Flow structures and heat transfer of swirling jet impinging on a flat surface with micro-vibrations

This study focuses on the changes in the flow characteristics of a round jet issuing from a straight tube inserted with longitudinal swirling strips and impinging on a constant-heat-flux flat surface undergoing forced vibrations in the vertical plane. Smoke flow visualization is used to investigate the nature of the complicated flow phenomena under the swirling-flow jet for this impingement cooling. Effects of flow Reynolds number (440 ⩽ Re ⩽ 27 000), the geometries of the nozzle (BR, LSS and CSS), jet-to-test plate placement (3 ⩽ H/d ⩽ 16), and surface vibration frequencies, f [0.3-10.19 Hz (the relative amplitude of the flat surface ranged from 0.5 to 8.1 mm)] are examined. In addition, correlations were developed to predict the Nusselt number for the vibration using the results of Wen and Jang [An impingement cooling on a flat surface by using circular jet with longitudinal swirling strips, Int. J. Heat Mass Transfer 46 (2003) 4657-4667] for the no-vibration case of the present study.