The Effect Of Rotating Stall On Performance Of A Centrifugal Compressor With Adjustable Inlet Guide Vanes

Centrifugal compressor is an equipment to convey gas and increase the gas pressure.It plays an important role in many areas of the national economy.The development level of centrifugal compressor is one of the symbols to reflect the overall industry strength of a country.Due to the urgent demand of the rapid developing industry,it attracts considerable attention that how to keep centrifugal compressors operating at both high pressure ratio,high efficiency and safe condition.Nowadays,as an unsteady flow,rotating stall limits the steady working range of compressors and threats their reliability seriously.Considering the unremitting pursuit of centrifugal compressors with not only high load,high efficiency but also large safety margin and high mechanical reliability,it's greatly meaning to study on the aerodynamic characteristics of rotating stall.Research on the mechanism of rotating stall and its aerodynamic influence on centrifugal compressors is valuable to broaden the scope of the stable operation of centrifugal compressors and to improve performance design further.This paper chooses a centrifugal compressor as the research object.Steady and unsteady calculations are performed by CFD technology.Calculating model consists of adjustable inlet guide vanes,unshrouded impeller,vaned diffuser and volute.The whole annulus is used to show the circumferential non-uniform fluid field.Simulations is performed according to two real operating conditions.The paper is organized as follows:Based on the asymmetric rectangle volute of the centrifugal compressor,three kinds of hybrid grid is compared first.Computing scale,the precision of results and the ability to capture the details of flow field are considered.It aims to provide a reference of asymmetric rectangle volute meshing in the simulations of rotating stall in centrifugal compressor.In the second section,numerical analysis to rotating stall of the centrifugal compressor is done.Combined impeller internal unsteady flow field and the aerodynamic excitation on blades,aerodynamic characteristics of rotating stall in summer condition of the centrifugal compressor is analyzed in details including the characteristics of stall cells,development process,propagating mechanism and the aerodynamic excitation on blades in both time and frequency domains.It turns out that tip clearance flow plays a pivotal role in both the origin of unsteady flow and the spread of stall cells.Flow instability incepts by the mixing of tip clearance flow and main flow.Tip clearance flow spillage below the blade tip at leading edge is a criteria for formation of spike rotating stall disturbances in centrifugal compressors which leads to spike stall cell formation.The third section includes two parts.The influence of the opening of inlet guide vanes(IGV)over rotating stall is investigated in the centrifugal compressor first.Compared with IGV=30°,rotating speed of stall cells is slower in IGV=50°condition.Besides,the development process and the frequency composition of aerodynamic excitation are more complicated.The impeller blade aerodynamic load is increased obviously.Then,a smaller tip clearance at leading edge is tried to weaken the instability of rotating stall.The result shows that the decrease of leading tip clearance height can effectively improve the flow field of rotating stall.It also changes the characteristics of rotating stall and reduces the blade aerodynamic load.