Flow and heat transfer behavior of acoustically excited pulsating air jet impinging on a flat surface

Abstract

Experiments are carried out to understand the flow and thermal behavior of a pulsating jet. The pulsating jet is generated using acoustic excitation. The study considered variations in Reynolds number (Re = 2800, 4900, and 6800), Strouhal number (St = 0–0.84), pulsation amplitude (A = 0–60 %), and nozzle-to-surface distance (z/d = 1–8). Findings revealed that the potential core length of the pulsating jet is shorter compared to the steady jet. The potential core length initially decreases with an increase in St up to 0.42, then begins to increase. Pulsating jets improve thermal performance in the wall jet region due to greater entrainment and mixing from the surrounding fluid. Results demonstrated that pulsating jets could increase average heat transfer rate by up to 58 % at Re = 2800 compared to the steady jet. Although heat transfer rates are higher in pulsating jets, changes in pulsation frequency or amplitude had a minimal effect. The enhancement in average heat transfer rate diminishes as the Reynolds number increases for the same Strouhal number. Each tested Reynolds number showed at least a 10 % improvement in heat transfer in pulsating jet over steady jet. The improved thermal performance of the acoustically pulsating chamber offers the potential for enhanced thermal management in various applications.