Effects of Pulsed Jet Intensities on the Performance of the S-Duct

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The high curvature of modern S-ducts causes a strong secondary flow, which seriously affects the uniformity of the compressor inlet flow. In this study, the flow control method of a pulsed jet was applied in the S-duct at an incoming Mach number of 0.4. The jet holes were with an angle of 45° and were symmetrically distributed on the upper wall. Three jet intensities of 0.16%, 0.24%, and 0.31% were simulated using the unsteady Reynolds-averaged Navier–Stokes equations (URANS) and were validated by experiments. The mechanism of the pulsed jet, with respect to controlling the flow separation in the S-duct, was analyzed through secondary flow behaviors and boundary layer characteristics. The results indicated that the radial and axial pressure gradients were crucial to the formation of the large-scale vortices and reversed fluids in the S-duct. The pulsed jets were found to resist the adverse pressure gradient by exciting the turbulent kinetic energy of the boundary layer fluids. In addition, the dissipation process of vorticity was accelerated due to the promotion of the mixing effect by these devices. Moreover, in the current study, the area with high total pressure loss coefficients decreased gradually along with the intensity increase. Specifically, a maximum loss reduction of 5.9% was achieved when the pulse jet intensity was set to 0.31%, which means that the pulsed jet has great potential in controlling the flow separation in the S-duct.