High Speed Heat Dissipation Using Flow Control

Abstract

The heat dissipation for high speed vehicle is a major public and scientific concern and an area of research of high fundamental and practical significance. Traditional methods of heat dissipation generally rely on heat resistant materials and ablators, and so are constrained by the material temperature limits, weight penalties and subsequent lowering of vehicle aerodynamic performance and thus incur high energy costs for operation. In this dissertation, using both physical experiments and numerical simulations, the flow characteristics and merits of using passive and active flow control methodologies were examined to seek solutions to the problems associated with heat dissipation. Investigations on mechanical spike, counterflow jet, focused energy deposition and their combinations were carried out to establish their heat reduction potentials as a consequence. The studies conducted in this study have produced several interesting outcomes, such as the establishment of the crucial role of the mechanical spike length in both drag and heat dissipation, the identification of the axial and transverse counter flow jet induced fluctuations of the shock wave as novel modes of heat dispersion and the demonstration that through appropriately optimised ejection pressure ratios of the counter flow jet, substantial heat reduction may be achieved with lower energy input. Another important feature of this thesis has been the introduction and investigation of the concept of a “hybrid system” that can be developed by combining two or more flow control methods for heat dissipation. The results obtained to test the conjecture are very promising. The hybrid system appears better in performance than a single stand-alone system. Thus, apart from providing a greater insight into the overall flow mechanisms associated with the flow control techniques considered, the results obtained in this thesis have also demonstrated the enormous potential of deploying or adapting various flow control techniques, particularly the hybrid ones, into the design of heat protection systems of high speed vehicles of the future.