bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Pressure Surface Winglets on the Tip Leakage Flow in a Compressor Cascade With High Subsonic Mach Numbers
Authors: Wu Wanyang , Zhong Jingjun , Kan Xiaoxu , Huang Zhenyu
Published: January 2021

The improvement of compressor performance is facing a new technological challenge, as the compressor is considered as one of the core components in a gas turbine. Tip leakage flow affects the aerodynamic performance of the compressor rotor directly, then the compressor performance can be improved by reasonably controlling it. In recent years, the blade tip winglet has been certainly concerned as an effective flow control method for reducing the leakage loss. The mechanism of using tip winglets to control tip leakage flow in compressor cascade has been investigated in the condition of low Mach number, whereas the research in high subsonic incoming conditions also needs to be considered.

To investigate the effect of the pressure surface winglet on the aerodynamic performance of a compressor cascade at high subsonic inlet Mach numbers, an experiment compared cascades with no winglet and different width pressure surface tip winglets at different inlet Mach numbers (Ma = 0.5, 0.6 and 0.7). Results show that the pressure surface winglet weakened the pressure gradient on both sides of the blade and reduced flow loss in the condition of high subsonic Mach numbers, which in turn tip clearance flow. When pressure surface tip winglet width increased, the improving degree is increased. At the same time, a change in Mach number had a proportional the effect on tip leakage flow control. The most effective pressure surface winglet was PW2.0 at the inlet Mach number of 0.7, which produced the most significant cascade loss reduction of 6.53% when compared to the original cascade at the same inlet Mach number.

To investigate the characteristics of the compressor cascade at different incidences, the Mach number was set at 0.7 and the characteristics of cascade flow at −6°, −3°, 0°, +3° and +6°were studied. Pressure surface winglets with different widths reduced both the influence range of the leakage flow and the strength of the leakage vortex. As the tip winglet width increased, the influence of the tip winglet on the cascade flow increased. When incidences moved from negative to positive, the improvement effect of the cascade flow field with the pressure surface winglet was enhanced. When the incidence was+6°, for example the improvement effects the PW2.0 on cascade loss was 12.4%.

The flow characteristics in the compressor cascade with the pressure surface winglets behave better at different Mach numbers and incidences. Through the research in this paper, the improvement effect and mechanism of the aerodynamic performance of the pressure surface winglet in high subsonic Mach number are clearer, and the application range of the winglet is widened, which provides a rich reference for the optimization design of compressor with high subsonic Mach number.
Reduced Order Method Based on an Adaptive Formulation and its Application to Fan Blade System With Dovetail Joints
Authors: Yuan Jie , Schwingshackl Christoph , Salles Loic , Wong Chian , Patsias Sophoclis
Published: January 2021

Localized nonlinearities due to the contact friction interfaces are widely present in the aero-engine structures. They can significantly reduce the vibration amplitudes and shift the resonance frequencies away from critical operating speeds, by exploiting the frictional energy dissipation at the contact interface. However, the modelling capability to predict the dynamics of such large-scale systems with these nonlinearities is often impeded by the high computational expense. Component mode synthesis (CMS) based reduced order modelling (ROM) are commonly used to overcome this problem in jointed structures. However, the computational efficiency of these classical ROMs are sometimes limited as their size is proportional to the DOFs of joint interfaces resulting in a full dense matrix. A new ROM based on an adaptive formulation is proposed in this paper to improve the CMS methods for reliable predictions of the dynamics in jointed structures. This new ROM approach is able to adaptively switch the sticking contact nodes off during the online computation leading to a significant size reduction comparing to the CMS based models. The large-scale high fidelity fan blade assembly is used as the case study. The forced response obtained from the novel ROM is compared to the state-of-the-art CMS based Craig-Bampton method. A parametric study is then carried out to assess the influence of the contact parameters on the dynamics of the fan assembly. The feasibility of using this proposed method for nonlinear modal analysis is also characterised.
Noise Attenuation Potential Using Helmholtz Absorbers Integrated in Low Pressure Turbine Exit Guide Vanes and Turbine Exit Casing End Walls
Authors: Zenz Manuel , Simonassi Loris , Bruckner Philipp , Pramstrahler Simon , Heitmeir Franz , Marn Andreas
Published: January 2021

To further reduce the noise emitted from modern aircrafts, every possibility has to be taken into account. Acoustic liners are successfully used in the inlet or the bypass duct of aircraft engines to mitigate the noise emitted by the fan. Due to the rough environment (high temperature, flow velocity, higher order duct modes), the exhaust duct is of limited use concerning the application of acoustic liners. It is well known that the last stage low pressure turbine (LPT) has a dominant influence onto the emitted noise of an aircraft engine especially at low load conditions such as approach. A noise reduction in this area could lead to a beneficial result of decreasing the noise content which is directly emitted in the environment.

This paper is about noise attenuation using Helmholtz absorbers in various parts of a turbine exit casing (TEC). These single degree of freedom absorbers have been integrated in turbine exit guide vanes (TEGVs), with the openings on the vanes suction side, as well as in the inner and outer duct end walls. Different absorber neck diameters were investigated and combined with different vane designs. The vane designs studied included a state of the art set-up as well as vanes with a lean. Test runs were performed with altered combinations of vanes and end walls under engine relevant operating conditions in a subsonic test turbine facility for aerodynamic, aeroacoustic and aeroelastic investigations (STTF-AAAI) located at the Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. Comparisons between all these setups and the respective hard wall reference cases were done. The resulting sound pressure levels as well as sound power levels of all investigated combinations are listed and compared concerning each configurations noise attenuation potential. Additionally, the flow field downstream of every setup is analysed if the aerodynamic behaviour is changing.

The investigated operating point is the noise certification point Approach (APP) which is of high importance because of the high acoustical impact onto the environment around airports during the landing procedure of an aircraft.

The acoustical data has been obtained by using flush mounted condenser microphones located downstream of the TEC. The whole test section was rotated over 360 deg around the flow channel. To detect if the aerodynamical behaviour changes by including openings into the flow channel end walls as well as into the vanes, aerodynamic measurements have been performed downstream of the TEC. The aerodynamical data was obtained by using an aerodynamic five-hole-probe (5HP) as well as a trailing edge probe.
Finite Element Velocity Perturbation Application in Investigating Compressor Dovetail Fretting in Time Domain
Authors: Duong Loc Q. , Lamicq Olivier J.
Published: January 2021

In the design of a gas turbine airfoil, avoiding resonance at all conditions is impossible. The airfoil may vibrate fiercely during resonant passages, which then may induce small oscillation motion at the disk attachment. Due to microslip at the contact regions, fretting would occur in conjunction with the reduction of material fatigue properties. This paper presents a finite element analysis using the Velocity Perturbation Method (VPM) in predicting airfoil attachment nonlinear fretting-behavior in the time domain at a resonant frequency of interest. Numerical simulation, showing design fretting fatigue characteristics based on fundamental Ruiz and Smith-Watson-Topper (SWT) criteria, is demonstrated on two models, simplified and representative. The simplified model was used for detail analysis set-up and basic post-processing while the representative model illustrated the difference in nonlinear contact response of an industrial compressor under bending and torsional modes in the time domain.

This Finite Element velocity perturbation approach can be used to study the main factors affecting fretting of any two bodies in contact: load, coefficient of friction, contact geometry and impact of different frequencies or modal shapes in the time domain.
Effect of the In-Hole Vortical Structures on the Cylindrical-Hole Film-Cooling Effectiveness
Authors: Agarwal Shubham , Gicquel Laurent , Duchaine Florent , Odier Nicolas , Dombard Jérôme
Published: January 2021

Understanding the flow from a cooling hole is very important to be able to properly control film cooling of turbine blades. For this purpose, large eddy simulation (LES) investigation of the flow inside a cylindrical film cooling hole is presented in this paper. Two different geometries, with different hole metering lengths, are investigated at a blowing ratio of 0.5. The main flow structure in the hole are the hairpin vortices that originate from a shear layer formed due to flow separation near the hole entry. The comparison of these hairpin vortices in the two cases with different hole metering length is presented in detail. The results show that in case of the hole with longer length the hairpin vortices dissociate within the hole itself. In such a case a uniform flow is seen at the hole exit. However, when the hole length is significantly decreased, it is shown that these vortices exit the hole and effect the vortex structures outside the hole, thereby accounting for the reduction in film cooling effectiveness. Overall, these results bring forth one other major reason for the reduction in film cooling effectiveness with reduction in hole length, i.e. the exit of in-hole hairpin vortices into the crossflow.
Non-Uniform Two-Phase Flow of Supercritical Carbon Dioxide Centrifugal Compressor
Authors: Bao Wenrui , Yang Ce , Fu Li , Yang Changmao , Ji Lucheng
Published: January 2021

An asymmetric structure of volute in a supercritical carbon dioxide centrifugal compressor induces a non-uniform circumferential distribution of the upstream flow field, which inevitably affects the formation of a two-phase region of carbon dioxide in an impeller. In this work, unsteady simulations for centrifugal compressors were conducted. First, the influence of low static strip induced by low static pressure near volute tongue on the impeller flow field was presented. Then, the non-uniform flow field distribution in the impeller passages and flow characteristics of the passages at the impeller inlet were obtained. Finally, the two-phase regions in the impeller were presented. The results demonstrate that for a centrifugal compressor with volute, the two-phase region appears not only on the suction surface of the leading edge of the blade, but also in some impeller passages, on the pressure surface of the blade near the leading edge, and in the leading edge and mid-chord of tip clearance, under the design conditions. The low static pressure strip induced by the volute leads to a high-speed region in the impeller passages where the temperature and pressure of supercritical carbon dioxide fall below the critical point and carbon dioxide enters the two-phase region. Meanwhile, the static pressure on the blade surface is distorted under the influence of a high-speed region in the passages, resulting in the formation of a two-phase region at the tip clearance. The flow distortion of passages at the impeller inlet results in the appearance of two-phase regions on the both sides of leading edge of the blade. The dryness on the suction side of the blade leading edge and the leading edge of the tip clearance is lower, which indicated that the proportion of liquid-phase carbon dioxide is higher in these two-phase regions.
Potential of Decentralized Container-Scale PtL Plants for Aviation: From Crude to Post-Processed FT-SPK
Authors: Jürgens Sophie , Selinsek Manuel , Bauder Uwe , Rauch Bastian , Köhler Markus
Published: January 2021

In today’s pressing quest of emission and pollution reduction in all energy sectors, research on renewable and sustainable fuels is a key component. The Institute of Combustion Technology at the German Aerospace Center strives to assess new, renewable fuel in a gear wheel approach of interdependent linked experiments, database comparison and model-based assessment, allowing for a fast iterative feedback to the fuel producer and giving a detailed valuation of fuels as well as a distinguished preselection when presented with numerous fuel samples.

Synthetic fuels as a substitute for fossil fuels are becoming increasingly important within the framework global climate protection goals. Power-to-X technologies such as Fischer-Tropsch synthesis can be used to produce carbon-neutral fuels using carbon dioxide from air (direct air capture) and hydrogen obtained by water electrolysis using green electricity. This fuel assessment has been iteratively performed for the post-processing of a Fischer-Tropsch fuel, produced in the module-based, compact and highly innovative PtL plant erected by INERATEC GmbH.

The aim of the present work was to evaluate the postprocessing steps hydration and distillation of the crude Fischer-Tropsch products with hindsight to “fit-for-purpose” properties of the resulting products for aviation. The chemical composition was determined using comprehensive two-dimensional GCxGC chromatography. Numerical blending analysis was performed utilizing the DLR SimFuel platform to evaluate the range of blending ratios of the Fischer-Tropsch fuels with conventional jet fuels. It could be demonstrated that the post-processed Fischer-Tropsch fuels display a beneficially high blending potential with conventional jet fuels considering the chemical composition and combustion behavior.
Conditioning of Leakage Flows in Gas Turbine Rotor-Stator Cavities
Authors: Darby P. W. , Mesny A. W. , De Cosmo G. , Carnevale M. , Lock G. D. , Scobie J. A. , Sangan C. M.
Published: January 2021

Ingress is the penetration of hot mainstream fluid into the cavity formed between the turbine disc (rotor) and its adjacent casing (stator). Gas turbine engine designers use rim seals fitted at the periphery of the discs and a superposed sealant flow — typically fed through the bore of the stator — is used to reduce, or in the limit prevent, ingress. Parasitic leakage enters the cavity through pathways created between mating interfaces of engine components. Owing to the aggressive thermal and centrifugal loading experienced during the turbine operating cycle, the degree of leakage and its effect on ingress are difficult to predict.

This paper considers the potential for leakage flows to be conditioned in order to minimise their parasitic effect on disc cooling, and ultimately engine, performance. Measurements of static and total pressure, swirl and species concentration were used to assess the performance of a simple axial clearance rim-seal over a range of non-dimensional leakage flow-rates. A computational model was used to provide flow visualisation to support the interpretation of flow structures derived from the experiments.

Data is presented to investigate the effects of swirling the leakage flow in accordance with, and counter to, the disc rotation. The injected momentum from the leakage created a toroidal vortex in the outer part of the cavity. Co-swirl was found to improve the sealing effectiveness by up to 15% compared to the axially-introduced baseline and counter-swirled configurations. Varying the momentum of the leakage flow was considered by passing consistent mass-flows through a range of leakage outlet areas. Increasing the momentum was seen to increase the influence of the toroidal vortex on the flow structure in the cavity, which in turn influenced the sealing effectiveness.
Rotordynamic Performance of the Interlocking Labyrinth Seal With a Tilting Rotor
Authors: Zhang Wanfu , Wang Yingfei , Gu Qianlei , Yin Lu , Yang Jian-gang
Published: January 2021

Numerical analysis model of an interlocking labyrinth seal (ILS), including 6 seal cavities and 7 seal teeth (3 teeth on the rotor, 4 teeth on the stator), is established for studying the effect of tilting rotor on its rotordynamic characteristics. The dynamic characteristic identification method based on infinitesimal theory is applied to solve the dynamic force coefficient of the annular seal with arbitrary elliptical orbits and eccentric positions under field conditions. The paper investigated the dynamic characteristics of the interlocking labyrinth seal with various misalignment angles (θ = 0, 0.1°, 0.2°, 0.3°, 0.4°, 0.5°, 0.6°), different pressure ratios (Pin = 6.9 bar, PR = 0.5, 0.8), locations of misalignment center (Loc = 0, L/2, L). Results show that the tilting rotor could minimize the leakage flow rate of the ILS. When the misalignment angle θ = 0.6°, the mass flow rate can be reduced about 2.5%. The tilting rotor will cause the geometric deformation of the ILS cavity and the changes in the radial clearance of the teeth, which results in an increasing pressure drop in the seal cavity. The effect of each cavity in the ILS on the stability of the system is different. The cavity with the inlet close to the rotor and the outlet away from the rotor helps to improve the system stability due to its locally anti-rotational flow. The effective damping of the entire ILS increases as the misalignment angle increases. The system shows the best stability when the misalignment center is close to the seal inlet. The stability of the seal cavity C1 can be improved for any misalignment centers. The stability of the seal cavity C2 decreases when the misalignment center moves toward the seal outlet. For the seal cavities C3∼C6, their stability can be improved for Loc = 0, L/2, and decreases for Loc = L. The tilting rotor has a positive effect on the stability of the ILS only except for high whirling frequency (> 100 Hz) under Loc = L.
The Investigation of Axial Compressor With Aggressive Flow Path Near Stall Condition
Authors: Ming Lele , Wu Yadong , Ouyang Hua
Published: January 2021

Rotating stall is an unsteady flow phenomenon in flow rate reduction process of axial compressor. Single or multiple stall cells can be found in blade passage, rotating circumferentially at frequency ranging from 20% to 80% of compressor rotating frequency. Rotating stall may further lead to surge, then mass flow and pressure ratio of the compressor decrease rapidly while vibration amplitude of bearing fulcrum increases significantly, which would affect safety operation of the aero-engine. This paper reports the study on a multistage compressor with special-shaped aggressive flow path, which is significantly different from the conventional compressor with its meridian flow path midline parallel or nearly parallel to the rotating shaft axis.

To study rotating stall and surge characteristics of multistage compressor with inlet distortion, this paper takes a 4.5-stage axial compressor as research object which has special S-shaped meridian flow path. On SJTU compressor test facility, the author carries out multidisciplinary tests on compressor dynamic performance (stator LE/TE and inter-stage fluctuating pressure measured by fluctuating pressure transducers, vibration measured by acceleration transducers, and dynamic stress measured by pasting strain transducers on the surface of stator blade). And in subsequent surge experiment, stall and surge signals at different rotating speeds are successfully captured. With above test data, axial, radial and circumferential instability development characteristics are studied by time domain correlation analysis, frequency domain power spectrum and coherence analysis, which preliminarily reveals the generation, development, propagation and elimination characteristics of rotating stall and surge.

Meanwhile, in view of time-frequency characteristics of two instability transition processes, time-frequency analysis method based on Choi-Williams distribution model is adopted to capture instantaneous frequency characteristics. The results show that instability phenomenon exhibits quasi-exponential change in instability transition processes. Compared with traditional methods, time-frequency method is more effective in characterizing strong time-varying instability signals such as rotating stall and surge.
Acceleration Method for Evolutionary Optimization of Variable Cycle Engine
Authors: Hao Wang , Zhou Li , Zhang Xiaobo , Wang Zhanxue
Published: January 2021

Variable cycle engine (VCE) is considered as one of the best options for advanced military or commercial supersonic propulsion system. Variable geometries enable the engine to adjust performance over the entire the flight envelope but add complexity to the engine. Evolutionary algorithms (EAs) have been widely used in the design of VCE. The initial guesses of the engine model are generally set using design point information during evolutionary optimization. However, the design point information is not suitable for all situations. Without suitable initial guesses, the Newton-Raphson solver will not be able to reach the solution quickly, or even get a convergent solution. In this paper, a new method is proposed to obtain suitable initial guesses of VCE model during evolutionary optimization. Differential evolution (DE) algorithm is used to verify our method through a series of optimization cases of a double bypass VCE. The result indicates that the method can significantly reduce the VCE model call number during evolutionary optimization, which means a dramatic reduction in terms of evolution time. And the robustness of the optimization is not affected by the method. The method can also be used in the evolutionary optimization of other engines.
Windmilling Characteristics of a Contra-Rotating Fan
Authors: Madasseri Payyappalli Manas , Karmakar Arghya , Pradeep A. M.
Published: January 2021

In the present experimental study, a low aspect ratio, low hub-tip ratio contra-rotating axial fan is investigated to understand its performance under windmilling conditions. Two configurations are tested; in the first configuration (event A), the front rotor of the contra-rotating fan is powered and the rear rotor is allowed to windmill; in the second configuration (event B), the rear rotor of the contra-rotating fan is powered and the front rotor is allowed to windmill. The spanwise distribution of the loading coefficient and the flow angles at different streamwise positions reveal the details of the flow development across the rotors. The performances of event A and event B are nearly similar; however, event A stalls earlier than event B. Though the average total pressure drops across the windmilling rotor for both the events, a small spanwise region behaves as a fan or a stirrer. Thus, a “neutral radius” on the windmilling rotor is identified for both events A and B. The neutral radius appears close to the tip for event A and it appears close to the hub for event B. On the windmilling rotor in either events, the span regions close to the tip for event A behaves as a fan and the span regions close to the hub for event B behaves as a stirrer. It is also observed that the neutral radius shifts its position to a lower span location as the flow coefficient reduces. Thus, the flow coefficient is a significant parameter that decides the position of the neutral radius. Further, the unsteady pressure measurements recorded at the casing captures the fundamental phenomena during the stall inception. The paper thus relates the similarities and unveils the contrasting features of the windmilling events A and B. In summary, this paper discusses the performance, flow physics and stall inception characteristics of a contra-rotating axial fan under windmilling conditions.
Improved LP-Stage Design for Industrial Steam Turbines
Authors: Brunn Oliver , Harbecke Ulrich , Mokulys Thomas , Salit Victor , Schwarz Mark Andre , Dornbusch Felix
Published: January 2021

This publication deals with the improvement of the design and life steam testing of a low-pressure steam turbine module for utilization in industrial applications. Extensive numerical investigations were carried out and validated with experimental measurements. For the validation of the final blade design, the LP module was integrated and tested in a 12.5MW steam turbine test rig. During the balancing of the rotor in a vacuum chamber, tip-timing and strain gage measurements were conducted for testing the mechanical behavior of the airfoils. In the succeeding assembly of the steam turbine, tip-timing probes and flow measurement probes were integrated around the LP module to evaluate the blade load and performance under realistic conditions. To obtain a good understanding of the improved performance and mechanical behavior the thermodynamic tests were carried out under no-load, part load and design load conditions to cover the whole operating range of the LP stages. The paper also describes how an existing rotor from the test rig could be retrofitted, to accommodate the new turbine stages with additive manufacturing of the base material on the shaft.
Numerical Investigation on the Nonlinear Dynamics of Anisotropic Breathing Cracked Rotor Systems
Authors: Zheng Zhaoli , Li Zixuan , Zhang Di , Xie Yonghui , Zhang Zheyuan
Published: January 2021

The nonlinear breathing crack behaviors and anisotropy of the bearing are important sources of severe vibration of rotor systems. However, the rotor system considering both of these factors has not gained sufficient attention in the existing studies. In this paper, the nonlinear dynamics of such anisotropic breathing cracked rotor system is investigated based on three-dimensional finite element model (FEM). Firstly, the equations of motion of the rotor system are established in the rotating frame to facilitate the modeling of the breathing crack. The fixed-interface component mode synthesis (CMS) is used to reduce the system’s degrees of freedom (DOFs). Then, in the process of solving the equations by harmonic balance method (HBM) and Newton-Raphson method, an original method for fast calculating tangent stiffness matrix is proposed. Finally, the effects of the crack depth, the anisotropy of bearing and relative angle between bearings on the nonlinear dynamics of the system are studied. The results show that the breathing behavior will complicate the vibration and introduce additional transverse stiffness. The increase of crack depth will deteriorate the vibration. The anisotropy and relative angle of bearing will lead to the splitting and merging of the resonant peaks, respectively.
Near Wall Resolution Requirements for High-Order FR/CPR Method for Wall-Resolved Large Eddy Simulations
Authors: Bhaskaran Rathakrishnan , Ledezma Gustavo
Published: January 2021

This study aims to establish near wall resolution requirements for wall-resolved Large Eddy Simulations (LES) using the Flux Reconstruction / Correction Procedure via Reconstruction (FR/CPR) method. The FR/CPR method is relatively new and its numerical capabilities for LES are not well established. A high-order unstructured LES solver (GENESIS) based on the FR/CPR approach is used to study two canonical near wall turbulent flow problems. The first problem concerns spatial development of a turbulent flat plate boundary layer. The grid resolution requirement for various polynomial orders is established and the skin-friction and near wall turbulence is compared to theory and Direct Numerical Simulation (DNS) results. The second problem studied is the two-dimensional wall film case of Kacker and Whitelaw (1968, 1969). This is a thermal mixing problem consisting of a two-dimensional jet for various mass flow ratios and plate thicknesses. This study focuses on one of the cases from this data set, corresponding to a thick plate. Well resolved LES simulations show an excellent agreement with measured adiabatic film effectiveness. The effect of polynomial order and grid resolution is investigated and near wall resolution requirements are established.
Laminar Flame Speeds of Oxy-Methane Flames With CO2 Dilution at Elevated Pressures
Authors: Turner Mattias A. , Kulatilaka Waruna D. , Petersen Eric L.
Published: January 2021

Spherically expanding, laminar flame experiments have been conducted for oxy-methane mixtures diluted in CO2. Test conditions consisted of pressures of 5 atm and 10 atm, an ambient initial temperature of 298 K, and a full range of equivalence ratios from lean to rich. Schlieren imaging was used to image the flames. The mixtures tested in this study contained helium for the purpose of increasing the Lewis number to suppress onset of thermal-diffusive instabilities. Flame speeds ranged from 24.3 to 30.4 cm/s at 5 atm initial pressure and from 17.9 to 22.6 cm/s at 10 atm, resulting in an approximately 26% decrease in flame speed across all tested equivalence ratios as a result of the doubling in initial pressure. Predicted flame speeds from AramcoMech2.0 tended to be higher than the experimental data by 3% at 5 atm initial pressure and 8% at 10 atm initial pressure, indicating that the performance of the mechanism is quite good for this mixture, but diminishes slightly as pressure increases.
Reduced-Order Modelling of Rotating Stall
Authors: Schlüter Dominik , Grewe Robert P. , Wartzek Fabian , Liefke Alexander , Werner Jan , Kunkel Christian , Gümmer Volker
Published: January 2021

Rotating stall is a non-axisymmetric disturbance in axial compressors arising at operating conditions beyond the stability limit of a stage. Although well-known, its driving mechanisms determining the number of stall cells and their rotational speed are still marginally understood. Numerical studies applying full-wheel 3D unsteady RANS calculations require weeks per operating point. This paper quantifies the capability of a more feasible quasi-2D approach to reproduce 3D rotating stall and related sensitivities.

The first part of the paper deals with the validation of a numerical baseline the simplified model is compared to in detail. Therefore, 3D computations of a state-of-the-art transonic compressor are conducted. At steady conditions the single-passage RANS CFD matches the experimental results within an error of 1% in total pressure ratio and mass flow rate. At stalled conditions, the full-wheel URANS computation shows the same spiketype disturbance as the experiment. However, the CFD underpredicts the stalling point by approximately 7% in mass flow rate. In deep stall, the computational model correctly forecasts a single-cell rotating stall. The stall cell differs by approximately 21% in rotational speed and 18% in circumferential size from the experimental findings. As the 3D model reflects the compressor behaviour sufficiently accurate, it is considered valid for physical investigations.

In the second part of the paper, the validated baseline is reduced in radial direction to a quasi-2D domain only resembling the compressor tip area. Four model variations regarding span-wise location and extent are numerically investigated. As the most promising model matches the 3D flow conditions in the rotor tip region, it correctly yields a single-cell rotating stall. The cell differs by only 7% in circumferential size from the 3D results. Due to the impeded radial migration in the quasi-2D slice, however, the cell exhibits an increased axial extent. It is assumed, that the axial expansion into the adjacent rows causes the difference in cell speed by approximately 24%. Further validation of the reduced model against experimental findings reveals, that it correctly reflects the sensitivity of circumferential cell size to flow coefficient and individual cell speed to compressor shaft speed. As the approach reduced the wall clock time by 92%, it can be used to increase the physical understanding of rotating stall at much lower costs.
Soot Formation and Emission From Jet A-1 and a 30% HEFA Blend in a Multisector Combustor at Realistic Operating Conditions
Authors: Hassa Christoph , Magens Eggert , Voigt Lena , Diers Olaf , Otterpohl Ingo , Heinze Johannes
Published: January 2021

The production and emission of soot from Kerosene JET-A1 and a blend of a different JET-A1 and 30% HEFA was investigated in a realistic multisector combustor of Rolls-Royce Deutschland. Soot concentration measurements were performed at the exit as well as in the optically accessible primary zone of the combustor. There, information of soot mass concentration is available from measurements using Laser induced incandescence and Laser extinction. At the exit of the combustor, soot particles were measured with a scanning mobility particle sizer. This resulted in particle size distributions from which soot number and mass concentrations were calculated.

Within the pressurized combustor, low load points, scaled cruise and high load points were operated. For the investigated operating range which reaches to ∼50% of max pressure but preserves engine AFR, up to 75% reduction of both soot particle mass and number EI were observed for the HEFA blend in part load and 50% at the scaled high-power condition. However at the end of the primary zone, a reduction increasing with soot concentration and fuel load was recorded. This guides attention to the different oxidation characteristics for the fuels in the investigated combustor. Accordingly, larger particles were consistently measured at the exit for the HEFA blend.
Vibration Analyses of an Axial Turbine Wheel With Intentional Mistuning
Authors: Beirow Bernd , Kühhorn Arnold , Weber Robby , Popig Frederik
Published: January 2021

The last stage bladed disk of a steam turbine is analyzed with respect to both flutter susceptibility and limitation of forced response. Due to the lack of variable stator vanes unfavorable flow conditions may occur which can lead to flow separation in some circumstances. Consequently, there is the risk of flutter in principle, particularly at nominal speed under part load conditions. For this reason, intentional mistuning is employed by the manufacturer with the objective to prevent any self-excited vibrations. A first step in this direction is done by choosing alternate mistuning, which keeps the manufactural efforts in limits since only two different blade designs are allowed. In this sense, two different series of blades have been made. However, it is well known that small deviations from the design intention are unavoidable due to the manufacturing procedure, which could be proved by bonk tests carried out earlier. The influence of these additional but unwanted deviations is considered in numerical simulations. Moreover, the strong dependence of blade frequencies on the speed is taken into account since centrifugal stiffening effects significantly attenuate the blade-to-blade frequency difference in this particular case.

Focusing on the first flap mode it could be shown that a mitigation of flutter susceptibility is achieved by prescribing alternate mistuning, which indeed evokes an increase of originally small aerodynamic damping ratios. Nevertheless, the occurrence of negative damping ratios could not be completely precluded at part load conditions. That is why optimization studies are conducted based on genetic algorithms with the objective function of maximizing the lowest aerodynamic damping ratios. Again only two different blade designs are admitted. Finally, mistuning patterns could be identified causing a tremendous increase of aerodynamic damping ratios. The robustness of the solutions found could be proved by superimposing additional random mistuning.
The CFD Design and Optimisation of a 100 kW Hydrogen Fuelled mGT
Authors: Devriese Cedric , Penninx Gijs , de Ruiter Guido , Bastiaans Rob , De Paepe Ward
Published: January 2021

Against the background of a growing deployment of renewable electricity production, like wind and solar, the demand for energy storage will only increase. One of the most promising ways to cover the medium to long-term storage is to use the excess electricity to produce hydrogen via electrolysis. In a modern energy grid, filled with intermittent power sources and ever-increasing problems to construct large power plants in densely populated areas, a network of Decentralised Energy Systems (DES) seems more logical. Therefore, the importance of research into the design of a small to medium-sized hydrogen fuelled micro Gas Turbine (mGT) unit for efficient, local heat and electricity production becomes apparent. To be able to compete with Reciprocating Internal Combustion Engines (RICEs), the mGT needs to reach 40% electrical efficiency. To do so, there are two main challenges; the design of an ultra-low NOX hydrogen combustor and a high Turbine Inlet Temperature (TIT) radial turbine. In this paper, we report on the progress of our work towards that goal. First, an improvement of the initial single-nozzle swirler (swozzle) combustor geometry was abandoned in favour of a full CFD (steady RANS) design and optimisation of a micromix type combustion chamber, due to its advantages towards NOx-emission reduction. Second, a full CFD design and optimisation of the compressor and turbine is performed. The improved micromix combustor geometry resulted in a NOx level reduction of more than 1 order of magnitude compared to our previous swozzle design (from 1400 ppm to 250 ppm). Moreover, several design parameters, such as the position and diameter of the hydrogen injection nozzle and the Air Guiding Panel (AGP) height, have been optimized to improve the flow patterns. Next to the combustion chamber, CFD simulations of the compressor and turbine matched the 1D performance calculations and reached the desired performance goals. A CFD analysis of the impact of the tip gap and exhaust diffuser cone angle led to a choice of these parameters that improved the compressor and turbine performance with a limited loss in efficiency.
Numerical Investigation of an In-Wall Cooling Design Approach for Improved Thermal Efficiency of Additively Manufactured Gas Turbine Ring Segments
Authors: Wimmer Thomas , Mick York , Weigand Bernhard
Published: January 2021

Raising the combustion temperature continues to be a major driver for increasing the overall efficiency of industrial gas turbines. Therefore, active cooling has become a necessity as gas temperatures have surpassed the allowable temperature of the base material. Thus, cooling schemes need to be improved for higher heat loads. However, the thermal efficiency of cooling schemes, which can be manufactured employing conventional machining is limited. With the geometrical freedom offered by Additive Manufacturing (AM), advanced cooling designs for gas turbine parts have become viable and can provide superior thermal efficiency. A promising cooling design approach which exploits this freedom is In-Wall cooling. Here cooling channels are placed within the structural wall close to the heat-loaded surface. In order to develop this design approach further, In-Wall cooling schemes for a ring segment have been modeled numerically with different topologies and varying design parameters. These include wall thickness, channel pitch, size and length, and several more. The design parameters’ influence on thermal efficiency of In-Wall cooling schemes are quantified. The wall thickness between channels and the heat loaded surface is adapted locally. The employed approach leads to a more homogeneous temperature distribution and is reported in the paper. This work can help designers to focus on the most important factors when designing a new In-Wall cooling scheme and shows how the capabilities of AM can be employed in gas turbine cooling design.
Louver Slot Cooling and Full-Coverage Film Cooling With a Combination Internal Coolant Supply
Authors: Click Austin , Ligrani Phillip M. , Hockensmith Maggie , Knox Joseph , Larson Chandler , Fairbanks Avery , Liberatore Federico , Patel Rajeshriben , Ho Yin-Hsiang
Published: January 2021

Within the present investigation, a louver slot is employed upstream of an array full coverage film cooling holes. Cooling air is supplied using a combination arrangement, with cross-flow and impingement together. The louver consists of a row of film cooling holes, contained within a specially-designed device which concentrates, and directs the coolant from a slot, so that it then advects as a layer downstream along the test surface. This louver-supplied coolant is then supplemented by coolant which emerges from different rows of downstream film cooling holes. The same coolant supply passage is employed for the louver row of holes, as well as for the film cooling holes, such that different louver and film cooling mass flow rates are set by different hole diameters for the two different types of cooling holes. The results are different from data provided by past investigations, because of the use and arrangement of the louver slot, and because of the unique coolant supply configurations. The experimental results are given for mainstream Reynolds numbers from 107000 to 114000. Full-coverage blowing ratios are constant with streamwise location along the test surface, and range from 3.68 to 5.70. Corresponding louver slot blowing ratios then range from 1.72 to 2.65. Provided are heat transfer coefficient and adiabatic effectiveness distributions, which are measured along the mainstream side of the test plate. Both types of data show less variation with streamwise development location, relative to results obtained without a louver employed, when examined at the same approximate effective blowing ratio, mainstream Reynolds number, cross flow Reynolds number, and impingement jet Reynolds number. When compared at the same effective blowing ratio or the same impingement jet Reynolds number, spanwise-averaged heat transfer coefficients are consistently lower, especially for the downstream regions of the test plate, when the louver is utilized. With the same type of comparisons, the presence of the louver slot results in significantly higher values of adiabatic film cooling effectiveness (spanwise-averaged), particularly at and near the upstream portions of the test plate. With such characteristics, dramatic increases in thermal protection are provided by the presence of the louver slot, the magnitudes of which vary with experimental condition and test surface location.
Experimental Investigation on Cooling Performance of Impingement-Effusion Full Coverage Film on Suction Surface of Vane
Authors: Zhang Fan , Liu Cunliang , Zhang Shuaiqi , Ye Lin , Li Bingran
Published: January 2021

To study the film cooling performance of impingement-effusion structures, it is important to study their adiabatic film cooling effectiveness. To improve the adiabatic film cooling effectiveness on a vane, some rows of cylindrical effusion holes are changed into fan-shaped holes. This experiment measured the adiabatic film cooling effectiveness of the double-walled system on the suction surface via the pressure-sensitive paint (PSP) technique. The film cooling effectiveness obtained by the PSP technique is coupled with the transient liquid crystal (TLC) technique to determine the heat transfer coefficient. This combination of techniques reduces the time required for the experiment and improves the efficiency of the experiment. The heat transfer coefficient ratio is used to evaluate the level of heating transfer. The net heat flux reduction (NHFR) is used to quantify the net benefit of film cooling. Two experimental vanes’ (A and B) film holes are both arranged in 6 rows of holes. There are 15 holes in each row. Only the positions of the fan-shaped holes are different. The experimental conditions include the mainstream Reynolds number (Re = 151,000) based on the chord length and inlet velocity, the turbulence intensities (Tu = 0.77%, 16.9%), and the mass flux ratios (ṁc/ṁg = 0.4%, 0.8%, 1.6%).

The findings show that when the mass flux ratio increases to a point, the film cooling effectiveness does not improve. Increasing the turbulence intensity leads to a decrease in the film cooling effectiveness except for the region after Row 6 on Vane B. Using the coupling of PSP and TLC to determine the heat transfer coefficient can yield credible results. The turbulence intensity and the arrangement of the film holes have obvious effects on the distribution of the heat transfer coefficient ratio. The effects of turbulence intensity, mass flux ratio and hole arrangement on NHFR were studied.
Influence of Water Addition Upstream Diffuser Inlet on Lean Blowout and Emissions in the TeLESS-II Combustor
Authors: Yang Siheng , Xu Tao , Xu Quanhong , Lin Yuzhen
Published: January 2021

Water is likely to be ingested into aeroengines under conditions of rainfall or hail, increasing the risk of flame blowout and posing great influence on the combustion characteristics. The chemical and thermal effects of inlet water addition on lean blowout and emissions in the TeLESS-II centrally staged LPP (Lean Premixed Prevaporized) combustor are investigated in this paper. Experiments are carried out at various conditions relevant to gas turbine combustors: the inlet temperature range is 450 K – 533 K, the inlet pressure range is 0.3 Mpa – 0.4 Mpa. The range of water mass fraction investigated is 0% – 5%. Chemical kinetics calculations are conducted to analyze the chemical effect of water addition on combustion characteristics of aviation kerosene. Time-averaged CH chemiluminescence imaging is applied to provide information of flame front and heat release. Combustion emission concentrations (CO, UHC, and NOx) are measured by a gas analyzer Based on Lefebvre’s model, an updated semi-analytical correlation is proposed to predict lean blowout limits of centrally staged combustor considering water addition. Chemical calculation results show that the addition of water leads to lower laminar flame speed and lower adiabatic flame temperature. The lower flame speed and higher flow velocity due to water injection result in higher lean blowout limits. Higher combustor inlet temperature can extend the LBO (lean blowout) limits to lower values at the same water fraction. Flame observations indicate that during the flame blowout process with the decrease of fuel flow rate, the post flame region first extinguished, and then upstream to the flame root. Flame close to the lean blowout presents a V shape and stabilizes in the recirculation zone near the nozzle. The heat release decreases with the increasing water injection. Emission results show that the water injection can reduce NOx emissions due to the thermal effects of flame temperature, while the CO, UHC emission increase on the contrary. The semi-analytical correlation to predict LBO limits shows fair agreement with experiments values at different water fractions. The prediction error compared to experiment data is within −11.3% to +12.8% in the present centrally staged combustor configuration.