Displacement thickness based recycling inflow generation method for spatially developing turbulent boundary layer simulations

An improved method for generation of turbulent inflow for simulations of developing boundary layers is presented, based on prior recycling methods for flow over smooth (Lund et al., 1998) and rough (Yang and Meneveau, 2015) surfaces. Both these methods rely on obtaining δ₉₉ from the mean velocity profiles based on a velocity threshold. Being dependent on the profile shape, δ₉₉ can be noisy and can suffer from large undesirable fluctuations, despite being time averaged. To cushion the effects of unusual mean velocity profiles, a profile-integrated quantity, like the displacement thickness (δ*), can be used instead of δ_99. In the recycling method, velocities on a sample plane are rescaled and recycled back to the inlet, as the inflow velocity. A surface geometry dependent, roughness-length related scale is chosen to rescale the inner layer and δ* is chosen instead of δ₉₉ as the length scale to rescale the outer layer. The blending function, dependent on both the inner and the outer length scales, is used to combine the two profiles, to obtain the inflow velocity. Since δ* depends on the profile shape, an iterative scheme is implemented. Several applications and test cases are presented.