Role of pulsation generation mechanism on the heat transfer performance of an impinging jet: A contraction-cone configuration

Pulsating impinging jets have emerged as a promising approach for enhancing convective cooling; however, the reported thermal performance remains highly dependent on the characteristics of the pulsation-generation mechanism in addition to the operating conditions. This study experimentally investigates the thermo-fluid performance of a loudspeaker-driven pulsating jet issuing from a contraction cone nozzle. The effects of Strouhal number (0.1–0.8), pulsation amplitude (30–80%), stand-off distance (H/D = 1–6), and Reynolds number (5000–10000) on local and average Nusselt numbers are systematically evaluated. Surface temperature measurements are obtained using infrared thermography under constant heat-flux conditions. The results show that the heat transfer enhancement depends on the evolution of pulsation-induced coherent vortices. When the nozzle is positioned close to the target surface, the vortical structures remain underdeveloped, resulting in lower heat transfer than the corresponding steady jet. As the stand-off distance increases, enhanced shear-layer instability and coherent vortex evolution intensify near-wall mixing, thereby improving convective transport. The maximum enhancement in average Nusselt number reaches approximately 22–24% compared with the corresponding steady jet case. An optimal pulsation amplitude of 60% is identified, beyond which further increases reduce thermal performance due to excessive entrainment and dilution of the jet momentum. The findings demonstrate that the effectiveness of pulsating jet impingement is governed by the combined effects of pulsation frequency, amplitude, Reynolds number, and the loudspeaker-driven actuation mechanism, and provide useful guidelines for the design of high-performance jet impingement cooling systems.