Flow dynamics and heat transfer enhancement of single pulsed jet impingement in a confined crossflow channel

Abstract

The flow dynamics and heat transfer behaviors of single pulsed jet impingement in a specified confined crossflow channel of H/D=4 is studied by using large-eddy simulation methodology mainly, together with the schlieren flow visualization and convective heat transfer measurement. The effects of pulsation frequency and jet-to-crossflow velocity ratio are concerned in a wide range of f=20 Hz∼200 Hz and VR=1.5∼10.0, by fixing the jet Reynolds number at Re_j=10000. The results confirm that the use of pulsed jet on enhancing impingement heat transfer is more appreciated in situations with stronger crossflow effects. Its key mechanism is mainly reflected in that the pulsation excitation alters the inherent flow regime of steady jet impingement, such as the transitions from ‘weak normal contact’ of steady jet impingement to ‘strong normal contact’ of pulsed jet impingement under VR=2.5, and ‘faint normal contact’ to ‘weak normal contact’ under VR=1.5. According to the computational results, the peak spanwise-averaged Nu could be increased to 106% under VR=2.5 by high-frequency pulsed jet impingement with respect to the steady jet impingement. Even at f=20 Hz, an increase of about 16% in the peak spanwise-averaged Nu is still identified by the pulsed jet impingement. However, in the situations of VR=10.0, low-frequency pulsation generally results in an obvious reduction of jet impingement heat transfer. Generally, f=100 Hz is suggested to be a more promising pulsation frequency within the scope of current study, on account that it could create a closed heat transfer level as that at f=200 Hz and it is more realistic in the practical uses.