Numerical research of the velocity at the inlet to 2D and 3D impeller blade cascade

Recently, the interest has been returning to the design of the new series of compressor model stages and their experimental verification. Two series of model stages were designed at the scientific and research laboratory "Gas Dynamics of Turbomachines" in the framework of cooperation with an industrial partner. The calculation results showed a sharp decrease of the efficiency for low mass flow rate stages in comparison with medium mass flow rate ones. Analysis and comparison of the flow parameters showed that the cause is sharply increasing losses in the impellers. The relative velocity at the entrance of the impeller blade cascade was calculated by the Universal Modeling Method, increases sharply, which leads to an increase in losses, despite the fact that according to the results of profiling, in the program of inviscid quasi-three-dimensional calculation. Its value should be moderate. A numerical study was conducted for solving the problem. The aim of the study was a comparison of the velocities at the entrance to the impeller blade cascade that was calculated according to the 3DM.023 inviscid quasi-three-dimensional calculation program and according to the Universal Modeling Method program. The approximating formulas of coefficients have been created that take into account velocity differences separately for 2D and 3D impellers. The RMS approximation accuracy for 2D impellers is 88.3%, for 3D impellers - 99.1%.