Numerical Analysis of Pulsatile Flow of Supercritical Fluids Through a Vertical Pipe

ABSTRACT The study focuses on characterizing the application of self‐excited pulsatile flow, especially for Helmholtz oscillators in vertical upward flows of supercritical fluids. The impact of the Strouhal number ( Sr ) and the pulsation amplitude is numerically investigated for mild to severe cases of heat transfer deterioration. Dynamic mode decomposition analysis reveals that the secondary non‐linear pulsations facilitate the convective heat transfer from the hot fluid near the wall to the cold fluid in the mean flow. The increase in amplitude disrupts the pseudocritical layer, thereby reducing the wall temperature. The results indicate the maximum heat transfer enhancement occurred at Sr = 0.25, as higher frequencies cause a significant pressure drop, although heat transfer recovery is faster. The pulsations with higher amplitudes overcome the buoyancy forces by increasing turbulent production near the wall, thereby reversing the M‐shaped velocity profile and opposing the thermal acceleration. The pulsation at lower frequencies and lower amplitudes minimally reduces the wall‐temperature peak; however, it enhances convection from the vapor‐film interface that forms near the wall beyond the pseudocritical temperature. The strength and position of boundary vortex rings are crucial in the generation of near‐wall turbulence. An average performance enhancement of 1.52 is observed, which depends on the non‐dimensional heated length , as the effect of pulsations diminishes beyond for an amplitude of 10%. These results enable the design of an optimal structure for Helmholtz oscillators, which are active control strategies that mitigate heat transfer deterioration and ensure the safe operation of supercritical power cycles.