Understanding the Heat Transfer Characteristics and Axis Switching Phenomenon in High Aspect Ratio Elliptical Orifice Impinging Synthetic Jets

The present experimental study focuses on analyzing the heat transfer characteristics and understanding the axis switching phenomenon for impinging elliptic jets with high aspect ratios. The hot-wire anemometry is used to study the flow characteristics of synthetic jet, while heat transfer characteristics are studied by using a thermal imaging technique. The heat transfer characteristics of elliptical orifices with aspect ratios 10 & 14 are being studied and compared to an equivalent circular orifice. Results show that in the near-field region ( \(z/d\le 3\) ), the average Nusselt number of elliptical orifices (AR = 10 &14) is obtained to be higher than the circular counterpart. However, with the rise of AR from 10 to 14, thermal performance of elliptical orifices decreases in the near-field region. In the intermediate and far-field region, the thermal performance of such elliptical orifices depreciates, since most of the momentum of the elliptic jet is lost before arriving at the impingement plate due to significant entrainment and substantial mixing with the ambient fluid. It is also observed that with orifice to surface spacing, circular orifice jet produces a single peak in the average heat transfer rate, while elliptical orifice produces double peaks in the average heat transfer rate lying in near-field (z/D = 1 to 3) and mid-field regions (z/D = 6 to 10).