Aero-Optical Mitigation of Shocks Around Turrets at Transonic Speeds Using Passive Flow Control

Abstract

Experimental studies of the aero-optical effects around a partially-protruding cylindrical turret for a range of incoming transonic Mach numbers are presented and discussed. Spatially-temporally resolved wavefronts were collected using a high-speed Shack- Hartmann sensor and flow visualization was performed with a Schlieren system. Different flow regimes with a local shock, either a steady or an unsteady one, were described for the baseline case and the shock dynamics was found to be sensitive to a local flow speed. In addition, several passive flow control devices, consisted of a single spanwise row of vertically-placed small-diameter pins or porous screens, were tested in order to mitigate detrimental unsteady-shock-related aero-optical effects. It was found that passive flow control devices with large blockage values slowed the flow near the cylinder surface down to subsonic speeds by introducing total pressure losses in the wall region upstream of the cylinder, thus eliminating the shock formation over a wide range of transonic Mach numbers and significantly improving aero-optical environment at some elevation angles.