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 less than or equal to Re less than or equal to 27000), the geometries of the nozzle (BR, LSS and CSS), jet-to-test plate placement (3 less than or equal to Hld less than or equal to 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. (C) 2004 Elsevier Ltd. All rights reserved.