Design Optimization of Axisymmetric Endwall in Axial.doc
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1、精品论文Design Optimization of Axisymmetric Endwall in AxialCompressor S-Shaped DuctJin Donghai, Zhao Weiguang, Gui Xingmin5(School of Energy and Power Engineering, Beihang University, Beijing 100191) Abstract: This paper presents a numerical investigation on the potential aerodynamic benefits of using
2、endwall contouring in a fairly aggressive duct with six struts based on the platform of the endwall design optimization. The platform was built with Adaptive Genetic Algorithm (AGA), Design of Experiments (DOE), Response Surface Methodology (RSM) based on the Artificial Neural Network10(ANN) and a 3
3、D Navier-Stokes solver. Visual analysis method based on DOE was used to define the design space and analyse the impact of the design parameters on the target function (response).Optimization of axisymmetric endwall contouring in the duct has been performed and evaluated. The objective was to minimiz
4、e the total pressure loss. The optimal duct was found to reduce the hub corner separation and suppress the migration of the low momentum fluid. The axisymmetric endwall15contouring was shown to suppress the separation and reduce the net duct loss by 22%.Keywords: s-shaped duct; axisymmetric endwall;
5、 design optimization; secondary flow0IntroductionAn S-shaped duct is used to connect the low pressure and high pressure compressors of20aircraft gas turbine engines. Within the duct, flow separation should be avoided to minimize the total pressure loss. In addition, a uniform flow filed at the duct
6、exit should also be achieved. However, modern turbo-fan engines demand on improved efficiency and reduced noise level which lead to high by-pass ratio. These demands result in engines with large fans and small high pressure compressors which will bring about a significant radial difference between t
7、he25low-pressure and high-pressure systems. The higher by-pass ratio is, the more aggressive S-shaped ducts are needed. This makes duct design increasingly important. Firstly, transition ducts play a significant role in determining the overall length and weight of the engine. The advantages are obvi
8、ous if the duct length could be shorten without other penalties. Secondly, if the thickness of the non-turning struts in the duct could be increased, then it would allow improved service access30to the core of engine.Several researchers have investigated the flows in S-shaped ducts. Bailey1 investig
9、ated the aerodynamic performance of a compressor S-shaped duct with a single strut (thickness-to-chord ratio is 0.12). The blockage of strut was found to have a significant effect on pressure field of the duct, which has a direct influence on the turbulent flow field. Ortiz Duenas et al2 had35experi
10、mentally investigated the effect of reducing the duct length and keeping duct inlet height (hin) and inlet to exit radius change ( R ). It was found that the length of original duct without strut reducing to 74% caused a small rise in loss, However, reducing the length to 64% caused a much larger ri
11、se in loss. The researches have shown that the limit of the design space of annular S-ductsis set by duct corner separation. Reducing the length or increasing the change in radius or the40thickness-to-chord ratio has a similar effect on ducts performance. The streamlines with the highest deceleratio
12、n occur in the hub-strut corner and the flow might occur to separation. The separation results in a sharp rise in duct loss coefficient, and a large-scale blockage entering the downstream compressor.In order to reduce the extent of the corner separation and avoid higher loss coefficient in45ducts, t
13、he focus lie on intermediate S-shaped duct endwall profiling and its influence on the flowBrief author introduction:Jin Donghai, (1977-), male, associate professor, aerodynamic design optimization of turbomachinery and research of secondary flow mechanism. E-mail: - 11 -field in the 3D annular duct
14、in this paper. A numerical optimization coupling with Adaptive Genetic Algorithm (AGA) and Response Surface Methodology (RSM) is undertaken to design the axisymmetric endwall profiling. Finally, the performance of optimal endwall profiling is compared with the original S-shaped duct.501Endwall desig
15、n optimization methodThe use of design optimization in turbomachinery is possible today thanks to Computational Fluid Dynamics (CFD) analysis. Fig.1 shows the algorithm of the endwall design optimization system. One of its advantages is the use of a response surface model based on an Artificial Neur
16、al Network (ANN) to approximate the goal-function. It reduces the tremendous computational cost55of evaluating the endwall performance by 3D-CFD.The optimization system consists of three steps. The first one is the training of ANN based on the database provided by the Orthogonal Design of Experiment
17、 (ODOE). The second one is the prediction of the optimal aerodynamic performance of endwall contouring by the combination of AGA and ANN, as shown in Fig.1 with red arrows. Finally, comparison of the performance60obtained by CFD with one predicted by the ANN is performed. If the design requirements
18、are not achieved, the evaluations computed by CFD are added to the database and the cycle is repeated until the optimal geometry is obtained. For a more detail description of the optimization method,please refer to JIN3,4 and NING5. The following subsections summarize some components andtheir applic
19、ation.StartODOEDesignVariablesEnd wallCountouringFlowSolverAGADesignVariablesPerformancePredictionANNPerformanceAnalysisDatabaseTrainingEnd65Fig. 1 Endwall design optimization system1.1Endwall parameterizationFig.2presentstheparameterizationof axisymmetric endwallcontouring.The70parameterization was
20、 performed using a B-Spline curve controlled by six points in axial direction.The axial direction represents the direction of engine axis. In order to maintain C0 continuity of endwall contouring in axial direction, points 1 and 6 are fixed. Second point from each end of the curve is used to maintai
21、n an approximate C1 continuity. For instance, height of the dependent control point 2, as shown in Fig. 2, is set in the way that the slop of line passing through points 175and 2 is close to the slope of starting of contoured. The independent control points 3 and 4 canmove freely. So, there are four
22、 design variables for each endwall.12Fitted b-spline Control polygon Fixed control pointsDependent control points3Independent control points456Fig. 2 Axisymmetric endwall parameterization1.2Design of experiment80It is well known that the purpose of using RSM is to construct an approximation of the t
23、rue goal-function (response) from training datas. The accuracy of RSM mostly depends on the quality of the training data selection. In order to minimize the size of training data, a reasonable strategy for training data selection needs to be application. This theory of choosing suitable designs for
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