Journal
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
Volume 126, Issue -, Pages 256-280Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijheatmasstransfer.2018.01.061
Keywords
Impinging jet; Passive control; Flow structure; Heat transfer; PIV; IR thermography; LES
Categories
Funding
- National Key Research and Development Program of China [2016YFB1200503-04]
- Shanghai Automotive Wind Tunnel Technical Service Platform [16DZ2290400]
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The present study experimentally and numerically investigated the passive control on flow structure evolution and convective heat transfer enhancement for impinging jet. Four different impinging jets, including a baseline circular jet (CJ) and three passive controlled jets, i.e., an elliptic jet (EJ), a circular-chevron jet (CCJ) and an elliptic-chevron jet (ECJ), were comparatively analyzed by utilizing the Particle Image Velocimetry (PIV) technique, infrared (IR) thermography and large eddy simulation (LES) over a wide range of jet-to-wall distances (H/D) at the jet Reynolds number (Re) of 20,000. The results showed that, unlike CJ which presented a general shedding of axisymmetric toroidal vortices, EJ showed highly deformed toroidal structures accompanied with the axis switching effect, both CCJ and ECJ exhibited the well-organized counterrotating streamwise vortex pairs developing from the chevron notches. All the three passive controlled strategies were found to induce a stronger mixing and fluctuating activity near around the stagnation region, especially for ECJ (i.e., the passive-passive controlled device) which showed the highest turbulence level approaching the target wall due to the double-passive enhancement. Moreover, compared with the baseline jet CJ, all the passive controlled jets achieved a significant heat transfer improvement in the vicinity of the stagnation point, particularly for ECJ which presented the highest heat transfer enhancement of about 41% at H/D = 5. Whereas both CCJ and ECJ were found to exhibit a less-than-ideal heat transfer performance at a small H when the heat transfer uniformity was specifically considered, due to the anisotropic thermal imprint distributions. (C) 2018 Published by Elsevier Ltd.
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