Performance Improvement Of Centrifugal Compressor With Static Components Based On Energy Gradient Theory

Centrifugal compressors consume a lot of energy in industries. Enhancing the efficiency of centrifugal compressors can make full use of the limited energy and increase economic benefit. Although many researchers have made much effort to improve the performance of centrifugal compressors, efficiency and flow stability remain to be two issues to be resolved. In recent 20 years, along with development of numerical calculation technology, CFD method can be used to shorten the cycle of research and development. It can reduce a lot of experimental cost, so that it has become widely used. In this thesis, CFD method is used to simulate flow field of centrifugal compressor, and the energy gradient theory is applied to analyze stability of internal flow. On the basis of distributions of energy gradient function K, improvement measures are put forward for static components including diffuser and return channel. Some attempts and explorations are performed to research flow stability and study on performance optimization of centrifugal compressor according to analysis results of the energy gradient theory.In this thesis, the main contents include the following aspects: 1) studying on internal stability of centrifugal compressor model stage based on the energy gradient theory; 2) optimizing structure of vaned diffuser on the basis of analysis results of the energy gradient theory; 3) optimizing structure of return channel to improve performance of centrifugal compressor model stage. First, computational domain is obtained including impeller, vaned diffuser and return channel. Structured hexahedral cells are generated to define these zones. Experimental results are compared with numerical results with different density of girds and different turbulence models to determine suitable grid size and turbulence model. Then calculated parameters of whole flow field of centrifugal compressor model stage are obtained through numerical calculation, within the scope of discharge coefficient φ=0.12--0.168. Prediction curves of polytropic efficiency and pressure ratio are in good agreement with experimental results. Finally, improvement measures of vaned diffuser and return channel are put forward based on analysis of the energy gradient theory, and performance of improved model has a good improvement.All of analysis results in this paper demonstrate that it is feasible to apply the energy gradient theory in the study of internal flow in centrifugal compressor model stage. Distributions of the energy gradient function K provide theoretical guidance to optimize the performance of centrifugal compressor model stage. It is meaningful to research stability of internal flow and deepen the theory of performance improvement of centrifugal compressor.