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.

Estimation of Aero-Optical Wavefronts Using Optical and Non-Optical Measurements

“…The shock creates unsteady density gradients in the flow and promotes an earlier separation of the flow off the turret. All these shock-related features add additional strong aero-optical distortions to the outgoing beam [5,9,10].…”

“…One approach is to manipulate the flow using the flow control. The passive flow control utilizes a porous screen, which introduces total pressure losses near the surface of the turret and, as a result, slows the flow down to subsonic speeds, thus eliminating the unsteady shock [10]. The active flow control shows some promise in directly manipulating the shock [11].…”

The Comparison of Unsteady Pressure Field over Flat- and Conformal-Window Turrets using Pressure Sensitive Paint

“…Thus, in order to find a Machnumber-independent POD modes, it is necessary to repeat PSP experiments at a higher Mach number of at least 0.4. Also, the outlined approach to analyze the unsteady pressure fields can be highly-useful at transonic speeds, where additional effects from a local shock on the separated flow from the turret are present [1,28].…”

Investigation of turbulent shock boundary interaction unsteadiness and its effects on aero-optics in a Mach 2 ramp flow

“…34 In terms of interaction of aeroptics with shock waves, the study by Gordeyev et al 31 placed a wedge in the windtunnel and measured through a weak mach wave. A more recent work by Gordeyev et al 35 looked at passive flow control devices to eliminate shock formation on a turret in transonic flow. Burns et al 36 investigated Artificial Neural Networks and Linear Stochastic Estimation to attempt to construct an estimated wavefront.…”