Acoustic pulsation for heat transfer abatement in supersonic channel flow

Abstract

The impact of periodic pulsation normal to the flow passage on the heat and momentum transport is studied using direct numerical simulations. The selected test case is the fully developed supersonic turbulent flow at Reynolds numbers Reb=ρ¯bU¯bδ/μ¯wall=3000 and 6000 and Mach number Mcl=U¯cl/c¯cl≈1.5, bounded by isothermal walls. The pulsation is introduced by imposing a time-periodic uniform body-force in the spanwise directions, mimicking two acoustic drivers placed on the side-walls that are operating with a 180° phase difference. Results indicate that the spanwise pulsation at a moderate forcing amplitude, with the spanwise velocity oscillation amplitude W̃cl≈12% of bulk streamwise velocity or W̃cl+=W̃cl/uτ≈2, can create about 8% reduction in the Nusselt number (Nu), as well as in the skin friction coefficient (Cf), if applied at the optimal pulsation period T+=Tuτ2/ν¯wall within [173, 346], where T=2π/ωf. The excitation outside this band fails to achieve such high levels of modulations in heat and momentum transport processes near the walls. Visualizing the instantaneous temperature field reveals a periodic tilting of the near-wall turbulent structures that is translated into a decay in the energy of the streamwise vortices and an increase in the mean spanwise distance of such structures. The effect of the excitation on reducing the turbulent heat flux and Reynolds shear stress is studied, and the resulting streaming temperature and velocity profiles are discussed.