Controlling the separation of laminar boundary layers in water - Heating and suction

An analysis is presented of the minimum surface overheat that will delay separation of a laminar boundary layer for a prescribed adverse pressure gradient in water. The analysis is for a Falkner-Skan wedge flow corresponding to negative values of beta. The heat-transfer and viscosity variations are localized to a thin layer near the wall, well within the momentum boundary layer, and their primary effect on separation is to provide a 'slip' velocity for the outer main parts of the flow, enabling the outer, shear-layer like part of the flow to sustain a more adverse pressure gradient than it could in the absence of heating. Although heating does delay separation, its effect is shown to be small for practical values of wall overheat, particularly compared to the effect of suction.