Experimental and numerical investigation on the flow field within a compact inlet duct

A combined experimental and numerical investigation of the flow field in a short, rectangular, diffusing S-shape inlet duct was conducted. The inlet duct had a length-to-hydraulic diameter ratio of 1.5 and an inflow Mach number of 0.44. The flow field was diagnosed utilizing stereoscopic particle image velocimetry, surface static pressure measurements, and high frequency total pressure measurements both on the lower surface and at the duct’s aerodynamic interface plane. To complement the experimental investigation and to aid in understanding the flow field associated with this complex geometry, a numerical flow simulation was undertaken. The flow field exhibited massive flow separations and shear layer formations at both turns of the compact inlet. Moreover, secondary flow structures along the duct’s lower surface and along the duct’s side walls were identified. It was shown that the two counter-rotating flow structures along the duct’s lower surface resulted in high levels of total pressure loss at the aerodynamic interface plane. A high fidelity spectral analysis of the pressure signals at the aerodynamic interface plane and along the lower surface was conducted and demonstrated that a high frequency surface static pressure sensor could identify flow separation in a non-intrusive fashion, allowing for future use in a closed-loop control scheme for active flow control. This work was part of a more comprehensive study which was to utilize active flow control to improve performance metrics of such compact inlets.