Cavity Flows Control by High Frequency Forcing

In the surfaces of vehicles, such as airplanes, cars and trains, open cavities are an important source of aerodynamically generated noise, drag increase, and dangerous pressure fluctuations. Many different methods have been tested to suppress these undesired effects; some of them reached a partial success. In general, it can be seen that methods which are simple, economic and easy to apply achieve an effect that is restricted to a small operational range, while those which offer a wider operational range are complex and expensive. It has been recently discovered that exciting the flow at high frequencies it is possible to suppress or weaken the undesired effects in a wide range of flow conditions. Additionally, this forcing can be generated by a simple Von Karman wake. In this way both advantages, simplicity and a wide operational range, can be achieved at the same time. The physical mechanisms leading to cavity flow control by high frequency forcing is not well understood yet. The author of this thesis intends to offer a contribution toward a physical explanation for them, based on the analysis of data acquired with the Time Resolved PIV technique.