Unsteady shock–boundary‐layer separation and energy dissipation in low-re transonic dusty flow over a mars drone airfoil

This study investigates the aerodynamic behavior of a Mars drone airfoil in low–Reynolds-number (Re = 1 × 10⁴–5 × 10⁴) transonic flow by combining delayed detached-eddy simulation (DDES) with proper orthogonal decomposition (POD) to unravel the coupled dynamics of shock waves, boundary layers, and flow separation. At a freestream Mach number of 0.85, the leading-edge λ–shock on the RAE2822 profile and its separation bubble undergo periodic oscillations that dominate 78.5 % of the flow-field energy, with the first two POD modes accounting for 41.996 % and 36.518 %, respectively. A multi-scale coupling is observed: as Ma increases from 0.6 to 0.7, the separation–vortex shedding peak shifts from St = 0.7–0.9 toward lower Strouhal numbers and grows in amplitude from = 0.01 to 0.02; at Ma = 0.8, classical buffet emerges with a dominant peak at St = 0.62 (amplitude = 0.7) accompanied by its second harmonic; accelerating further to Ma = 0.85 shifts the main peak to St = 0.5 with reduced amplitude (= 0.1), marking the onset of attenuation; for Ma ≥ 0.9, distinct oscillations vanish except for a residual DC component (St → 0, amplitude ≤0.02), and by Ma = 1.1 only minor noise at St = 0.03 remains, indicating the near disappearance of unsteady excitation. As the Mach number rises from 0.6 to 1.1, energy dissipation shifts from viscous shear losses, evidenced by wake-centered entropy production at Ma = 0.6, to shock-driven losses, with maximum entropy production localized at the leading-edge shock at Ma = 1.1. POD-based reconstruction using only the first three modes captured 94.8 % of the density-field energy; notably, the third mode illuminated the amplification of boundary layer disturbances at the shock foot. These results reveal a universal instability mechanism in low-Reynolds-number transonic shock–separation interactions, offering critical insights for stall-control strategies and aerodynamic refinement of Mars drone airfoils.