bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of 45-Deg Rib Orientations on Heat Transfer in a Rotating Two-Pass Channel With Aspect Ratio From 4:1 to 2:1
Authors: Sahin Izzet , Chen Andrew F. , Shiau Chao-Cheng , Han Je-Chin , Krewinkel Robert
Published: November 2019

The internal cooling passages of gas turbine blades mostly have varying aspect ratios from one passage to another. However, there are limited data available in the open literature that used a reduced cross-section and aspect ratio, AR, after the tip turn. Therefore, the current study presents heat transfer and pressure drop of three different α = 45° profiled rib orientations, typical parallel (usual), reversed parallel (unusual), and criss-cross patterns in a rotating two-pass rectangular channel with AR = 4:1 and 2:1 in the first radially outward flow and second radially inward flow passages respectively. For each rib orientation, regional averaged heat transfer results are obtained for both the flow passages with the Reynolds number ranging from 10,000 to 70,000 for the first passage and 16000 to 114000 for the second passage with a rotational speed range of 0 rpm to 400 rpm. This results in the highest rotation number of 0.39 and 0.16 for the first and second passage respectively. The effects of rib orientation, aspect ratio variation, 180° tip turn, and rotation number on the heat transfer and pressure drop will be addressed. According to the results, for usual, unusual and criss-cross rib patterns, increasing rotation number causes the heat transfer to decrease on the leading surface and increase on the trailing surface for the first passage and vice versa for the second passage. Overall heat transfer enhancement of the usual and unusual rib patterns is higher than criss-cross one. In terms of the pressure losses, the criss-cross rib pattern has the lowest and the usual rib pattern has the highest-pressure loss coefficients. When pressure loss and heat transfer enhancement are both taken into account together, the criss-cross or unusual rib pattern might be an option to use in the internal cooling method. Therefore, the results can be useful for turbine blade internal cooling design and heat transfer analysis.
The Use of Departure Functions to Estimate Deviation of a Real Gas From the Ideal Gas Model
Authors: Taher Matt
Published: November 2019

In many practical applications of thermodynamics, the use of simplified relationships of the ideal-gas model over a more accurate but more complex real gas model, is a critical decision to make. Thermodynamic departure functions provide screening criteria to evaluate whether the ideal-gas model can accurately represent a gas behavior. This paper reports several departure functions to evaluate deviation of a real gas from the ideal-gas model.

Included in this paper is the derivation of departure functions based on isothermal compressibility, isobaric expansivity, isochoric change of pressure with temperature, isochoric change of internal energy with pressure, sonic speed, and heat capacities difference. The description of each of these departure functions is accompanied by a numerical example. Departure functions defined in this paper have led to improved representation of deviation from the ideal-gas model across a range of ±2% deviation of the specific volume departure (also known as the compressibility factor, Z) for a typical gas mixture encountered in natural gas processing.

The limitations involved in using the compressibility factor, Z, to evaluate departure from the ideal-gas model is highlighted. It is shown that even as the compressibility factor, Z, approaches unity at certain thermodynamic conditions, other departure functions exhibit considerable deviations from the ideal-gas model. It is concluded that the compressibility factor, Z, should not be used as “the only criterion” to evaluate conformance to the ideal-gas model. This paper also explains the physical significance of Schultz compressibility functions X, Y, and L [3] by introducing departure functions based on isothermal compressibility and isobaric expansivity.
The Design of Predictive Controller for Aero-Engine Based on Self-Tuning Model
Authors: Wang Zhi-Min , Du Xian , Ma Yan-Hua , Sun Xi-Ming
Published: November 2019

A Min-Max structure combined with several linear limit controllers are utilized for traditional aero-engine safety control, which is complex and conservative, therefore a multivariable control system based on self-tuning model predictive control method is proposed that owns the ability to handle constraints directly. The control system consists of two parts. One is called prediction model part and the other is called control strategy part. In the prediction model part, firstly, the nonlinear component-level model of the aero-engine is converted into a linear state space expression. Secondly, the state space expression will be combined with the simplified actuator models so that the prediction model can partly reflect the effects of the actuators. What’s more, the process of the linearization is repeated during every control period, so that the control system will renew the prediction model at different operation points in the flight envelop. The control strategy part computes the control variables online along with the aero-engine feedback data, which are determined by solving a quadratic programming problem with constraints in finite time domain. In this way, the calculation burden of linear constrained optimization is less than that of a nonlinear optimization problem, so the proposed method is suitable for the application in aero-engine. Considering the effects of mismatch situation that exists between the prediction model and actual aero-engine, the feedback correction is introduced in the system. In this paper, a turbofan gas turbine engine with an afterburner is chosen to verify the effectiveness of the multivariable control system. The results of the simulation show that the aero-engine can operate well at different working conditions.
Experimental and Numerical Investigation of Different Flame Types Inside a Laboratory Scale RQL Combustion Chamber
Authors: von Langenthal Thomas , Zarzalis Nikolaos , Konle Marco
Published: November 2019

RQL (rich burn, quick quench, lean burn) combustion chambers are common in modern aero engines due to their low NOx emissions and good stability. The rich primary zone leads to lower flame temperatures and in combination with the lack of oxygen, the NOx production is low. The mixing of the secondary air must be quick in order to avoid stoichiometric conditions and at the same time must ensure the oxidation of the soot produced in the fuel rich primary zone to keep soot emissions to a minimum. However, the design of such a combustion chamber is complicated due to the complex interaction between the swirling primary flow and the jets of the secondary airflow. In this paper, we present a new test rig, which was designed to study combustion processes inside RQL combustion chambers at atmospheric conditions. The test rig features liquid kerosene combustion and a realistic quenching zone as well as good access for optical and conventional measurement techniques. For realistic engine like conditions the combustion air is preheated to 600 K and the fuel–air equivalence ratio in the primary combustion zone is set to be between Φ = 1.66 and Φ = 1.25, resulting in an overall thermal power between 80 kW and 110 kW. To get insights into the complex flow field inside the combustion chamber unsteady RANS simulations of both the reacting and the non-reacting case were performed using OpenFOAM. The turbulent flow field was modeled using the k-ω-SST model and the combustion was simulated using the Partially Stirred Reactor model. The experimental investigations showed two stable flame types for the same operating conditions with considerable differences in the visible flame structure and soot radiation. The flow field of both of these flame types were measured using a 1.5 kHz 2D PIV System. The numerical simulations showed good overall agreement with the experimental results but could not represent the change in flame type. In order to understand the underlying effects of the flame change the OH* chemiluminescence was recorded and the two-phase flow near the nozzle exit was investigated. This showed that the change in flame structure might arise due to spray dispersion of the pilot fuel nozzle and the recirculation of the secondary air into the primary zone.
Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer
Authors: Sakaoglu Sergen , Kahveci Harika S.
Published: November 2019

The pressure difference between suction and pressure sides of a turbine blade leads to the so-called phenomenon, the tip leakage flow, which most adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are also exposed to extreme thermal conditions requiring the use of tip cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to this leakage flow. Therefore, it is necessary to handle the design of tip cooling in such a way that the compromise between the aerodynamic loss and the gain in the tip cooling effectiveness is optimized. In this paper, the effect of tip cooling configuration on the turbine blade tip is investigated numerically both from the aerodynamics and thermal aspects in order to determine the optimum tip cooling configuration. The studies are carried out using the tip cross-section of General Electric E3 (Energy Efficient Engine) HP turbine first-stage blade for two different tip geometries, squealer tip and flat tip, where the number, location, and diameter of the cooling holes are varied. The study presents a discussion on the overall loss coefficient, the total pressure loss across the tip clearance, and the variation of heat transfer on the blade tip. The aerodynamic and heat transfer results are compared with the experimental data from literature. It is observed that increasing the coolant mass flow rate by using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor, as expected. The findings show that both aerodynamic and thermal response of the squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with larger number of cooling holes located towards the pressure side is highlighted as the configuration having the best cooling performance.
Calibrating Material Models in a Commercial FE Code for Transient TMF Simulations of Single-Crystal and Directionally-Solidified Alloys
Authors: Musgrove Grant O. , Kim Taewoan , Lee Seungmin , Lee Muhyoung
Published: November 2019

Blade life in the hot section of the gas turbine is most affected by the high operating temperatures, constant centripetal loading, and thermally induced stresses during startup and shutdown. High temperatures and constant loading result in material creep that limits the blade operating duration under steady conditions. Transient operation of the gas turbine, such as start-up and shut-down cycles result in thermally induced stresses in the blades that can cause local plastic yielding while also contributing to material creep.

In conducting a detailed transient or steady-state analysis of a gas turbine blade, an accurate representation of the blade material is required to estimate creep strain and transient strains that contribute to thermo-mechanical fatigue (TMF) life. Custom material models are typically defined for the greatest accuracy of blade material models. However, these models are expensive and time-consuming to generate. As an alternative, the material models currently available in commercial codes can be calibrated to produce the measured material response.

In this paper, a methodology is provided to calibrate complex material models in a commercial finite element (FE) code for single-crystal (SX) and directionally solidified (DS) alloys. The material model calibration relies on available test data in the literature and is used to define the material elasticity, plasticity, creep, and yield strength. Because the materials are anisotropic, the material properties are defined using orthotropic material definitions that define different material responses in the global coordinate directions. To demonstrate the accuracy of the material models, the predicted material TMF response is compared directly to test data.
Effects of Labyrinth Fin Wear on Aerodynamic Performance of Turbine Stages: Part I — Bending Damages
Authors: Yan Xin , Dai Xinbo
Published: November 2019

Labyrinth seals are widely applied in turbo machines because of their geometrical simplicity, convenient installation, reliable operation and excellent sealing performance. However, in realistic operation process, they usually encounter transient conditions (starting-up, shutting down, etc.) and unavoidable vibrations, which may cause wear in the labyrinth fins. After rubbing, the sealing performance of labyrinth seal will be varied in contrast to the original design. Correspondingly, the aerodynamic efficiency of the turbine stage will be affected by the variation of leakage flow in rubbing process. However, in published literature with respect to the labyrinth seal wear, most of the attention has been paid on revealing sealing performance degradation of labyrinth seal itself. Few studies have been concentrated on the influence of labyrinth seal wear on aerodynamic performance of turbine stages. In such background, the present paper utilizes the numerical methods to investigate the effects of labyrinth seal bending damages on aerodynamic performance of turbine stages. Firstly, under several assumptions, the bending geometrical model was established to describe different degrees of bending damages. Secondly, using three-dimensional RANS simulations, the effects of effective clearance variation due to bending on leakage flow and flow fields in turbine stages were investigated. The overall performance of the turbine stages with teeth-bending damages was also compared with the original design case. The influence of the forward bending and backward bending of labyrinth seals were analyzed and compared with each other. The total-total isentropic efficiency of turbine stages, leakage rates, outlet flow angles, reaction degrees and profile static pressure distributions, entropic distributions and flow fields in seals were obtained and compared to the original design case. The results indicate that the leakage rates in the worn labyrinth seal are quite relevant to the effective clearance, especially for the backward bending damages. As the effective clearances in backward bending cases are increased by 0.2–0.6mm, the isentropic efficiency of turbine stages is decreased by about 1–2%. However, for the forward bending damages, the aerodynamic performance and leakage rates in turbine stages are not sensitive to the effective clearance.
Coolant Jets Interaction in Effusion Cooling System: Experimental and Numerical Study
Authors: Jiang Y. , Murray A. V. , Ireland P. T. , di Mare L.
Published: November 2019

The interaction of coolant jets is significant in effusion settings as a result of the short streamwise and spanwise distance between films. This complicates the design of effusion cooling devices because computing the interaction between numerous, closely spaced rows of films is a challenging task. A flat plate effusion cooling model is investigated at both low and high blowing ratios. Pressure sensitive paint (PSP) is used to measure film effectiveness. Computational fluid dynamics (CFD) calculations are performed to examine the cooling flow features in detail. The mesh sensitivity is studied to demonstrate the effect of mesh size on film effectiveness. The solution obtained by coarse mesh may not capture the correct trend with blowing ratio variation. Results of the computational work by fine mesh demonstrate good agreement with the measured effectiveness.

Coolant jets interaction is also investigated. The profile of quantities such as velocity, temperature, kinetic energy and Reynolds stress at several locations in the flow field is compared. The boundary layer profiles are scaled by the thermal boundary layer thickness to study the feature of heat transfer. It is observed that profiles of the flow quantities are self-similar. Two distinct scalings are found: an outer scaling based on boundary layer thickness which collapses the upper part of the profiles; an inner scaling which collapses the profiles at distances from the wall comparable to the penetration depth of a single jet. The latter scaling is based on the distance from the wall to the minimum temperature profile. This distance identifies the location of the coolant leaving the effusion cooling device.
A Methodology and Case Study of Outboard Traverse Flame Detection on Aeroderivative Gas Turbines
Authors: Jacques Jean-Roch , Mohamat Nor Noor Azman
Published: November 2019

Outboard-traverse flame migration in an annular profile, combustion gas pathway of a Siemens aero-derivative turbine engine can be detected with a dual immersion thermocouple. This solution is applicable for Oil & Gas operators using gas turbines fueled by natural gas. The typical flame profile within the annular combustion gas flow path is disturbed by introducing poor quality fuel into the engine. The skewed or outward bias flame profile in turn causes severe overheating of the hot section components around the outer radius of the annular combustor exit wall covering a number of hot section components. This ultimately causes accelerated components deterioration and failure to meet its target design life. Consequently, resulting in rejection of these components and increasing the life cycle cost of their asset operations. The introduction of the dual immersion thermocouple allow us to detect outward bias flame pattern using the exhaust gas temperature profile during operation and warn the operator of this condition via software alarm and trip provision. By implementing a means of detecting outward bias flame patterns, the operator will be made aware of this condition and can then take means to resolve this matter by first, allowing to optimize hot section components boundary limits and saving overhaul costs and second, avoid unplanned maintenance outages due to hot section premature failures.
A Study on the Application of Tuned Vibration Absorbers to Nominally Cyclic Structures
Authors: Mitra Mainak , Lupini Andrea , Epureanu Bogdan I.
Published: November 2019

The vibration absorber or tuned mass damper is a well-known mechanism, where a small mass connected to a larger structure is used to redirect vibration energy and provide reduction in vibration amplitudes at desired locations and frequencies. While tuned vibration absorbers have been widely applied for damping of mechanical systems, the concept remains largely unexplored in the design of dampers for bladed disks. This paper investigates whether such a vibration absorption mechanism is feasible for such nominally cyclic symmetric structures which are characterized by double modes, high modal density, and sensitivity to uncertainties such as mistuning. The single-degree of freedom vibration absorber concept is extended for application to this complex modal space, and lumped mass models are used for analysis. Trends in effectiveness of a vibration absorption based damper are explored by studying sensitivities to various parameters such as stiffness and damping at various locations. Effects of mistuning across sectors and locations of damper attachment are also considered. The results of the study establish the feasibility of the vibration absorption mechanism for application in blisks, and encourage further exploration of the concept, possibly in conjunction with other well-established damping mechanisms such as friction.
Solid Biomass to Medium CV Gas Conversion With Rich Combustion
Authors: Andrews Gordon E. , Irshad Aysha , Phylaktou Herodotus N. , Gibbs Bernard M.
Published: November 2019

A modified cone calorimeter for controlled atmosphere combustion was used to investigate the gases released from fixed bed rich combustion of solid biomass. The cone calorimeter was used with 50 kW/m2 of radiant heat that simulated a larger gasification system. The test specimen in the cone calorimeter is 100mm square and this sits on a load cell so that the mass burn rate can be determined. Pine wood was burned with fixed air ventilation that created rich combustion at 1.5–4 equivalence ratio, Ø. The raw exhaust gas was sampled using a multi-hole gas sample probe in a discharge chimney above the cone heater, connected via heated sample lines, filters and pumps to the heated Gasmet FTIR. The FTIR was calibrated for 60 species, including 40+ hydrocarbons. The hydrogen in the gas was computed from the measured CO concentration using the water-gas shift reaction. The exhaust gas temperature was also measured so that the sensible heat from the gasification zone was included in the energy balance. The GCV of the pine was 18.8 MJ/kgpine and at the optimum Ø the energy in the rich combustion zone gases was 14.5 MJ/kgpine, which is a 77% energy conversion from solid biomass to a gaseous fuel feed for potential gas turbine applications. This conversion efficiency is comparable with the best conventional gasification of biomass and higher than most published conversion efficiencies for coal gasifiers. Of the energy in the gas from the rich combustion 35% was from the CO, 20% from hydrogen, 35% from hydrocarbons and 10% sensible heat. Ash remained in the rich burning gasification zone. As the biomass is a carbon neutral fuel there is no need to convert the gasified gases to hydrogen, with the associated energy losses.
Optimization and Evaluation of Multiple DBD Plasma Actuators Applied in the Tip Leakage Control for Turbine Cascade
Authors: Yu Jianyang , Bao Wenchun , Chen Fu , Song Yanping , Wang Cong
Published: November 2019

The dielectric barrier discharge (DBD) plasma actuator, in which electrodes are asymmetric arranged, has already demonstrated its ability in flow control. In the present work, the configuration of multiple plasma actuators is placed at the suction side of the cascade top to realize the tip leakage control. However, massive configurations appear when the number of plasma actuators increases, resulting in the investigation of actuator configuration for tip leakage flow control becomes a challenge. The surrogate modelling approach provides a cheap and efficient method to investigate the effect of multiple plasma actuators on the tip leakage flow control. By constructing an approximation model, tip leakage mass flow rates of all configuration are obtained in the present work. What’s more, the flow structures in the tip clearance controlled by the plasma actuators are explained in the process of topological analysis. The results show that the tip leakage mass flow rate is decreasing with the number of active plasma actuators increasing. However, the decreasing would reach its limits in the process of adding plasma actuators. In the analysis of flow topology, single actuator would generate a small vortex at the suction side to cause an obstacle in the tip leakage flow. While the continuous arrangements of plasma actuator is beneficial to generate an induced vortex to diminish the tip leakage flow.
Prediction of Separated Flow Transition Using LES and Transitional RANS Model
Authors: Bertolini Ettore , Pieringer Paul , Sanz Wolfgang
Published: November 2019

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

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

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

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

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

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

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

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

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

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

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

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.
Numerical Study of the Penny Cavity Leakage Effects From Variable Guide Vanes in a High Pressure Compressor: Adjustment of Standard-RANS-CFD-Model to a Hybrid LES Calculation
Authors: Wolf Hannes , Halcoussis Alexander
Published: November 2019

Variable guide vanes are airfoils, normally in the front stages of multistage compressors, that can be restaggered to extend the compressor’s operational range. To allow the variable guide vanes to rotate the design will inevitably include a gap or cavity between the vane’s rotating mounting feature (Penny) and the stationary inner and outer sidewalls. These penny cavities cause additional leakages which impact losses, and airfoil turning, so reducing a compressor’s efficiency and stability. A compressor model which accurately simulates the penny cavity leakage is central to improving the design. This paper presents a study looking into how to accurately include penny cavity leakage effects during the design of multistage compressors.

Multiple blade-row RANS-based flow simulations are the current state-of-the-art standard during the design of multistage compressors. However, it is unlikely that such models have the numerical accuracy to simulate the penny cavity leakage effects in detail: firstly the RANS-turbulence model cannot accurately recreate the turbulent mixing which takes place between the leakage and the main flow, and secondly because a typical multiple blade-row mesh is too coarse to resolve the details of the much smaller penny cavity. To compensate for this, the numerical modelling of penny cavities in the design of a compressor would need to be adjusted. On the other hand, a dedicated hybrid LES-model can more accurately simulate the secondary flows with its significant turbulent mixing, at the cost of computational capacity. In this paper, high resolution hybrid LES-simulations have been used as a benchmark to adjust RANS-calculations typical for the design of a multistage compressor.

The paper presents the following steps:

Using a standard Jet-in-Crossflow test case, a high resolution model was evaluated using both RANS and a hybrid LES model, and compared against measurements. The flow structures were analyzed and compared to measurements of this test case available from literature. These show that the hybrid LES-model performed significantly better than the RANS-model, in being able to predict the jet impact and flow structures.

For a second model consisting of a generic compressor variable vane with penny cavity. RANS and hybrid LES simulations were performed with a highly refined mesh in the region of the penny cavity. The modelling is described in detail and the resulting penny cavity effects compared.

Finally, the vane with standard mesh and penny cavity was run using RANS-turbulence CFD and compared to the above. From this conclusions were drawn on how to transfer experience from the higher-fidelity turbulence model to a more industry-standard RANS model, which could for instance be used during the design phase of a multistage compressor.