Active heat transfer enhancement roles by an acoustic actuator integration into square array of continuous jets in the presence of crossflow

The present study focused on the active heat transfer enhancement roles by integrating a center-positioned acoustic actuator into a specific continuous-jet square array in the crossflow. Experimental tests are conducted on the heat transfer behaviors, wherein four continuous-jet Reynolds numbers (ReCJ=3000, 5000, 7000 and 10,000) are taken into consideration, while the acoustic actuator is kept at a fixed exciation frequency of f = 250 Hz, providing the corresponding synthetic jet velocity ratios as R SJ-CJ =2.0, 1.2, 0.86 and 0.6 respectively. Numerical simulations are also performed on the flow dynamics in such an actively modulated jet impingement configuration. In the crossflow situations, the acoustic actuator integration generally demonstrates two aspects in its active role on heat transfer enhancement. Firstly, the synthetic jet has a more vigorous penetration capacity to exhibit its stronger impingement onto the target. Secondly, the synthetic jet is of high-pulsating capacity to pulsate the nearby flow. Therefore, it could achieve the most possibilities for a more effective heat transfer enhancement in the strong crossflow, unless the synthetic-jet characteristic velocity is far less than the continuous-jet ejecting velocity. In the viewing of spatially-averaged Nu s-av on a specificd zone, an increased about 220 % is identified under Re CJ =3000 (or R SJ-CJ =2.0) when R CF-CJ >= 0.66. Under Re CJ =5000 (or R SJ-CJ =1. 2 ), an increased up to 100 % is achieved when R CF-CJ >= 0.6. Even under Re CJ =7000 (or R SJ-CJ =0.86), greater improvements of Nu s-av are still indicated by an increase of about 60 % (under R CF-CJ =0.43) to 80 % (under R CF- CJ =0.71). However, the increase of Nu s-av becomes faint under Re CJ =10,000 (or R SJ-CJ =0.6), limited within 10 %.