Active and passive control of supersonic cavity flow

Transient, irregular and complicated nature of high speed flow over cavities which represents the rectangular ammunition store bays of aircrafts presents an important and practical problem in aeronautical applications. Cavity flow contains turbulence in company with pressure fluctuations, severe acoustic effects and instabilities. In order to understand the structure of cavity flow, and to alleviate pressure fluctuations and severe acoustic effects it is necessary to conduct accurate flow simulations and apply appropriate control methods. In this dissertation, flow over a rectangular cavity with Mach number of 1.5 is investigated using Computational Fluid Dynamics methods. Open cavity characteristics are observed in geometry with a length to depth ratio of 5.07. Simulation results are verified by experiment in literature. Active and passive control methods are applied to decrease the high pressure values and fluctuations, reduce the severe acoustic effects. Passive methods are geometrical changes such as inclination of trailing edge wall, inserting plate on cavity entrance and implementation of wall spoilers. Active control methods are air blowing with microjets and jets from cavity walls. To make detailed examination of flow physics, Proper Orthogonal Decomposition is applied to velocity data obtained from flow inside cavity in uncontrolled and controlled cases, and dominant modes of flows are revealed. In the final part of the dissertation sensor locations for real-time flow control are determined by applying one-dimensional Proper Orthogonal Decomposition to pressure values obtained from cavity walls. High sound pressure level decreases are obtained by passive control methods and the most effective passive control method is selected as inclination of trailing edge wall. As the angle of trailing edge wall increases, the amplitude of pressure oscillations decreases by reducing the interaction between shear layer and back wall. Changes in flow properties are observed by applying active control methods. The most effective results in air blowing with microjets and jets are obtained when the application is made through the cavity entrance. Structure of shear layer is changed by giving external energy input at cavity entrance. Active control methods, which are less effective than passive control methods in terms of pressure fluctuation suppression, are quite suitable for real-time flow control since they are adaptable to flow conditions. Keywords: Supersonic cavity flow, Computational Fluid Dynamics, Flow control, Proper Orthogonal Decomposition