On the criteria for reverse transition in a two-dimensional boundary layer flow

Abstract

Experiments on reverse transition were conducted in two-dimensional accelerated incompressible turbulent boundary layers. Mean velocity profiles, longitudinal velocity fluctuations$\tilde{u}^{\prime}(=(\overline{u^{\prime 2}})^{\frac{1}{2}})$and the wall-shearing stress (T_W) were measured. The mean velocity profiles show that the wall region adjusts itself to laminar conditions earlier than the outer region. During the reverse transition process, increases in the shape parameter (H) are accompanied by a decrease in the skin friction coefficient (C_f). Profiles of turbulent intensity (u’²) exhibit near similarity in the turbulence decay region. The breakdown of the law of the wall is characterized by the parameter\[ \Delta_p (=\nu[dP/dx]/\rho U^{*3}) = - 0.02, \]whereU* is the friction velocity. Downstream of this region the decay of$\tilde{u}^{\prime}$fluctuations occurred when the momentum thickness Reynolds number (R) decreased roughly below 400.