Linearised Reynolds-averaged predictions of secondary currents in turbulent channels with topographic heterogeneity

A rapid predictive tool based on the linearised Reynolds-averaged Navier-Stokes equations is proposed in this work to investigate secondary currents generated by streamwise-independent surface topography modulations turbulent channel flow. The derived coupling momentum equation Spalart-Allmaras transport for eddy viscosity, using a nonlinear constitutive relation Reynolds stresses capture correctly motions. Linearised equations, describing steady flow response arbitrary modulations, are assuming that shallow. Since linear, superposition principle holds and induced an modulation can be obtained combining appropriately elementary responses over sinusoidal at multiple spanwise length scales. permits exploration of large parameter spaces characterising structured topographies previously examined literature. Here, channels with walls longitudinal rectangular ridges considered. For walls, observed two wavelengths scaling inner outer units respectively, mirroring amplification mechanisms shear flows from transient growth analysis. ridges, model suggests analysis interpretation topology structures facilitated when ridge width gap between used instead other combinations