Abstract: The heat transfer and flow characteristics of square wave impinging jets under different duty cycles are studied by numerical simulation method.This paper presents the heat transfer characteristics of target varied with traditional variables such as Reynolds number,pulse frequency and jet to plate spacing.The heat transfer and flow characteristics in the stagnation area with different duty cycles are analyzed emphatically.The numerical result is verified with the experimental result of impinging jet and pulsating jet.The results show that in the stagnation area,with the duty cycles of 0.5 and 0.7,the Nusselt numbers are very closed to each other.In the wall jet region,the Nusselt number with duty cycle of 0.5 is improved by 10% than that with duty cycle of 0.7.The Nusselt number with duty cycle of 0.9 is improved by 3% than that of steady jet in the whole jet region.Under duty cycle of 0.7,the vortex structure movement is much stronger in the stagnation area,compared to that under duty cycles of 0.5 and 0.9,and steady jet.

Key words: square wave impinging jets, duty cycle, heat transfer characteristics, flow characteristics

摘要： 应用数值模拟方法研究了不同工作因数下方波冲击射流的换热及流动特性,并分析了冲击靶面换热特性的变化规律。研究了冲击靶面换热特性随Reynolds数、脉冲频率、喷嘴距冲击靶面距离与喷嘴直径之比等参数的变化规律,重点分析了不同工作因数对冲击射流滞止区域换热与流动特性的影响,并将数值计算结果与连续冲击射流、脉动冲击射流实验结果进行对比验证。计算结果表明:当工作因数为0.5与0.7时,冲击靶面滞止区域Nusselt数非常接近;当工作因数为0.5时,壁面射流区域Nusselt数比工作因数为0.7时提高了10%;工作因数为0.9时,冲击靶面Nusselt数比连续冲击射流提高3%;工作因数为0.7时,相对于工作因数为0.5、0.9及连续冲击射流时,冲击靶面滞止区域存在强烈的涡结构变化。

关键词: 方波冲击射流, 工作因数, 换热特性, 流动特性