bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of the Effect of the Tip Clearance Flow on Rotor-Stator Interaction Tone Noise in Axial-Flow Fan
Authors: Liangfeng Wang , Kangshen Xiang , Luqin Mao , Hang Tong , Weiyang Qiao
Published: January 2021

The present study is focused on the sound generation due to the rotor tip clearance flow interaction with stator in an axial flow fan. A hybrid URANS/Goldstein’s equations method is applied to calculate the unsteady flow and tone noise in a high loaded axial-flow fan with different rotor tip clearance. The numerical simulation results show that the main sound sources of fan tip clearance tone noise are concentrated in the leading edge of downstream stator blades. It is found that when the rotor tip clearance increases from zero to 2.5 mm (0.94% relative blade height), the mass flow of the fan decreases by about 2% and the efficiency of the fan decreases by about 1 percentage, and the sound power level at 1BPF forward tone increases by 1.47dB, and that of backward tone increases by 0.65dB. However, the influence of tip clearance on the tone noise intensity at 2BPF and 3BPF is more complex, and the variation range is less than 1dB. It is found that the wake width and wake strength at the rotor exit increase with the increase of tip clearance. The tip secondary flow caused by rotor clearance seriously affects the circumferential inhomogeneity of stator leading edge inflow conditions.
A Feature Weighted Kernel Extreme Learning Machine Ensemble Method for Gas Turbine Fault Diagnosis
Authors: Yan Liping , Dong Xuezhi , Zhang Hualiang , Chen Haisheng
Published: January 2021

Fault diagnosis is a very important section of gas turbine maintenance. Kernel extreme learning machine (KELM), a novel artificial intelligence algorithm, is a potentially effective diagnosis technology. The existing KELMs are all assumed that there is the same influence to the optimal separating hyperplane from all features, which reduces its generalization performance. In this study, a feature weighted kernel extreme learning machine ensemble method (FWKELM-RF) is developed for application in the field of gas turbine fault diagnosis. First, information gain ratio is introduced to assign different weights to the feature space. Furthermore, random forest is used to enhance stable performance of feature weighted KELM. The fault datasets from a gas turbine with three shafts is generated to validate the performance of the developed method, and the results demonstrate that FWKELM-RF can achieve better accuracy and stability for detecting fault in gas turbine.
On the Effects of a Shaft Crack Propagation on the Dynamic Behavior of a Steam Turbine
Authors: Chatterton Steven , Pennacchi Paolo , Vania Andrea
Published: January 2021

The symptoms of the propagation of shaft cracks in rotating machines, which can be brought out of the vibration data collected by condition monitoring systems, are often not very evident, especially when the crack depth is not very high. In fact, shaft cracks commonly propagate rather far from the cross-sections where the vibration probes have been mounted. At these measurement planes, the sensitivity of the machine dynamic behavior to the effects caused by a shaft crack can be fairly low. Therefore, it is very important to improve the capabilities of diagnostic techniques aimed at the early detection of shaft cracks.

In this paper, the dynamic behavior of the cracked shaft of a HP-IP steam turbine is shown. The results of investigations on the influence of the periodic and non-periodic breathing of the crack on the rotor response, measured in different machine thermal states and at unusual cross-sections of the shaft, are shown and discussed.
Coupled Level Set Volume of Fluid Simulations of Prefilming Airblast Atomization With Adaptive Meshing
Authors: Wetherell Jack R. J. , Garmory Andrew , Skarysz Maciej
Published: January 2021

The fuel atomisation process and the resultant spray affects nearly all aspects of combustion system performance, and must be well understood to enable the design of future combustion systems. The design of a fuel injector makes both numerical and experimental testing difficult, so simplified test pieces are often used, however, this does not accurately capture atomisation mechanisms and fuel distributions. This paper presents a computational method combining a Coupled Level Set Volume of Fluid model with Adaptive Mesh Refinement. A simple prefilmer has been used to validate the method. Comparisons of the flow field and ligament length distributions show good agreement with published DNS data. The use of AMR allows a lower total cell count, and so a reduction in computational cost of over 60% compared to previously reported results for the same case has been achieved. Further work will look to apply this method to more realistic injector geometry.
Numerical and Experimental Investigation of the Reynolds Number and Reduced Frequency Effects on Low-Pressure Turbine Airfoils
Authors: Bolinches-Gisbert Marc , Cadrecha David , Corral Roque , Gisbert Fernando
Published: January 2021

This paper compares experimental and numerical data for a low-speed high-lift Low Pressure Turbine (LPT) cascade under unsteady flow conditions. Three Reynolds numbers representative of LPTs have been tested, namely, 5 × 104, 105, 2 × 105; at two reduced frequencies, fr = 0.5 and 1, also representative of LPTs. The experimental data was obtained at the low-speed linear cascade wind-tunnel at the Polytechnic University of Madrid using hot-wire, LDV and pressure tappings. The numerical solver employs a sixth order compact scheme based on the Flux Reconstruction method for spatial discretization and a fourth order Runge-Kutta method to march in time. The longest case ran 550 hours on 40 GPUs to reach a statistically periodic state. Pressure coefficients around the profile, boundary layer profiles and exit cross-section distributions of velocity, pressure loss defect, shear Reynolds stress and angle are compared against high-quality experimental data. Cascade loss and exit angle have also been compared against experimental data. Very good agreement between experimental and numerical data is seen. The results demonstrate the suitability of the present methodology to predict the aerodynamic properties unsteady flows around LPT linear cascades accurately.
Loss Predictions in the High-Pressure Film-Cooled Turbine Blade Cascade T120D by Mean of Wall-Resolved Large Eddy Simulation
Authors: Harnieh Mael , Odier Nicolas , Dombard Jérôme , Duchaine Florent , Gicquel Laurent
Published: January 2021

Film cooling is commonly used to protect turbine vanes and blades from the hot gases produced in the combustion chamber. The design and optimization of these systems can however only be achieved if a precise prediction of the fluid mechanics and film efficiency is guaranteed at a level where induced losses are fully mastered. Such a prerequisite induces at the numerical level to be able to identify and assess losses. In this context, the present study addresses loss assessment in a wall-resolved Large Eddy Simulation (LES) of the film-cooled high-pressure turbine blade cascade T120D from the European project AITEB II. The objectives are twofolds: (1) to evaluate the capacity of LES to predict adiabatic film cooling effectiveness in a mastered academic case; and (2) to investigate loss generation mechanisms in a fully anisothermal configuration. When it comes to LES predictions of T120D, the flow structure around the blade and the coolant jet organization are coherent with literature findings. Satisfactory agreements are furthermore retrieved for the pressure load prediction as well as the adiabatic film effectiveness if compared to the experiment. Loss generation is then investigated illustrating the fact that aerodynamics losses dominate mixing losses which are mainly located in the coolant film. This is in line with the temperature difference between the hot and coolant flows that is low for this experimental condition. Distinct contributions can however be made available by studying the local loss generation maps by means of Second Law Analysis if recast in the specific context of anisothermal flows when simulated by LES.
Experimental Study on the Performance of a See-Through Labyrinth Seal With Two-Phase, Mainly-Liquid Mixtures
Authors: Zhang Min , Childs Dara W.
Published: January 2021

With the increasing demand of the oil & gas industry, many pump companies are developing multiphase pumps, which can handle liquid-gas flow directly without separating the liquid from a mixed flow. The see-through labyrinth seal is one of the popular types of non-contact annular seals that act as a balancing piston seal to reduce the axial thrust of a high-performance centrifugal pump. The see-through labyrinth seal also generates reaction forces that can significantly impact the rotordynamic performance of the pump. Multiphase pumps are expected to operate from pure-liquid to pure-gas conditions. Zhang et al. (2019) conducted a comprehensive experimental study on the performance (leakage and rotordynamic coefficients) of a see-through labyrinth seal under mainly-gas conditions. This paper continues Zhang et al.’s (2019) research and studies the performance of the see-through TOS (tooth-on-stator) labyrinth seal under mainly-liquid conditions. The test seal’s inner diameter, length, and radial clearance are 89.256 mm, 66.68 mm, and 0.178 mm, respectively. The test fluid is a mixture of air and silicone oil (PSF-5cSt), and the inlet GVF (gas volume fraction) varies from zero to 12%. Tests are conducted at an exit pressure of 6.9 bars, an inlet temperature of 39.1 °C, three pressure drops PDs (27.6 bars, 34.5 bars, and 48.3 bars), and three rotating speeds ω (5 krpm, 10 krpm, and 15 krpm). The seal is always concentric with the rotor, and there is no intentional fluid pre-rotation at the seal inlet.

The air presence in the oil flow significantly impacts the leakage as well as the dynamic forces of the test seal. The first air increment (increasing inlet GVF from 0% to 3%) slightly increases the leakage mass flow rate, while further air increments steadily decrease the leakage mass flow rate. For all test conditions, the leakage mass flow rate does not change as ω increases from 5 krpm to 10 krpm but decreases as ω is further increased to 15 krpm. The reduction in the leakage mass flow rate indicates that there is an increase in the friction factor, and there could be a highly possible flow regime change as ω increases from 10 krpm to 15 krpm. For ω ≤ 10 krpm, effective stiffness Keff increases as inlet GVF increases. Keff represents the test seal’s total centering force on the pump rotor. The increase of Keff increases the seal’s centering force and would increase the pump rotor’s critical speeds. Ceff indicates the test seal’s total damping force on the pump rotor. For ω ≤ 10 krpm, Ceff first decreases as inlet GVF increases from zero to 3%, and then remains unchanged as inlet GVF is further increased to 12%. For ω = 15 krpm, Keff first increases as inlet GVF increases from zero to 3% and then decreases as inlet GVF is further increased. As inlet GVF increases, Ceff steadily decreases for ω = 15 krpm.
The Data Driven Surrogate Model Based Dynamic Design of Aero-Engine Fan Systems
Authors: Zhu Yun-Peng , Yuan Jie , Lang Z. Q. , Schwingshackl C. W. , Salles Loic , Kadirkamanathan V.
Published: January 2021

High cycle fatigue failures of fan blade systems due to vibrational loads are of great concern in the design of aero engines, where energy dissipation by the relative frictional motion in the dovetail joints provides the main damping to mitigate the vibrations. The performance of such a frictional damping can be enhanced by suitable coatings. However, the analysis and design of coated joint roots of gas turbine fan blades are computationally expensive due to strong contact friction nonlinearities and also complex physics involved in the dovetail. In this study, a data driven surrogate model, known as the Nonlinear in Parameter AutoRegressive with eXegenous input (NP-ARX) model, is introduced to circumvent the difficulties in the analysis and design of fan systems. The NP-ARX model is a linear input-output model, where the model coefficients are nonlinear functions of the design parameters of interest, such that the Frequency Response Function (FRF) can be directly obtained and used in the system analysis and design. A simplified fan bladed disc system is considered as the test case. The results show that by using the data driven surrogate model, an efficient and accurate design of aero-engine fan systems can be achieved. The approach is expected to be extended to solve the analysis and design problems of many other complex systems.
Experimental Validation of an Analytical Prediction Model for Fan Buzz-Saw Noise
Authors: Moreau Antoine , Guérin Sébastien
Published: January 2021

This paper is focused on the application of an analytical model, which was previously developed and published for the prediction of buzz-saw noise emitted by supersonic fan rotors. The application test cases are six different fan stages equipped with hardwall inlet ducts and clean inflow conditions. The model is validated through a comparison with experimental sound power levels measured along the working line of each fan in high subsonic, transonic and supersonic regimes. In terms of overall evolution and maximum levels, the model provides a reasonable prediction; the sensitivity to parameters such as the intake axial Mach number or the intake duct length is well reproduced. However the significant discrepancies observed locally show that the prediction of buzz-saw noise is still a difficult task. The model is then extended to the case of distorted mean flow impinging on the rotor. Following this extension, the maximum levels of buzz-saw noise are expected to occur over a wider range of Mach number compared to the case with clean inflow.
Experimental and Numerical Study of Flow and Dynamics on LSB at 34 MW Steam Turbine
Authors: Hoznedl Michal , Sedlák Kamil , Mrózek Lukáš , Dadáková Tereza , Kubín Zdeněk , Gregor Karel
Published: January 2021

The paper deals with experimental research of the flow and dynamics of the blades in the last stage of a steam turbine with nominal output of 34 MW and a connected axial exhaust hood. The experiments were carried out on a turbine with relatively low inlet steam parameters “- 64 bars and 445 °C. It was possible to change the operating modes of the turbine during the course of measurement so that significant ventilation would be achieved in the last stage up to the point when aerodynamic throttling occurred in the last stage. In other words the turbine output varied from about 2 to 35 MW. The output of 2 MW was for the case of the island mode turbine operation.

The experiments were carried out using static pressure taps and measurements of temperatures at the root and tip limiting wall. In addition to static pressure taps and temperature measurement, it was also possible to carry out probing by pneumatic probe with a diameter of 30 mm. Blade vibration monitoring sensors, so called last stage blade tip-timing, were also installed. The blade tip-timing acquisition hardware was used to monitor rotor blades tip amplitude.

Due to the obtained experimental data, it was possible to verify the behaviour of the last stage and the connected exhaust hood for four measured variants. The courses of pressures and steam angles along the length of the LSB were determined. Furthermore, basic parameters of the last stage were determined, i.e. reactions of the stage, Mach and Reynolds numbers and values of pressure recovery coefficients.

Based on experimental data the boundary conditions for CFD calculations were determined. Comparison of CFD calculations done for ventilation modes and for a nominal mode was also included. Another phenomenon which occurred during the probing of the flow parameters, particularly in ventilation modes, was the inability to determine parameters of steam due to low values of measured dynamic pressure in the vortex area at the root of the blade. The probe was able to detect dynamic pressure at the level of 50 Pa and more. In other words the transition point between backward and forward flows was identified. This limit point was used for further analysis of ventilation character of the steam flow depending on the ventilation coefficient c2x/u. where c2x is the average axial velocity at the LSB outlet, calculated from volumetric mass flow and u is LSB circumferential velocity calculated at LSB middle diameter.

Due to the fact that it was also possible to measure vibration amplitudes of blades using the tip-timing method for a variety of modes, the relationships between pressure ratio over the tip and root of the last moving blade and vibration amplitude were also determined. This verified that the highest amplitude of blade tips occurred just when the compression of the medium on the blade tip was maximum, i.e. c2x/u = 0.05.
Numerical Characterization of the Performance Curve of a Regenerative Pump-As-Turbine
Authors: Cantini Giulio , Salvadori Simone
Published: January 2021

Energy companies in the power generation field are continuously searching for green technologies to reduce pollutant emissions. In that context, small hydropower plants represent an attractive solution for distributed electricity generation. Reverse-running centrifugal pumps (also known as “pump-as-turbines”, PaT) are increasingly selected in that field. Amongst the existing type of pumps, drag-type regenerative pumps (RP) can perform similarly to radial centrifugal pumps in terms of head and efficiency for low specific speed values. For a fixed rotational speed, RPs with linear blades work as pump or turbine only depending on the flow rate. Such peculiarity makes it particularly intriguing to evaluate RPs working characteristic in the turbine operating mode. In the present paper, the performance of three Regenerative Pump-as-Turbine (RPaT) are analyzed using Computational Fluid Dynamics (CFD). The analysis is supported by an already validated in-house 1D code developed in cooperation with Pierburg Pump Technology Italy SPA. The obtained results are also discussed considering the theoretical behavior of the circulatory velocity in a regenerative machine as described by a widely used 1D model, which is extended in the present paper to the turbine working region. The numerical approach is validated using experimental data for both an RP (in the pump working region) and a regenerative turbine (RT) (in the turbine working region). Finally, the numerical simulation of a small-scale RP allows for the detailed characterization of both the pump and the turbine regions. The numerical analysis shows that for a RPaT it is possible to find a “switch region” where the machine turns from behaving as a pump to behaving as a turbine, the losses not being overcome by the turbine power output. The analysis of the RPaT also shows the inversion of the flow pattern and the positioning of the pivot around which the flow creates the typical helical structure that characterizes RPs.
Reynolds and Mach Number Effects on the Flow in a Low-Pressure Turbine
Authors: Fiore Maxime
Published: January 2021

This paper presents the Large Eddy Simulation (LES) of a Low-Pressure Turbine (LPT) Nozzle Guide Vane (NGV) for different Reynolds (Re) and Mach number (Ma). The analysis is based on a slice of the blade that may be representative of midspan flow where secondary flows, hub and shroud contributions are lower. In LPT, the variation of the Re during the mission of the gas turbine is a well-known effect since its value can vary of a factor four between take-off and cruise. This can induce performance variations due to various phenomena with among them suction side boundary layer separation on the aft portion of the blade due to an adverse pressure gradient and laminar boundary layer that can be maintained due to the relatively low Re in LPT. Similarly, the Ma in the LPT may vary depending on the thrust required from the gas turbine at the considered mission phase. The current paper investigates through numerical simulation the flow representative of a medium-sized LPT with three different Reynolds number Re = 175’000 (cruise), 280’000 (mid-level altitude) and 500’000 (take-off) keeping the same characteristic Mach number Ma = 0.2 and three different Mach number Ma = 0.2, 0.5 and 0.8 keeping the same Reynolds number Re = 280’000. The study focuses on different flow characteristics: pressure distribution around the blade, near-wall flow behavior and wake analysis. This includes the related generation of losses and the effect of Re and Ma on these different phenomena. A special emphasis is given to the generation of loss based on an entropy approach and the redistribution of mean kinetic energy towards turbulent kinetic energy. The results show that the increase of the Re has a destabilizing effect on potential separation while the increase of the Ma has a stabilizing effect. The peak in the TKE downstream of the blade is also moved upstream closer to the trailing edge when the Ma is increased.
Blowing Control in Serpentine Inlet and its Effect on Fan-Stage Performance
Authors: He Yubo , Yang Qingzhen , Yang Huicheng , Zhang Saile , Yang Haoqi
Published: January 2021

Serpentine inlet is widely used in military and civil aircraft due to its good stealth performance. However, it generates a high total pressure loss and swirl distortion which significantly affects the performance and the stability of the compressor. In order to improve the quality of the flow field at the aerodynamic interface plane (AIP), a flow control is required inside the serpentine inlet.

The objective of this paper was to study the effectiveness of the blowing active flow control on reducing the swirl distortion and on improving the total pressure recovery at the AIP, by reducing the low-momentum flow in the serpentine inlet. The mechanism of the blowing control and the effect of the design parameters (i.e. blowing angle, blowing position and blowing flow rate) on the aerodynamic performance at the AIP were studied. The optimal solution was applied to the full flow path of the serpentine inlet and the fan-stage.

The numerical results showed that the quality of the flow field at the AIP were effectively improved by blowing high-energy airflow into the boundary layer of the serpentine inlet. The blowing position had a high influence on the blowing effect, and upper wall blowing scheme obtained greater benefits than lower wall blowing scheme and combination blowing scheme. In addition, the blowing angle should be selected to avoid the high-energy air from pipes mixing with mainstream in the serpentine inlet which will result in an additional total pressure loss. When the ratio of the blowing mass flow rate to the designed mass flow rate of the serpentine inlet was about 1.5%, the swirl distortion on the AIP reached a minimum value, which then did not show a significant difference in performance with blowing ratio increased. When the upper wall blowing scheme was adopted with a blowing angle of 6 degrees and a blowing ratio of 1.5%, the AIP aerodynamic performance achieved the highest improvement, with an increase of the total pressure recovery factor by about 1%, and a decrease of the circumferential total pressure distortion and the swirling distortion by 60% and 61%, respectively. With the optimal control scheme, the area of the low-pressure region near the upper wall was remarkably reduced, and the performance of fan-stage was improved, with an increase of the pressure ratio by about 1.5%, and the efficiency of the single-stage compressor by about 3.1%, respectively.
Evaluation of the Uniform Conditional State Method for Turbulence-Chemistry Interaction Modelling of Swirl-Stabilized Flames
Authors: De Graaf Stefanie , de Guillebon Ludovic , Konle Marco , Bushe W. Kendal
Published: January 2021

This paper considers a variation on Conditional Moment Closure (CMC) modelling for turbulence-chemistry interaction called the Uniform Conditional State (UCS) model and its application to the prediction of swirl-stabilized flames. UCS is essentially a zero-spatial dimensional, multi-condition CMC method. Unlike conventional CMC methods, for flames that are in (statistically) steady flows, the chemistry can be solved a priori in conditional space only. The reactive scalars are then mapped into real space by taking the inner product of the resulting conditional averages with the joint probability density function of the conditioning variables, here taken to have a presumed form that is a function of the mean and variance of the conditioning variables. Two conditioning variables are used, mixture fraction and progress variable. The combination of these allows for the resulting chemistry table to be applicable to both premixed and non-premixed combustion but also in the partially-premixed regime. In doing so, this new approach is promising to be highly suitable for simulating industrial applications and complex geometries. Another promising aspect is the universal applicability to different fuels and kinetic mechanisms providing great flexibility to the user of this method. Ultimately it is intended to aid the development of industrial burners by providing detailed information about the local composition and emission production, while keeping computational costs significantly low. Not only does this provide additional insight into global emissions and fuel consumption of a new design, but it allows for variability between different stages of mixedness as well as the testing of, for example, alternative fuels in established burner configurations. In this present study a comparison of different fuels and initial conditions is being conducted to analyze their effect on the resulting UCS solution — meaning the chemical source-terms, composition and thermodynamic state in conditional space. Furthermore the use of the UCS solutions as a predictive method in a RANS simulation is being presented here. The paper illustrates the UCS predictions and compares them to experimental data, as well as previously published simulation results of more established modelling approaches. The experimental test case chosen is a model combustor with a swirl-stabilized flame and high technical relevance which demonstrates the applicability of the UCS method to industrial designs for aero engines.

Further investigations have begun including the application of this new tool to a real industrial combustor within the framework of this collaboration with MTU Aero Engines AG.
Impact Investigation on the Aerodynamic Performance for Seal Leakage at the Stator Root of Multistage Axial Compressor
Authors: Wang Qi , Ren Lanxue , Zhang Zhou , Wang Ting , Luo Mingcong
Published: January 2021

This paper presents a numerical model based on the mass flow rate of seal leakage. This numerical model is considered as a correct method for 3-D numerical simulation. It can be used to simulate the effect of seal leakage at the stator root of a multistage axial compressor. Implementation of the correct method is using a numerical model based on the flux conservation which can control the mass flow rate of seal leakage accurately at the seal cavity of compressor. The mass flow rate of seal leakage is chosen as the key research parameter on the aerodynamic performance effect of the seal engineering application in a multistage axial compressor. Combined with the 3-D numerical simulation methods, an engineering numerical approach is set up in this study. A nine-stage axial compressor is taken as the research object in this paper and its aerodynamic performance is tested for proving the applicability of the numerical model for seal leakage. In the cases of several operating rotation speeds, numerical results of the nine-stage axial compressor performance characteristic curves are in good agreement with the experimental data. It is considered that the numerical approach based on the simplified numerical model in this paper can predict the performance of multistage axial compressor accurately. Then, comparisons are made against different cases of seal leakage mass flow rate for analyzing the impact of seal leakage increasing on the aerodynamic performance of the nine-stage axial compressor. The main point of comparisons is focused on the changes of the overall performance and the flow distribution in the compressor with the seal leakage changing. The results indicate that performance of multistage axial compressor is degenerated faster and faster with seal leakage increasing in all operating working points. An overall decline is appeared in the flow capacity, working capacity, efficiency and surge margin of the compressor. For the impact investigation on the changes of flow distribution, the total pressure loss coefficient, the relative Mach number contours and the movement of streamlines are studied in different seal leakage cases under several operating working points. The result also shows that stators located in front stages of multistage axial compressor are affected more seriously with the increasing mass flow rate of seal leakage. Under the influence of seal leakage, degradation of flow condition in stators located in front stages is more severely than that in back stages, the total pressure loss coefficient and entropy are increased, and the flow separations at the root of stators in front stages are developed faster with seal leakage increasing. So it can be confirmed that relatively larger flow losses in front stages bring significant impact on the decay of aerodynamic performance for a multistage axial compressor.
Structural Integrity Assessments for Validating Directed Energy Deposition Repairs of Integrally Bladed Rotor
Authors: Scott-Emuakpor Onome , Runyon Brian , George Tommy , Goldin Andrew , Holycross Casey , Sheridan Luke , Celli Dino , Langley Bryan , Gillaugh Daniel , Kannan Manigandan , Shrestha Sulochana , Gyekenyesi Andrew
Published: January 2021

Considerable steps to assess the structural capability of laser directed energy deposition (DED) aim to determine the viability of repair processes for integrally bladed rotors (IBRs). Two laser DED processes are under investigation in this study: wire fed and blown powder feedstock. Using a small subsonic Titanium 6Al-4V fan as the component of interest, a series of tests and associated models for laboratory specimens, subcomponents, and components are necessary for proper assessment of material structural properties pertaining to the intended mission of the IBR. Experimentation on laboratory specimens acquire properties such as tensile strength, elongation, low cycle fatigue (LCF), high cycle fatigue (HCF), crack growth rate, and fracture toughness. Subcomponent test articles fabrication occurs by sectioning an operational IBR into individual blades for vibration HCF assessment. Component level testing focuses on LCF and overspeed strength acquired from spin rig testing. Even though the full IBR repair validation of laboratory specimen, subcomponent, and component testing has yet to be completed, the results to-date for laser DED repairs are promising. Furthermore, this plan for structural integrity assessment can serve as a reference for validation of future IBR repair processes.
Multi-Objective Modelling of Leading Edge Serrations Applied to Low-Pressure Axial Fans
Authors: Biedermann Till M. , Reich M. , Paschereit C. O.
Published: January 2021

A novel modelling strategy is proposed which allows high-accuracy predictions of aerodynamic and aeroacoustic target values for a low-pressure axial fan, equipped with serrated leading edges. Inspired by machine learning processes, the sampling of the experimental space is realized by use of a Latin hypercube design plus a factorial design, providing highly diverse information on the analyzed system. The effects of four influencing parameters are tested, characterizing the inflow conditions as well as the serration geometry. A total of 65 target values in the time and frequency domains are defined and can be approximated with high accuracy by individual artificial neural networks. Furthermore, the validation of the model against fully independent test points within the experimental space yields a remarkable fit, even for the spectral distribution in 1/3rd-octave bands, proving the ability of the model to generalize. A meta-heuristic multi-objective optimization approach provides two-dimensional Pareto optimal solutions for selected pairs of target values. This is particularly important for reconciling opposing trends, such as the noise reduction capability and aerodynamic performance. The chosen optimization strategy also allows for a customized design of serrated leading edges, tailored to the specific operating conditions of the axial fan.
Numerical Study of the Fan Blades Design and Operating Parameters for a High Bypass Ratio Engine
Authors: Liu Huoxing , Tang Zhongfu , Shirokov Igor
Published: January 2021

High bypass ratio turbofan engine is the dominant side of civil aviation engines market at present. This trendency will not change in the coming decades. In a turbofan engine with high thrust, high mass flow and high bypass ratio, the fan blade is the key component. But most investigations only focus on the individual part design and validation. As the multi-disciplines coupling research are more and more important. The systemlevel research will be an important investigation trend in the future.

The purpose of this paper is the source design of the fan blade, which starts from the aircraft requirement and consists of the turbomachine design and operating parameters design. The main research area is from the inlet section of the engine to the outlet section of the fan rotor (single stage). So, different from the traditional axial compressor design, this paper also considers the overall operating parameters of the engine and organically combines the fan design with the overall engine design by the aerothermodynamic analysis.

Based on the partial data of fan components of Russian PD-20 engine, The process, which consist of the overall performance design of the engine, fan components performance design, fan aerodynamic design and modeling, CFD method, flow field mechanism analysis, fluid-solid coupling, are formed into a simply systematical design of the fan blade. All the work except the CFD solver are programmed for the future research in propulsion system.
Characterization of Transient Wall Heat Load for a Low NOx Lean Premixed Swirl Stabilized Can Combustor Under Reacting Conditions
Authors: Ramakrishnan Kishore Ranganath , Ahmed Shoaib , Ekkad Srinath , Liberatore Federico , Ho Yin-Hsiang
Published: January 2021

Modern combustor design optimization is contingent on the accurate characterization of the combustor flame side heat loads. Knowledge of regions of high and low heat loads on the liner wall helps designers optimize the cooling designs. The present work focuses on the experimental measurement of the transient heat load along a fused silica (quartz) optical can combustor under reacting conditions for a swirl stabilized premixed methane-air flame. Equivalence ratio was varied from 0.55 to 0.65. Reynolds number based on combustor diameter was varied from 12500 to 18000, where the preheated air temperature was approximately 373 K. The percentage of pilot fuel was varied from 6% to 10% of the main fuel flow rate. Inner and outer walls of the liner were painted with a high temperature flat black paint with an azimuthal offset to aid in infrared measurement of the wall temperature using an infrared camera. Particle Image Velocimetry (PIV) was employed to visualize the flow field for various reacting conditions studied in this work. Based on the heat transfer study, a detailed report of transient heat load along the length of the liner wall for varying reacting conditions has been presented here. The location of impingement of the flame onto the liner and velocity of the flow field were obtained from PIV measurements. Wall heat load at various planes along the length of the liner have been presented. Repeatability of this transient experiment was within 10% between eight different runs for various locations along the length of the liner, except for the region close to flame impingement zone. In the impingement zone, liner heat load varied by about 25% between different runs. It was observed that the change in heat load upstream of the location of impingement on the liner was insignificant with change in pilot ratio as the system tends towards a steady state, contrary to the regions downstream. Higher Reynolds number and equivalence ratios increased the heat load on the liner as expected.
High-Fidelity Simulations of a High-Pressure Turbine Vane Subject to Large Disturbances: Effect of Exit Mach Number on Losses
Authors: Zhao Yaomin , Sandberg Richard D.
Published: January 2021

We report on a series of highly resolved large-eddy simulations of the LS89 high-pressure turbine (HPT) vane, varying the exit Mach number between Ma = 0.7 and 1.1. In order to accurately resolve the blade boundary layers and enforce pitchwise periodicity, we for the first time use an overset mesh method, which consists of an O-type grid around the blade overlapping with a background H-type grid. The simulations were conducted either with a synthetic inlet turbulence condition or including upstream bars. A quantitative comparison shows that the computationally more efficient synthetic method is able to reproduce the turbulence characterictics of the upstream bars. We further perform a detailed analysis of the flow fields, showing that the varying exit Mach number significantly changes the turbine efficiency by affecting the suction-side transition, blade boundary layer profiles, and wake mixing. In particular, the Ma = 1.1 case includes a strong shock that interacts with the trailing edge, causing an increased complexity of the flow field. We use our recently developed entropy loss analysis (Zhao and Sandberg, GT2019-90126) to decompose the overall loss into different source terms and identify the regions that dominate the loss generation. Comparing the different Ma cases, we conclude that the main mechanism for the extra loss generation in the Ma = 1.1 case is the shock-related strong pressure gradient interacting with the turbulent boundary layer and the wake, resulting in significant turbulence production and extensive viscous dissipation.
Large Eddy Simulations of High Rossby Number Flow in the High Pressure Compressor Inter-Disk Cavity
Authors: Saini Deepak , Sandberg Richard D.
Published: January 2021

The focus of the present study is to understand the effect of Rayleigh number on a high Rossby number flow in a high pressure compressor (HPC) inter-disk cavity. These cavities form between the compressor disks of a gas turbine engine, and they are an integral part of the internal air cooling system. We perform highly resolved large eddy simulations for two Rayleigh numbers of 0.76 × 108 and 1.54 × 108 at a fixed Rossby number of 4.5 by solving the compressible Navier–Stokes equations.

The results show a flow structure dominated by a toroidal vortex in the inner region of the cavity. In the outer region, the flow is observed to move radially outwards by Ekman layers formed on the side disks and to move radially inwards through the central core region of the cavity. An enhancement in the intensity of the radial flares is observed in the outer region of the cavity for the high Rayleigh number case with no perceivable effect in the inner region. The near shroud region is mostly dominated by the centrifugal buoyancy-induced flow and the wall Nusselt number calculated at the shroud is in close agreement with centrifugal buoyancy-induced flow without an axial bore flow.
Optimization of Supersonic Axial Turbine Blades Based on Surrogate Models
Authors: Waesker Markus , Buelten Bjoern , Kienzle Norman , Doetsch Christian
Published: January 2021

Due to the transition of the energy system to more decentralized sector-coupled technologies, the demand on small, highly efficient and compact turbines is steadily growing. Therefore, supersonic impulse turbines have been subject of academic research for many years because of their compact and low-cost conditions. However, specific loss models for this type of turbine are still missing. In this paper, a CFD-simulation-based surrogate model for the velocity coefficient, unique incidence as well as outflow deviation of the blade, is introduced. This surrogate model forms the basis for an exemplary efficiency optimization of the “Colclough cascade”.

In a first step, an automatic and robust blade design methodology for constant-channel blades based on the supersonic turbine blade design of Stratford and Sansome is shown. The blade flow is fully described by seven geometrical and three aerodynamic design parameters. After that, an automated numerical flow simulation (CFD) workflow for supersonic turbine blades is developed. The validation of the CFD setup with a published supersonic axial turbine blade (Colclough design) shows a high consistency in the shock waves, separation zones and boundary layers as well as velocity coefficients.

A design of experiments (DOE) with latin hypercube sampling and 1300 sample points is calculated. This CFD data forms the basis for a highly accurate surrogate model of supersonic turbine blade flow suitable for Mach numbers between 1.1 and 1.6. The throat-based Reynolds number is varied between 1*104 and 4*105.

Additionally, an optimization is introduced, based on the surrogate model for the Reynolds number and Mach number of Colclough and no degree of reaction (equal inlet and outlet static pressure). The velocity coefficient is improved by up to 3 %.
Influence of Purge Temperature Variation on the Performance of Turbine Center Frames
Authors: Jagerhofer Patrick , Peters Andreas , Göttlich Emil , Sanz Wolfgang , Farisco Federica
Published: January 2021

High-bypass ratio turbofan engines are commonly employed in aircrafts. Their usage is essential to guarantee low specific fuel consumption, reduced CO2 emissions and low noise levels. Such modern aero-engines benefit from high efficiencies by operating at turbine inlet temperatures in excess of the melting point of the turbine components. To enable this, compressor air is supplied to the turbine for cooling and purging purposes. The re-introduction of the cooling air back into the mainstream flow is known to alter the flow field and to affect the aerodynamic performance of the turbine components. A component especially susceptible to the interaction between the mainstream and purge flow is the Turbine Center Frame, located between high-pressure turbine (HP) and low-pressure (LP) turbine. For ever higher bypass ratios, this turbine transition ducts need to be designed with axial lengths as short as possible and larger radial offsets to avoid engine weight penalties while at the same time maintaining aerodynamic performance. More detailed experience in the field of intermediate turbine ducts is needed to identify further opportunities to improve turbofan engine performance, including an in-depth understanding of the interaction between mainstream and purge flows.

This paper presents a Computational Fluid Dynamics (CFD) study of the effect of the purge flow temperature, and hence density, on the aerodynamic performance of an engine representative Turbine Center Frame (TCF). Several steady-state Reynolds-averaged Navier–Stokes (RANS) simulations were conducted for varying purge flow temperatures using an in-house code called LINARS. Time-averaged five-hole-probe measurements acquired in the Transonic Test Turbine Facility (TTTF) at Graz University of Technology were used as inlet boundary conditions to impose an engine-relevant flow field. The results obtained from two reduced and two increased purge flow temperature conditions were compared to a reference case. The reference case results showed agreement with static wall pressure measurements, hence validating the simulation. Changing the purge flow temperature significantly affected the main flow locally as well as overall. The position and size of vortices in the TCF were changed under the presence of hotter or cooler purge flows. Additionally, a flow separation on the outer duct wall observed in the baseline case was suppressed in the cold-purged flow case. The cold-purged TCF showed a 28.8% lower total pressure loss than the hot-purged one. This indicates that a more aggressive TCF design may be feasible in a cold-purged operation.
Numerical Evaluation of Surface Roughness Effects on Film-Cooling Performance in a Laidback Fan-Shaped Hole
Authors: Zamiri Ali , You Sung Jin , Chung Jin Taek
Published: January 2021

This study numerically investigates the influences of cooling hole surface roughness in a laidback fan-shaped hole on the flow structure and film-cooling effectiveness. The three-dimensional compressible LES approach (large eddy simulation) is conducted in a baseline 7-7-7 laidback fan-shaped hole. The cooling hole is located on a flat plate surface with a 30-degree injection angle at a constant density ratio DR = 1.5 and two blowing ratios M = 1.5 and 3. The computational results were validated by the measurements in terms of velocity and thermal fields for both the smooth and rough holes. In order to numerically consider the influences of the surface roughness on cooling hole side, the equivalent sand grain roughness method was utilized. Different correlations between the equivalent sand grain roughness height and arithmetic average roughness height were numerically tested to find an accurate correlation in comparison to the measurements. The computational data revealed that the surface roughness of the hole interior walls increases the thickness of the boundary layers within the hole. This leads to a higher jet core flow at the hole exit and lower film-cooling performance at the surface of flat plate compared to those of the smooth cooling hole. The minimum area-averaged film-cooling performance was observed in the case of the highest blowing ratio and the largest surface roughness height. The present work reveals that the current LES approach by considering the proper equivalent sand grain roughness height is a powerful tool to obtain the accurate solution in the prediction of the heat transfer characteristics and the flow structures in the fan-shaped cooling holes.
Experimental LCF Study of a Probabilistically Optimized Double Notch Specimen Geometry for Validation of Deterministic and Probabilistic Design Concepts
Authors: Adam Marcel , Schmitz Sebastian , Suresh Suhas , Kulawinski Dirk , Erbe Alexander , Mäde Lucas , Gundavarapu Sesha , Kontermann Christian , Oechsner Matthias
Published: January 2021

In this work, the design and testing of a new LCF double notch specimen geometry is presented. The deterministic CMB model and a probabilistic model for LCF which considers size effects are simultaneously applied as shape optimization functional. In order to demonstrate the potential of the statistical size effect consideration, the probability of crack initiation is maximized in the milder notch while the deterministic LCF life is minimized in the sharp notch. This also increases the likeliness of an experimental validation success considering the issues of high scatter in material properties and limited test resources (test plan optimization). Specimens of a high-chromium forged steel for elevated application temperatures have been manufactured according to this specimen design and a systematic and advanced experimental testing campaign is conducted to prove the hypothesis. In-situ time-resolved alternating current potential drop measurements in combination with load-triggered digital image acquisition at both notches are applied in order to enable determination and quantification of crack initiation and growth at superior accuracy during LCF cycling. These experimental and further post-experimental analyses confirm that cracking in the mild notch always occurred in the first place which has been expected for most test outcomes according to the probabilistic model predictions. Crack initiation in the sharp notches on the other hand, which has been expected to occur first on the basis of conventional deterministic predictions, could not be detected at all.