Heat Transfer Measurements to Examine Surface Roughness and Blowing Effects in Hypersonic Flows

Experimental studies have been conducted in the LENS supersonic and hypersonic tunnels to examine surface roughness and blowing effects on the heating and skin friction to blunt nosetip and slender blunted cones in regions of laminar, transitional and turbulent flows. Heat transfer measurements have been made on rough surfaces, and smooth and rough porous surfaces, with specially designed and constructed thin-film and calorimeter instrumentation. The rough surfaces employed in these studies were constructed with both sand grain roughness and patterned roughness with well-defined surface geometries constructed with hemispherical and conical roughness elements. The spacing of the hemispherical and conical roughness elements were varied to obtain measurements with which to generate correlations of the roughness-induced heating enhancement in terms of parameters which characterize the surface geometry of the rough surfaces. The well-defined geometric character of the patterned roughness also provides well-defined boundary conditions for future computations that compute the flow over the roughness elements. Unique thin-film heat transfer instrumentation and rough porous surfaces have been constructed and employed to examine the separate and combined effects of surface blowing on the heat transfer to these surfaces in laminar, transitional and turbulent flows. The measurements made in these studies have been analyzed to correlate the roughness-enhanced heating with the height, shape and spacing of the surface roughness and the freestream conditions. The results of this analysis suggest that roughness augmented heating cannot be correlated simply in term of roughness Reynolds number. Our correlations of the effective roughness height with shape and spacing parameters differ significantly from measurements in subsonic flows. The heat transfer and skin friction measurements made with surface blowing on a blunted cone for a series of different gaseous injectants have been correlated with a blowing parameter which incorporates the molecular weight and specific heat of the injectant. These correlations indicate that surface roughness effects persist to relative high blowing rates. During these studies, we employed high-frequency thin-film instrumentation to measure the heating rate in the stagnation regions of the flow and concluded that in high Reynolds number flows, heating enhancement can result from disturbances to the boundary layer in the stagnation region origi