Experimental and Numerical Investigation of grooved shroud Effects on Tip Leakage Fluctuation in an axial compressor

In this paper the effect of the casing treatment on suppression of rotating stall in an isolated axial compressor rotor blade row has been experimentally investigated. The continuous grooved casing treatment, covering the whole compressor circumference, is of 1.8 mm in depth located between 90% and 108% of the blade tip chord measured from its leading edge. Measurements of unsteady pressure in compressor’s casing as a stall precursor have been made using high frequency responce pressure Kulite sensors positioned in properly pressure taps. Results obtained from these latter measurements together with signal frequency analyses, provides the description of the stall process and consequent flow induced fluctuations and also stall alleviation due to casing treatment. The results show that casing treatment has augmented the loading coefficient, indicating improvement in the blade row performance. Hence, stepped tip gap extends the stable operating range of compressor and delays the occurrence of stall phenomenon. Results of the present research, show that by using stepped tip gap, stall margin of the proposed compressor was improved by 6%. Numerical results show that the Casing treatment causes flow blockages to reduce due to alleviation of backflow regions. Eventually, it can be concluded that the casing treatment of the circumferential groove type could increase the stall margin of the compressor.