Reynolds number scaling of turbulent pipe flow relaminarisation induced by streamwise travelling waves of blowing and suction using direct numerical simulation

Most of the energy used to pump fluids through pipes worldwide is dissipated by turbulence near the wall. Koganezawa et al. (2019) showed for the low friction Reynolds number of Reτ = uτR/ν = 110, where uτ is the friction velocity, ν is the kinematic viscosity and R is the pipe radius, that for certain parameters, streamwise travelling waves of wall blowing/suction can lead to relaminarisation. However, as reported in the recent review paper by Fukagata et al. (2024), higher Reynolds number data are required for engineering applications. Thus, we adapted our fourth-order finite volume solver (Bauer et al., 2017) to perform direct numerical simulations of turbulent pipe flow with streamwise travelling wave boundary conditions of the wall-normal velocity of friction Reynolds numbers up to Reτ = 720 (see Figure 1). In particular, we are conducting a parametric study varying Reτ , as well as the travelling wave amplitude a, length λ, and the speed c. At the conference we will present the Reynolds number scaling of the blowing/suction parameters that lead to relaminarisation, minimum drag, and maximum net energy saving and elucidate the underlying mechanisms.