quantities have enabled inference on the effects present during run-up, run-out and stable state operation at a constant speed. As confirmed, the applied distribution of the integrated sensors allows for temperature readings on the entire outer surface of the foil, and therefore, provides useful data for the bearing characterization. The work is concluded with presentation of the recommended directions regarding future improvements of the proposed measurement technique and more comprehensive study of the bearing's characteristics. [ABSTRACT FROM AUTHOR]

In gradient-based aerodynamic optimisation, the functional gradient required by the optimiser can be obtained as a product of adjoint-based functional sensitivities to volume grid nodes and the volume mesh sensitivities to the design parameters. For turbomachinery applications, it is desirable to use the actual blade design variables as degrees of freedom for the optimisation process, but this can lead to tedious programming tasks. As an alternative, a Machine Learning (ML) model is created to mimic and differentiate the blade geometry and the mesh generation processes. The typical ML forward pass is followed by a back differentiation operation enabling the computation of the volume mesh derivatives with respect to design parameters. The model is tested by comparing the ML-predicted and reference grid, and the modelled sensitivities are verified through algorithmic differentiation. The modelled mesh sensitivities are successfully employed for adjoint-based reverse engineering and design optimisation problems on a turbine blade. [ABSTRACT FROM AUTHOR]

Cross-flow fans (CFFs) have become increasingly popular in recent years. This is due to their use in several domains such as air conditioning and aircraft propulsion. They also show their utility in the ventilation system of hybrid electric cars. Their high efficiency and performance significantly rely on the design parameters. Up to now, there is no general approach that predicts the CFFs' performance. This work describes a new methodology that helps deduce the performance of CFFs in turbomachinery, using both analytical modeling and experimental data. Two different loss models are detailed and compared to determine the performance–pressure curves of this type of fan. The efficiency evaluation is achieved by realizing a multidisciplinary study, computational fluid dynamics (CFD) simulations, and an optimization algorithm combined to explore the internal flow field and obtain additional information about the eccentric vortex, to finally obtain the ultimate formulation of the Eck/Laing CFF efficiency, which is validated by the experimental results with good agreement. This approach can be an efficient tool to speed up the cross-flow fans' design cycle and to predict their global performance. [ABSTRACT FROM AUTHOR]

A multi-passage harmonic balance method is presented for flutter prediction in multi-row configurations, and particular focus is on simulation of more than two blade rows. The unsteady flows in such configurations contain two kinds of multiple perturbations: one refers to those who have different frequencies and the other one refers to those who have the same frequency but different inter-blade phase angles (IBPAs). Most of current harmonic balance methods only consider the former one and the applications have been restricted to two-blade-row configurations. In the few studies that consider more rows, a one-to-one correspondence assumption between frequency and IBPA is usually made putting extra limitation on the used modes. This motivates our work, and a simple but effective idea is proposed by adding passages adopted per row. The theoretical basis of this work is provided by the spinning mode analysis. The present method is developed based on the time-spectral and multi-frequential form of harmonic balance. The treatment of pitchwise and inter-row boundary conditions in the case of multi passages are particularly addressed. A recently-developed Jacobian-free Newton-Krylov method with a simplified LU-SGS preconditioner is employed to solve the resultant harmonic balance equations. For validation, two typical multi-row flutter cases are investigated. The numerical results show the validity and accuracy of the developed method. [ABSTRACT FROM AUTHOR]

For the first time, a fully-coupled Harmonic Balance method is developed for the forced response of turbomachinery blades. The method is applied to a state-of-the-art model of a turbine bladed disk with interlocked shrouds subjected to wake-induced loading. The recurrent partial opening and closing of the pre-loaded shroud contact causes a softening effect, leading to turning points in the amplitude–frequency curve near resonance. Therefore, the coupled solver is embedded into a numerical path continuation framework. Two variants are developed: the coupled continuation of the solution path, and the coupled re-iteration of selected solution points. While the re-iteration variant is slightly more costly per solution point, it has the important advantage that it can be run completely in parallel, which substantially reduces the wall clock time. It is shown that wake- and vibration-induced flow fields do not linearly superimpose, leading to a severe under-/overestimation of the resonant vibration level by the influence-coefficient-based state-of-the-art methods (which rely on this linearity assumption). [ABSTRACT FROM AUTHOR]

Early and efficient harmonization between product design and manufacturing represents one of the most challenging tasks in engineering. Concepts such as simultaneous engineering aim for a product creation process, which addresses both, functional requirements as well as requirements from production. However, existing concepts mostly focus on organizational tasks and heavily rely on the human factor for the exchange of complex information across different domains, organizations, or systems. Nowadays product and process design make use of advanced software tools such as computer-aided design, manufacturing, and engineering systems (CAD/CAM/CAE). Modern systems already provide seamless integration of both worlds in a single digital environment to ensure a continuous workflow. Yet, for the holistic harmonization between product and process design, the following aspects are missing: (i) the digital environment does not provide a complete and data consistent digital twin of the component; this applies especially to the process design and analysis environment, (ii) due to the lack of process and part condition data in the manufacturing environment, an adaptation of product and process design for a balanced functionality and manufacturability is hindered, and (iii) systematic long-term data analytics across different product and process designs with the ultimate goal to transfer knowledge from one product to the next and to accelerate the entire product development process is not considered. This paper presents an exploration concept which couples product design (CAD), process design (CAM), process simulation (CAE), and process adaptation in a single software system. The approach provides insights into correlations and dependencies between input parameters of product/process design and the process output. The insights potentially allow for a knowledge-based adaptation, tackling well-known optimization issues such as parameter choice or operation sequencing. First results are demonstrated using the example of a blade integrated disk (blisk). [ABSTRACT FROM AUTHOR]

Machining level and manufacturing accuracy have an important influence on the reliability of turbomachinery flow physics and dynamic performance. This article proposes a hybrid uncertainty analysis method for fluid dynamics problems with manufacturing constraints. The parameters with sufficient and insufficient experimental samples are processed by the stochastic method and interval method, respectively, which can quickly solve the difficulties of epistemic uncertainty modelling caused by the lack of experimental samples. On this basis, an efficient iterative algorithm is proposed to solve the hybrid reliability model based on the update response surface, and the interval of the failure probability of fluid dynamics for turbomachinery is calculated. Two examples of cooling axial flow and centrifugal turbomachinery are given to verify the validity of the proposed method. The results show that the reliability of the turbomachinery flow performance can be significantly improved by increasing the uncertainty level of key parameters. [ABSTRACT FROM AUTHOR]

With the development of gas turbine towards higher load capacity and improved efficiency, blade flutter has emerged as a significant obstacle in the further development of turbomachinery due to fluid-structure coupling phenomenon. However, the traditional numerical simulation methods lengthen the design cycle and reduce the optimization efficiency due to the expensive time and resource cost. To solve this problem, a fast prediction model of blade flutter based on the graph convolutional neural network is proposed. The blade flutter prediction graph convolutional neural network containing two sub-networks. The flow field prediction network is used to realize prediction from design variables to flow field parameters. The flutter parameter identification network is adopted to realize identification from flow field parameters to 15 flutter parameters. The prediction performance for physical fields, modal forces, aerodynamic damping and aeroelastic stability are discussed. The influence of training size is explored. The results show that the network can not only accurately capture the trends and details of the physical field, but also obtain the accurate modal force curve, so as to calculate the aerodynamic damping parameters and finally judge the aeroelastic stability. [ABSTRACT FROM AUTHOR]

Most data-driven methods used in condition monitoring and early faults alarming of large turbomachines need to manually extract features for modeling, which inevitably introduces subjectivity and uncertainties. In addition, conventional deep learning methods are able to automatically classify fault types using shaft orbit images constructed from the vibration data, but image-based deep learning methods have yet been investigated for the long-term condition monitoring of a turbomachine. This study presented a novel image-based encoder–forecaster deep learning model, OrbitLSTM, to address these issues by modeling the dynamic behaviors of orbit image sequences for condition monitoring of turbomachines. The model is constructed and trained by using orbit image series in the healthy operation status through convolutional long short-term memory network. Then the temporal evolution of orbit shapes is predicted by the trained OrbitLSTM model, and used as a reference to evaluate the machine status under unknown conditions. The early fault warning is triggered when the mean square error or the structural similarity index between measurements and predictions exceeds the predefined threshold. The proposed model seamlessly combines the CNN's capability of automatic feature extraction from images and the LSTM's advantage of long-term memory in historical sequence behaviors. The capability and accuracy of the proposed model for fault monitoring and early warning are demonstrated using both the simulation data and the raw vibration signals collected from sensors installed in different real-world industrial turbomachines. This study provides a new image-based deep learning method for automatic condition monitoring towards the predictive maintenance of large turbomachines in various industrial fields. • An orbit-based encoder–forecaster DL model to model dynamic behaviors of image sequences. • Bayesian wavelet denoising to enhance convolutional LSTM model accuracy. • Generalized procedure to apply new method for condition monitoring of turbomachines. • Method validation with simulated and sensor data from various large turbomachines. [ABSTRACT FROM AUTHOR]

Accurate prediction of real gas flows with strongly variable properties is an essential prerequisite for turbomachinery performance analysis. This paper presents a density-based solver for real gas flows in turbomachinery. The solver employs a third-order discretization scheme to improve computational accuracy. Real gas equations of state and look-up table are utilized in the solver to account for the strong nonlinear variations of thermophysical properties. The preconditioning method is adopted for simulations, including low-Mach flow regions, to address convergence difficulties. The implicit Time Consistent Preconditioned Gauss-Seidel Scheme (TCPGS) is employed for the time-stepping. The solver is validated by transonic compressor cascade wind tunnel experiments. Numerical test cases are adopted to evaluate the solver performance, including NASA Rotor 67, NASA Rotor 37, real gas flows in the Laval nozzle, and compressor seal. It has been proved that the numerical test results are consistent with published technical data. The advantages of this solver include numerical stability, computational efficiency, and physical accuracy, which indicate its applicability in the turbomachinery design process for real gases. • A high-order density-based solver for turbomachinery of the real gases is presented. • Strong changes in thermophysical properties of real gases can be calculated. • Preconditioning method is utilized for solving low-Mach flow regions. • The solver validation is conducted by transonic cascade wind tunnel experiments. • The performance of solver is evaluated by numerical tests. [ABSTRACT FROM AUTHOR]

Computational cost of high-fidelity simulations limits the number of evaluations which may be performed in design exploration and optimization. Surrogates based on samples of multiple fidelities are used to decrease computational cost and lower error from single-fidelity surrogates. This paper develops a novel multi-fidelity surrogate model based on principal components which are shared between multiple fidelities of finite element model samples. This method does not require a common grid between the fidelities, further reducing computational cost. The new method was tested on various design spaces of the Transonic Purdue Research Compressor and compared to other common and novel multi-fidelity methods. The new method was more accurate and required less computational cost than the other tested methods. Little to no increase in computational cost was needed to reduce surrogate error to 50% of the single-fidelity error. For fixed error, the computational cost was reduced by more than 75%. These results were also validated by testing the method on a more complex turbomachinery blade, Parametric Blade Study Rotor 4. The decreased error and computational cost improve effectiveness of design exploration and optimization. Such improvements help meet the demand for cleaner and safer engines by allowing high-fidelity design exploration within reasonable time frames. [ABSTRACT FROM AUTHOR]

An unplanned breakdown in power generation or chemical plant due to the component failure of turbomachines often results in a huge loss of property and productivity as well as a significant increase in maintenance costs. It has become of paramount importance to predict component damage in a turbomachine using instrumented data. Most existing models, however, are obtained from multiple assumptions, resulting in a high false detection ratio due to various data uncertainties. In this article, we present a novel model-free probabilistic methodology for damage detection to resolve the drawbacks of the classical methods. The proposed method adeptly integrates Bayesian inference, wavelets signal processing, probabilistic principal components analysis, and entropy information theory. Bayesian inference is developed for denoising raw data by integrating with multiscale discrete wavelet packets transform and reducing multivariate dimension by combining with principal components analysis. The entropy information theory has been proposed to extract the feature from principal components as a precursor of the event. A multimetric hierarchical alerting strategy is proposed to predict component damage to enhance the accuracy. The feasibility of the presented novel pattern recognition methodology is demonstrated with the detection of blade damage events in a real-world steam turbine using sensor data. [ABSTRACT FROM AUTHOR]

This paper is focusing on diagnosis for longitudinal and radial vibrations of turbomachinery coupled with induction motors. In this context, extensive field vibration measurements are conducted and analysed to identify the source of predominant vibrations on rotor bearing system in a chosen centrifugal compressor in the radial and longitudinal directions. As a first step, the measured overall vibration levels at multiple locations on bearing surface are compared with the existing ISO standard limits. These measurements showed severe longitudinal vibration values and failure of thrust collar assembly which were not considered in turbomachinery (API) design standards. The second step in diagnosis for vibration spectrum measurements are conducted both in longitudinal and radial directions during transient and steady state operations to find the vibration source and thrust collar assembly failure mechanism. This study on vibration diagnosis and analysis on turbomachinery is useful in correcting the severe longitudinal vibrations and damage control measures and corrections associated with static eccentric airgaps through motor air gap diagram. [ABSTRACT FROM AUTHOR]

Due to small footprint and high efficiency, a Supercritical CO2 (S-CO2) power cycle is considered to be one of the promising next-generation power cycles. Although S-CO2 is reported as a powerful cleaning agent, the performance of a power system operating with S-CO2 will also inevitably degrade over time. Previous researchers have shown that turbomachinery deterioration could be a major subject regarding the system performance degradation. Nevertheless, no quantitative evaluation has yet been made so far. In this study, the impact of the performance degradation of the S-CO2 turbomachinery on the overall performance of the system is analyzed quantitatively. The concept of Health Parameter is used to simulate turbomachinery degradation. To quantify the impact, an S-CO2 direct-cycle small modular reactor is selected as a target system. A transient analysis platform is built using a nuclear system safety analysis code and the deep neural network (DNN)-based S-CO2 turbomachinery off-design performance model. System dynamics are evaluated for primary frequency control ability and secondary load-following capability. Results show that the control problems during the transient state can occur when the output fluctuations are large and the performance degradation is severe. It has been confirmed that even control failures of the PID controllers can occur. Therefore, the performance degradation of turbomachinery must be monitored and considered, for an operation strategy for S-CO2 systems. [ABSTRACT FROM AUTHOR]

Reduced order modelling (ROM) techniques allow to reduce the cost of shape optimisation problems. In the present work, the compressible turbulent flow around a gas turbine profile is studied by a Discontinuous Galerkin (DG) scheme. The simulations are accelerated by the combination of two existing ROM approaches: Domain Decomposition and Local Proper Orthogonal Decomposition in a DG (LPOD-DG) framework. In particular, the focus is fixed on the aerofoil suction side which is deformed while the pressure side remains fixed. The proposed method allows to reduce significantly the number of degrees of freedom in the simulation. The method is evaluated by performing a set of random predictions for shapes not included in the training database and comparing the obtained results with high-fidelity simulations. The approach is also compared to a p-adaptive scheme. Finally, the use of an automatic adaptive technique is investigated in order to improve the prediction accuracy at runtime. [ABSTRACT FROM AUTHOR]

Purpose: The paper aims to present an outline of the technology of the active anti-surge algorithm based on high-frequency pressure measurement. The presented system is fast, inexpensive and reliable and does not limit the machine-operating range. Many contemporary anti-surge systems are based on theoretical surge margin. This solution limits machine operating range by about 10-15 per cent in the region of the highest pressure ratios. It is also often sensitive to change in external conditions such as temperature or density, as the system reacts to limits calculated theoretically. Design/methodology/approach: This paper presents results of pressure measurements obtained on the low-speed centrifugal blower DP1.12. The pressure signals were presented in the form of phase diagrams, and conclusions were drawn from their phase portraits to develop the surge indication parameter. Findings: The presented safety system uses the signal to develop the so-called (rate of derivative fluctuation) RDF parameter. In nominal working conditions, this parameter keeps the value close to 1. When RDF reaches values over 3, the anti-surge procedure should be implemented. Experimental studies have shown that this algorithm assures enough time to incur actions suppressing unstable phenomena. Originality/value: The system reacts to real machine working conditions and is hence reliable. The RDF algorithm could also be used to identify local flow instabilities, as well as off-design operation. [ABSTRACT FROM AUTHOR]

An aerodynamic inverse design method, which is used in compressors, is introduced in this paper. This inverse design method is based on the exact solution of the local Riemann problem on moving blade surfaces. Furthermore, an improved relaxation factor is added to control the induced velocity for reasonable deformation sizes in different cases. The viscous flow analysis and the inverse design are integrated in the computational fluid dynamics software ANSYS Fluent using the dynamic mesh user-defined function, which reduces the time spent on remeshing the computational domain. A compressor cascade is taken to illustrate the effect of this inverse design method. Using the compressor model, the case of a different loading pattern design under a high subsonic flow regime and the case of a loading smooth design under a transonic flow regime have proved the capability of this inverse design method to realize the prescribed pressure loading distribution. [ABSTRACT FROM AUTHOR]