Comparison of active and passive control techniques for flow field quality in a linear cascade wind tunnel

The flow quality of the linear cascade tests for compressor airfoils is always poor under high-load conditions, it is necessary to improve flow quality of linear cascade by adjusting methods to ensure the availability of test data. A passive control scheme of adjustable tailboard was designed based on a subsonic linear cascade wind tunnel. The effect of tailboard angle on flow quality and performance of cascade was investigated, and compared with the results of active control scheme of upper end-wall suction previously studied. The results indicate that the tailboards adjust the flow quality by changing the exit static pressure distribution. As the tailboard angle decreases, the exit static pressure near the upper tailboard decreases while it increases near the lower tailboard, leading to an improvement in the cascade flow quality. However, if the tailboard angle is decreased beyond a certain limit, the uniformity of the inflow and the periodicity of the outflow will decline. Therefore, to achieve the best overall flow quality, the tailboard angle needs to be controlled within a specific critical range. And the outlet flow angle shows the best periodicity due to the isolating effect of tailboard, with a periodicity index less than one. The flow quality of cascade declines when the tailboard angle is over the critical value. The improvement of inflow quality of cascade by upper end wall suction is better than that of tailboard. Due to the difference of control mechanism and flow quality between these two methods, the outlet flow angle of cascade adjusted by tailboard is about 2° smaller than that of upper end wall suction, and the loss is about 0.02 larger than that of upper end wall suction. The difference of static pressure ratio and distribution of isentropic Mach number between the two methods is small.