Turbulence enhancement in body force opposed flows

Turbulence may be strongly influenced by near-wall nonuniform body forces. A widely encountered example is buoyancy acting in mixed convection flows. Here we use direct numerical simulations to present two key ideas: First we show that introducing opposing body forces whilst maintaining the pressure gradient does not cause key turbulence characteristics to change. It follows that the concept of “apparent Reynolds number” introduced by He et al. [J. Fluid Mech. 809, 31 (2016)] to explain laminarization can now be extended to explain the opposite phenomena of turbulence enhancement by opposing body forces. This new understanding has allowed turbulent shear stress and skin friction to be easily predicted simply from the nonuniform body force profile and reference data despite the nonequilibrium nature of the flow. Second, we analyze the flow in the context of turbulence regeneration cycle and provide evidence that complements the recent study from Jiménez [J. Fluid Mech. 945, R3 (2022)], which suggests that streaks are more decoupled from the regeneration cycle than previously thought.