Liam McQuelin

Abstract:

A comprehensive study of the fundamental characteristics of leading-edge separation in rarefied hypersonic flows is undertaken and its salient features are elucidated. Separation of a boundary layer undergoing strong expansion is typical in many practical hypersonic applications such as base flows of re-entry vehicles and flows over deflected control surfaces. Boundary layer growth under such conditions is influenced by effects of rarefaction and thermal non-equilibrium, thereby differing significantly from the conventional no-slip Blasius type. A leading-edge separation configuration presents a fundamental case for studying the characteristics of such a flow separation but with minimal influence from a pre-existing boundary layer. In this work, direct simulation Monte Carlo computations have been performed to investigate flow separation and reattachment in a low-density hypersonic flow over such a configuration. Distinct features of leading-edge flow, limited boundary layer growth, separation, shear layer, flow structure in the recirculation region and reattachment are all explained in detail. The fully numerical shear layer profile after separation is compared against a semi-theoretical profile, which is obtained using the numerical separation profile as the initial condition on existing theoretical concepts of shear layer analysis based on continuum flow separation. Experimental studies have been carried out to determine the surface heat flux using thin-film gauges and computations showed good agreement with the experimental data. Flow visualisation experiments using the non-intrusive planar laser-induced fluorescence technique have been performed to image the fluorescence of nitric oxide, from which velocity and rotational temperature distributions of the separated flow region are determined.

Abstract:

This work discusses the design of a panel flutter experiment in a Mach 5.8 free-piston compression-heated Ludwieg tube. Small test duration, low freestream pressure and limited space available within the coreflow have driven the choice of boundary conditions, material and panel geometry. The test piece is a 100 mm long and 40 mm wide aluminium panel. The panel boundary condition is clamped-free-clamped-free, with the free edges parallel to the flow direction. The aerodynamic load can be varied by changing the inclination of the panel with respect to the freestream. The pressure in the cavity underneath the panel is reproduced passively by channelling the external flow and creating a recirculation region. Several strategies are employed to reduce the pressure differential between windward and cavity side of the panel. On the basis of steady-state simulations, analytical results and empirical laws, it is possible to state that panel can experience flutter during the test. Further investigation should focus on start-up transients and temperature effects.