High-enthalpy shock/boundary layer interaction on a double wedge

Experiments were performed in the T5 Hypervelocity Shock Tunnel to investigate nonequilibrium real-gas effects on separation length and reattachment heating using a double-wedge geometry and nitrogen test gas. Local external flow conditions were estimated by computational reconstruction of the inviscid nonequilibrium flow field. Application of results from triple-deck theory to a simple model for separation led to a new scaling parameter which approximately accounts for the effects of wall temperature on separation length for a laminar nonreacting boundary layer and extends previous results to arbitrary viscosity law. A classification was introduced which divides mechanisms for real-gas effects into mechanisms acting internal and external to viscous regions of the flow, with internal mechanisms further subdivided into those arising upstream and downstream of separation. Application of the ideal dissociating gas model to a scaling law for separation length, based on local external flow parameters and a nonreacting boundary layer, showed that external mechanisms due to dissociation decrease separation length at low incidence but depend on the free-stream dissociation at high incidence, and have only a small effect on reattachment heating. A limited numerical study of reacting boundary layers showed that internal mechanisms due to recombination occurring in the boundary layer upstream of separation cause a slight decrease in separation length and a large increase in heat flux relative to a nonreacting boundary layer with the same external conditions. Correlations were presented of experimentally measured separation length using local external flow parameters computed for reacting flow, which scales out external mechanisms but not internal mechanisms. These showed the importance of the new scaling parameter in high-enthalpy flows, a linear relationship between separation length and reattachment pressure ratio as found previously for supersonic interactions, and a Reynolds-number effect for transitional interactions. A significant increase in scaled separation length was observed for high-enthalpy data in the laminar regime, and this was attributed to an internal recombination mechanism arising in the free-shear layer downstream of separation. Experimental data for reattachment heating agreed roughly with existing correlations and exhibited an increase due to an internal recombination mechanism, but could not provide further insight due to large scatter.