Abstract This study examined the flow structure and heat transfer characteristics of a sweeping jet generated from a feedback-free fluidic oscillator. A feedback-free sweeping jet (FFSJ) was proposed to enhance impinging heat transfer with a large jet-to-wall spacing. The surface temperature field of a plate cooled by a jet impingement was measured by thermographic phosphor thermometry using the decay-slope method according to a range of Reynolds number (Re) and various jet-to-wall spacing (Z/dh). The results were compared with those of a square jet (SJ) and conventional feedback sweeping jets (FSJ). Time-resolved particle image velocimetry, proper orthogonal decomposition analysis, and smoke visualization were conducted to determine the external flow characteristics of the FFSJ. The FFSJ oscillated with the 7dh wavelength. The frequency and sweeping angle were higher and smaller, respectively, that of the FSJ. The heat transfer performance of an impinging FFSJ was superior to that of an SJ when the jet-to-wall spacing was lower than 5dh. The peak Nusselt number increased with increasing Reynolds number. At a fixed Reynolds number of 32,000, the local heat transfer performance of the FFSJ was superior to that of the FSJ. As the jet-to-wall spacing increased, the effect of heat transfer enhancement also increased. At Z/dh = 8, the peak Nusselt number of the SJ surpassed the FFSJ, but the integrated heat transfer rate of an FFSJ was comparable to that of an SJ.

中文翻译：

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无反馈扫掠射流撞击平面传热与流动结构的实验研究

摘要 本研究研究了无反馈流体振荡器产生的扫射射流的流动结构和传热特性。提出了一种无反馈清扫射流（FFSJ），以通过大射流到壁的间距来增强撞击传热。根据雷诺数 (Re) 范围和各种射流与壁间距 (Z/dh)，使用衰减斜率法通过热成像磷光体温度测定法测量由射流冲击冷却的板的表面温度场。将结果与方形射流 (SJ) 和传统反馈扫掠射流 (FSJ) 的结果进行了比较。进行了时间分辨粒子图像测速、适当的正交分解分析和烟雾可视化，以确定 FFSJ 的外部流动特性。FFSJ 以 7dh 波长振荡。FSJ 的频率和扫描角分别更高和更小。当射流与壁面间距小于 5dh 时，撞击式 FFSJ 的传热性能优于 SJ。峰值努塞尔数随着雷诺数的增加而增加。在固定雷诺数 32,000 时，FFSJ 的局部传热性能优于 FSJ。随着射流与壁面间距的增加，传热增强的效果也增加。在 Z/dh = 8 时，SJ 的峰值努塞尔数超过 FFSJ，但 FFSJ 的综合传热率与 SJ 相当。峰值努塞尔数随着雷诺数的增加而增加。在固定雷诺数 32,000 时，FFSJ 的局部传热性能优于 FSJ。随着射流与壁面间距的增加，传热增强的效果也增加。在 Z/dh = 8 时，SJ 的峰值努塞尔数超过 FFSJ，但 FFSJ 的综合传热率与 SJ 相当。峰值努塞尔数随着雷诺数的增加而增加。在固定雷诺数 32,000 时，FFSJ 的局部传热性能优于 FSJ。随着射流与壁面间距的增加，传热增强的效果也增加。在 Z/dh = 8 时，SJ 的峰值努塞尔数超过 FFSJ，但 FFSJ 的综合传热率与 SJ 相当。