Numerical investigation on the design of circumferential groove casing treatments in a radial compressor

A parametrized numerical study is performed to assess the design of circumferential grooves in a radial compressor. The validation with experimental data shows good agreement for the baseline case. Groove location, shape and number are varied, based on an initial design. The results show clear trends, which correlate with the impeller performance. Improvements in terms of pressure rise and efficiency are observed for groove locations towards the inducer. Moreover, high inclination angles and a normalized width at the casing of 4% to 10% of the meridional blade length are found to be most effective for all locations. Results obtained with multiple groove configurations suggest that the respective single groove effects can be partially superimposed and do not degenerate the performance by interference. The subsequent evaluation of the near tip flow field shows a weakening and deflection of the tip vortex for inducer grooves resulting in decreased blockage. Additionally, a splitter blade leading edge separation, emerging towards lower flow rates, is effectively suppressed. This is supported by grooves in the bend region, which prevent local leakage backflows.  In contrast to that, grooves near the outlet are found to be ineffective as losses increase.