Research On Inverse Method For Centrifugal Compressor Blade Design

With inverse method allowing the relationship between the geometry of the blades and the flow parameters, the blade meeting the requirements can be solved depending on the specified parameters. Compared with the analyzing design method, inverse method has multiple advantages such as short-period design, clear designing direction, weak dependence of designers' experiences and so on. The flow and the distributions of flow parameters distribution in centrifugal compressors are complex. Allowing the direct control over the specified flow parameters, inverse method is an attractive and efficient method for the centrifugal impeller blade design. Basing on the research on the inverse method of axial compressor blades carried out at the Von Karman Institute, this paper puts forward a three-dimensional inverse method that is suitable to design the blade of centrifugal compressor impeller. The inverse method is built in view of the strong three-dimensional flow characteristics and blade profiling of centrifugal compressor blade. The inverse method is employed to for redesigning the blade of centrifugal compressor impeller. The main research work of this paper includes:1. The analysis of the key principle of the inverse method for the compressor blade and its valid confirmation.Based on the discrete compatibility relation inferred from the unsteady Euler equation, the principle of permeable wall boundary is analyzed in this paper. Tracking Streamline is achieved by applying the conservation of mass in the cell between the wall and the streamline. Using a centrifugal compressor impeller as an example, the consistent comparison of numerical results between direct and inverse methods at the same wall pressure is studied. The validity of the permeable wall boundary condition for the numerical computation of the centrifugal compressor is verified.2. Research on the modification of inverse methods in dealing with the strong three-dimensional flow characteristics in centrifugal compressorThrough theoretical analysis and numerical computation, it is shown that there are violent three-dimensional flow characteristics including the slip and radial flow in the centrifugal compressor impeller. The strong three-dimensional flow leads to the deviation between streamlines near the blade surface and the blade surface. This fact brings about an inherent offset if using the method proposed by VKI to solve the blade surface of centrifugal compressor impellers. The method proposed by VKI solves the blade surface based on the idea that inviscid streamlines coincide with the blade surface. In order to improve the accuracy of solving the blade surfaces, the surface modification based on the relation of streamlines between direct and inverse flow field is proposed and studied.3. The inverse design program is realized, which is suitable for the structural characteristic of centrifugal compressor bladesWith load and thickness being prescribed parameters, the inverse design program is realized and the constraining mechanism is achieved. The validity of constraining mechanism is verified by the returning test. By analyzing the work principle of centrifugal compressors, the decoupling of the pressure on the blade surface is done. The reduced pressure and the centrifugal pressure are investigated in this paper. The optimization of pressures on the centrifugal compressor impeller blade should focus on the reduced pressure, which stands for the loads of blades. For convenience of giving the target parameters, the parameterization of pressure based on the Bezier spline is done. The preliminary optimization principles of the pressure distribution are put forward.4. The redesign of centrifugal compressor impellers by the inverse design programRespectively through inviscid and viscous inverse design program in this paper, an impeller is redesigned. According to the computational simulation using Euler equations, compared with the initial impeller, the peak isentropic efficiency of the new impeller obtained by the inviscid inverse design program is increased by 0.48%, and the pressure ratio increases by 1.05%. According to the computational simulation of using N-S equations, compared with the initial impeller, the peak isentropic efficiency of the new impeller obtained by the inviscid inverse design program is increased by 1.08%, and the pressure ratio increases by 0.87%. According to the computational simulation using N-S equations, compared with the initial impeller, the peak isentropic efficiency of the new impeller obtained by the viscous inverse design program is increased by1.38%, and the pressure ratio increases by 1.05%.