Research On Parametric Design Of A Kaplan Turbine Airfoil And Blade

It is great potential for China to explore the hydropower resources, but the utilization of exploitable hydropower is much lower than that in the developed countries from Europe and the United States. Therefore, supporting by the national policy, there is a rapid devepment for China’s hydropower. A large proportion of Kaplan tubines are among them, but when the traditional hydraulic method to design Kaplan turbine combined with modern design theory and CFD calculation optimization, some model experiments are still needed which have to cost much time and money. However, parametric method based on existing model can change the blade profile more flexibly to generate the 3D blades for CFD analysis, which can save much time and manufacture expense. So it is necessary for parametric method to apply to the geometry and optimization design of runner blade airfoil. In this paper, a modeling method to design Kaplan turbine 2D airfoils and 3D blades based on parametric curve design was proposed.The main research contents and innovations are as following:1. A system analysis and summary of regulation on the existing blade airfoils was made, and a parametric method to design airfoil was proposed preliminarily.The blade airfoils were extracted by different circular cross sections in the existing Kaplan turbine. Some airfoil characteristic variables, such as maximum thickness and the maximum thickness location, may be determined in the parameterization after drawing the inscribed circle with the characteristics of meridian contour and analyzing and comparing some different parameters in each cross section.Based on the aerodynamic performance distribution regulations of conventional airfoil, the airfoil was divided into four parts to parameterize. Muti-order polynomial relationship was used to fit the airfoil 4 parts respectively, the number of polynomial orders was obtained. The number and location of controlled points of the parametric curve were determined combined with the characteristics of the Bezier function. After modelling the airfoils in the Matlab, based on Bezier curve, the parametric method of 4 parts, 10 points and 10 parameters were determined to design airfoils.After that, the parametric method was applied to typical symmetrical airfoil NACA 0015 and one Kaplan turbine blade airfoil GOE 430. It can be concluded that when the method was applied to typical symmetrical airfoil NACA 0015, the similarity degree is at 87.2%, so the relative error is small. However, when this method is applied to one Kaplan turbine blade airfoil GOE 430, there is a big deviation, and the original airfoil similarity degree is only 69.9%, and there is a great influence on the overall performance of airfoil due to the deviation.2. In terms of the deviation of the preliminary parametric airfoil, an optimized parametric method was proposed to design airfoils.In order to improve the fitting precision of the parametric method, on the basis of the original parametric method, one controlled point was added at each side of the tail part of the airfoil to meet the fitting accuracy improvement. And the optimized method was applied to the previous deviation airfoil GOE 430, then to the typical symmetrical airfoil NACA 0015.When this optimized method is applied to the Kaplan turbine blade airfoil GOE 430, the parametric airfoil is relatively close to the original airfoil on the geometric shape, the similarity degree has been improved, over 85%. And aerodynamic performance is also improved. Then CFD calculation and flow field analysis were needed to simulate the optimized parametric airfoil to analyze the pressure coefficient on the both sides of the airfoil. After calculating lift and drag force coefficients of original and parametric airfoils at different attack angles, it could be seen that the parametric airfoil was better than the original one at 0°attack angle, while both performance of airfoils were similar at-5°and 5°attack angle.When this optimized method is applied to typical symmetrical airfoil NACA 0015, the parametric airfoil is much closer to the original airfoil on the geometric shape, the similarity degree is at 89.6%. And in terms of aerodynamic performance, simulated coefficients of lift and drag force is also much closer to the original airfoil.3. A parametric method based on optimized airfoil parametric method was proposed to design 3D Kaplan turbine blade.Based on airfoil paramrtric method, the airfoil setting angle and the maximum thickness and camber of different cross sections were parameterized. So the parametric method to design Kaplan turbine blade was made.In this paper, one Kaplan turbine blade was chosen as an example to validate its application. Each airfoil of different cross sections was chosen as the standard one to model the blade. Then the cross section at radius of 0.165 m was determined as the closest result by CFD simulation. After that, pressure analysis was needed to analyze the flow field. The parametric blade method can be applied to the three dimentional design of Kaplan turbine blade.