A TURBULENT BOUNDARY LAYER WITH MASS ADDITION, COMBUSTION, AND PRESSURE GRADIENTS

A subsonic turbulent boundary layer with mass addition and combustion is studied to investigate the effects of combustion on the velocity field in constant pressure and accelerating flows. Particular attention is given to determining (1) the extent to which combustion alters the flow and (2) the mechanism whereby combustion interacts with the flow field. The experimental results demonstrate that combustion alters the velocity profiles in both constant pressure and accelerating flows. The velocity gradients at the surface in combusting flows differ markedly from those of corresponding isothermal flows and the velocity in the flame regions of accelerating flows actually exceed the freestream value. The results of analysis indicate that in a subsonic turbulent boundary layer with combustion the Reynolds stress is essentially kinematic and does not explicitly involve density fluctuations. This in turn indicates that the experimentally observed changes in the velocity profiles are attributable to the temperature dependence of the local mean density and molecular viscosity. Analytical results also indicate that the combustion-induced changes in velocity profile are strongly dependent on the axial pressure gradient. The consequence of combustion with regard to skin friction is also examined and it is found that effects on the skin friction coefficient are similar to those on the wall velocity gradient. A method of determining the velocity profiles in a combusting turbulent boundary layer is also presented. (Author)