Shock System Dynamics of a Morphing Bump Over a Flat Plate

Abstract

The shock wave boundary layer interaction (SW-BLI) phenomenon over transonic and supersonic airfoils captured the attention of aerospace engineers, due to its disastrous effect on the aerodynamic performance of these vehicles. Thus, the scientific community numerically and experimentally investigated several active and passive flow control elements to reduce the effect of the phenomenon, such as vortex generator, cavity, and bump. They focused on designing and optimizing the shape and location of the bump control element. However, the transit movement of the bump from the state of a clean airfoil to the state of an airfoil with a bump needs more investigation, especially the dynamics of the shock system. Thus, it is preferred to start with simple geometry, such as a flat plate, to fully understand the flow behavior with a morphing bump. In this paper, the shock dynamics due to the movement of a bump over a flat plate flying at supersonic speed are numerically investigated. The bump is located at the impingement position of the shock wave and is moved at different speeds. This study determines the suitable speed that achieves the minimum entropy change, which is the representation parameter of the transition period. The two-dimensional unsteady Navier-Stokes equations are solved using OpenFOAM to simulate the flow field variables, while the motion of the bump is tracked using the Arbitrary Lagrangian-Eulerian (ALE) technique. The results show that a spatial lag on the shock system from the steady-state solution occurs due to the movement of the bump. Further, the spatial lag increases with the increase in the bump’s speed. This causes a high increase in the flow parameters and consequently the total entropy changes on the bump surface. Generally, it is common to move the bump over the longest possible time to approximate a quasi-steady flow during the motion. However, this causes a deviation in the flow parameters between the final time of transition and the steady-state case of bump existence. Thus, it is concluded that the optimal non-dimensional time for a morphing bump in a supersonic flow of Mach number of 2.9 is 2, which is different than the longest time of 10.