Abstract This experimental study is focused on a rectangular synthetic (zero-net-mass-flux) jet impinging on a wall. The working fluid is air. A novel variant of a synthetic jet actuator (SJA) is proposed. Following biomimetic principles, the actuator incorporates a nozzle in which the cross-sectional area periodically oscillates during the driven cycle. Two independent actuating systems are used to drive the main SJA diaphragm (as seen in common SJAs with rigid nozzles) and the oscillating nozzle walls (unique to this study). Namely, the diaphragm is driven electrodynamically, and the nozzle walls are driven using a pair of piezoelectric transducers. The operating frequency of 62 Hz is selected by tuning both systems at their resonances. The nozzle slot width oscillates around an average value of approximately 6 mm. Four experimental methods were used: phase-locked visualization of the oscillating nozzle lips, direct measurement of the jet momentum flux using a precision scale, hot-wire anemometry, and an evaluation of the heat transfer coefficients on the exposed wall using heat flux sensors. The local distribution of the heat transfer coefficient on the wall (Nusselt number in a dimensionless form) indicated the three-dimensional character of the flow field with an axis-switching effect. It was concluded that the momentum flux and the heat transfer rate could be enhanced by the phase delay between the diaphragm and nozzle cycles. The reason is the fact that the nozzle cross-sectional area during the extrusion stroke is smaller than the area during the suction, thus the SJ velocity and momentum flux are promoted during extrusion while the losses are reduced during suction. The maximal effect was found at the phase shift of 270° for the ratio of the cross-section areas during the extrusion and suction of 0.74.

中文翻译：

---

对从具有振荡截面的喷嘴发出的合成射流的冲击传热

摘要 本实验研究的重点是撞击墙壁的矩形合成（零净质量通量）射流。工作流体是空气。提出了一种合成射流致动器 (SJA) 的新型变体。遵循仿生原理，执行器包含一个喷嘴，其中的横截面面积在驱动循环期间周期性振荡。两个独立的驱动系统用于驱动主 SJA 隔膜（如具有刚性喷嘴的常见 SJA）和振荡喷嘴壁（本研究独有）。即，隔膜是电动驱动的，喷嘴壁是使用一对压电换能器驱动的。62 Hz 的工作频率是通过调整两个系统的共振来选择的。喷嘴狭缝宽度在大约 6 毫米的平均值附近波动。使用了四种实验方法：振荡喷嘴唇的锁相可视化，使用精密刻度直接测量射流动量通量，热线风速测量，以及使用热通量传感器评估暴露壁上的传热系数。壁上传热系数的局部分布（无量纲形式的努塞尔数）表明具有轴切换效应的流场的三维特征。得出的结论是，隔膜和喷嘴循环之间的相位延迟可以提高动量通量和传热速率。原因是挤出行程时的喷嘴截面积小于吸入时的截面积，因此，在挤压过程中提高了 SJ 速度和动量通量，而在抽吸过程中减少了损失。对于 0.74 的挤出和抽吸过程中的横截面积比，在 270° 的相移处发现了最大效果。