Transonic Shock Wave Patterns Over an Airfoil in an Accelerated Flow

摘要

It is well known that in a high subsonic flow over an airfoil, there exists a local supersonic pocket and similarly in a supersonic flow over the same, there exists a local subsonic pocket. But, how the transonic shock wave pattern over the airfoil changes when the freestream flow accelerates uniformly from high subsonic to supersonic - i.e. how a subsonic flow with a supersonic pocket changes into a supersonic flow with a subsonic pocket- is not reported so far. This study is an attempt to explore the above phenomena. In order to study the accelerated flow, Navier-Stokes equations are extended to acceleration frame of reference. Using these equations, numerical simulation of transonic flow over NACA0012 airfoil is carried out with freestream acceleration. The influence of acceleration on the flow field is studied with different levels of acceleration and retardation. This study revealed that both acceleration and retardation do influence the movement of transonic shock movement, and it is more pronounced in high levels of retardation. But, the shock wave pattern during the change from high subsonic to supersonic remains the same for various levels of acceleration. The continuous change of shock wave pattern over the airfoil is visualized in a single simulation and the underlying physical phenomena are investigated.