Simulation of Various Turret Configurations at Subsonic and Transonic Flight Conditions Using OVERFLOW

Abstract

In this work, the flow fields associated with two canonical turret geometries, a fully exposed hemisphere on a flat plate and a 50% submerged hemisphere on a flat plate, were simulated using the OVERFLOW 2 flow solver. Both turret geometries utilize a flat-window aperture with an aperture ratio (ratio of the aperture diameter to the turret diameter) of 0.295 and an elevation angle of 57 • . The forward field of regard was the particular focus in this study, and both symmetric (azimuth angle of 0 • ) and asymmetric (azimuth of 45 • ) window orientations were examined. Two flight conditions were also studied; a subsonic case with M = 0.45 and ReD = 6.30 × 10 6 and a transonic case with M = 0.85 and ReD = 9.53 × 10 6 . The flow field was simulated using the Delayed Detached Eddy Simulation capability of OVERFLOW in conjunction with the spatially fifth-order Weighted Essentially Non-Oscillatory (WENO) scheme to capture the off-body vortical structures The incoming boundary layer was set a the same height for both geometries, which corresponded to a quarter of the height of the fully exposed hemisphere and half of the height of the submerged turret. The impact of the turret aerodynamics on the performance of the turrets for directed energy applications is inferred through consideration of the flow features, density and pressure fluctuations, and forces on the turrets.

Modal Analysis of the Surface Pressure Field Around a Hemispherical Turret using Pressure Sensitive Paint

“…This work includes characterizing both the aerodynamic [1,2,3] and aero-optic [4,5,6] performance of the flow around the turrets at subsonic and transonic speeds. In addition to these experimental studies, there have been extensive CFD studies into the flow around hemispherical turrets [7,8,9,10,11].…”

“…One way to study the shock-wake coupling is to analyze the spatio-temporal pressure field on the surface of and around the turret using fast-response Pressure Sensitive Paint (PSP). PSP measurements are based on oxygen-sensing molecules known as luminophore, which fluoresce when exposed to ultraviolet light [8,9]. Before the luminophore is added to the model surface, a permeable paint binder is applied, which allows oxygen diffusion.…”

Comparison of Aero-Optical Measurements from the Flight Test of Full and Hemispherical Turrets on the Airborne Aero-Optics Laboratory

“…Recently, additional CFD studies on both flat and conformal window turret configurations at subsonic and transonic speeds have also been performed [6], where flow fields around a hemisphere-only turret and a submerged hemisphere turret were computed and compared. It was shown that, on one end, altering turret geometry can reduce the size of the necklace vortex, but on the other end, it might have a larger effect on aero-optical distortions at forward-looking angles as the aperture will be closer to the vortical structures near the bottom of the turret; the same is true of the full hemisphere-on-cylinder turret and the hemisphere-only turret.…”

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

“…There has been a large parametric study of the aero-optical properties of this geometry in flight using the Airborne Aero-Optics Laboratory, AAOL [2,3]. Additionally a variety of CFD studies have been performed on the turret geometry [4][5][6][7]. Finally, various flow control mechanisms have been studied on this geometry [7,8,9].…”