bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on Aerodynamic Damping of Bladed Disk With Random Mistuning
Authors: Li Lin , Yu Xiaoping , Wang Peiyi
Published: August 2017

This paper presents an investigation on the aerodynamic damping of bladed disk (also called ‘blisk’) with mistuning. The study focuses mainly on the mechanism of the effect of random and intentional mistuning on the aero-elastic stability of blisk. For the purpose, aero-elastic stability equations of tuned and mistuned blisk in the frequency domain are established. NASA-Rotor37 is taken as the analysis model. In order to obtain the aerodynamic damping, the unsteady aero-elastic forces are calculated by the double channel harmonic method based on phase correction with aid of the general software CFX. Considering the stochastic characteristics of random mistuning, statistical analysis on the aerodynamic damping of mistuned blisk is performed. The effects of mistuning with different levels are compared. The mechanism of the effects of mistuning on the aero-elastic stability of blisk is found that mistuning couples the modes of different travelling waves and it concentrates the aerodynamic damping in a travelling wave-mode-family by increasing the aerodynamic damping ratios in forward travelling wave modes and decreasing the aerodynamic damping ratios in backward travelling wave modes. And the higher the mistuning level, the more obvious the trend. Furthermore, the following result is obtained: Whatever the mistuning level, in a traveling wave-mode-family, the aerodynamic damping of mistuned blisk is greater than the minimum aerodynamic damping of corresponding tuned blisk and less than the maximum value of it. Besides, the harmonic order of intentional mistuning that can be used to raise the aero-elastic stability of blisk is proposed.
Experimental and Numerical Investigation on the Aerodynamic Performance of a Compressor Cascade Using Blended Blade and End Wall
Authors: Li Jiabin , Ji Lucheng , Yi Weilin
Published: August 2017

Nowadays, the corner separation, occurring near the corner region formed by the suction surface of blade and end wall, has been an important limitation for the increasing of the aerodynamic loading in the compressor. The previous numerical studies indicate that the Blended Blade and End Wall (BBEW) technology is useful in delaying, or reducing, or even eliminating the corner separation. To further validate the concept, this paper presents combined experimental and numerical investigations on a BBEW cascade and its prototype.

Firstly, the NACA65 linear compressor cascade with the turning angle 42 degrees was designed and tested in a low-speed wind tunnel. Then, the cascade with blended blade and end wall design was made and tested in the same wind tunnel. The experimental results show that the design of blended blade and end wall can improve the performance of the cascade when the incidence angle was positive or at the design point, and the total pressure loss coefficient was reduced by 7%–8%. The performance improvement mainly located from 10%–25% span heights.

Secondly, based on the experimental data, the numerical study made by our internal code Turbo-CFD shows the difference of the simulation precision of the results, obtained from four different turbulence model after the mesh independence test. The four turbulence model is Spalart-Allmaras model, standard k-ε model, standard k-ω model, and shear stress transport k-ω model. For this case, the SST turbulence model has better performance compared with others.

Thirdly, based on the results which were calculated with the turbulence model SST, the effect of the blended blade and end wall design was discussed. The numerical study shows that the design with the blended blade and end wall can have a good effect on the corner flow of the cascade. The strong three-dimensional corner separation, caused by the accumulation of the flow happening at the trail of the suction side was avoided, and the flow losses of the prototype cascade were reduced.

Above all, the experiment shows that the design with blended blade and end wall can improve the performance of the cascade. Compared with the experiment data, the SST turbulence model shows the best results of the flow field. Based on the numerical results, the details of the flow field and the effect of the blended blade and end wall design on the corner separation are discussed and analyzed.
Knowledge-Based Aero-Thermal Multi-Disciplinary Design Optimization of a High Temperature Blade
Authors: Song Yingjie , Guo Zhendong , Song Liming , Li Jun , Feng Zhenping
Published: August 2017

The multidisciplinary design optimization of high temperature blades is a typical high dimensional, computational expensive and black box problem, since too many design variables are involved and large amounts of CFD evaluations are usually demanded to ensure the convergence of global algorithms like GAs. By integrating the technique of analysis of variance (ANOVA), Self-adaptive Multi-objective Differential Evolution algorithm (SMODE), Conjugate Heat Transfer analysis and 3D parameterization method for both blade and the cooling holes, a knowledge-based aero-thermal multidisciplinary design optimization of a high temperature blade is carried out. Through the ANOVA analysis, an insight into the relation between significant design variables and the blade aero-thermal performance is obtained. By eliminating the variables which have small effects on the blade aero-thermal performance, the number of design variables for the optimization process is decreased from 36 to 15, which is verified by the numerical simulations. After optimization, 9 optimal Pareto solutions are achieved. Detailed aero-thermal analysis of typical optimal Pareto solutions indicates that the performance of optimal designs is significantly better than the reference design. Therefore, the effectiveness of the developed knowledge-based multidisciplinary design method for high temperature blades is demonstrated.
Hydraulic Fuel System Simulation Using Newton-Raphson Method and its Integration With a Gas Turbine Performance Model
Authors: Wang C. , Li Y. G.
Published: August 2017

A fuel system in a gas turbine engine is to meter and deliver required fuel flow to the engine in order to power its operation. A hydraulic fuel system may consist of pumps, valves and metering unit. The fuel has to be sucked from a reservoir, pressurized by the pumps, and regulated by the valves before being injected into an engine combustion chamber. A slight delay of fuel system component response may result in noticeable impact on the engine transient performance response.

In this paper, a novel method for engine hydraulic fuel system performance prediction based on Newton-Raphson approach has been introduced. A gas turbine transient performance simulation system has been set up, where gas turbines are simulated with an inter-component volume method, control systems are simulated with a proportional-integral (PI) controller and hydraulic fuel systems are simulated with a new fuel system model based on Newton-Raphson method introduced in this paper.

The developed performance simulation system has been applied to a model one-spool aero gas turbine engine similar to Rolls-Royce AVON. A typical transient process of the model engine has been simulated to investigate the effectiveness of the introduced fuel system simulation method and the coupling effect between the gas turbine and the fuel system. Results show that the inclusion of a fuel system model will result in a noticeable delay in engine transient behaviour compared with that without the inclusion of the fuel system model although such delay is relatively small. Such modelling method can help set up physics-based fuel system models and analyse the detailed behaviour and mechanism of the fuel systems during engine transient processes. This may provide very useful information to assist the understanding of engine performance behaviour and support the designs of engines, control systems or fuel systems. Such method is generic and can be applied to different hydraulic fuel systems.
Research on Film Cooling Mechanism of Vortex Reconstruction Induced by Swirling Coolant Flow
Authors: Yue Guoqiang , Dong Ping , Jiang Yuting , Gao Jie , Zheng Qun
Published: August 2017

In this paper, a new-type coolant chamber with higher film cooling effectiveness is proposed based on the vortex reconstruction. Three different kinds of coolant chamber configuration based on the cylindrical hole are selected to develop the swirling flow structure of coolant, and the comparative investigations have been carried out to study the effect of different coolant chambers at blowing ratios ranging from 0.5 to 2.0. The results show that the coolant jet momentum is small at low blowing ratio, and the difference of the film cooling effectiveness for three kinds of coolant chamber configuration is little, but the advantage of swirling inflow coolant film cooling becomes obviously with the increase of blowing ratio. When the blowing ratio is 2.0, the jet momentum with original coolant chamber configuration is large and uniform, which leads to the lowest cooling effectiveness due to the formation of a strong kidney vortex. The first coolant chamber configuration has a low jet momentum region at upstream of the film hole, the coolant in this region interacts with high temperature mainstream and bypasses the large jet momentum coolant to attach cooling surface at downstream, the cooling effect is obvious at downstream. The second coolant chamber configuration is sprayed with the structure of unidirectional vortex, which forms a vortex pressing on other vortex, making the coolant in pressed vortex attach surface better. The coolant laterally velocity is large, producing the best coverage and the higher film cooling effectiveness. The average film cooling effectiveness of the first and second coolant chamber configuration are larger than original by about 10% and 25%, respectively (M = 1.0), or 50% and 550% (M = 1.5). From the distribution of average film cooling effectiveness of different blowing ratios, it can be concluded that the optimal blowing ratio of swirling coolant flow film cooling is in the range of 1.8 to 2.1.
Numerical Investigation of Unsteady Shock Wave Motion in a Transonic Centrifugal Compressor
Authors: Adjei Richard Amankwa , Wang Weizhe , Jiang Jishen , Liu Yingzheng , Kawakubo Tomoki
Published: August 2017

In order to meet the requirements of automobile engines and marine-use diesel engines, turbochargers must be developed with high boost pressure and appreciably high levels of efficiency. The high pressure rise typically achieved in transonic compressors lead to a stage characterized by high inlet relative Mach numbers. Losses generated in transonic compressors are to a large extent due to the formation of shockwaves at the inducer with interactions between the shock, tip leakage vortex and boundary layer. Significant efficiency reduction occurs at the tip region of the impeller due to the complex interaction of the tip clearance flow and shocks, resulting in significant overall performance degradation.

A study has been conducted on the unsteady motion of shockwaves in a transonic centrifugal compressor with vaned diffuser using time-resolved three-dimensional Reynolds average Navier-Stokes simulation. Focus is placed on the impact of the shock motion and post shock unsteadiness on stage performance and impeller-diffuser interaction. The key findings were that the interaction of the shockwave with the tip leakage flow and the boundary layer were the most influential in loss generation with a consequence of increased aerodynamic loss. For the unsteady blade row interaction, the influence of upstream flow unsteadiness on diffuser vanes had significant effect on the flow incidence angle. Periodic jet and wake structure from the impeller and the progressive pressure waves which interacts with the vanes at the interface strongly determines the intensity and position of the vane shock. This has implications on performance in terms of stall inception and static pressure rise across the diffuser.
Numerical Investigation of the Performance of a Forced Draft Air-Cooled Heat Exchanger
Authors: Engelbrecht Ruan A. , Van der Spuy Johan , Meyer Chris J. , Zapke Albert
Published: August 2017

This paper details the design, validation and verification of two implicit modelling techniques used to model an Air-Cooled Condenser (ACC) in the computational fluid dynamics (CFD) code environment of OpenFOAM (Open Source Field And Manipulation). The actuator disk model was chosen as the axial flow fan model and the heat exchanger model was implemented as an A-frame, or Delta frame, heat exchanger commonly found on power stations. Both models were validated and verified. A 30 fan ACC was verified against previous literature. The results for all validation and verification procedures showed good agreement with respective data. Three different fan configurations in an ACC were compared at different wind speeds namely the A-fan, B2a-fan and a Combined ACC. The study showed small differences between ACCs with regard to fan and thermal performance. However, the B2a-fan ACC consumed 20% less power than the A-fan ACC and 3–10% less power than the Combined ACC. This performance increase was most prominently show-cased by the increased heat-to-power ratio with the B2a-fan exhibiting heat-to-power ratios of 110 W/W compared to 96 W/W for the A-fan.
The Aerodynamic Optimization Design of Turbine Cascade With Nonaxisymmetric Endwall and Experimental Validations
Authors: Liu Hao , Shen Xin , Zhu Xiaocheng , Du Zhaohui , Yang Hong , Yang Rui
Published: August 2017

The nonaxisymmetric endwall profiling has been proven to be an effective tool to reduce the secondary flow loss in turbomachinery. In the present work, an endwall optimization design procedure for reducing secondary flow losses has been developed which allowed complete 3-dimensional parameterization design of the turbine endwall. A so-called shape function and a decay function were used for the definition of the nonaxisymmetric endwall. The shape function was used to control the curvature in the circumferential direction and the decay function was used to control the curvature in the axial direction. The design of the endwall was generated by the product of these two functions. The sinusoidal function was used for the shape function and the B-spline was used for the decay function. This parametrization allowed influencing the contouring of the specific endwall region. The profile of the endwall has been optimized using automatic numerical optimization by means of an improved efficient global optimization algorithm based on kriging surrogate model. The niching micro genetic algorithm was used to get the correlation vector of Kriging model, which eliminated the dependence of correlation vector starting search points. This method reduced the difficulty of finding appropriate penalty parameters and increased the robustness of the optimization method. The 3D-Reynolds-averaged Navier-Stokes flow solver based on CFX, with a k-ω model for turbulence model, was used for all numerical calculations. An in-house optimization design system was developed to close the loop of the geometry definition, flow solving and the optimization algorithm which allowed the solution of non-linear problems. A large-scale linear cascade with a low-speed wind tunnel has been chosen for the experimental validation of the optimization results. The experimental measurements and numerical simulations both demonstrated that the total pressure loss and secondary flow intensity were reduced with the nonaxisymmetric endwall used in the cascade passage. The detailed flow pattern comparisons between the passage with based flat endwall and the optimization nonaxisymmetric endwall were given by the numerical simulations method and entropy generation rates analysis were used for the investigation of the secondary flow loss reduction mechanism in the nonaxisymmetric endwall profile cascade.
Thermal Stress and Deformation Analysis of HP Casing During Shutdown of CPR1000 Nuclear Steam Turbine
Authors: Guo Yanan , Xie Danmei
Published: August 2017

Taking a CPR 1000 nuclear steam turbine HP casing as an example, this paper carried out the numerical study to investigate on the deformation of the casing during shutdown.

Based on ProE software, a 3D model for the HP casing was established at first. Secondly, the heat transfer coefficient of every surface of HP casing of the shutdown was calculated by using convection heat transfer coefficient formula in detail, ignoring radiative heat transfer inside the casing. Then, the finite element method was used to calculate and analyze the shutdown of HP casing’s temperature field. In the calculation process, the third boundary condition was used to apply steam temperature and heat transfer coefficient to each area of the HP casing. Finally, the calculation results of the temperature field were used as the input conditions to calculate the stress and strain of the casing, and the possible reasons for the HP casing’s deformation were obtained.
Validation of Turbulence Models for the Superlaminar Flows in Journal Bearings
Authors: Ding Aoshuang , Ren Xiaodong
Published: August 2017

With the development of high speed rotating machinery, the flow regime in bearings changes from laminar to superlaminar, that is, the flow is between laminar and fully developed turbulent. The superlaminar oil flow in an oil–lubricated tilting–pad journal bearing is analyzed in this study. A three–dimensional model for the oil domain is established and the CFD results obtained using laminar and seventeen turbulence models are compared with the experimental results obtained by S.Taniguchi. The seventeen turbulence models are divided into three groups, namely, classical fully developed turbulence models, transition turbulence models, and turbulence models with low–Re correction. The laminar and classical turbulence models cannot simulate the superlaminar flow correctly; accordingly, corrections should be applied to classical fully developed turbulence models for superlaminar flows to consider the turbulent effect properly. However, not all corrections are suitable. Among all the compared turbulence models, the SST model with low–Re correction performs the best. Furthermore, this model can capture the turbulent effect in superlaminar oil flow, as indicated in the analysis of turbulent viscosity ratio. A comparison of the velocity profiles shows that the mechanism of the superlaminar flow in journal bearings is near–wall turbulence. The buffer layer plays an important role in superlaminar flows. The SST model with low–Re correction can likewise capture the characteristics of the buffer layer and simulate the near–wall turbulence properly in superlaminar flows. Thus in superlaminar journal bearings, the low–Re correction is the most suitable correction for the SST turbulence model for simulating oil flows.
Numerical Investigation of Diffuser Flow Field and Rotating Stall in a Centrifugal Compressor With Vaned Diffuser
Authors: Zhao Yang , Zhao Jiayi , Wang Zhiheng , Xi Guang
Published: August 2017

The diffuser rotating stall in a centrifugal compressor with vaned diffuser is one of important unsteady flow phenomena, which limits the operating range of the compressor. In this paper, the unsteady CFD analysis on a low-speed centrifugal compressor has been performed to investigate the flow characteristic in the diffuser and the propagation of the diffuser rotating stall.

The flow behaviors at the outlet of the impeller at design and off-design conditions are firstly investigated. It is found that a reversal flow, induced by the tip leakage flow, exists near the shroud at the impeller outlet and becomes serious with the mass flow rate reduced. Due to the span-wise variation of the flow angle at the diffuser inlet and the inversed pressure gradient in the passage, the leading-edge vortex (LEV) generates on the diffuser leading edge. The LEV then induces the secondary flow in the diffuser passage and then causes the hub-corner separation. Furthermore, the propagation of the diffuser rotating stall is presented in details.

The suction-side separation near the hub induces the blockage in the passage. And the shedding vortex from the suction side moves toward the leading edge of the adjacent blade. When the vortex reaches to the leading edge of the adjacent blade, the incidence increase and a new separation occurs on the suction side. With the development of the new separation, the passage becomes blocked gradually and the upstream stalled passage recovers to a normal condition. The rotating stall propagates along the direction of the impeller rotation at about 4.5% of the impeller rotational speed.
Dynamic Analysis of Flexible Rotor Systems Subjected to Time-Varying Base Excitations
Authors: Chen Liqiang , Wang Jianjun , Han Qinkai , Chu Fulei
Published: August 2017

Rotor systems carried in transportation system or under seismic excitations are considered to have a moving base. The objective of this paper is to develop a general model for flexible rotor systems subjected to time-varying base excitations and study the direct effects of angular base motions on the dynamic behaviors of a simple rotor. The model is developed based upon finite element method and Lagrange’s equation. Two groups of Euler angles are introduced to describe the rotation of the rotor and the base, respectively. Six types of base motions are considered in the model. In the numerical simulations, three types of angular base motions (pitching, rolling and yawing) are considered and assumed to be sinusoidal varying with time. The effects of base angular amplitudes, base frequency and rotation speed on the system dynamic behaviors are discussed in detail. It is shown that pitching and yawing have a great influence on the response amplitudes and the shape of the rotor orbits. Especially, resonances occur when the base frequency meets the natural frequencies. The FFT and waterfall plots of the disk horizontal and vertical vibrations are marked with multiplications of the base frequency and sum and difference tones of the rotating frequency and the base frequency.
Numerical Investigation on Effect of Compressor Performance in Single Rotor With Micro-Vortex Generator
Authors: Ma Shan , Chu Wuli , Zhang Haoguang , Lang Jinhua , Kuang Haiyang
Published: August 2017

The performance of axial compressor is considerably influenced by secondary flow, like corner separation between wall and blade in a compressor stage. An extensive experimental study of vortex generator (VG) applied on axial compressor was conducted by many scholars, in order to control these effects and improve the aerodynamic performance. According to their size, they are classified as traditional VGs (h/δ>0.5) and Micro-vortex generators (MVGs, h/δ = 0.1∼0.5).MVGs is one of the hot spots of present research to restrain the secondary flow.

In order to investigate the effect of MVGs used in rotor, this study was carried out on Northwestern Polytecnical University rotor (NPU rotor), which is a subsonic axial flow compressor rotor. The Vane-MVGs were placed at a distance of 11% chord length ahead of the leading edge on the end-wall. The characteristic line of 54% (8130RPM), 71% (10792RPM) and 84% (12768RPM) design speed were calculated by steady 3D RANS simulations with Spalart-Allmar turbulence model and compared with the corresponding MVGs cases, respectively. Results show that the stall margins of the 3 speeds with MVGs were larger than baseline, but the efficiency and pressure ratio were reduced in different degrees. In this paper, the flow characteristics at 54% (8130RPM) design speed and the development process of vortex generated by MVGs are analyzed in detail. The influence of MVGs height and stagger angle on rotor performance is also discussed. Moreover, flow simulation of MVGs used on axial compressor single rotor’s hub offered a guideline to future research.
Velocity Field Response of a Forced Swirl Stabilized Premixed Flame
Authors: Manoharan Kiran , Smith Travis , Emerson Benjamin , Douglas Christopher M. , Lieuwen Tim , Hemchandra Santosh
Published: August 2017

This study is motivated by the necessity to develop a low order prediction approach for unsteady heat release response characteristics in lean premixed gas turbine combustors. This in turn requires an accurate description of the coherent hydrodynamic oscillations induced in the combustor flow by acoustic forcing. Time resolved velocity and flame position fields are obtained using sPIV and OH-PLIF measurements on a single nozzle, swirl-stabilized, premixed, methane-air flame in a model “unwrapped” annular combustor rig. A natural acoustic oscillation in the rig at 115 Hz results in a coherent flow oscillation that is concentrated primarily within the shear layer between the annular jet flow and the central recirculation zone. A linear stability analysis performed about time averaged base flow fields shows that the flow does not have any self-excited hydrodynamic modes. We then compare predictions from a forced response analysis at a forcing frequency of 115 Hz, based on the linearized Navier-Stokes equations for this coherent response. Good qualitative agreement between linear forced response analysis predictions and experimental response results, is seen for the spatial variation of velocity oscillation amplitude fields, away from the burner centerline. Further, good quantitative agreement between predictions and the experimental response is seen for the phase speed of velocity oscillations along the shear layer between the annular jet and the central recirculation zone. This phase velocity is an important flow field characteristic that has a significant impact on the heat release response that results from these coherent velocity oscillations. Present methods for forced response analysis assume uniform forcing amplitude along the radial direction at the forcing location, as well as, open flows along the streamwise direction. Both these assumptions are not strictly true for the present burner which has a center body on its axis. This maybe the reason for somewhat poor qualitative and quantitative agreement between experiments and predictions at the centerline.
Investigations on the Influence of Rib Orientation Angle on Film Cooling Performance of Cylindrical Holes
Authors: Ye Lin , Liu Cun-liang , Zhu Hui-ren , Luo Jian-xia , Zhai Ying-ni
Published: August 2017

This paper presents an experimental and numerical investigation on the film cooling with different coolant feeding channel structures. Two ribbed cross-flow channels with rib-orientation of 135° and 45° respectively and the plenum coolant channel have been studied and compared to find out the effect of rib orientation on the film cooling performances of cylindrical holes. The film cooling effectiveness and heat transfer coefficient were measured by the transient heat transfer measurement technique with narrow-band thermochromic liquid crystal. Numerical simulations with realizable k-ε turbulence model were also performed to analyze the flow mechanism. The results show that the coolant channel structure has a notable effect on the flow structure of film jet which is the most significant mechanism affecting the film cooling performance. Generally, film cooling cases fed with ribbed cross-flow channels have asymmetric counter-rotating vortex structures and related asymmetric temperature distributions, which make the film cooling effectiveness and the heat transfer coefficient distributions asymmetric to the hole centerline. The discharge coefficient of the 45° rib case is the lowest among the three cases under all the blowing ratios. And the plenum case has higher discharge coefficient than the 135° rib case under low blowing ratio. With the increase of blowing ratio, the discharge coefficient of the 135° rib case gets larger than the plenum case gradually, because the vortex in the upper half region of the coolant channel rotates in the same direction with the film hole inclination direction and makes the jet easy to flow into the film hole in the 135° rib case.
Effects of Increasing Blade Hub Loading on Instability Evolution in a Low-Speed Compressor
Authors: Li Qiushi , Li Simin , Pan Tianyu , Arshad Ali , Gong Yifang
Published: August 2017

Based on previous results showing that a compressor stall can be initiated from hub region, a hypothesis is further proposed: the type of stall inceptions is related to the loading distributions. A series of experiments are designed to examine the effects of radial loading to the stall inception and its evolution. Well-designed distortion screens installed at the inlet of a single-stage low-speed axial compressor induce various radial distributions of blade loading. The uniform inflow situation, i.e. without screen, is defined as the baseline, in which case the compressor shows the modal type stall inception. With hub distortion screens, the hub loading is keeping to be increased, however, the compressor still shows modal type of stall inception. After further data processing, it is found that there is a period between linear growth of modal wave and the formation of a large amplitude stall cell. In that period, the tip pressure signal does not show any clear traveling disturbances. In further investigation, it is found that there are large disturbances formed in the hub region during this period. With increasing the hub loading, the large amplitude disturbances in hub region appear earlier and earlier. In our previous work, the compressor showed spike type stall inception with a tip distortion screen. Combining these observations, it is proposed that radial loading of the blade does have significant effects on both the type of stall inception and the evolution which is in particular corresponding to transient process from small linear disturbance to final formation of stall cell in our compressor.
Reducing Nacelle Pressure Drag
Authors: Cerantola D. J. , Zawislak M. S. , Birk A. M.
Published: August 2017

Decreasing drag on aircraft components was beneficial towards improving fuel economy and operational range. A generic axisymmetric nacelle-strut configuration typical of those housing fuselage-mounted engines was evaluated at a Reynolds number of 6 × 105 based on the nacelle maximum diameter d = 26.5 cm and an angle of attack of 20 deg. It was estimated that drag could be reduced by 20%. Three case studies were evaluated that added a fillet to the nacelle-strut corner, vortex generating triangular tabs, and flow-path obstructing vanes to improve flow control by reducing suction-side separation. Experimental results showed that a 0.11 d radius of curvature fillet reduced drag by 8% with respect to the baseline case. Numerical results employing the realizable k-ε turbulence model with wall functions predicted no improvements with the tabs and an 8% reduction with the vanes.
Characterization of a Novel Porous Injector for Multi-Lean Direct Injection (M-LDI) Combustor
Authors: Li Jianing , Bhayaraju Umesh , Jeng San-Mou
Published: August 2017

A generic novel injector was designed for multi-Lean Direct Injection (M-LDI) combustors. One of the drawbacks of the conventional pressure swirl and prefilming type airblast atomizers is the difficulty of obtaining a uniform symmetric spray under all operating conditions. Micro-channels are needed inside the injector for uniformly distributing the fuel. The problem of non-uniformity is magnified in smaller sized injectors. The non-uniform liquid sheet causes local fuel rich/lean zones leading to higher NOx emissions. To overcome these problems, a novel fuel injector was designed to improve the fuel delivery to the injector by using a porous stainless steel material with 30 μm porosity. The porous tube also acts as a prefilming surface. Liquid and gaseous fuels can be injected through the injector. In the present study, gaseous fuel was injected to investigate injector fuel-air mixing performance. The gaseous fuel was injected through a porous tube between two radial-radial swirling air streams to facilitate fuel-air mixing. The advantage of this injector is that it increases the contact surface area between the fuel-air at the fuel injection point. The increased contact area enhances fuel-air mixing. Fuel-air mixing and combustion studies were carried out for both gaseous and liquid fuel. Flame visualization, and emissions measurements were carried out inside the exit of the combustor.

The measurements were carried out at atmospheric conditions under fuel lean conditions. Natural gas was used as a fuel in these experiments. Fuel-air mixing studies were carried out at different equivalence ratios with and without confinement. The mass fraction distributions were measured at different downstream locations from the injector exit. Flame characterization was carried out by chemiluminescence at different equivalence ratios and inlet air temperatures. Symmetry of the flame, flame length and heat release distribution were analyzed from the flame images. The effects of inlet air temperature and combustion flame temperature on emissions was studied. Emissions were corrected to 15% O2 concentration. NOx emissions increase with inlet air temperature and flame temperature. Effect of flame temperature on NOx concentration is more significant than effect of inlet air temperature. Fuel-air mixing profile was used to obtain mass fraction Probability Density Function (pdf). The pdfs were used for simulations in Chemkin Pro. The measured emissions concentrations at the exit of the injector was compared with simulations. In Chemkin model, a network model with several PSRs (perfectly stirred reactor) were utilized, followed by a mixer and a PFR (plug flow reactor). The comparison between the simulations and the experimental results was investigated.
Multall: An Open Source, CFD Based, Turbomachinery Design System
Authors: Denton John D.
Published: August 2017

Turbomachinery design systems are usually the jealously guarded property of large companies, the author is not aware of any for which the source code is freely available. The present paper is aimed providing a freely available system that can be used by individuals or small companies who do not have access to an in-house system.

The design system is based on the 3D CFD solver Multall, which has been developed over many years. Multall can obtain solutions for individual blade rows or for multi-stage machines, it can also perform quasi-3D blade-to-blade calculations on a prescribed stream surface and axisymmetric throughflow calculations. Multall is combined with a one-dimensional mean-line program, Meangen, which predicts the blading parameters on a mean stream surface and writes an input file for Stagen. Stagen is a blade geometry generation and manipulation program which generates and stacks the blading, combines it into stages, and writes an input file for Multall.

The system can be used to design the main blade path of all types of turbomachines. Although it cannot design complex features such as shroud seals and individual cooling holes these features can be modeled and their effect on overall performance predicted. The system is intended to be as simple and easy to use as possible and the solver is also very fast compared to most CFD codes. A great deal of user experience ensures that the overall performance is reasonably well predicted for a wide variety of machines.

This paper describes the system in outline and gives an example of its use. The source codes are written in FORTRAN77 and are freely available for other users to try.
Comparison of Experimental and Numerically Predicted Three-Dimensional Wake Behaviour of a Vertical Axis Wind Turbine
Authors: Saverin Joseph , Marten David , Holst David , Pechlivanoglou George , Paschereit Christian Oliver , Persico Giacomo , Dossena Vincenzo
Published: August 2017

The evolution of the wake of a wind turbine contributes significantly to its operation and performance, as well as to those of machines installed in the vicinity. The inherent unsteady and three-dimensional aerodynamics of Vertical Axis Wind Turbines (VAWT) have hitherto limited the research on wake evolution. In this paper the wakes of both a troposkien and a H-type VAWT rotor are investigated by comparing experiments and calculations. Experiments were carried out in the large-scale wind tunnel of the Politecnico di Milano, where unsteady velocity measurements in the wake were performed by means of hot wire anemometry. The geometry of the rotors was reconstructed in the open-source wind-turbine software QBlade, developed at the TU Berlin. The aerodynamic model makes use of a lifting line free-vortex wake (LLFVW) formulation, including an adapted Beddoes-Leishman unsteady aerodynamic model; airfoil polars are introduced to assign sectional lift and drag coefficients. A wake sensitivity analysis was carried out to maximize the reliability of wake predictions. The calculations are shown to reproduce several wake features observed in the experiments, including blade-tip vortex, dominant and submissive vortical structures, and periodic unsteadiness caused by sectional dynamic stall. The experimental assessment of the simulations illustrates that the LLFVW model is capable of predicting the unsteady wake development with very limited computational cost, thus making the model ideal for the design and optimization of VAWTs.
Low Load Operation Range Extension by Autothermal On-Board Syngas Generation
Authors: Baumgärtner Max H. , Sattelmayer Thomas
Published: August 2017

The increasing amount of volatile renewable energy sources drives the necessity of flexible conventional power plants to compensate for fluctuations of the power supply. Gas turbines in a combined cycle power plant (CCPP) adjust the power output quickly but a sudden increase of CO and UHC emissions limit their turn-down ratio. To extend the turn-down ratio, part of the fuel can be processed to syngas, which exerts a higher reactivity. An autothermal on-board syngas generator in combination with two different burner concepts for natural gas and syngas mixtures are presented in this study.

A mixture of natural gas, water vapor and air reacts catalytically in an autothermal reactor test rig to form syngas. At atmospheric pressure, the fuel processor generates syngas with a hydrogen content of ∼30 vol% and a temperature of 800 K within a residence time of 200 ms.

One concept for the combustion of natural gas and syngas mixtures comprises a generic swirl stage with a central lance injector for the syngas. The second concept includes a central swirl stage with an outer ring of jets. The combustion is analyzed for both concepts by OH*-chemiluminescence, lean blow out (LBO) limit and gaseous emissions.

The central lance concept with syngas injection exhibits an LBO adiabatic flame temperature that is 150 K lower than in premixed natural gas operation. For the second concept an extension of almost 200 K with low CO emission levels can be reached. This study shows that autothermal on-board syngas generation is feasible and efficient in terms of turn-down ratio extension and CO burn-out.
Rib Cross Section Optimization of a Ribbed Turbine Internal Cooling Channel With Experimental Validation
Authors: Kiyici Firat , Yilmazturk Sefa , Coban Kahraman , Arican Ercan , Costa Emiliano , Porziani Stefano
Published: August 2017

Due to the recent developments of the engine industry, turbine internal channel cooling is a need. In fact, in order to supply more power efficiently, the fluid temperature at turbine inlet approaches to 2000 K when common turbine materials cannot resist temperature values higher than 1500 K. The crucial point is that the engine cycle efficiency and thrust highly depend on the turbine inlet temperature and, so, such a thermal problem needs to be overcome by cooling. Coolant air of the internal channel cooling systems is mostly taken from valuable compressor bleed that makes it to circulate through the serpentine internal passages. The coolant air flow is commonly fully turbulent, incompressible and with 3D characteristics because of the complex shape of the cooling passage. Considering this latter aspect, the pressure drop also plays a relevant role because, in order to minimize the cooling mass flow, it needs to be reduced. In this study, rib cross-section shape optimization of a ribbed internal cooling channel is conducted to assess the trade-off between two conflicting objectives: heat transfer performance and pressure drop. For this purpose, a novel mesh morphing based optimization tool is developed which uses radial basis functions (RBF) for morphing and meta-model assisted evolutionary algorithms (EA) for optimization. Experimental tests characterized by Reynolds number of 20000 are performed to validate such an optimization tool. The local Nusselt number is calculated using hydraulic diameter of channel and air thermal conductivity corresponding to bulk temperature. The cooling effectiveness of the channel is quantified using the ratio of the Nusselt number of the ribbed case to the Nusselt number of the smooth case. With the gained optimized geometry, the heat transfer shows better results than initial case with a pressure loss improvement of 8%.
Investigation of Tip Clearance Flow Effects on an Open 3D Steam Turbine Flutter Test Case
Authors: Sun Tianrui , Petrie-Repar Paul , Qi Di
Published: August 2017

Blade failure caused by flutter is a major problem in the last stage of modern steam turbines. It is because rotor at this stage always has a large scale in spanwise, which provides low structural frequency as well as supersonic tip speeds. Since most of the unsteady aerodynamic work is done in the tip region, transonic tip-leakage flow that influences the tip region flow could have a remarkable effect on the aerodynamic stability of rotor blades. However, few research had been done on the tip-leakage flow influence on flutter characteristic based on full-scale steam turbine numerical models. In this paper, an open 3D steam turbine stage model designed by Durham University was applied, which was widely analyzed and representative for the last stage of modern industrial steam turbines. The average Mach number at the rotor outlet is 1.1. URANS simulation carried by both numerical software CFX and LUFT code is applied, and the two solvers show an agreement on steady and unsteady results. The numerical results indicate that the influence of tip leakage flow on blade stability is based on two types of flow mechanisms. Both mechanisms act on the suction side of near tip region. The first type of mechanism is produced by the reduction of passage shock near the leading edge, and the other type of mechanism at the rear of blade is caused by the interaction between tip leakage vortex and trailing edge shock of the neighbor blade. In conclusion, tip leakage flow has a significant influence on steam turbine flutter boundary prediction and requires further analysis in the future.
Modeling Capability for Cavity Flows in an Axial Compressor
Authors: Mahmood Syed Moez Hussain , Turner Mark G.
Published: August 2017

Seal-teeth cavity leakage in a shrouded stator blade deteriorates the performance of an axial compressor. This impact of shrouded stator seal-teeth cavity flows on compressor performance is demonstrated by presenting a sensitivity study with different seal-teeth clearances. A parametric definition of the cavity geometry (including the seal teeth) is created for an axial compressor, which allows for variation in seal teeth design, clearance and cavity shape. One and a half subsonic stages (rotor-stator-rotor) of a 10 stage axial compressor derived from the EEE design is considered to perform a computational fluid dynamic study. A NLH calculation is performed to account for the unsteady effects across the rotor-stator interface. Accuracy of the NLH calculations is determined by a comparison with time-marching results. For mixing plane calculations the location of the rotor-stator interface relative to the upstream and down-stream cavity connections is crucial. Comparison for mixing plane calculation at different rotor-stator interface is made with NLH results.

For this configuration the low momentum leakage flow through the cavities gets entrained in the power stream upstream of the stator which increases the near hub blockage for the stator. Excessive near hub blockage alters the outlet flow conditions for the stator which changes the incoming flow for the down-stream rotor. A vortical flow structure exists at the upstream and downstream cavity connections which changes with the increase in clearance and defines the flow going into and coming out of the cavity. An increase in seal-teeth cavity clearance is shown to deteriorate compressor efficiency up to 0.86% for the largest clearance analyzed. The parametric design and simulation process presented represents the first step in a design optimization process that accounts for cavity flows and seal leakage. The seal-teeth cavity should be modeled correctly to account for the correct blockage and loss distribution. It should also be integrated into the airfoil design at an early stage.
Numerical Investigations on Partial Surge Initiated Inception and Stall Evolution in a Transonic Compressor
Authors: Hu Jiaguo , Pan Tianyu , Wu Wenqian , Li Qiushi , Gong Yifang
Published: August 2017

The instability has been the largest barrier of the high performance axial compressor in the past decades. Stall inception, which determines the route and the characteristics of instability evolution, has been extensively focused on. A new stall inception, “partial surge”, is discovered in the recent experiments. In this paper full-annulus transient simulations are performed to study the origin of partial surge initiated inception and explain the aerodynamic mechanism. The simulations show that the stall inception firstly occurs at the stator hub region, and then transfers to the rotor tip region. The compressor finally stalled by the tip region rotating stall. The stall evolution is in accord with the experiments. The stall evolution can be divided into three phases. In the first phase, the stator corner separation gradually merged with the adjacent passages, producing an annulus stall cell at the stator hub region. In the second phase, the total pressure rise of hub region emerges rapid decline due to the fast expansion of the annulus stall cell, but the tip region maintains its pressure rise. In the third phase, a new rotating stall cell appears at the rotor tip region, leading to the onset of fast drop of the tip region pressure rise. The stall cells transfer from hub region to the tip region is caused by two factors, the blockage of the hub region which transfers more load to the tip region, and the separation fluid fluctuations in stator domain which increase the circumferential non-uniformity in the rotor domain. High load and non-uniformity at the rotor tip region induce the final rotating stall.