Numerical simulation of pulsatile flow in rough pipes

Direct numerical simulation (DNS) of pulsatile turbulent pipe flow is carried out over three-dimensional sinusoidal surfaces mimicking surface roughness. The simulations are performed at a mean Reynolds number of $Re_\tau \approx$ 540 (based on friction velocity, $u_\tau$, and pipe radii, $\delta$) and at various roughness profiles following the study of Chan et al. (JFM 771, 743 - 777, 2015), where the size of the roughness (roughness semi-amplitude height $h^+$ and wavelength $\lambda^+$) is increased geometrically while maintaining the height-to-wavelength ratio of the sinusoidal roughness element. Results from the pulsatile simulations are compared with non-pulsatile simulations to investigate the effects of pulsation on the Hama roughness function, $\Delta U^+$. Other turbulence statistics including mean turbulence intensities, Reynolds stresses and energy spectra are analysed. In addition, instantaneous phase (eg. at maximum and minimum flow velocities) and phase-averaged flow structures are presented and discussed.