Numerical Simulation And Mode Decomposition Of Unsteady Flow In Centrifugal Compressor

Unsteady flow phenomena may occur in the components of the centrifugal compressor when the mass flow rate goes small,such as stall and surge.These phenomena not only severely limit the safe and stable flow range of the centrifugal compressor,but also plant hidden dangers for the systems working in changing operating conditions,sometimes even lead to tragic crash.In order to eliminate the above-mentioned situations and enhance the reliable flow range of the centrifugal compressor,it is necessary to carry out in-depth study on unsteady phenomena occurring at small mass flow rate.In the paper,the POD and DMD mode decomposition methods were applied to analyze the flow field date obtained by the CFD numerical simulation of vaneless diffuser and volute.The characteristic structures modes with high energy ratio were caught at various mass flow rates,which offered detailed information to study the unsteady phenomena.Following are the main work and findings of this research project:1.The numerical simulation of Honeywell's GT70 centrifugal compressor was carried out by CFD method.The geometrical throttle valve structure was simulated by the dynamic mesh technique at the outlet of the exhaust pipe.2.The results of numerical simulation were given as blow: the characteristic curve of the whole centrifugal compressor;the spectrum analysis of the data at monitoring points;the original flow field of vaneless diffuse and volute under several kinds of view angles at 1.8kg/s design conditions,1.4kg/s mild surge condition and 1.0kg/s surge condition.3.The POD and DMD methods were used to decompose the flow field data of vaneless diffuser at 1.8kg/s design condition.The large-scale structures with high energy ratio in the original complex flow field were captured successfully like average flow field,Jet-Wake structures.At the same time,the resolution accuracy and the amount of information provided by these two mode decomposition methods were compared.4.The DMD method was used to decompose the flow field in the vaneless diffuser and volute at 1.4kg/s mild surge condition.Average flow field,Jet-Wake structure and unsteady flow structures were successfully identified.At the meanwhile,the vaneless diffuser was divided into six parts to finish the 3D DMD decomposition.5.Single-mode reconstruction of the stall mode at 1.4kg/s mild surge condition and 1.0kg/s surge condition were carried out.The development and propagation of unsteady flow structures inside the vaneless diffuser and volute was studied.