Numerical Reserch On An Unshrouded Compressor With Holed Casing Treatment

Centrifugal compressors are widely used in many different areas especiallyin petro-chemical industry. The operating range of a compressor is limited by theonset of the well-known phenomena, rotating stall and surge. Therefore, a widevariety of stall and anti-stall research in centrifugal compressors is reported inthe literature.Based on a new type of self-adaptive casing treatment developed by theresearch group, this paper analyzed the internal flow in an unshroudedcentrifugal compressor by detailed numerical methods, including flow in thehole、tip clearance flow、unsteady flow, details as followed.1. Use BladeGen for the three‐dimensional modeling of the compressorpassage, and a structure mesh was grid by TurboGrid. A mesh with770000elements was selected according to the mesh‐independentvalidation, while SST turbulence model was adopted by the comparisonof the results of several different models with experiment. The casingtreatment was modeled by PROE, then an optimized structure mesh wasgrid by ICEM.2. The numerical simulation was based on1passage for the researchgroup in the past, this paper will use4passages to simulate the wholeworking range of the compressor both with and without casingtreatment. Flow details in the passage and holes are analyzed in threetypical working condition: near stall, near design and near choke.3. Steady calculation is not appropriate way to simulate the unsteady flowbehavior in the un‐designed working condition. Therefore, this papersimulate in unsteady method with steady outlet static boundarycondition. The result shows the performance of the compressor in theun‐design working conditions are different from the results of steadysimulation. A further analysis for the three typical working condition was done to get the details in the tip clearance and holes in compressor both with and without casing treatment.Due to the stationary calculation results are not suitable for simulation of compressor in the non‐design conditions of the unsteady flow characteristics, so this paper firstly adopts the same boundary conditions of the unsteady calculation method, the calculation results show that in the non‐design condition, the compressor characteristic curve is different from the steady calculation results. This paper studies the changes of tip clearance and characteristics of the flow in hole of the compressor in the machine box processing and inorganic box with three kinds of typical working conditions.4. Rotating stall or surge happened when the system flowrate was reducedduring the compressor operating process. To simulate the process,unsteady outlet boundary condition was provided. A linearly increasingback pressure from135kPa to139kPa in0.04s was set up.Besides, avariety monitors of pressure in different positions were created to getthe mechanism of stall and the influence of casing treatment.5. In order to get a better understanding of the parameters of the casingtreatment, this paper simulated different cases by adjusting threeimportant parameters, including different hole radical position, differentvan position, different van width, an optimized structure was obtain bycompare the performance of the compressor.