Slot Influence in Boundary Layer Suction for Secondary flow control in a High Speed Compressor Cascade

Abstract

A numerical and experimental study is presented in order to clarify more the influence of a suction slot design with respect to mass flow rate and slot area in a compressor with active flow control for secondary loss diminution. While the numerical simulations unveil no influence of the shape at constant mass flow rates, the experimental investigations show such a dependency of the suction efeficiency. For the study a suction slot in side walls has been examined, the peacock slot in the junction between vane suction side and side wall at 50% to 100% chord, with a slot width of 0.6mm, 1mm and 2mm. The parameter study has in part been done numerically; the paper concentrates on the comparison with the experimental results at Mach number 0.67 and Reynolds number of 560.000. This experimental study shows the dependency of the efficiency of the cascade with the mass flow and the slot width, respectively. Both parameters can be varied independently. It is shown that the slot width has a remarkable influence on the efficiency. With larger slot widths, the mass flow rate can be increased. While a slot width of 0.6mm allows for only about 2% of the main mass flow to be sucked from the cascade, with a slot width of 2mm more than 5% of the main mass flow can be drawn off the compressor. An increased suction rate in combination with an appropriate slot design decreases the total pressure loss, as soon as the suction rate is high enough to guarantee a constant suction mass flow in the slot. Otherwise, a recirculation appears that destroys the effect of the flow suction.