2007 Vol. 22, No. 4

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Modelling internal air systems ingas turbine engines
J Michael Owen
2007, 22(4): 505-520.
Abstract PDF(1348KB) icon1413 icon628
Abstract:
Rotating-disc systems can be used to model,experimentally and computationally,the flow and heat transfer that occur inside the internal cooling-air systems of gas turbine engines.These rotating-disc systems have been used successfully to simplify and understand some of the complex flows that occur in internal-air systems,and designers have used this insight to improve the cooling effectiveness,thereby increasing the engine efficiency and reducing the emissions.In this review paper,three important cases are considered:hot-gas ingress;the pre-swirl system;and buoyancy-induced flow.Ingress,or ingestion,occurs when hot gas from the mainstream gas path is ingested into the wheel-space between the turbine disc and its adjacent casing.Rim seals are fitted at the periphery of the system,and sealing flow is used to reduce or prevent ingress.However,too much sealing air reduces the engine efficiency,and too little can cause serious overheating,resulting in damage to the turbine rim and blade roots.Although the flow is three-dimensional and unsteady,there are encouraging signs that simple ‘orifice models’ could be used to estimate the amount of ingress into the wheel-space.In a pre-swirl system,the cooling air for the gas-turbine blades is swirled by stationary nozzles,and the air is delivered to the blades via receiver holes in the rotating turbine disc.Swirling the air reduces its temperature relative to the rotating blades,and the designer needs to calculate the air temperature and pressure drop in the system.The designer also needs to calculate the effect of this swirling flow on the heat transfer from the turbine disc to the air,as this has a significant effect on the temperature distribution and stresses in the disc.Recent experimental and computational studies have given a better understanding of the flow and heat transfer in these systems.Buoyancy-induced flow occurs in the cavity between two co-rotating compressor discs when the temperature of the discs is higher than that of the air in the cavity.Coriolis forces create cyclonic and anti-cyclonic circulation inside the cavity and,as such flows are three-dimensional and unsteady,the heat transfer from the discs to the air is difficult either to compute or to measure.The flow also tends to be unstable and one flow structure can change quasi-randomly to another,which makes it hard for designers of aero-engines to calculate the transient temperature changes and thermal stresses in the discs during take-off,cruise and landing conditions.Although recent CFD research has been successful in computing these flows,it will be many years before the designer can rely on computations unless they have been validated on reliable experimental data.
LES of film cooling for different jet fluids
P. Renze, W. Schrder, M. Meinke
2007, 22(4): 521-530.
Abstract PDF(1289KB) icon1272 icon497
Abstract:
The present paper investigates the impact of the velocity and density ratio on the turbulent mixing process in gas turbine blade film cooling.A cooling fluid is injected from an inclined pipe at α=30° into a turbulent boundary layer profile at a freestream Reynolds number of Re∞=400000.This jet-in-a-crossflow(JICF) problem is investigated using large-eddy simulations(LES).The governing equations comprise the Navier-Stokes equations plus additional transport equations for several species to simulate a non-reacting gas mixture.A variation of the density ratio is simulated by the heat-mass transfer analogy,i.e.,gases of different density are effused into an an air crossflow at a constant temperature.An efficient large-eddy simulation method for low subsonic flows based on an implicit dual time-stepping scheme combined with low Mach number preconditioning is applied.The numerical results and experimental velocity data measured using two-component particle-image velocimetry (PIV) are in excellent agreement.The results show the dynamics of the flow field in the vicinity of the jet hole,i.e.,the recirculation region and the inclination of the shear layers,to be mainly determined by the velocity ratio.However,evaluating the cooling efficiency downstream of the jet hole the mass flux ratio proves to be the dominant similarity parameter,i.e.,the density ratio between the fluids and the velocity ratio have to be considered.
Enhancing the efectiveness of film cooling
Tom H-P. Shih, Sang kwon Na
2007, 22(4): 531-539.
Abstract PDF(874KB) icon1310 icon519
Abstract:
Advanced gas turbine stages are designed to operate at increasingly higher inlet temperatures to increase thermal efficiency and specific power output.To maintain durability and reasonable life,film cooling is needed in addition to internal cooling,especially for the first stage.Film cooling lowers material temperature by forced convection inside film-cooling holes and by forming a layer of coolant about component surfaces to insulate them from the hot gases.Unfortunately,each cooling jet forms a pair of counter-rotating vortices that entrains hot gas and causes the film-cooling jet to lift off from the surface that it is intended to protect.This paper gives an overview of efforts to enhance the effectiveness of film-cooling.This paper also describes two new design concepts.One design concept seeks to minimize the entrainment of hot gases underneath of film-cooling jets by using flow-aligned blockers.The other design concept shifts the interaction between the approaching hot gas and the cooling jet to occur further above the surface by using an upstream ramp.For both design concepts,computational fluid dynamics results are presented to examine their usefulness in enhancing film-cooling effectiveness.
Numerical study on the influences of pin-fin diameter on the flow resistance and heat transfer of leaning vent hole lamilloy
TAO Zhi, L Dong, DING Shui-ting, XU Guo-qiang
2007, 22(4): 540-546.
Abstract PDF(1247KB) icon1592 icon437
Abstract:
The influence of pin-fins diameter of minimum elements in the leaning vent hole lamilloy upon the flow resistance and heat transfer was studied through numerical simulation.A locally increased grid density was applied to the bigger area of flow angle with the help of unstructured grid method.k-ε model equation was used to resolve the steady lamilloy along with fixed wall function.The coupling heat transfer was calculated using fluid area and solid area coupling solution.The calculated results were presented,helping to analyze the flow and heat transfer.The research results show that,proper increase of pin-fins diameter is helpful to decrease the flow resistance and increase the cooling efficiency.
Investigation on intensifying combustion setting of kerosene/air pulse detonation engine
LI Jian-zhong, WANG Jia-hua
2007, 22(4): 547-553.
Abstract PDF(844KB) icon1580 icon455
Abstract:
In order to investigate the effect of different intensifying combustion setting on detonation initiation of kerosene/air mixture, and to choose optimal intensifying combustion setting for kerosene/air aero-valve pulse detonation engine, several kinds of intensifying combustion setting were designed and tested. Much detonation experimentation was carried out and the kerosene/air aero-valve PDE could be operated at different frequency. The mechanism of intensifying combustion setting was analyzed, and the effect of different intensifying combustion setting on detonation initiation of kerosene/air mixture was described. This investigation is of importance to supply theory and practice for optimizing intensifying combustion setting and kerosene/air aero-valve pulse detonation engine.
A preliminary experimental study of pattern factor for a triple swirler combustor
PENG Yun-hui, LIN Yu-zhen, LIU Gao-en
2007, 22(4): 554-558.
Abstract PDF(652KB) icon1847 icon496
Abstract:
To reduce the requirement of high-temperature combustor on pattern factor,a triple swirler was used to test the pattern factors of three different triple swirler packages.The focus of the research was placed on the effects of vane angle of triple swirler and equivalence ratio of the combustor dome on the combustor’s pattern factor.Gas analysis method was used for the measurement of combustor exit temperature.The result show that,when the swirl air from the third swirler and the second swirler was counter-rotating,the combustor exit temperature distribution became more uniform;and the lower the equivalence ratio of the combustor dome,the more uniform the combustor exit temperature distribution was.The vane angle and the equivalence ratio of the combustor dome should be taken into account in order to optimize the combustor’s pattern factor.
Numerical simulation of hydrocarbon gas combustion and supersonic shear flow
WANG Hui, HOU!Ling-yun
2007, 22(4): 559-564.
Abstract PDF(354KB) icon1555 icon415
Abstract:
A turbulent combustion of hydrocarbon fuel-rich gas with air two-dimensional supersonic shear flow was numerically simulated. NND difference scheme of convection item was used to capture shock wave with high precision, while turbulent viscid coefficient was calculated from B-L and Prandtl mixed length models. To simulate non-equilibrium combustion, Arrhenius reaction dynamic formula was used to confirm the chemical reaction rate. The simulated wall pressure results are in agreemant with the experimental data.The wave system suitable for flame stabilization was also analyzed.The combustion state was evaluated from the distribution of flow parameters and chemical components, providing a reference for improvement and optimization of combustion chamber.
Hybrid system-a promising way solving future energy problems
Dieter Bohn
2007, 22(4): 565-576.
Abstract PDF(1366KB) icon1233 icon496
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With the increasing demand for electricity,an efficiency improvement and thereby reduced CO2 emissions of the power plants are expected in order to reach the goals set in the Kyoto protocol.In comparison to conventional systems,the hybrid-systems with the use of synergetic effects offer the possibility to provide a substantial contribution to spare our natural resources and protect our environment.Combined Cycle Power Plants belongs innately hybrid system in the centralized energy market.They can provide large amounts of power and have a quick start-up time.The MGT/FC hybrid system is quite promising in the decentralized energy market.It is widely used in stand-alone applications.Furthermore,the combination of fossil and renewable power plant technologies contains a large synergy potential to increase the efficiency of processes for power plants.New materials,innovative cooling technology,new combustion concepts and optimized production methods are needed to make the potential of these new technologies accessible for a quantum leap in the efficiency.For this it needs considerable research work and good coordinated research projects between the state,industry,research laboratories and universities.
Aerodynamic stability assessment of fan component running in turbofan engine
WANG Zhan-xue, WANG Peng, QIAO Wei-yang, CAI Yuan-hu
2007, 22(4): 577-582.
Abstract PDF(721KB) icon1618 icon445
Abstract:
A new model was presented for predicting of aerodynamic stability limit of compressor in turbofan engine. Firstly, a quasi one-dimensional, time dependent compression system model was used to model the dynamic flow in compressor and the actuator-lag-volume model was adopted to model the stage of compressor. Secondly, Lyapunov stability theory was used to identify the aerodynamic stability of compression component. Finally, this aerodynamic stability numerical model was coupled with steady state thermodynamic cycle model of turbofan for predicting of aerodynamic stability limit of compression component in turbofan engine environment. A turbofan engine with 3 stages fan and 5 stages compressor as an example was simulated. Numerical results show that the model presented in this paper is reasonable and reliable and can be used to predict aerodynamic stability limit of fan and compressor in real turbofan engine environment.
Improvement of sub-grid model in large eddy simulation and applications in turbulent channel flow
XIAO Hong-lin, LUO Ji-sheng
2007, 22(4): 583-587.
Abstract PDF(638KB) icon1435 icon486
Abstract:
If large eddy simulation method is used to calculate the turbulent channel flow with strong shear, the commonly used sub-grid stress models, including wall modification model, will generate excessively high mean velocity profiles. It indicates that sub-grid stress model cannot describe the situation nearby the wall. To this end, the wall function of the sub-grid Reynolds stress model was modified to obtain a better result. The mean velocity profiles, the RMS(root-mean-square) velocity profiles and Reynolds stress profiles calculated by the modified model are consistent with the results of DNS.
Experimental study of flow field in twin circular synthetic jet arrays using PIV
SHA Jiang, XU Jing-lei, LIN Chun-feng, Li Nian, ZHANG Kun-yuan
2007, 22(4): 588-593.
Abstract PDF(750KB) icon1654 icon415
Abstract:
A PIV experimental study of flow structures of synthetic jet arrays which had different orifice spacing was carried out. To capture the instantaneous flow velocity vectors, the phase-locked technique was designed for the experimental system. The experiment images show the complete forming process of single jet synthesized by the interaction of vortex rings produced by twin synthetic jet respectively. It is found that the spatial distance needed for synthesizing is varied with the spacing of the jet arrays. It is similar to the conventional 2-D jet that the cross-velocity profiles at different stations after the synthesizing position are self-simulation. The property is also suitable for the lateral sides of jet arrays in the synthesizing distance.
Mechanical behavior and properties of fiber reinforced ceramic matrix composites for high temperature use
Chongdu Cho, Qiang Pan, Sangkyo Lee
2007, 22(4): 594-601.
Abstract PDF(3806KB) icon1321 icon442
Abstract:
Ceramics can keep their mechanical characteristics up to 2 000℃ or higher.In this paper,A model to predict ultimate strength of continuous fiber-reinforced brittle matrix composites is developed.A statistical theory for the strength of a uni-axially fiber-reinforced brittle matrix composite is presented.Also a semi-empirical frictional heating method for estimating in-situ interfacial shear in fiber-reinforced ceramic matrix composites was improved.Local uneven fiber packing variation as well as uneven micro-damage during fatigue can be expected to have effects on the composites:generation of frictional heating,thermal gradients,and residual stresses around local fiber breaks.This study examined those engineering interests by the finite element method.
Progressive fatigue damage analysis method of laminated composites
XU Ying, WEN Wei-dong, CUI Hai-tao
2007, 22(4): 602-607.
Abstract PDF(1994KB) icon2101 icon427
Abstract:
A progressive fatigue damage analysis method was developed to predict damage propagation and life of laminated composites subjected to constant amplitude cyclic loading. It consists of stress analysis, fatigue damage analysis and material property degradation technique. Stress analysis of composite laminates was performed by creating a three-dimensional finite element model using the ANSYS FE code. Modified Hashin failure criterion was used to fatigue damage analysis. The rules of sudden degradation and gradual degradation were applied in material property degradation technique for modifying element stiffness and strength. Simulation results show that this progressive fatigue damage method is competent for simulating progressive damage and predicting fatigue life of laminated composites with arbitrary geometry and ply stacking sequence. A parametric progressive fatigue damage analysis programme was developed based on the ANSYS FE code. The error between the predicted results and the test data is within 10%.
Method to predict the blade vibration stress induced by wake flow
WANG Mei, JIANG He-fu, Lü Wen-lin
2007, 22(4): 608-613.
Abstract PDF(1645KB) icon1723 icon473
Abstract:
This paper aims at researching the influence of the wake flow from the stator vanes of the previous stage acting on the following rotor blades.The wake flow of stator vanes and the unsteady flow in the passage of rotor blades were solved by using oscillating fluid mechanics theory and parametric polynomial method.Then the aerodynamic pressure field obtained from the analysis of unsteady aerodynamics was transformed to the form of load pressure field which is suitable to the analysis of structure dynamics.The damping coefficient of response applied to the analysis was achieved from the experimental result.Thus,the response of each harmonic can be calculated first,and then the whole response can be achieved by superimposing the responses of all harmonics.From solving the flow fluid to solving the structure response,a semi-empirical method for engineering application was established to predict the vibration stress of blades induced by wake flow.
Application of complex normal form method for stability judgement of limit cycle of nonlinear flutter
CHEN Yan-mao, LIU Ji-ke
2007, 22(4): 614-618.
Abstract PDF(1381KB) icon1899 icon445
Abstract:
The bifurcations of the flutter system of a 2D airfoil with cubic nonlinearity were investigated in this paper.Hopf bifurcation theory was applied to verify Hopf bifurcation at the critical point of flutter.The high-dimensional system was transformed into a lower-dimensional one by center manifold theorem.And,the complex normal form method of Hopf bifurcation was used to analyze the stability of the limit cycle,with the results consistent with numerical solutions.
Study on solid rocket motor computer aided design/computer simulation(SRMCAD/CS) system based on dynamic combination of arithmetic components
HE Yun-qin, LIANG Guo-zhu
2007, 22(4): 619-624.
Abstract PDF(755KB) icon1482 icon448
Abstract:
A new software model was developed to obtain the desired design/simulation arithmetic by combining arithmetic components dynamically according to rocket motor designers’ design/simulation tasks.This software model could be used to finish a variety of SRMCAD/CS tasks while offering excellent expandability for software system.The purpose of this research is to create a standard and open arithmetic component interface system,whereby a reusable,expandable arithmetic components library and a combined arithmetic components mechanism could be established.In this way,the designers’ tasks of compiling design/simulation arithmetic can be turned to combine dynamically into a desired one using the existing arithmetic components.This software model enables the designers to reuse the existing arithmetic in the arithmetic component library,while maintaining the liberty of designers for easier and efficient work.
Experimental study of a variable-area propelling nozzle dual-mode ramjet
LI Da-peng, PAN Yu, WU Ji-ping, LIU Wei-dong, WANG Zhen-guo
2007, 22(4): 625-631.
Abstract PDF(846KB) icon1697 icon446
Abstract:
Several direct-connect hot tests were done for a variable-area propelling nozzle dual-mode ramjet model combustor on the simulated fly condition of Ma=6 and H=25km. By use of the variable-area propelling nozzle, ignition performance and thrust of the dual-mode combustor were improved. Once flame can be hold in the combustor during subsonic combustion procedure, the supersonic combustion can be achieved by adjusting nozzle area thus a mode transition can be realized also. Finally, It is promising that the operating region of a fixed-geometry dual-mode ramjet can be extended by the variable-area propelling nozzle which simplified a fully variable dual-mode ramjet.
3D heat transfer investigation on plug nozzle in different operation condition
HAN Fei, LIU Yu
2007, 22(4): 632-638.
Abstract PDF(1218KB) icon1555 icon386
Abstract:
To understand different heat transfer characteristics of regenerative cooling in plug nozzle in different operation conditions,computational model of three dimension plug nozzle was established and numerical simulation was employed.Pressure,heat flux and temperature contour in different operation conditions were obtained.Governing equations were discretized with one order upstream scheme.The results show:at lower pressure ratio,heat transfer condition on the plug surface is the worst,peak values of pressure and temperature appear along the wall of plug nozzle,temperature and temperature gradient along the section of wall reach the highest.
Performance calculations and analysis of multi-module aerospike nozzles with round to rectangle inner nozzles
WANG Yi-bai, WANG Chang-hui, LIU Yu, QIN Li-zi
2007, 22(4): 639-644.
Abstract PDF(460KB) icon1885 icon411
Abstract:
Based on an non-oscillatory and non-free parameters dissipation difference (NND) scheme to solve three-dimensional Reynolds averaged Navier-Stokes equations, performance calculations and analysis of multi-module aerospike nozzles with round to rectangle inner nozzles were investigated. Flow characteristics and performance of four inner nozzles including bell nozzle, two-dimensional nozzle, round to square inner nozzle and square throat to square exit nozzle were compared. Then performance of round to rectangle inner nozzles that have different structures such as contour changing points, contours after changing points and exit arc radiuses were discussed. The effects of different structures of inner nozzles, different nozzle obliquities and different plug contours on the multi-module linear aerospike nozzles were also presented. And a design scheme of the optimized aerospike nozzle was given. Conclusions can provide some reference for studying design of the multi-module linear aerospike nozzles with round to rectangle inner nozzles.
Applications of numerical optimization techniques to design of axial compressor blades
Choon-Man Jang, Kwang-Yong Kim
2007, 22(4): 645-652.
Abstract PDF(595KB) icon1334 icon483
Abstract:
This paper describes the shape optimization of NASA rotor 37 and rotor and stator blades in a single-stage transonic axial compressor.Shape optimization of the blades operating at the design flow condition has been performed using the response surface method and three-dimensional Navier-Stokes analysis.Thin-layer approximation is introduced to the Navier-Stokes equations,and an explicit Runge-Kutta scheme is used to solve the governing equations.The three design variables,blade sweep,lean and skew,are introduced to optimize the three-dimensional stacking line of the blades.The objective function of the shape optimization is an adiabatic efficiency.Throughout the optimization of rotor and stator blades, optimal blade shape can be obtained.It is noted the increase of adiabatic efficiency by optimization of the blade shape with the stacking line in the single-stage transonic axial compressor is more effective in a rotor blade rather than a stator blade because of the large deformation of blade shape in the stator blade.
Development trend of short-duration turbine experiments
ZHAO Xiao-lu, TANG Fei
2007, 22(4): 653-659.
Abstract PDF(666KB) icon1457 icon431
Abstract:
The development and expansion of overseas short-duration turbine testing techniques were summarized and analyzed by comparing the advantages and disadvantages of short-/long-duration turbine testing techniques. Spurred by the demand of developing high performance aeroengine, the short-duration turbine testing technique was improved greatly to achieve the measurement accuracy of long-duration turbine testing technique.The purpose of short-duration turbine testing technique is to replace partially long-duration turbine testing technique by developing from a mechanics investigation platform into a performance investigation platform. As an important basic study platform, short-duration turbine testing platform has developed in the mechanism research field and has now been applied to validation of new design concept and check of CFD software.
Influence effect of supersonic airfoil’s leading edge geometric shape on aero-dynamical performance of cascade
JIN Jun, LIU Bo, NAN Xiang-yi, CHEN Yun-yong
2007, 22(4): 660-665.
Abstract PDF(1017KB) icon1619 icon479
Abstract:
NURBS method was applied to reshape some supersonic airfoils, and two controlling parameters were used to adjust the geometric shape of supersonic airfoil’s leading edge, these methods were adopted to investigate the supersonic airfoil’s aero-dynamic performance influence effect with different leading edge geometric shape; The contrastive analysis results, which were obtained from a series of airfoil’s flow field structure with changing each controlling parameter, shown ellipse shape controlling factor not only could weaken the shock wave intensity near the leading edge region of airfoil but also could improve the flow field structure; At the same time, this paper demonstrated that the matching between some ellipse shape controlling factor and some ellipse direction controlling factor could make the responding supersonic airfoil’s aero-dynamic performance reach to the best while its chord keeping no change.
Research on bearing cage through expanded-model test
YANG Ru-ping, DENG Si-er, LI Jian-hua, MA Fu-jian
2007, 22(4): 666-671.
Abstract PDF(528KB) icon1402 icon428
Abstract:
The dynamic similarity criterion of bearing cage was analyzed based on similarity theory.According to the model analysis theory,the similarity ratios of the main modal parameters were obtained to make an expanded model in the ratio of 3∶1,and test its dynamic performance.The inherent frequency of the real-size cage has been achieved from the test results,meanwhile the results were verified through dynamic response test on the bearing components.

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