带集气腔的脉冲射流冲击换热实验和数值研究

实验和数值研究了带集气腔的单股脉冲射流冲击平直靶面对流换热特性。实验测试的脉冲频率(f)为5~40 Hz,射流雷诺数(Re)为5 000~15 000,脉冲占空比(R)为0.2~0.8,射流冲击间距比(H/d)为2~10;相对于实验测试,数值计算的参数范围有所拓宽,即5 Hz≤f≤200 Hz,5 000≤Re≤20 000,0.2≤R≤1.0。研究结果表明,与无集气腔脉冲射流相比,带集气腔的脉冲射流能够增强对流换热,在驻点附近的努塞尔数大约有8%~19%的提高;集气腔的存在,在射流出口处形成紧缩效应而提高脉冲值班阶段的射流趋近靶面速度,同时在非值班阶段能够形成一定的流动惯性效应。在研究的参数范围内,存在特定的、相对较优的脉冲参数,如f=80 Hz,R=0.8,对于受限空间的脉冲射流冲击,H/d=4是相对较优的射流冲击间距比。 

Experimental and numerical study on pulsed-jet impingement heat transfer with an additional collection chamber

An experimental and numerical study was performed to study the impingement heat transfer on the flat target surface produced by a pulsed-jet with an additional collection chamber. The current test was conducted under the following conditions, such as pulse frequency (f) ranged from 5 Hz to 40 Hz, jet Reynolds number (Re) ranged from 5 000 to 15 000, pulsation duty cycle (R) ranged from 0.2 to 0.8, jet-to-surface distance (H/d) ranged from 2 to 10. In the numerical simulations, the above parameter ranges were relatively extended, for example, 5 Hz≤f≤200 Hz, 5 000≤Re≤20 000 and 0.2≤R≤1.0. With respect to the pulsed-jet impingement without collection chamber, the pulsed-jet with an additional collection chamber was found to enhance the convective heat transfer, with a 8%-19% increase of the stagnation Nusselt number. Due to the additional collection chamber, the vena contracta effect near the jet orifice increased the approaching velocity towarded the target surface at the jet-on process. At the jet-off process the inertia role inside the additional collection chamber behaved. Among the current research conditions, the relatively optimal pulsation parameters such as f=80 Hz and R=0.8 were demonstrated. For the pulsed-jet impingement on a confined target, H/d=4 was a relatively optimal jet-to-surface distance.