bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endwall Boundary Layer Development in a Multistage Low-Speed Compressor With Tandem Stator Vanes
Authors: Hopfinger Michael , Gümmer Volker 
Published: September 2021

Abstract
The development of viscous endwall flow is of major importance when considering highly-loaded compressor stages. Essentially, all losses occurring in a subsonic compressor are caused by viscous shear stresses building up boundary layers on individual aerofoils and endwall surfaces. These boundary layers cause significant aerodynamic blockage and cause a reduction in effective flow area, depending on the specifics of the stage design. The presented work describes the numerical investigation of blockage development in a 3.5-stage low-speed compressor with tandem stator vanes. The research is aimed at understanding the mechanism of blockage generation and growth in tandem vane rows and across the entire compressor. Therefore, the blockage generation is investigated as a function of the operating point, the rotational speed and the inlet boundary layer thickness.
Binary Repetitive Model Predictive Active Flow Control Applied to an Annular Compressor Stator Cascade With Periodic Disturbances
Authors: Fietzke Benjamin , King Rudibert , Mihalyovics Jan , Peitsch Dieter 
Published: September 2021

Abstract
Novel pressure gain combustion concepts invoke periodic flow disturbances in a gas turbine’s last compressor stator row. This contribution presents studies of mitigation efforts on the effects of these periodic disturbances on an annular compressor stator rig. The passages were equipped with pneumatic Active Flow Control (AFC) influencing the stator blade’s suction side, and a rotating throttling disc downstream of the passages inducing periodic disturbances. For steady blowing, it is shown that with increasing actuation amplitudes Cμ, the extension of a hub corner vortex deteriorating the suction side flow can be reduced, resulting in an increased static pressure rise coefficient Cp of a passage. The effects of the induced periodic disturbances could not be addressed intrinsically, by using steady blowing actuation, Considering a corrected total pressure loss coefficient ζ*, which includes the actuation effort, the stator row’s efficiency decreases with higher cμ due to the increasing costs of the actuation mass flow. Therefore, a closed-loop approach is presented to address the effects of the disturbances more specifically, thus lowering the actuation cost, i.e., mass flow. For this, a Repetitive Model Predictive Control (RMPC) was applied, taking advantage of the periodic nature of the induced disturbances. The presented RMPC formulation is restricted to a binary control domain to account for the used solenoid valves’ switching character. An efficient implementation of the optimization within the RMPC is presented, which ensures real-time capability. As a result, Cp increases in a similar magnitude but with a lower actuation mass flow of up to 66%, resulting in a much lower ζ* for similar values of cμ.
Adaptive Geometry Representation of Turbine Vane Frames for Use in Optimization
Authors: Riebl Sebastian F. , Wakelam Christian , Niehuis Reinhard 
Published: September 2021

Abstract
Turbine Vane Frames (TVF) are a way to realize more compact jet engine designs. Located between the high pressure turbine (HPT) and the low pressure turbine (LPT), they fulfill structural and aerodynamic tasks. When used as an integrated concept with splitters located between the structural load-bearing vanes, the TVF configuration contains more than one type of airfoil with sometimes pronouncedly different properties. This system of multidisciplinary demands and mixed blading poses an interesting opportunity for optimization. Within the scope of the present work, a full geometric parameterization of a TVF with splitters is presented. The parameterization is chosen as to minimize the number of parameters required to automatically and flexibly represent all blade types involved in a TVF row in all three dimensions. Typical blade design parameters are linked to the fourth order Bézier-curve controlled camber line-thickness parameterization. Based on conventional design rules, a procedure is presented, which sets the parameters within their permissible ranges according to the imposed constraints, using a proprietary developed code. The presented workflow relies on subsequent three dimensional geometry generation by transfer of the proposed parameter set to a commercially available CAD package. The interdependencies of parameters are discussed and their respective significance for the adjustment process is detailed. Furthermore, the capability of the chosen parameterization and adjustment process to rebuild an exemplary reference TVF geometry is demonstrated. The results are verified by comparing not only geometrical profile data, but also validated CFD simulation results between the rebuilt and original geometries. Measures taken to ensure the robustness of the method are highlighted and evaluated by exploring extremes in the permissible design space. Finally, the embedding of the proposed method within the framework of an automated, gradient free numerical optimization is discussed. Herein, implications of the proposed method on response surface modeling in combination with the optimization method are highlighted. The method promises to be an option for improvement of optimization efficiency in gradient free optimization of interdependent blade geometries, by a-priori excluding unsuitable blade combinations, yet keeping restrictions to the design space as limited as possible.
Influence of Stator Hub Cavities on the Forced Response Behaviour of an Embedded Compressor Rotor
Authors: Hegde Shreyas , Kielb Robert , Zori Laith , Campregher Rubens 
Published: September 2021

Abstract
This paper focuses on the impact of hub labyrinth seal leakage flows on the aeromechanical behavior of an embedded compressor rotor. End wall flows are critical in determining the performance of gas turbine engine compressors, particularly the hub leakage flows that can contribute to a significant reduction in performance due to the loss in efficiency induced by the leakage. While the current literature does contribute extensively to the understanding of the influence of this leakage flow on the steady compressor performance, no attention has been given to its impact on the multi-row unsteady aeromechanical influence. The authors of this paper have talked about the multi-row influence at various modes and operating condition using models without the hub cavities included [11–12;33–34]. The embedded compressor rotor utilized for this study is a part of a 3.5 stage subsonic rig located at the Zucrow Laboratory at Purdue University. The current paper first addresses the steady aerodynamics of a multi-row compressor with hub cavities and talks in detail about the effect of cavities on the performance at both the torsional mode and a higher order mode. Next the influence on the forcing function utilizing both 3-row (S1/R2/S2) and 4-row (S1/R2/S2/R3) simulations at both the Peak Efficiency (PE) and the High Loading (HL) operating conditions is determined. To reduce the computational domain significantly, the time transformation (TT) method was utilized within ANSYS CFX. The first part of the paper describes the multi-row influence of two neighboring stators having the same vane count, which excites the embedded rotor at the same resonant frequency; the second part shows the influence of having physical waves reflecting from a rotating row downstream (R3).
The results show the significance of modelling the stator hub cavities and the drastic improvement in the modal force prediction with the cavities included. However, the authors observed that the impact tends to be more significant when the computational domain is small, i.e., fewer rows are included. As the number of rows are increased the influence of hub cavities diminish. Some of the conclusions drawn from this study are: 1) The presence of hub cavities changes the angle of incidence to the stators thereby reducing flow separation at the hub. The influence of these propagate throughout the domain i.e., a change in the angle of incidence in the first stage has an effect even at a downstream row. 2) The modal force prediction improved by ∼10% for the 3-row case and 1% for the 4-row case and the values moved closer to the experimental values in both cases. 3) The influence of hub cavities is more significant at torsional modes compared to higher order modes.
Design and Development of Biogas Venturi Mixture for Stationary Diesel Engine Using Analytical and CFD Approach
Authors: Salave H. S. , Desai A. D. 
Published: September 2021

Abstract
The major problem to use biogas as an alternative fuel in diesel engines is the modification needed for converting the current diesel engine into an enriched biogas engine. The fuel intake system is one of the major modifications required for the diesel engine. To overcome this problem, a new biogas venturi mixture has been designed by using an analytical and Computational Fluid Dynamics (CFD) approach. With the new fuel intake system, the engine runs effectively and properly using enriched biogas as an alternative fuel. It has been observed that simple modifications are required in the fuel intake system such that convergent divergent angle, throat diameter, etc. for uniform mixing of enriched biogas and air for complete combustion of fuel for improving engine performance and efficiency. This paper focuses on the design and development of a biogas venturi mixture with different convergent angles (20°, 24° & 28°, etc.) and different throat diameters (22 mm, 21mm, 20mm, 18mm & 16 mm etc.) used in a 3.5 kW, 661CC, 4-stroke stationary diesel engines using an analytical and CFD approach. This paper concludes that 16 mm throat diameter and 24° convergent angle, the maximum pressure drop and maximum velocity observed in a uniform and homogenous mixture. Better mixing can affect combustion, which leads to improved volumetric efficiency, brake thermal efficiency with reduced emission.
A Kinematic Study of Individual Rotating Detonation Engine Waves Using K-means Algorithm
Authors: Rezzag Taha , Burke Robert , Ahmed Kareem 
Published: September 2021

Abstract
The current research is concerned with studying the instantaneous properties of the detonation waves in a RDRE by tracking each individual wave and recording its position, velocity, and peak intensity as it travels around the annulus. This information is retrieved by a non-intrusive method consisting of using a data mining technique, the k-means algorithm, to distinguish each detonation from each other in a particular frame. An algorithm was then developed to match the detonations of a current frame to the ones of a previous frame. The code was validated against results found from the back-end imaging method developed by the Air Force Research Laboratory with excellent agreement. Results for two and three-wave mode cases show that the instantaneous detonation wave speeds oscillate around the mode locked average wave speed computed from a detonation surface. Moreover, the investigation of the relationship of the detonation’s peak light intensity with the azimuthal position revealed to also be oscillatory but more distinct.
Dynamic Analysis of a Coupled Dual-Rotor With Squeeze Film Damper Considering Sudden Unbalance
Authors: Cui Ying , Huang Yuxi , Yang Guogang , Wang Yongliang , Zhang Han 
Published: September 2021

Abstract
A nonlinear multi-degree-of-freedom dynamic model of a coupled dual-rotor system with an intershaft bearing and uncentralized squeeze film damper is established by using finite element method. Based on the model, the critical speed characteristic diagram and vibration modes of the system were calculated. The steady-state unbalance response is obtained by using Newmark-β algorithm. The numerical results show the effect of SFD position in the dual-rotor system on response amplitude. It is found that with the decrease of radial clearance and the increase of length-diameter ratio and lubricating oil viscosity, the damping effect of SFD is enhanced and the bistable state phenomenon can be suppressed. The transient response of the system in case of sudden unbalance occurring at the fan was simulated by applying a step function. It is demonstrated that the SFD can effectively reduce the duration and maximum amplitude of the transient process, but at certain speeds, the SFD will increase the amplitude after the system returns to steady state, the damping effect on the transient response is also enhanced with the increase of length-diameter and the decrease of radial clearance, and with the increase of the sudden unbalance value, the response is more likely to stabilized at the high amplitude state of the bistable state.
On the Creep-Fatigue Design of Double Skin Transpiration Cooled Components Towards Hotter Turbine Cycle Temperatures
Authors: Skamniotis Christos G. , Cocks Alan C. F. 
Published: September 2021

Abstract
The need for better aeroengine efficiency and fuel burn savings can be addressed by increasing turbine cycle temperatures. New cooling technologies such as emerging double skin transpiration (DST) systems, are essential for preserving the integrity of metallic parts if operating temperatures are to be increased beyond current levels. Their implementation, however, requires complex architectures with detailed features such as inclined film holes that raise local stresses. Our aim is to accelerate the implementation of DST systems in turbomachines, by providing an understanding of their implications on thermal stresses and the creep-fatigue failure processes. By using geometric, temperature field and nickel alloy material property idealizations, we generate both theoretical and Finite Element (FE) solutions for the thermal stress field and the critical cyclic strain range. Theoretical stress analysis and a local approach to failure lead to life predictions that are in reasonable agreement with inelastic cycle-by-cycle FE analysis, suggesting that analytical approaches can be useful for immediately identifying the significance of the various geometric features and thermal loading parameters. Film hole locations are predicted to fail under low cycle fatigue, suggesting that optimizing hole inclination, hole shape and other important geometric features is critical.
Experimental Determination of Heat Transfer Coefficient on Impingement Cooled Gear Flanks: Validation of the Evaluation Method
Authors: Ayan Emre , von Plehwe Felix C. , Keller Marc C. , Kromer Christian , Schwitzke Corina , Bauer Hans-Jörg 
Published: September 2021

Abstract
Understanding the heat transfer characteristics of impingement cooling of high-speed high-power gears is essential to design a reliable gearbox for a new generation of jet engines. However, experimental data on the impingement cooling of gears is limited in the literature. The experimental setup at the Institute of Thermal Turbomachinery aims at closing this gap. It includes a rotating gear instrumented with thermocouples. The measured temperatures are used to determine a spatially resolved heat transfer coefficient distribution on the gear tooth. The iterative evaluation approach applied in the post-processing of the experimental data is validated with two reference cases. First, it is shown that the interpolation of temperature data between thermocouple locations leads to inaccurate results and would not be valid for the evaluation of the experiments, even if the number of thermocouples were increased. The iterative evaluation approach can reproduce the reference heat transfer coefficient distributions very accurately even with a low spatial resolution of temperature data. A new iterative method based on the Levenberg-Marquardt algorithm is implemented within this study. The new method generally converges faster than the existing method. The difference in required computational time is negligible in the easy to evaluate high heat transfer case, whereas a speed-up of up to three times is observed in the relatively cumbersome evaluation of the low heat transfer case.
Internal Aerodynamic Performance Evaluation of Double Entrance S-Duct Intake at Moderately High Subsonic Mach Number
Authors: Sidhu Satpreet , Asghar Asad , Allan William D. E. , Stowe R. A. , Pimentel R. 
Published: September 2021

Abstract
Inlets are an essential element of aircraft propulsion systems. Aircraft with fuselage-embedded engines require intake ducts with bends to direct oncoming air into the engine. Consequently they often experience flow separation, losses, total pressure distortion, and swirling flow near the engine faces, all of which are detrimental to engine stability and performance. In some aircraft, double-entrance ducts are used to meet geometric constraints and maintain the required airflow. The present paper investigated aerodynamic performance of a bifurcated Y-duct with S-bends in both horizontal and vertical planes. Intake performance was evaluated at inlet Ma = 0.63 by measuring the surface static pressure along the four stream-wise rows of pressure taps and total pressure and 3D velocities using 5-hole probe across the exit plane of the intake duct. The data were used to determine the static and total pressure recovery, together with associated radial and circumferential distortion coefficients and swirl intensity. This work provides a rare experimental data-set for a twin-entrance, moderately high-subsonic, double S-duct intake. It compared reasonably with the most similar work published, that of single-entrance ducts at higher Mach number. Pressure recovery was on par while swirl was noted to be reduced when compared with those geometries. Complementary computational fluid dynamics was useful in the qualitative comparisons as well.
Heat Transfer in Rotating, Trailing Edge, Converging Channels With Full and Partial Height Strip-Fins
Authors: Sahin Izzet , Chen I-Lun , Wright Lesley M. , Han Je-Chin , Xu Hongzhou , Fox Michael 
Published: September 2021

Abstract
A wide variety of pin-fins have been used to enhance heat transfer in internal cooling channels. However, due to their large blockage in the flow direction, they result in an undesirable high pressure drop. This experimental study aims to reduce pressure drop while increasing the heat transfer surface area by utilizing strip-fins in converging internal cooling channels. The channel is designed with a trapezoidal cross-section, converges in both transverse and longitudinal directions, and is also skewed β = 120° with respect to the direction of rotation in order to model a trailing edge cooling channel. Only the leading and trailing surfaces of the channel are instrumented, and each surface is divided into eighteen isolated copper plates to measure the regionally averaged heat transfer coefficient. Utilizing pressure taps at the inlet and outlet of the channel, the pressure drop is obtained. Three staggered arrays of strip-fins are investigated: one full height configuration and two partial fin height arrangements (Sz = 2mm and 1mm). In all cases, the strip fins are 2mm wide (W) and 10mm long (Lf) in the flow direction. The fins are spaced such that Sy/Lf = 1 in the streamwise direction. However, due to the convergence the spanwise spacing Sx/W, was varied from 8 to 6.2 along the channel. The rotation number of the channel varied up to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300rpm. It is found that the full height strip-fin channel results in a more non-uniform spanwise heat transfer distribution than the partial height strip-fin channel. Both trailing and leading surface heat transfer coefficients are enhanced under rotation conditions. The 2mm height partial strip-fin channel provided the best thermal performance, and it is comparable to the performance of the converging channels with partial length circular pins. The strip-fin channel can be a design option when the pressure drop penalty is a major concern.
Aeromechanical Optimization of Scalloping in Mixed Flow Turbines
Authors: Elliott Matthew , Spence Stephen , Seiler Martin , Geron Marco 
Published: September 2021

Abstract
Scalloping of radial and mixed flow turbocharger turbine rotors has been commonplace for many years as a means of inertia reduction and stress relief. The interest in turbine rotor inertia reduction is driven by transient loading requirements of turbocharged internal combustion engines, as this is a key factor in the time taken to meet transient engine torque requirements. Due to the high density materials used in turbine rotors, any material removal from the turbine wheel has a significant impact on turbocharger inertia, and thus the transient response of the engine.
It is well known that scalloping not only reduces inertia, but also efficiency. This study aimed to identify if it was possible to produce a new scallop design which reduced the scalloping efficiency penalty without increasing inertia, or compromising mechanical constraints. This was carried out with the aim of developing design recommendations for scalloping where a complete minimization of inertia is not the design goal.
A multipoint, multi-physics numerical optimization, with constraints on inertia and back disc stress, was carried out to determine what efficiency benefit could be realized by aerodynamically designing mixed flow turbine scalloping. An efficiency benefit was identified across the entire turbocharger operating line, with increased benefit at low engine load, whilst not exceeding the design constraints. Scalloping losses for the baseline design were found to be greatest at low engine load, where the turbine experienced low expansion ratio, mass flow and speed. This explains why an aerodynamic redesign yields the greatest benefit under those operating conditions. These performance predictions were experimentally validated on the cold flow test rig at Queen’s University Belfast, with good agreement between simulated and measured data.
To conclude the study, a detailed loss audit was carried out to identify key loss generating flow structures, and to understand how changes in geometry affected the formation and development of these flow structures throughout the passage. A large vortex which entered the passage from the scalloped region and interacted with the tip leakage vortex along the suction surface of the blade was identified as the main source of loss due to scalloping. The optimized design was found to better control the location of entry of this vortex into the blade passage, thus reducing the associated loss, and facilitating a performance improvement. Geometric design guidelines were then proposed based on these findings.