An experimental investigation on the influence of Strouhal number and amplitude on the flow and heat transfer behavior of synthetic jet impingement

Abstract

ABSTRACT Here, tests are performed to analyze the effect of Strouhal number (St) and amplitude on thermo-fluid characteristics of synthetic jet (SJ) impingement for varied range of Reynolds numbers (Re = 3000–6000) and three different SJ actuation amplitudes (Vrms = 4, 6, 8 V). The hot wire anemometer and the infrared thermal imaging camera are used to measure the flow velocity and surface temperature, respectively. At a constant amplitude of the SJ actuation, discrete pairs of Strouhal numbers, i.e. low St ( S t L ) and high St ( S t H ), are found to exhibit the same Re. The heat transfer characteristics are expressed in three different regions such as the region of recirculation, the region of high Strouhal number dominance, and the region of low Strouhal number dominance. At lower orifice-to-surface spacings (z/d < 6), the thermal efficacy of SJ with S t H is found to be lower compared to the SJ with S t L . At z/d = 2, SJ with S t H exhibits the decrease in the average Nusselt number upto 53.4% corresponding to S t L at Re = 4000 and 4 Vrms. However, at intermediate spacings (z/d ≥ 6 ), the SJ with S t H tends to outperform the S t L , which may be due to vortex pairing at high St synthetic jets. At larger z/d, the dominance of S t L is reestablished due to matching of the SJ actuation frequency with the natural frequency of a steady jet. Correlations have been proposed for the average Nusselt number at both S t L and S t H as a function of Re, St, and z/d. The results of the study provide information on the selection of the operating frequency of SJ to achieve higher heat transfer at varied orifice-to-surface spacings.