Control of unsteady separated flows inside axial compressors by synthetic jets

By means of planar cascade wind tunnel experiments and relevant numerical simulations, synthetic jets have been used to control boundary layer unsteady separation from the suction side of a compressor airfoil. The reliability of the numerical simulations was validated by experimental results, and optimal analyses of various excitation parameters were carried out by means of numerical simulations. The excitation effects reached the best when the unsteady excitation frequency is equal to (or close to) the characteristic frequency of trailing edged vortex shedding, when the excitation was forced at the separation point and when the excitation direction was vertical to the profile. Generally, the larger the excitation amplitude, the better the excitation effects. The studies showed that this kind of unsteady excitation could regulate boundary layer evolution and development, promote the merging of small vortexes and enhance time-averaged aerodynamic performances in wide incidence, in which the loss coefficient decreases from 0.297 to 0.232 (δω̄=-21.9%), and the static pressure ratio increases from 1.058 to 1.103 (δp̄ =77.6%). Based on these optimal analyses, the discrepancy between the experimental and simulation results could be explained, and an improved experiment scheme was thereby put forward.