Analysis of the transonic flow around a generic UCAV configuration

Abstract

The present investigation has been carried out as part of the NATO/STO AVT-201 Task Group on “Extended Assessment of Reliable Stability & Control Prediction Methods for NATO Air Vehicles”. The SACCON configuration is considered. Its geometry as well as the low speed aerodynamics and the corresponding flow physics are well known from the literature: For medium angles of attack the flow around the leading edge is governed by three sections, namely an apex vortex in the front part, a region of attached flow in the middle portion and a tip vortex in the outer part of the leading edge. The size of these regions varies with the angle of attack. In the present study the compressible flow around this configuration has been calculated using the CFD TAU code in the Mach number range 0.55 ≤ M∞ ≤ 0.85 and angles of attack 0° ≤ α ≤ 16° for a constant Reynolds number Re = 23x106 corresponding to the cruise condition of the UCAV. With increasing Mach number the flow in the central region of the leading edge becomes supersonic. Therefore, the upstream movement of the tip vortex with increasing angle of attack is hindered. However, at the rear end of the supersonic zone shockinduced separation takes place forming an additional vortex. This shock-induced vortex joins the tip vortex. Thus, the onset of the tip vortex now moves again upstream with increasing angle of attack passing the rear end of the supersonic zone. The corresponding very complex vortex formation is analyzed by means of Mach number and angle of attack variation. The effects of these flow phenomena on the aerodynamic characteristics are demonstrated.