Numerical study of the effect of the tip gap size and using a single circumferential groove on the performance of a multistage compressor

The effect of the tip gap size on the performance of a multistage axial compressor was studied by means of computational fluid dynamics (CFD). It was found that the performance of the compressor was very sensitive to the size of the tip gap. By increasing the gap size, the stall margin value, the total pressure ratio and the compressor efficiency reduced considerably. The flow field at the tip region of the blades at the near-stall point showed that the size of the blockage grew with an increase in the gap size.  Afterward, the effect of various single circumferential grooves- having specified widths and depths at different placement positions- on the performance were investigated in the reference gap. The stall margin increased about 7% with negligible reduction of the peak efficiency using one of the grooves which placed next to the trailing edge of the first-stage rotor. Also, this groove increased the stall margin in other tip gap sizes. Investigation of the flow field of the tip region in the reference gap showed that when the groove was used, there was a reduction in the back-flow near the trailing edge of the first-stage rotor. Consequently, the stall occurred at a lower mass flow rate.