Laminar Hypersonic Leading Edge Separation

A numerical and analytical investigation of hypersonic leading edge separation has been conducted. This particular configuration was first analyzed by Chapman in the 1950s for supersonic flows. This study will look at this configuration under hypersonic flow conditions, numerically, analytically, and also with basic surface pressure measurements taken in T-ADFA. Effects of wall temperature and leading edge bluntness have been considered in the study, including perfect and real gas simulations to examine their effects on separation. Slip corrections have also been implemented. A compressible Navier-Stokes solver, US3D, specifically developed for hypersonic flows has been used to carry out the numerical simulations. The simulations revealed many interesting features caused by wall temperature and bluntness effects. Firstly, while the size of separation has been shown to increase with the increase in wall temperature, wall cooling seems to give rise to secondary vortices within the separated region. An explanation for the existence of these secondary vortices has been presented in terms of gradients, characteristic angle, and the Reynolds number on the dividing streamline. The numerical results have also been analyzed in the context of the triple-deck theory, Chapman's isentropic recompression theory, and analytical work of Oswatitisch and Inger with particular emphasis on the streamline angles and curvatures at separation and reattachment. The most interesting finding has been in characterizing the separation in terms of the triple-deck scaled angle, which delineates stable and unstable secondary vortices. It is shown that a unique relationship exists between this angle and the size of separation and that it is independent of the agency provoking separation. Bluntness studies, on the other hand, showed a very complex interplay between bluntness which delays separation, viscous interactions which promote separation, and the incidence angle. In bluntness studies, map of pressure gradients revealed a complex mechanism in which disturbances can provoke secondary vortices. Analysis of streamline angles and curvatures revealed a very complex separation process on the microscale as a result of separation. Three-dimensional nozzle simulations using the same CFD solver have been carried-out to verify the freestream conditions. These simulations have been validated by performing a pitot pressure survey in T-ADFA. Both laminar and turbulent flow simulations were considered. Comparison with the experimental measurements showed that the laminar flow assumption overpredicts the size of the core flow, while the turbulent boundary layer assumption showed very good agreement with experiments. Limited surface pressure data were also obtained and overall showed good agreement with the numerical results