bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation and Repeatability Improvement Between Tie Bolt Stretch and Vibration Levels Using Automated Stretch Tool and Regression Analysis
Authors: Horvath Lajos H. , Savela Gregory M. , Mathuria Parag H. , Seyler Joshua R.
Published: August 2024

Many large commercial aircraft utilize an auxiliary power unit (APU) to provide ground and in-flight power and start assist. The gas turbine APU can have a radial flow rotor system made up of a compressor and turbine section which are joined mechanically for ease of assembly and later maintenance activity. In a typical application, these two modules are assembled using a tie-bolt, an adaptor and a curvic coupling. The tie-bolt stretch along with all the internal rotor geometric interfaces is known to greatly influence rotor generated vibration. The tie-bolt is loaded or stretched to achieve the required contact stiffness between the impeller and turbine. This contact stiffness must be maintained throughout the APU ground-flight cycle to ensure that the operational loads do not degrade the rotor condition throughout the design service life. The rotor system is mounted using two bearings, typically a ball bearing for thrust and a roller bearing. These bearings in-turn transit vibration to the APU components, housing, and surrounding aircraft hardware. In some applications, the APU also provides the bleed air to the main engine start. This model of APU is generally inclusive of an additional impeller, called a load compressor. In that case, the turbomachinery consists of the three rotors, whereas assembly features of those three rotors exist two curvic couplings, adapter and tie bolt as required.

It will be shown here how the tie-bolt stretch as a manufacturing assembly operation can be related to rotor generated vibration. Further, through regression analysis an approach to optimizing this stretch a priori for a given set of hardware to minimize vibration for a production unit subject to production style detail part and assembly tolerances is presented. The investigation focuses on optimizing any specific stretched state to best position a rotor assembly in the zone between elastic and plastic limits so to actively minimize vibration to best approach analytical prediction. As a result of knowledge gained here, this approach can be used as a predictive tool for optimizing and projecting operational characteristics of a complex jet engine rotor assembly system with curvic couplings involving dis-similar homogeneous metals. Included in this investigation is the impact of straightness of a rotor assembly with multiple curvics and its impact on vibration, where minimizing or eliminating the undesired post assembly trim balance process (a.k.a. in situ balancing) or other reworking of the assemblies at final engine test was the objective.
Investigation of Endwall Secondary Flows in a Low Aspect Ratio Transonic Turbine, Part I: Passage Normal Shock
Authors: Jennerjohn Christianer Mary K. , McQuilling Mark , McKeever Craig
Published: August 2024

A significant source of loss in turbines includes the generation of endwall secondary flows and subsequent mixing losses downstream of a blade row. In the case of reduced aspect ratios, these secondary flows assume a greater spanwise penetration attributing to increased loss generation. In the first part of this two part series, the endwall secondary flow of a low aspect ratio turbine with AR = 0.66 (airfoil span to axial chord length) and Zweifel loading coefficient (Zw = 1.0) is characterized at an exit isentropic Mach number of 0.95. Both experimental and numerical findings are compared. Numerical predictions are validated by airfoil static pressures and downstream survey measurements in the SLU linear turbine cascade polysonic wind tunnel facility. Numerical analysis is completed using Cadence Fine/Turbo employing RANS with the SST k-omega turbulence closure model. This paper discusses the development of the endwall secondary flows throughout the airfoil passage including the development of the main secondary flow vortices (passage, counter and corner vortices) in conjunction with trailing edge shock impingement. Further, the subsequent mixing losses of the endwall secondary flows are shown with contours of pressure loss coefficient for five downstream survey planes ranging from 0.2Cx to 2.0Cx downstream of the trailing edge. Results show the effect of shock impingement and resulting shock boundary layer interaction on the suction surface resulting in an impact on the endwall secondary flow vortex development unique to a low aspect ratio turbine. The combination of endwall secondary flows and suction surface shock result in shock vortex and shock boundary layer interactions which affect the downstream mixing losses. Finally, the resulting work presents a new schematic detailing the endwall secondary flow development for low aspect ratio turbines in the transonic regime.
Improved Stall Recovery in “Electrified” Gas Turbine Engines
Authors: Jing Zhenhao , Neumeier Yedidia , Prasad J. V. R. , James Darrell K.
Published: August 2024

This study investigates the potential for stall control and recovery of “electrified” gas turbine engines that incorporate advanced electric generator/motor system capable of adding or reducing torque from the engine shaft. In parallel to the conventional stall recovery action, such as reducing fuel flow, electric motors are utilized to drive the engine shaft to accelerate, thus enhancing the stall recovery process. This idea is assessed using simulations of compressor flow during engine transients using a recently developed model capable of capturing the propagation of compression and expansion waves as well as shock waves in the compressor. A lumped-parameter combustor-turbine model is coupled with the aforementioned compressor flow model to simulate flow transients. This study considers a single-shaft gas turbine engine equipped with an electric motor that encounters stall at 75% speed during a cold acceleration. It is found that, compared to the traditional engine that plunges to surge, the “electrified” engine recovers from stall and accomplish the engine acceleration after receiving assistance from an electric motor providing mechanical power equivalent to 3% of the maximum dry thrust fuel combustion power. Such an electric power corresponds to the power required to drive the engine shaft to continue accelerating while the control logic reduces the TIT to recover stall.
A Static/Dynamic Coupled Harmonic Balance Method for Dry Friction Systems Containing Rigid Body Modes
Authors: Liu Jiale , Fan Yu , Wu Jian , Wu Yaguang , Shen Qingyang , Zhang Dayi
Published: August 2024

A harmonic balance method for under-constrained dry friction systems containing rigid body modes (HBM-RBM) is proposed. This method aims to overcome the encountered obstacle when applying the harmonic balance method to turbine blades damped by underplatform dampers. The inspiration for HBM-RBM comes from the free interface modal synthesis method. The key innovation involves deriving the elastic inversion of the singular stiffness matrix through the elimination of rigid body modes. In this way, the general HBM framework can be adopted, and the frequency response of under-constrained dry friction systems can be solved in a static/dynamic coupled manner. The accuracy and efficiency are both verified on a lumped parameter model and a finite element model of turbines with UPDs from a real gas turbine. A comparative study between the HBM-RBM and the commonly adopted way of imposing artificial grounding springs (HBM-AGS) is conducted. Results demonstrate that the HBM-RBM holds a significant advantage over HBM-AGS, as it eliminates the need for artificial grounding springs (AGS) and avoids the necessity for numerous trial cases to determine AGS stiffness.
Off-Design Performance Analysis of Centrifugal Compressor of a Small Gas Turbine Engine
Authors: Dhinne Giridhar Kumar
Published: August 2024

This paper describes the work carried out to evaluate the off-design performance of a centrifugal compressor which consists of an impeller, a vaneless diffuser, a radial vaned diffuser, a radial-to-axial 90° bend and an axial diffuser (also called as de-swirl vanes), used for small gas turbine engine applications. As the flow through the centrifugal impeller is three dimensional, inviscid, and highly complex in nature, an effort is made to predict the performance as accurate as possible by exploring various flow and loss models from the literature. Impeller flow is analyzed using Jet-Wake theory (or Two-zone modeling). Losses due to mixing at impeller exit, clearance and leakage, and losses due to friction are included. Vaneless diffuser is analyzed by solving momentum integral equation in radial and tangential directions. Performance of the vaned diffuser is estimated based on the Runstadler’s data plots. Radial-to-axial bend and De-swirl vanes are analyzed based on fluid dynamics relations and necessary empirical correlations. A computer program is developed, to calculate aero-thermodynamic properties of each component and the overall stage performance characteristics at different speeds ranging from 60 percent to 100 percent of design speed. A performance map is generated which consists of adiabatic efficiency and total-total pressure ratio values with respect to mass flow function. Predicted results are validated with performance characteristics of a 3.5 pressure ratio centrifugal compressor used for aero-engine applications. The results are very encouraging when compared with the experimental values. Choking flow is well predicted and the estimation of surge flow is not included in this method and is to be developed as a continuation of this research work.
Numerical Investigations on the Aerodynamic Performance of Supercritical Carbon Dioxide Centrifugal Compressor
Authors: Cao Run , Yang Rui , Deng Qinghua , Li Jun , Song Liming , Gao Tieyu
Published: August 2024

Study on steady and unsteady aerodynamic performance of supercritical carbon dioxide (SCO2) has great significant on improving SCO2 centrifugal compressor performance. In this paper, the SCO2 centrifugal compressor volute has been designed under the assumption of equal density. The effects of the asymmetric volute structure on the upstream flow and flow characteristics in the volute are studied. The unsteady flow structures of pressure and radial velocity at the impeller-diffuser interface are captured. The results show that under the steady calculation the total-static isentropic efficiency of the SCO2 centrifugal compressor is 71.0%, and the total-static pressure ratio is 2.190 at the design condition; The uneven pressure distribution caused by the volute tongue will affect the pressure distribution at the diffuser outlet. While at the diffuser inlet, the periodic distribution of pressure is basically unaffected by the volute; Under the unsteady calculation, the time-average total-static isentropic efficiency is 71.7% and time-average total-static pressure ratio is 2.227 at the design condition; The different relative positions between the impeller blades and diffuser blades are the main causes for the unsteady flow structures of the impeller-diffuser interface. When the impeller blade and diffuser blade are at the same position, under the effects of the impeller blade wake and flow acceleration near the diffuser blade leading edge, the pressure is the lowest and the back flow at the impeller tip clearance is the most obvious; The overprediction of the blade tip clearance back flow causes the efficiency under the steady calculation lower than the time-average total-static efficiency under the unsteady calculation. This paper can provide reference for the aerodynamic performance analysis for SCO2 centrifugal compressor.
Understanding the Potential and the Challenges of a NGCC Integrated With Hydrogen-Assisted EGR and CO2 Capture
Authors: Vantaggiato Elettra , Riboldi Luca , Anantharaman Rahul , Carcasci Carlo , Andreini Antonio , Roussanaly Simon , Ditaranto Mario
Published: August 2024

CO2 capture plays an important role in the energy transition. As the integration of CO2 capture on a gas turbine energy system induces an efficiency penalty, there has been growing interest in the development of combustion systems integrated with CO2 capture with improved efficiency and operability. This study investigates the potential and the challenges of a NGCC integrated with H2-assisted EGR and CO2 capture. A fit-for-purpose model of a GT, along with an in-house tool to model the CO2 capture process, were employed to capture the key effects of EGR. The results show that the CO2 capture energy requirement and equipment sizes consistently decrease at increasing EGR rates, with the conclusion that the EGR level should be as high as possible. On the other hand, a higher EGR rate determines a decrease of the O2 concentration to the combustor, with problems with combustion stability. The addition of H2 piloting to stabilize the flame allows achieving otherwise unfeasible EGR rates with an overall positive impact on the system energy efficiency. The main energy consumption of the integrated system is associated with the CO2 capture, underscoring the importance of EGR in reducing it. The additional energy penalties of the overall system are minor. As the energy consumption and efficiency are proxies for operating costs, and the equipment sizes are proxies for capital costs, this study represents a basis for further economic evaluations.
Scale-Resolving Simulations of Turbulent Flow Retaining The Exact Blade Count With the Time-Inclined Method
Authors: Montiel Miguel , Corral Roque
Published: August 2024

Simulations of the T106 low-pressure turbine linear cascade with incoming wakes have been conducted to demonstrate the suitability of the time-inclined method for retaining the exact blade count in scale-resolving simulations. The time-inclined method has been implemented into a high-order unstructured time-marching code based on the flux-reconstruction method. The pitch ratio between the upstream incoming wakes and the cascade is not a small integer, and the time-inclined method is used to reduce the simulations to a single-passage computational domain. Three-way comparisons have been generated: the solution of the direct periodic full domain, spanning several blade passages, is compared to the single-passage time-inclined solution and to a single-passage solution that approximates the pitch ratio to the nearest integer. Two sets of virtual experiments, which differ in modelling of the incoming perturbations, are reported. Firstly, the immersed boundary approach is used to introduce a cascade of moving bars that act as the trailing edges of the preceding row and generate incoming wakes. The second set of simulations introduces wake-like perturbations at the inlet section of the computational domain. The present work shows that the time-inclined method, retaining the exact blade count, can produce very accurate results for turbulence-resolving simulations. Moreover, the time-inclined method outperforms the standard single-passage methodology in most of the variables of interest and is equivalent in the rest.
Design and Simulation of eVTOL Aircraft Thermal Management System
Authors: Kang Sangkeun , Saias Chana , Roumeliotis Ioannis , Broca Olivier
Published: August 2024

This paper focused on designing a Thermal Management System (TMS) for a parallel hybrid electric XV-15 tiltrotor aircraft used in Urban Air Mobility applications. The TMS is integrated into the aircraft system to assess its impact at aircraft and mission levels. Both liquid cooling and air-cooling TMS, along with using Phase Change Materials (PCMs) for heat storage, were designed and assessed. Two liquid-cooling configurations, series and parallel, were evaluated, with the series configuration proving more effective in the considered test cases. The study compared hover and cruise conditions to determine optimal design point for the liquid-cooling TMS. Designing for hover resulted in about fourfold increase in the TMS penalty in fuel burn during cruise. Designing for cruise, on the other hand, proved infeasible to comply with the thermal management requirements during hover. Two approaches were explored to address this: Approach A involves adding PCMs as a heat storage system, and Approach B entailed redesigning the TMS with the heat load at off-design conditions for the inverter and motor. Both approaches resulted in a 24% and 46% increase in the TMS penalty in fuel burn compared to the design that solely considering cruise condition, respectively. The assessment of the designed aircraft systems, integrating the TMS for the considered test cases, revealed that the liquid-cooling TMS designed at cruise condition with Approach B emerged as the optimal design, showcasing a 42% improvement in fuel burnt per payload compared to the air-cooling TMS at the mission level.
Adjoint Based Shape Optimization for Thermoacoustic Stability of Combustors Using Free Form Deformation
Authors: Ekici Ekrem , Juniper Matthew P.
Published: August 2024

We use the thermoacoustic Helmholtz equation to model thermoacoustic oscillations as an eigenvalue problem. We solve this with a Finite Element method. We parameterize the geometry of an annular combustor geometry using Free Form Deformation (FFD). We then use the FFD geometry, define the system parameters and impose the acoustic boundary conditions to calculate the eigenvalue and eigenvector of the problem using a Helmholtz solver. We then use adjoint methods to calculate the shape derivatives of the unstable eigenvalue with respect to the FFD control points. According to these gradients, we propose modifications to the control points that reduce the growth rate. We first demonstrate the application of this approach on the Rijke tube. Then we extend the method to a simulation of a laboratory combustor and lower the growth rate of the unstable circumferential mode. These findings show how this method could be used to reduce combustion instability in industrial annular combustors through geometric modifications.
Aerodynamic Performance of Partially Variable Geometry High-Pressure Turbine
Authors: You Lyu , Dong Xuezhi , Liu Xiyang , Tan Chunqing
Published: August 2024

Variable geometry turbine (VGT) technology changes the throat width of turbine guide vane to control the mass flow rate and adjust the operating condition of engine. With the development of variable cycle engine, the demand for VGT technology is getting urgent. In order to overcome the technical difficulties of current VGT technology, including large tip leakage and low adjustment accuracy, the partially variable geometry turbine (partially VGT) is considered as an alternative solution. Based on the original design of the General Electric Energy Efficient Engine (E3) high pressure turbine, this paper introduces a new structure with half vanes fixed and the other half adjustable. Numerical simulation and theoretical analysis are applied to investigate the effect of partially VGT on the aerodynamic performance of the high-pressure turbine. The results show that: 1) Within the required mass flow range, partially VGT can achieve a larger rotation angle of the guide vane. The guide vane throat width is linearly related to the setting angle, ensuring the accuracy of regulation. 2) Partially VGT has no significant variation with VGT in the fluid mechanism and distribution of the outlet section parameters. 3) Partially VGT can also play a role in controlling turbine power distribution. The above conclusions show that the partially VGT analyzed in this paper can replace the conventional VGT, which will provide a reference for the research on VGT technology.
Centrifugal Compressor Design Parameters Assessment for Hydrogen Compression
Authors: Aleksandrov Andrei , Jaatinen-Värri Ahti , Uusitalo Antti , Turunen-Saaresti Teemu
Published: August 2024

In recent years, hydrogen has gained a lot of interest, and it is considered as one part in the transition towards cleaner energy systems. With global hydrogen production increasing, the demand for hydrogen compression for storage and transportation has been increasing as well. The low molar mass of hydrogen creates challenges for compression, requiring higher enthalpy increase for the same pressure ratio compared to heavier gases. This, in turn, increases the required velocity which is limited by the compressor rotor material.

This paper aims to explore the initial design parameters of a hydrogen centrifugal compressor. A 1D design model was used to assess the loss distributions with varying initial design parameters. The most significant losses were analyzed and compared between hydrogen and air as working fluids. The results indicate that the velocity ratio and the de Haller number have more effect on the losses than hub-to-tip diameter ratio, with the de Haller number being the most important. The minimum total losses with hydrogen occur at much lower de Haller numbers than with air, therefore a hydrogen compressor would benefit more from utilizing low de Haller number compared to an air compressor.
Unsteady Flow Development and Reynolds Stress Measurements in a Centrifugal Compressor Vaned Diffuser
Authors: Meier Matthew A. , Gooding William J. , Key Nicole L.
Published: August 2024

Modern aeroengine designers face the challenge of reducing fuel consumption, which is pushing compressor technology into new design spaces. To optimize these design spaces, high-fidelity computational models are crucial to the compressor design process. It is important to validate these models with experimental data. Non-intrusive measurement techniques allow for acquisition of data well suited for this comparison, as they do not lead to local disruptions of the flow field.

This investigation utilized three-component laser Doppler velocimetry to acquire a unique dataset of detailed unsteady velocity measurements in the vaned diffuser of an aeroengine centrifugal compressor. These measurements allowed for a thorough study of the flow development in the vaneless & semi-vaneless space of the diffuser as well as through the diffuser passage. The components of the Reynolds stress tensor were also determined at multiple locations in the diffuser flow field. These data are used to study the jet and wake propagation from the impeller exit flow field into the diffuser passage and the resulting secondary flow structures.

Predictions from unsteady CFD simulations using the SST and BSL-EARSM turbulence models are also compared with these experimental data. Both turbulence models yielded results that qualitatively agreed with the experimental radial velocity profile through the vaneless and semi-vaneless space. With the experimentally determined Reynolds stress tensor, the turbulent kinetic energy (TKE) is calculated at multiple points through the flow field and is compared to the TKE at the same geometric locations in the computational flow field. This comparison highlights the difference in dissipation and production of turbulence between the experimental data and the computational predictions. Investigating the differences in TKE throughout the diffuser helps elucidate the differences in predicted flow structures in the diffuser passage.
Large Eddy Simulation of Ammonia-Hydrogen Non-Premixed Flames Stabilized on a Bluff Body Burner
Authors: Xia Yu , Verma Ishan , Shrivastava Sourabh , Nakod Pravin , Fletcher David F. , Dally Bassam
Published: August 2024

The demand for carbon-free fuels such as ammonia (NH3) and hydrogen (H2) has been growing rapidly due to stricter environmental policies on carbon emissions. Since ammonia is easier to store and transport, it is considered the leading alternative fuel for marine, aviation, and gas turbine industries. However, the narrow flammability, low reactivity, and potential emissions of nitrogen oxides (NOx) are important challenges that need to be overcome if ammonia is to be used as a practical fuel for industrial use. Recent works have provided important experimental data on the characteristics of NH3 flames under premixed and non-premixed combustion modes, focusing on flame speed, turbulence-chemistry interaction, and especially the dissociation/cracking of NH3 into H2 and N2. These measurements have encouraged the use of Computational Fluid Dynamics (CFD) for the simulation and scaling of practical ammonia systems, evaluating the performance of different numerical models for NH3 combustion. In this study, Large Eddy Simulation (LES) is utilized to predict a series of NH3/H2/N2 non-premixed flames stabilized on a bluff body burner. The accuracy of the Flamelet Generated Manifold (FGM) combustion model combined with LES has been examined, using a commercial CFD solver. The different cracking levels of NH3 into H2 and N2 lead to simulation cases ranging from an H2/N2 flame (i.e., “fully cracked”), to a flame with 50% NH3 (i.e., “half cracked”). The different flame shapes, temperature distributions, NOx and unburnt NH3 emissions have all been simulated, generally matching well the available experimental data. The developed model settings and numerical workflows may be applied to simulating more complex combustors which use NH3 as a fuel.
Prediction Method of Off-Design Aerodynamic Parameter Radial Distributions Between Blade Rows in a Multi-Stage Turbine Based on Stage Similarity Characteristics
Authors: Wang Xinggao , Zhao Wei , Sui Xiuming , Pu Jian , Zhao Qingjun , Xu Jianzhong
Published: August 2024

A method for predicting aerodynamic parameters radial distribution between blade rows in a multi-stage turbine under different operating conditions is proposed. The primary objective is to efficiently obtain the needed parameters, which are derived from the assessment of on-design and off-design conditions conducted during the design process of the turbine’s main flow path. This method is based on the stage similarity characteristics and radial balance of the turbine. By analyzing the flow characteristics, expansion ratio, and efficiency of each stage, as well as the total pressure recovery coefficient of each stage’s guide vanes, and the Mach number and flow angle of each axial clearance between blade rows, it is possible to determine the average velocity and density between blade rows under different operating conditions. The distribution of velocity and density between blade rows under various operating conditions can be estimated based on the circumferentially-averaged flow field at the design point. Additionally, the distribution of static pressure can be calculated using the radial-equilibrium equation. These distribution results enable the calculation of the turbine blade’s axial force and provide boundary conditions for secondary air system analysis. To validate the proposed method, a three-stage axial turbine is used as a case study. The results demonstrate that, for most operating conditions above idle, the predicted pressure exhibits a comparatively high level of accuracy, with a maximum error of less than 5%. Furthermore, the predicted axial blade forces have a maximum error of less than 5%. The validation demonstrates that the proposed method satisfactorily fulfills engineering requirements.
Methodology for Modeling Non Linear Thermomechanical Response With Wear at High-Speed Interactions: Application to a Pin-Disk Configuration
Authors: Pontonnier Soufiane , Quaegebeur Samuel , Thouverez Fabrice , Almeida Patricio
Published: August 2024

An aircraft engine is a complex structure for which some components can come into contact at high speed. Modelling this behaviour is very complex as multiple physics must be considered. State-of-the-art methodologies usually account for permanent contact and thermal modelling. In this paper, a new approach is proposed and embeds various phenomena such as non-regular and non linear contact mechanics, surface rubbing, wear and non linear heat transfer. A non linear version of Moreau-Jean algorithm is employed to compute the transient response of the system and to capture accurately the contact dynamics. Moreover, the full non linear coupling between the dynamics and the heating process is taken into account through both a semi-analytical formulation and the finite-element method. At the contact interface, heat flux is generated by dry rubbing and flows into both interacting bodies. The heat flux partition is evaluated thanks to a coefficient that depends on the material properties of the solids in contact. The proposed method also accounts for the adhesive wear between the solids through an energetic approach. This methodology is applied to an academic, yet realistic, disk connected to a rotor shaft that is free to move axially and to rotate around its revolution axis. Gyroscopic effects and variation of the rotation velocity are included leading to a full non linear mechanical behaviour. The disk undergoes aerodynamic load moving it to contact with a clamped free pin. The rotor shaft and the pin are both modelled as 1D elastic bodies while the rotor disk is assumed to be rigid. Through this example, the developed strategy shows its potential to compute the complete transient highly non linear response of the breaking phenomenon, in an acceptable time simulation.
Flow Variations in Transonic Compressors Tip Flow — An Experimental Perspective Utilizing High Speed PIV
Authors: Klausmann Fabian , Bargon Jonas , Schiffer Heinz-Peter
Published: August 2024

In modern compressor, the demand for highly loaded stages, coupled with lightweight design, necessitates a growing need for high manufacturing accuracy. However, it is challenging to eliminate the underlying sources of uncertainty. Investigating potential factors influencing compressor behaviour has been a crucial area of research. Understanding these influences is essential to enhance design capabilities and drive further advancements in the field.

This study explores flow variations in the tip flow of transonic compressors from an experimental perspective, utilizing high-speed Particle Image Velocimetry synchronized with blade passing frequency. This innovative approach, conducted in a high-speed compressor test rig, allows us to experimentally delve into the full annulus flow field and transient flow behaviour in a unique depth. This paper addresses the challenges encountered in the application of this measurement technique and examines the complete annulus information, focusing specifically on the variation in tip flow from passage to passage. Through the integration of blade tip timing data and 3D white light scan data of the BLISK, this study correlates aerodynamic variations with operational geometric discrepancies arising from manufacturing uncertainties.

The investigations were conducted at a transonic compressor test facility, utilizing a representative high-pressure compressor front stage configuration operated at engine relevant conditions. The experimental findings shed light on the intricate relationship between geometric uncertainties and compressor tip aerodynamics, furthering our understanding and contributing to the advancement of axial compressor technology.
Vaneless Diffuser Modelling for Real Gas Supercritical Carbon Dioxide Flows- Need for a Data Driven Approach
Authors: Seshadri Lakshminarayanan , Kumar Pramod
Published: August 2024

In this work, a real gas-based Vaneless diffuser (VLD) differential equation model is presented. The model requires the specification of the skin friction coefficient as input. However, the use of standard VLD friction coefficient estimation expressions require a re-examination for sCO2 flows. To establish the skin friction coefficient for real gas sCO2 flows, CFD data is generated using Latin Hypercube Sampling (LHS), with boundary conditions spanning the typical operating conditions of sCO2 centrifugal compressors in the kW to MW scale of power generation. The CFD computations are carried out using ANSYS® CFX software. The corresponding VLD friction coefficient for which the VLD stagnation pressure loss predicted by the 1D differential equation model matches with the 3D CFD result is back calculated for all the LHS designs. This is carried out using a root finding function in MATLAB® software. The existing empirical relation that characterizes the VLD skin friction coefficient using the inlet Reynolds number alone shows a poor correlation (R2 = 0.26), when compared to the CFD data. It is evident that a data driven approach is required to model the sCO2 VLD real gas flow for accurate results. Using the LHS data, the efficacy of an Artificial Neural Network (ANN)-based VLD model is demonstrated. A two hidden layer ANN is developed, which accurately predicts the skin friction coefficient for sCO2 real gas flows (R2 = 0.87). This proposed ANN based VLD model can be easily integrated into existing 1D codes for real gas sCO2 centrifugal compressor rating and sizing.
Control of Secondary Flow Losses in a Turbine Stage via Stator Endwall Fence at a Low Reynolds Number
Authors: Yuan Hang , Lu Xingen , Wu Yunfeng , Zhang Jianshe , Zhang Yanfeng
Published: August 2024

Under the demand for refined design and increase in turbine load, reducing secondary flow losses in the endwall region has become a research focus in the field of low-pressure turbines. To explore refined control methods of secondary flow in the endwall region, endwall fences with different geometric parameters are applied to the stator of a low-speed turbine stage at a low Reynolds number. The numerical results indicate that installing an endwall fence device with reasonable parameters on the stator of turbine stage can increase the stage efficiency by 0.21%. The cross migration of the endwall boundary layer within the stator passage is effectively blocked which makes the strength of counter vortex significantly reduced. Moreover, the uniformity of the flow field at the inlet of rotor blade row has been improved. The interaction between the fence vortex and the passage vortex is affected by the design parameters of the endwall fences. However, the endwall fence will introduce additional friction losses and vortices in the endwall region of stator passage. To achieve more efficient control of secondary flow in the endwall region, the XGBoost model and improved chaotic particle swarm optimization have been applied to the optimization design of an endwall fence with nonuniform height in the streamwise. The potential for secondary flow regulation of endwall fences has been more fully developed, and the isentropic efficiency of the turbine stage has been improved by 0.33%. The key design parameters of endwall fences are elucidated using sensitivity analysis methods.
Numerical and Experimental Investigation of the Inclination Angle Effect on the Cooling Effectiveness in a Liquid Fueled Can Type Combustor
Authors: Gulenc Gamze , Ozogul Hamdullah
Published: August 2024

Combustor liner cooling design has been more and more challenging due to increasing efficiency and output power of modern aircraft engines over the last decades. Therefore, not only improving the cooling performance but also investigating the cooling effectiveness accurately are difficult tasks for engineers. The main purposes of the present work are on one hand to propose a simple methodology of investigation of the metal temperature distribution for an effusion cooled combustor liner, and on the other hand to observe the effect of the inclination angle of effusion holes on cooling performance.

An experimental setup based on a liquid fueled can type combustor with effusion cooled liner and a swirler was built to obtain realistic swirling and reacting flow conditions in atmospheric conditions. Two coupons with different effusion hole’s inclination angles of 25 and 35 degrees were used. In addition, one more test coupon with 25 degrees inclination holes was used with thermal paint coating to obtain the metal temperature distribution through its color change on the cold side. Each coupon was equipped with several thermocouples to measure the liner metal temperature and the inlet air temperature. RANS based Computational Fluid Dynamics (CFD) analysis was performed for the can type combustor. Numerical results for metal temperatures were obtained with 1D and 3D thermal analysis. Heat flux values were deducted from the CFD analysis for the 3D thermal methodology. Thus, the pros and cons of each method were compared in the light of the numerical and experimental results. In addition, the effect of the inclination angle on the cooling effectiveness was investigated.
The Influence of Mode Shape on Flutter Stability of a Scaled Composite UHBR Fan
Authors: Goessling Jan , Maroldt Niklas , Stapelfeldt Sina
Published: August 2024

In literature, two common parameters to indicate flutter sensitivity are the reduced frequency and the amount of twist present in the combined first flap mode. A critical parameter is the plunge-to-twist incidence ratio, which is a function of both frequency and twist-to-plunge ratio in the mode shape. However, the limit of this stability criterion for real fan blades is not fully understood yet. This paper investigates the influence of plunge-to-pitch incidence ratio on a 3D transonic test case, the scaled composite UHBR fan of the CA3ViAR project, with the aim to understand the validity of the plunge-to-twist incidence ratio as a flutter parameter for transonic and three-dimensional fan blades. This fan was designed with the unconventional goal to achieve stable operation at the design point but flutter at throttled offdesign conditions. The design was done by varying the CFRP ply material and orientation towards specific reduced frequencies and twist-to-plunge ratios to drive the aerodynamic stability towards the desired behaviour. Here, the aerodynamic damping of a set of 3D mode-shapes based on variations in the composite ply-layup are simulated using TRACE Harmonic Balance for different reduced frequencies. Flutter stability for different reduced frequencies and twist-to-plunge ratio is mapped for several operating points. The results show that the stability boundary only follows lines of constant plunge-to-pitch incidence ratio in some regions of the map but deviates in others. The key deviations are then explained by analysing the aeroacoustic conditions. The study demonstrates that the validity of the plunge-to-twist incidence ratio parameter depends on the flutter mechanism. It is not valid inside the region where the acoustic wave is cut-on upstream but cut-off downstream. To the authors’ knowledge, this is the first time that limits of this stability criterion for fan flutter were explicitly shown and explained.
Numerical Study of Low Engine Order Excitations due to Manufacturing Variability Part 1: Characterization of the Geometric Scatter and its Effect on Forced Response
Authors: Pérez Escobar Óscar , Timón Vicente , Gallardo Juan Manuel
Published: August 2024

The geometric scatter in the surfaces of blades and vanes due to manufacturing variability has an impact on the dynamics (structural mistuning) that has been widely studied, but also on the aerodynamics. This geometric variability changes the fluid field, generating disturbances not directly related to the airfoil count. This work focuses on the aerodynamic forcing generated by this manufacturing variability on the adjacent rows.

In this paper, deviations from the nominal geometry are obtained from a set of scanned parts. The average manufactured geometry is computed through the point-by-point deviations between the scanned parts and the nominal geometry. Then, Principal Component Analysis is applied to the deviations from the average geometry to find a way to describe them in a compact and simple manner. The cold geometries are reconstructed using the mean geometry and the geometric modes; afterwards, a cold-to-hot process is applied to obtain the hot geometry, and finally the resulting aerodynamics are obtained using an in-house CFD solver. The loss of the spatial periodicity of the flow due to the geometric variations generates an aerodynamic forcing with a wave number different from the airfoil count.

The described method is applied to a representative row constituted by packets of vanes, and two forced response cases are generated. In the first one, the average packet geometry is used to analyze the aerodynamic forcing associated to the geometric variation of the airfoils inside the vane packet. The second one is a conceptual study carried out under some simplified assumptions in order to relate the geometric variability to random low engine order disturbances, using the geometric modes obtained from the PCA analysis. In both cases, the induced vibrations on the adjacent rotor row are comparable to the excitation due to the nominal blade-passing.
Influence of Engine Conditions on the Performance Prediction of a Two-Stage Transonic Low Pressure Compressor
Authors: Scheibel Julian Alexander , Stößel Marcel , Kožulović Dragan
Published: August 2024

The derivation of application-driven impact factors on the performance of real engine compressors is an essential prerequisite for the development of efficiency-enhanced modern compressor concepts. This study intends to extend the knowledge of the sensitivity of compressor operation simulation on real-engine design conditions, by investigating the impact of upstream and downstream engine components on the prediction of compressor map characteristics. The investigations are conducted on a two-stage transonic low pressure compressor of an unmixed low bypass ratio turbofan engine. Starting from the basic test case of a compressor operation under non-disturbed and homogeneous boundary conditions, the compressor is systematically subjected to aerodynamic conditions deriving from the compressor positioning downstream of the engine intake and upstream of the bypass splitter. The analysis focuses on both global compressor map characteristics and the causal relations in local aerodynamics, in terms of a radial redistribution of the blade loading, local resistance against flow separation and the role of stage interaction depending on the distinguished engine conditions. A strong sensitivity on the spinner geometry is derived and a less pronounced effect of the downstream throttling condition is analysed.
Lessons Learned From Pandemic-Driven Remote Learning and Sustaining Best Practices in Turbomachinery Laboratory Experiences
Authors: Reeping David , Villalva Rodrigo , Bellur Kishan , Cuppoletti Daniel , Khare Prashant
Published: August 2024

As online educational experiences have become more common for students to engage with while earning an engineering degree, instructors must become more attuned to best practices in digital pedagogies for all courses, including those with heavy laboratory components. Despite potential resistance among faculty to the idea that a laboratory course does not require an in-person experience, pandemic-driven remote learning serves as an intrinsic data point in how, under dire circumstances, laboratory courses could be offered through a digital medium. This paper describes a collaborative autoethnography of four mechanical and aerospace engineering instructors regarding lessons learned while teaching laboratory courses online during the COVID-19 pandemic. To bolster the quality of the research design, an engineering education researcher facilitated the collaborative autoethnography and co-constructed the individual instructor narratives to elicit best practices in online pedagogy for turbomachinery educators.
Schlieren Image Velocimetry and Modal Decomposition Study of Preheated Isothermal Flow From a Generic Multi-Swirl Burner
Authors: Vishnoi Neha , Saurabh Aditya , Kabiraj Lipika
Published: August 2024

This study presents an experimental investigation into the turbulent flow characteristics of an unconfined counter-rotating dual swirl burner under external acoustic excitation. Utilizing Schlieren image velocimetry (SIV), we capture the velocity field of the swirling jets. Mean velocity field analysis reveals the upstream propagation of the central recirculation zone within the burner passages. Through Proper Orthogonal Decomposition (POD) analysis on instantaneous axial velocity fields, coherent structures are identified and the impact of different actuation methods on spatial modes is illustrated. Spatial modes of the unforced (natural) flow show the presence of a single and double helical Precessing vortex core (PVC) modes at St = 0.53. Low-frequency acoustic actuation (St = 0.46) effectively suppresses the PVC mode, while high-frequency (St = 2) actuation stabilizes it. Broadband excitation of the flow field, however, induces the excitation of both single and double helical PVC modes.
Investigation of a Transonic Dense Gas Flow Over an Idealized Blade Vane Configuration
Authors: Hake Leander , aus der Wiesche Stefan , Sundermeier Stephan , Passmann Maximilian , Bienner Aurelien , Gloerfelt Xavier , Cinnella Paola
Published: August 2024

An experimental and numerical study of the flow of the organic vapor Novec 649 and air through an idealized vane was conducted. Due to the profiling of the passage, typical pressure and Mach number distributions for transonic and supersonic flow around an airfoil could be established. The comparable large trailing edge radius enabled the detailed investigation of corresponding flow phenomena. Schlieren pictures and pressure distributions were experimentally obtained and compared with numerical simulations. The trailing edge flow and the transonic and supersonic shock patterns were qualitatively similar to the ones observed in perfect gas flow. However, significant quantitative deviations were observed. The base pressure was lower in dense gas flows characterized by a fundamental derivative Γ < 1, and the corresponding loss contribution was stronger.
Effect of Reynolds Number and Tip Clearance on the Transonic Axial Compressor During Geometric Scaling
Authors: Zhao Wuan , Chen Jiang , Xiang Hang
Published: August 2024

The compressor often needs to adjust geometric dimensions in the process of design and testing to adapt to different use environments and save design costs. However, low Reynolds number conditions can lead to performance degradation in small-scale machines. At the same time, due to the limitations of processing conditions, the relative tip clearance of small machines is relatively large, which also affects the efficiency and stable working range. Therefore, it is necessary to study the impact of Reynolds number and tip clearance changes on the aerodynamic performance in the process of size scaling. This article first uses the similarity law to geometrically scale down the compressor. The calculated numerical results are used as standards to evaluate the published efficiency correction formula. The results show that the correction error can be controlled within 3%, which meets the engineering application standard. Through flow field analysis, it is found that the decrease of Reynolds number will lead to the increase of boundary layer thickness, the weakness of tip leakage vortex, and the aggravation of corner separation. The accumulation of low-energy fluid in the corner is the main reason for the decrease in flow rate under low Reynolds number. Then, the impact of tip clearance changes on aerodynamic performance under different Reynolds numbers is studied. Under different Reynolds numbers, there is a negative linear correlation between efficiency, pressure ratio and clearance, and the influence of Reynolds number variation on the correlation coefficient is inconspicuous. Under low Reynolds number, increasing relative tip clearance to a certain extent can help improve the stable working range.