Experimental characterization of turbulence spots on a flat plate at Mach 6

Transition modelling and prediction is a critical topic at hypersonic speeds because of the physically large extent of the transition region and the impact of large variations or uncertainties in heat transfer, skin friction and other flow properties. The experimental activity presented in this paper is concerned with the intermittent region of transition, which extends from the initial breakdown of the laminar layer into turbulent ‘spots’ up to the position where the boundary layer is fully turbulent. The turbulent spots and roughness induced transition are strongly affected by compressibility and wall temperature.To improve the quantitative understanding of these effects direct and large-eddy simulations can be performed for prescribed surface characteristics. The simulation output will provide details of boundary layer intermittency, heat transfer and skin friction for comparison with dedicated experiments conducted in an high-speed wind tunnel.The paper will presents the results of the simulations and the first set of experiment carried out in the framework of the ATLLAS project, for a flight configuration at Mach 6. A brief critical discussion of the results will also be presented