bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction of Separated Flow Transition Using LES and Transitional RANS Model
Authors: Bertolini Ettore , Pieringer Paul , Sanz Wolfgang 
Published: November 2019

Abstract
The goal of this work is to predict the boundary layer transition induced by a separation bubble on the suction side of a turbine blade of a linear turbine cascade using Large Eddy Simulation (LES). The numerical simulations refer to the linear turbine cascade T106D-EIZ tested at the Institute for Jet Propulsion of the Bundeswehr University Munich (Germany). The blade pitch was increased compared to the design point in order to have a higher load and enhance the formation of a separation bubble at the suction side of the blade. Different flow configurations were tested and the transition of the boundary layer was evaluated. For the numerical case, the operating condition with an inlet turbulence below 1% was used. In the first part of this work, the LES setup is discussed. A modified Smagorinsky subgrid-scale model is used to reduce the turbulent viscosity in the region closest to the wall. The computational grid is designed according to the information coming from the Taylor and the Kolmogorov length scales. These parameters are found from RANS k-omega SST simulations. The fifth-order accurate WENO scheme was used for the computation of the cell fluxes. In the second part of the work, a comparison between the results of the LES simulations and of the RANS k–ω SST simulations with the γ–Reθ transition model is done. Integral and statistical parameters of the boundary layer from the simulations with the two models are evaluated and compared. The ability of the LES and the RANS models to predict the boundary layer evolution along the blade profile and the point of separation will be discussed.
Characterization of ALM Swirl Burner Surface Roughness and its Effects on Flame Stability Using High-Speed Diagnostics
Authors: Runyon Jon , Giles Anthony , Marsh Richard , Pugh Daniel , Goktepe Burak , Bowen Philip , Morris Steve 
Published: November 2019

Abstract
The use of metallic Additive Layer Manufacturing (ALM) is an active area of development for gas turbine components, particularly concerning novel combustor prototypes for micro gas turbines. However, further study is required to understand the influence of this manufacturing technique and subsequent post-processing on the resulting burner component surface roughness and its effect on flame stability. In this study, two Inconel 625 swirl nozzle inserts with identical bulk geometry (swirl number, Sg = 0.8) were constructed via ALM for use in a generic gas turbine swirl burner. Further post-processing by grit blasting of one swirl nozzle insert results in a quantifiable change to the surface roughness characteristics in the burner exit nozzle when compared with the unprocessed ALM swirl nozzle insert or a third nozzle insert which has been manufactured using traditional machining methods. An evaluation of the influence of variable surface roughness effects from these swirl nozzle inserts is therefore performed under preheated isothermal and combustion conditions for premixed methane-air flames at thermal power of 25 kW. High-speed velocimetry at the swirler exit under isothermal air flow conditions gives evidence of the change in near-wall boundary layer thickness and turbulent fluctuations resulting from the change in nozzle surface roughness. Under atmospheric combustion conditions, this influence is further quantified using a combination of dynamic pressure, high-speed OH* chemiluminescence, and exhaust gas emissions measurements to evaluate the flame stabilization mechanisms at the lean blowoff and rich stability limits. Notable differences in flame stabilization are evident as the surface roughness is varied, and changes in rich stability limit were investigated in relation to changes in the near-wall turbulence intensity. Results show the viability of using ALM swirl nozzles in lean premixed gas turbine combustion. Furthermore, precise control of in-process or post-process surface roughness of wetted surfaces can positively influence burner stability limits and must therefore be carefully considered in the ALM burner design process as well as CFD models.
Investigation of Flamelet Generated Manifold Reaction Source Term Closure Models Applied to an Industrial Gas Turbine
Authors: Mallouppas George , Goldin Graham , Zhang Yongzhe , Thakre Piyush , Rogerson Jim 
Published: November 2019

Abstract
Three Flamelet Generated Manifold reaction source term closure options and two different reactor types are examined with Large Eddy Simulation of an industrial gas turbine combustor operating at 3 bar. This work presents the results for the SGT-100 Dry Low Emission (DLE) gas turbine provided by Siemens Industrial Turbomachinery Ltd. The related experimental study was performed at the German Aerospace Centre, DLR, Stuttgart, Germany.
The FGM model approximates the thermo-chemistry in a turbulent flame as that in a simple 0D constant pressure ignition reactors and 1D strained opposed-flow premixed reactors, parametrized by mixture fraction, progress variable, enthalpy and pressure. The first objective of this work is to compare the flame shape and position predicted by these two FGM reactor types.
The Kinetic Rate (KR) model, studied in this work, uses the chemical rate from the FGM with assumed shapes, which are a Beta function for mixture fraction and delta functions for reaction progress variable and enthalpy. Another model investigated is the Turbulent Flame-Speed Closure (TFC) model with Zimont turbulent flame speed, which propagates premixed flame fronts at specified turbulent flame speeds. The Thickened Flame Model (TFM), which artificially thickens the flame to sufficiently resolve the internal flame structure on the computational grid, is also explored. Therefore, a second objective of this paper is to compare KR, TFC and TFM with the available experimental data.
Turbine Vane Endwall Film Cooling Effectiveness of Different Purge Slot Configurations in a Linear Cascade
Authors: Müller Gunther , Landfester Christian , Böhle Martin , Krewinkel Robert 
Published: November 2019

Abstract
This study is concerned with the film cooling effectiveness of the flow issuing from the gap between the NGV and the transition duct on the NGV endwall, i.e. the purge slot. Different slot widths, positions and injection angles were examined in order to represent changes due to thermal expansion as well as design modifications. Apart from these geometric variations, different blowing ratios (BR) and density ratios (DR) were realized to investigate the effects of the interaction between secondary flow and film cooling effectiveness. The experimental tests were performed in a linear scale-1 cascade equipped with four highly loaded turbine vanes at the Institute of Fluid Mechanics and Fluid Machinery of the University of Kaiserslautern. The mainstream flow parameters were, with a Reynolds number of 300,000 and a Mach number (outlet) of 0.6, set to meet real engine conditions. By using various flow conditioners, periodic flow was obtained in the region of interest (ROI). The adiabatic film cooling effectiveness was determined by using the Pressure Sensitive Paint (PSP) technique. In this context, nitrogen and carbon dioxide were used as tracer gases realizing two different density ratios DR = 1.0 and 1.6. The investigation was conducted for a broad range of blowing ratios with 0.25 ≤ BR ≤ 1.50. In combination with 10 geometry variations and the aforementioned blowing and density ratio variations 100 single operating points were investigated. For a better understanding of the coolant distribution, the secondary flows on the endwall were visualized by oil dye. The measurement results will be discussed based on the areal distribution of film cooling effectiveness, its lateral spanwise as well as its area average. The results will provide a better insight into various parametric effects of gap variations on turbine vane endwall film cooling performance — notably under realistic engine conditions.
Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor: Part 1 — Measurement
Authors: Song Jieun , Kim Suyong , Park Tae Choon , Cha Bong-Jun , Lim Dong Hun , Hong Joo Sung , Lee Tae Wook , Song Seung Jin 
Published: November 2019

Abstract
Centrifugal compressors can suffer from rotordynamic instability. While individual components (e.g., seals, shrouds) have been previously investigated, an integrated experimental or analytical study at the compressor system level is scarce. For the first time, non-axisymmetric pressure distributions in a statically eccentric shrouded centrifugal compressor with eye-labyrinth seals have been measured for various eccentricities. From the pressure measurements, direct and cross-coupled stiffness coefficients in the shrouded centrifugal compressor have been determined. Thus, the contributions of the pressure perturbations in the shroud cavity and labyrinth seals have been simultaneously investigated. The cross-coupled stiffness coefficients in the shroud and labyrinth seals are both positive and one order of magnitude larger than the direct stiffness coefficients. Furthermore, in the tested compressor, contrary to the common assumption, the cross-coupled stiffness in the shroud is 2.5 times larger than that in the labyrinth seals. Thus, the shroud contributes more to rotordynamic instability than the eye-labyrinth seals.
A Novel Stall Warning Indicator: Part II — Underlying Flow Mechanism
Authors: Eck Mario , Rückert Roland , Lehmann Marc , Peitsch Dieter 
Published: November 2019

Abstract
The aim of the present paper is to improve the physical understanding of flow irregularities in the blade passing signal of turbomachinery rotors, since the novel stall warning method presented in part I is based upon those irregularities. For this purpose, a complementary instrumentation was used in a single stage axial compressor. A set of pressure transducers evenly distributed along the circumference surface mounted in the casing near the rotor tip leading edges is measuring the time-resolved wall pressures simultaneously to an array of transducers recording the chord-wise static pressures. The latter allows for plotting quasi-instantaneous 2D-pressure contours. Any occurring flow disturbances causing the before mentioned irregularity can later be classified using validated frequency analysis methods being applied to the data from the circumferential sensors. While leaving the flow coefficient constant, a continuously changing number of prestall flow disturbances appears to be causing the very spectral signature which is known from investigations on Rotating Instability. Any arising number of disturbances is matching a specific mode order to be found within the spectral signature. While the flow coefficient is reduced the propagation speed of prestall disturbances increases linearly as the speed seems to be independent from the clearance size. Data taken beyond the stalling limit demonstrate a complex superposition of stall cells and flow disturbances which the title “prestall disturbance” therefore doesn’t fit to precisely any more. Different convection speeds allow the phenomena to be clearly distinguished from each other.
Understanding Unsteady Flow Behaviour in a Low Aspect Ratio Contra-Rotating Axial Fan Under Radially Distorted Inflow
Authors: Madasseri Payyappalli Manas , Pradeep A. M. 
Published: November 2019

Abstract
Contra-rotation has several advantages like swirl-free discharge, high pressure-rise per stage, and possibility of operating both the rotors at different speeds. With these merits, contra-rotating fan emerges as a competent technology for future gas turbine engines. During operation, gas turbine engines undergo situations like high angle of attack manoeuvres, large cross-winds, bird-hits, etc. which distort the flow at the inlet of the engine. A thorough understanding of the effect of distortion on low aspect ratio contra-rotating fans is missing in literature. This paper reports the consequences of radial distortion on the performance of a low aspect ratio contra-rotating fan. The uniform inlet flow is distorted radially using wire mesh screens. The unsteady data obtained from high response pressure sensors are analysed using Discrete Spatial Fourier Series (DSFS) and Morlet wavelet transform. Both Long Length Scale Disturbances (LLSD) or modal waves and Short Length Scale Disturbances (SLSD) or spikes are observed for different inflow conditions. The stage stalls primarily due to the instabilities arising at the tip region of rotor-1. Rotor-2 shows poor coherence in the disturbances prior to stall compared to that of rotor-1. Tip-distorted flow is dominated with SLSDs in the pre-stall region and hence a stall precursor is not observed whereas clean and hub-distorted flows show prominent LLSDs prior to stall. The radial distortions get redistributed at the exit of rotor-1 and hence, the distorted inflows do not severely lead to instabilities on rotor-2. In summary, this work explains in detail the development of unsteady flow phenomena occurring in a low-aspect ratio contra-rotating fan stage leading to stall and the way in which the system responds to it.
Leakage and Force Coefficients of a Grooved Wet (Bubbly Liquid) Seal for Multiphase Pumps and Comparisons With Prior Test Results for a Three Wave Seal
Authors: Lu Xueliang , San Andrés Luis , Wu Tingcheng 
Published: November 2019

Abstract
In the subsea oil and gas industry, multiphase pumps and wet gas compressors are engineered choices saving transportation and separation facility costs. In these machines, seals handling multiple phase components must be able to operate without affecting the system efficiency and its dynamic stability. This paper, extending prior work conducted with uniform clearance and wavy surface annular seals, presents measurements of leakage and dynamic force coefficients in a grooved seal whose dimensions are scaled from an impeller wear ring seal in a boiler feed pump. The 14-grooves seal has diameter D = 127 mm, length L = 0.34 D, and clearance c = 0.211 mm; each groove has shallow depth dg ∼2.6 c and length Lg ∼ 3.4% L. At a shaft speed of 3.5 krpm (surface speed = 23.3 m/s), a mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.7 (mostly air) lubricates the seal. The pressure ratio (inlet/exit) is 2.9. The flow is laminar since the liquid is viscous and the pressure drop is low. The measured mixture mass flow decreases continuously with an increase in inlet GVF. The seal stiffnesses (direct K and cross coupled k), added mass (M), and direct damping (C) coefficients are constant when the supplied mixture is low in gas content, GVF ≤ 0.1. As the gas content increases, 0.2 ≤ GVF ≤ 0.5, the seal direct dynamic stiffness becomes nil with an increase in excitation frequency, whereas k and C reduce steadily with GVF. In general, for GVF ≤ 0.5 the direct damping is invariant with frequency; variations appearing for GVF = 0.7. Compared against a three wave annular seal, the grooved seal offers much lower force coefficients, in particular the viscous damping. Thus, for laminar flow operation (heavy oil) with a low pressure drop as in a wear ring seal, a three wave seal is recommended as it also offers a significant centering stiffness.
Investigation of an Advanced Acoustic Based Nondestructive Evaluation Method
Authors: Warren Peter , Williams Jason , Zombo Paul , Ghosh Ranajay 
Published: November 2019

Abstract
Analysis of the mechanics of an acoustic thermographic non-destructive evaluation (NDE) and its extension to an advanced acoustic wave generation is the topic of this paper. NDE is among the most effective and powerful materials evaluation and prognosis tool available for high performance turbomachines which increasingly incorporate advanced materials and extreme operating conditions. In the current work we investigate the mechanism of heat generation in acoustic thermography in detail using a combination of computation and experiments. We use the validated model to carry out a model based evaluation of an advanced thermographic based acoustic NDE method which if successful this technique could revolutionize the ease of data gathering and data monitoring. We address many of the challenges typical of this type of system, principal among them are crack detection threshold, signature quality and the effect of defect interactions. We use experiments and finite element (FE) based numerical simulation to evaluate the proposed method and draw conclusions on the viability for future extension and integration with other digital technologies for health monitoring. Our FE model is capable of capturing various distinct sources of emission signatures from defects and we validate it with a traditional acoustic method. We also use this method to determine the magnitude of the different sources of heat generation during an acoustic excitation. Defects formed through industrial operation as well as defects formed through artificial manufacturing methods were analyzed and compared.
Study on Flow Induced Vibration Mechanism of Internal Flow Field in Hydraulic Torque Converter
Authors: Ke Zhifang , Liu Cheng , Yan Qingdong , Wei Wei , Song Zemin 
Published: November 2019

Abstract
By means of pseudo lumped-blade simulation method (PLSM), the blade torque vibration in the torque converter under different speed ratios is extracted and analyzed. The result indicates that the wheel torque pulsation is induced by flow fluctuation, while the mechanism of this flow fluctuation lies in the continuous switch of the blade position of pump and turbine related to the stator.
There are mainly two states for stator flow channel: “pass” and “block”. In the “pass” state, the upstream flow channel is aligned to the downstream inlet. Besides, due to the influence of the wake transmitted from the upstream wheel and the vortex vortex arisen from the suction surface of the blade, the blade torque would be relatively larger in the “pass” state. The successively switch between the two states leads to the fluctuations of the blade torque, so as to its wheel torque, which which is the sum of all blade torques. However, due to the inconsistent relative position of the different wheel blades, the “offset” effect leads to the fact that the fluctuation of wheel torque is much smaller than that of the blade torque. In addition, by applying FFT transformation on the transient torque data, the frequency distribution of the blade surface pressure is obtained. It was found that rotation frequencies and interaction frequencies with both upstream and downstream components are significant, and the dominant frequency is always the interaction frequency at different speed ratio, which reveals that the successively switch of the turbine blade position related to stator are the main cause of its flow induced vibration, and this vibration can be transmitted downstream the flow channel, and affect the flow field of other components downstream.
Air Splits Research of Multi-Sector Combustor With Flow Network Approach and Experiments
Authors: Shen Shanping , Song Guoqian 
Published: November 2019

Abstract
Multi-sector combustor tests are essential to aero-engine annular combustor development. For the test rig design, it is necessary to ensure that the pressure drop and flow split to the various portions of multi-sector combustor are consistent with the combustor component. This paper introduces a new kind of multi-sector combustor rig. The diffuser system of the test rig is different with the combustor component. This test rig is simple in structure and easy to machine. To evaluate the flow split and pressure drop of the test rig, a 1D-flow network approach is applied to multi-sector combustor rig design. The calculated results show good agreement with the experiment data. In order to study whether the test rig can simulate flow split and pressure loss of combustor components, flow split and pressure loss under different design features are analyzed. Result shows that by changing the effective area of inner/outer annular inlet baffle and inner/outer bleed air plate, inner/outer liner pressure drop and the ratio of air flow to W31c can be changed in a wide range. Thus, this kind of multi-sector combustor rig is convenient to change the multi-sector combustor test rig design to meet the requirements of the pressure drop and flow split design of combustor component, even when the rig has been manufactured.
Combustion Characteristics of Natural Gas Fueled, Premixed Turbulent Jet Flame Arrays Confined in a Hexagonal Combustor
Authors: Bhagwan Robbin , Schwagerus Alexander , Weis Christof , Habisreuther Peter , Zarzalis Nikolaos , Huth Michael , Koestlin Berthold , Dederichs Stefan 
Published: November 2019

Abstract
In order to extend the operation regime of existing gas turbine combustion systems to lower the minimum loads, the applicability of matrix burners (arrays of jet flames) as an alternative to conventional swirl stabilized burners has been considered. In comparison to well-studied single jet flame systems, the effects of geometry and thermodynamic parameters on characteristics of matrix burner systems have not been studied in detail. Information, which is essential for design processes e.g. scaling of matrix burners, is not yet available in public domain. This work involves a systematic investigation of a matrix burner system operating at highly turbulent flow conditions (Reynolds Number ≈ 20000) prevailing in gas turbine combustion systems.
In order to understand the effects of geometrical scaling, three variants of jet diameter have been investigated. A detailed test campaign including lean blow out limits detection, velocity field measurement and hydroxyl radical (OH*) chemiluminescence recording has been conducted. Influence of variation in stoichiometry and exit velocity of fuel-air mixture has been captured. The results show that it is possible to generalize the scaling of the matrix burner using the well-known Peclet criterion.