Effects of Convection on Sound Radiation

Abstract

This dissertation explores the effects of convection on the structural response and sound radiation behavior of a simple structure. This behavior will be studied over a wide range of flow velocities, with a maximum of Mach 2. Previous work has established behavior for subsonic flow, so the first task is to expand this method for supersonic flow speeds. A method for modeling the structure is presented, along with a complimentary method for modeling the fluid flow. Coupling these two subsystems is discussed, along with a development for the equations that will be used to describe both structural response and energy flow between the structure and the flowing fluid. This is accomplished by analyzing the frequency response of a coupled aerodynamic and structural model. The difference in structural response is demonstrated as compared to that previously established for subsonic flow, and provides data on the nature of the power flow between the structure and the convected fluid at high flow velocities. A negative net power flow from the structure to the fluid is shown at high flow velocities. This method is then expanded to accommodate structures with externally imposed stresses. The subsystem used for modeling the structure is modified to allow variable states of stress to be imposed on the coupled model. This new coupled model is evaluated at both subsonic and supersonic flow speeds. Established relationships are used to evaluate the effect of the imposed stress on the structural response and on the energy flow between the structure and the flowing fluid. The effect of the state of stress in the structure is shown to affect the radiation efficiency of the structure. The effects of both unidirectional and bidirectional stresses are discussed. Finally, the method is further extended by making use of non-dimensional relationships in both the structural model and the aerodynamic model to allow an overview of the convection problem for a wide range of structural and fluid parameters. Engineering rules of thumb are established for when coupling the aerodynamic model and structural model are important for accurate predictions of the structural response and for the power flow between the structure and the convected fluid. The fact that the fluid dynamics must be included in the system model for accurate prediction of both phenomena is also established.