Influence of Active Flow Control on different kinds of Separation Bubbles - Experimental and numerical investigations with a highly loaded turbine exit case profile

摘要

The paper describes the influence of active flow control (AFC) by fluidic oscillators on the suction side boundary layer of a profile with different extent of flow separation. A highly loaded turbine exit case profile is used for the experimental investigations in a high speed cascade wind tunnel. Different sizes of the flow separation are gained by varying the Reynolds number at engine relevant levels. Without the usage of AFC an open flow separation is present on the suction side of the profile in the low Reynolds number regime. In this case the integrated total pressure losses can be reduced to about a quarter by AFC. The most beneficial tested actuation mass flow rate produces an oscillation frequency that is close to the estimated most amplified frequency according to linear stability theory. For moderate Reynolds numbers only short separation bubbles occur on the suction side of the profile. However, integrated total pressure losses can still be reduced by active flow control. For this operation mode the best results in terms of total pressure loss reduction are observed with an actuation mass flow rate without a detectable oscillation frequency. The paper aims at taking a closer look at the different kinds of separation bubbles by experimental as well as numerical methods in order to gain a better understanding of the working principle of AFC with fluidic oscillators.