Transonic Centrifugal Compressor Three-dimensional Flow Field Numerical Analysis

Compressor stall and surge which tie up and discriminative with each other are two difference non-steady flow phenomena. Compressor surge can lead dramatic fluctuations in impeller, even destroy the compressor. Rotating stall is a precursor to the pre-surge, depth analysis of the rotating stall is an important prerequisite and foundation to control compressor surge.In this paper, adopt three-dimensional numerical simulation method, using CFD technology to simulation some centrifugal compressor. One literature of NASA provided the compressor and diffuser blade computing model data set and use analytic geometry approach to process the arc of compressor blade leading edge. Then establish the compressor and the diffuser geometry model, and build three different mesh density of high, medium and low of the computational domain model, respectively, calculate 80% and 100% working condition of the three kinds of mesh density model for steady-state numerical calculation. By comparing three kinds of mesh density in the high and low operating conditions of the flow field characteristics, the pressure distribution properties, compressor performance, and numerical simulation results of machine errors, found that three kinds of mesh density model results more or less, compressor characteristics also the same, thus proving that low-density grid to fulfill the requirements of the compressor characteristic simulation.Use low-density grid to establish the compressor and diffuser calculation model for the entire machine to carry out three-dimensional unsteady calculations nearly the compressor surge point. This paper mainly studies the compressor stall phenomenon near the surge point. From calculation found that the event of compressor rotating stall has emerged asymmetry at the diffuser flow channel before it happens, and this non-uniform flow field distribution in the calculation of different moments also change. Before the stall occurs in the diffuser blade pressure surface and suction surface have emerged out of gas separation, and the location of gas separation change over time expand from the root to the tip of the blade.By calculating, when the compressor is running at high operating conditions, the rotating stall occurs faster, the stall frequency is 26.5Hz, and the range of compressor stall occurs in the compressor characteristics map corresponds to a very narrow range, the compressor surge immediately occurs after the rotate stall, in the calculation of 13th round, the compressor get into the deep surge, this coincide with the actual characteristics of the compressor. This study laid the theoretical foundation and pre requisite for further using active flow control technologies, such as diffuser hub or shroud jet active control the centrifugal compressor surge.