Amplitude variation in spanwise wall oscillations: Effects on drag reduction and heat transfer in compressible turbulent channel flow.

Spanwise Wall Oscillation is a promising active flow control technique for turbulent skin-friction drag reduction (DR). While the effectiveness of the method in incompressible flows is well documented, its performance in compressible regimes, and the underlying physical mechanisms, particularly those related to thermal fields, remain relatively unexplored. The present study employs Direct Numerical Simulation to investigate the effects of different oscillation amplitudes on compressible channel turbulent flow, with particular emphasis on wall heat transfer. A detailed analysis is performed on turbulent statistics, including mean velocity and temperature profiles, Reynolds stresses, decompositions of the skin friction and heat transfer coefficient, and the behavior of near-wall coherent structures. This analysis aims to elucidate the differences arising from varying oscillation amplitudes. The results indicate that both DR and heat transfer rate are enhanced with increasing oscillation amplitude. Furthermore, higher amplitudes promote the breakup of velocity and temperature streaks within the viscous sublayer, while exerting negligible influence on the buffer layer. Analysis of the decomposed skin-friction and heat-transfer coefficients further reveals that wall oscillations amplify the dominant role of Reynolds shear stress in DR and of turbulent viscous dissipation in heat transfer enhancement.