Momentum and energy transport in the accelerated fully rough turbulent boundary layer

The behavior of the fully rough turbulent boundary layer subjected to favorable pressure gradients was investigated experimentally using a porous test surface composed of densely packed spheres of uniform size. Measurements of profiles of mean velocity, mean temperature and the components of the Reynolds stress tensor are reported for both unblown and blown layers. Stanton numbers were determined from energy balances on the test surface and skin friction coefficients from measurements of the Reynolds shear stress and mean velocity. A new acceleration parameter, K/sub r/, for fully rough layers is defined and shown to be dependent on a characteristic roughness dimension but independent of molecular viscosity. For fully rough turbulent flow, acceleration causes an increase in Stanton number compared to zero pressure gradient values at the same enthalpy thickness, Reynold number, or position. The fully rough Stanton number behavior observed in this study is contrary to that previously reported for unblown accelerated smooth wall layers. Acceleration of a fully rough layer decreases the normalized turbulent kinetic energy and makes the turbulence field much less isotropic in the inner region (for F equal zero) compared to zero pressure gradient fully rough layers. Increasing values of roughness Reynolds number with acceleration indicate that the fully rough layer does not tend toward the transitionally rough or smooth wall state when accelerated.