Laminar hypersonic leading edge separation – a numerical study

Abstract

This paper describes laminar hypersonic leading edge separation. Such a configuration of separated flow was originally studied by Chapman et al. (NACA Tech. Rep. 1356, 1958) at supersonic Mach numbers as it is particularly amenable to theoretical analysis and assumes no pre-existing boundary layer. It can be considered as a limiting case of much studied generic configurations such as separation at a compression corner and separated flow behind a base. A numerical investigation is described using a compressible Navier–Stokes solver assuming perfect gas air, no slip boundary condition and a non-catalytic surface. A moderate enthalpy flow of $3.1\times 10^{6}~\text{J}~\text{kg}^{-1}$ with a unit Reynolds number of $1.34\times 10^{6}~\text{ m}^{-1}$ and a Mach number of 9.66 was considered. The resulting separated flow is analysed in the context of viscous–inviscid interaction and interpreted in terms of ‘triple-deck’ concepts. Particular emphasis is given to wall temperature effects. The effects of strong to moderate wall cooling on flow in the separated region as well as on processes of separation, reattachment and separation length, are highlighted. The numerical simulations have also shown the existence of a secondary eddy embedded within the primary recirculation region, with its size, shape and position, being strongly affected by the wall temperature.

Numerical study of bluntness effects on laminar leading edge separation in hypersonic flow

“…It is interesting to point out the similarity between the results of figure 11 and earlier results of wall temperature effects on leading edge separation (Khraibut et al. 2017; Khraibut 2018), which also showed that the second shear stress minimum becomes shallower but increases in magnitude with increasing wall temperature. It is possible that both effects (bluntness and wall temperature) result in an overall reduction of local Reynolds number relieving gradients near the second minimum.…”

“…It is worth noting that this particular feature also resembles the effect of wall temperature on the heat flux knee in a leading edge separation configuration shown in Khraibut et al. (2017).…”

“…Earlier studies by Khraibut et al. (2014) and Khraibut, Gai & Neely (2015) showed secondary vortices are particularly sensitive to grid resolution and solution progression with number of iterations. In this study, therefore, they are monitored along with the main vortex for convergence.…”

“…Surfaces, on the other hand, are taken as non-catalytically isothermal with no velocity slip or temperature jump taking place. Real gas and slip effects on the present flow conditions and geometry are discussed in Khraibut (2018), where they were found to be minimum for both sharp and blunt leading edge configurations. These simulations, furthermore, show a maximum temperature of nearly 2300 K near reattachment, and bluntness to have no major effect on the peak temperature.…”

“…In the study by Khraibut et al. (2017) wall temperature effects on a two-dimensional steady hypersonic laminar leading edge separation were considered. In this paper, we give special emphasis to bluntness effects on the leading edge separation.…”