Adaptive shock control bumps

Abstract

The evolution of Adaptive Shock Control Bumps (SCB) presented in this work is a result of an investigation into transonic flow control devices. The primary application is on transonic passenger jet aircraft during cruise and within supersonic intakes. It is in these locations that normal shocks of strength Mach 1.2-1.5 typically occur which SCB aim to manipulate and exploit. The original concept was developed by [Ashill et al., 1992] featured a flexible plate with actuators beneath the surface. The complex fluid-structure interaction (FSI) between the shock and plate has been a focus of this work with panel flutter studies heavily supplementing traditional SCB design methods. Adaptive SCB represent a required approach in order to negate poor off-design performance of static SCB. A coupled 2D aero-structural solver was developed using OpenFOAM [2017] and ABAQUS [2007] which provides a tool to evaluate the effects of varying plate proper- ties. Cavity pressure, plate length, thickness and material stiffness were found to be influential in the overall performance with four test cases developed. With lengths, lb = 150 − 200 mm and thicknesses t = 0.4 − 0.6 mm using Al-7075-T6, experimental models were produced and tested in a Mach 1.4 blowdown supersonic wind tunnel. These were sized using the coupled solver to deform passively and trigger the bifurca- tion of the shock. This new type of device showed potential for a passive adaptive SCB however all suffered from varying amounts of reacceleration over the rear surface. An aero-structural optimisation procedure is performed to position displacement con- straints beneath the flexible plate to control surface curvature. This was the driving force behind the detrimental reacceleration. The optimiser used a new performance metric which focussed upon smearing the adverse pressure gradient across the SCB which reduced the likelihood of plastic deformation. Optimal SCB have been shown to deploy and retract beneath an unsteady shock and successfully bifurcated the shock on demand.