Flow and heat transfer measurements in laminar and turbulent convex surface boundary layers

Abstract

Convex surface boundary layers have been experimentally investigated in a low speed wind tunnel, in the presence of pressure gradients (k) of -3.6x10(-6)less than or equal tokless than or equal to+3.6x10(-6) for laminar and -0.6x10(-6)less than or equal tokless than or equal to+0.6x10(-6) for turbulent flows. Flow and heat transfer measurements showed that stabilising effects of favourable pressure gradients caused thinner boundary layers, fuller velocity profiles and corresponding higher heat transfer rates. Downstream laminar and turbulent heat transfer measurements were below the flat plate laminar analytical solution and turbulent correlation by 54.2% and 25% respectively. It was also found that turbulent flow caused a heat transfer augmentation of 56.1% above the laminar values. Streamwise heat transfer variations, both in laminar and turbulent flows, appeared to be more affected by Reynolds number (Re-x) than streamwise pressure gradient (k(x)). The mild pressure gradient of k=2.0x10(-6) increased the laminar heat transfer rates by 10.4%, whereas similar augmentation (11.8%) were recorded at k=0.4x10(-6) for turbulent now, showing the significance of pressure gradients in turbulent flows. Furthermore by the new empirical equations, experimental flow and heat transfer parameters can be estimated with a precision of better than 6.8%.