波瓣喷嘴射流冲击平面靶板对流换热数值研究

Numerical Study on Convective Heat Transfer Characteristics of Lobed Nozzle Jet Impingement onto a Flat Target

运用Realizable k-ε湍流模型数值研究了射流雷诺数(Re)为10 000~20 000、冲击间距比(H/d)为2~8的射流冲击平面靶板对流换热,揭示了不同冲击间距下波瓣射流和圆形射流的流动和换热特征差异。研究结果表明:波瓣喷嘴在射流出口下游诱导出阵列的流向涡,强化了射流对周围流体的卷吸,导致波瓣射流的发展和冲击对流换热与常规圆形射流具有较大的差异,喷嘴形状的影响与射流冲击间距密切相关。在小冲击间距比下(H/d=2和4),波瓣射流趋向冲击靶面的核心区速度高于圆形射流,相对于圆形射流具有更高的驻点对流换热能力,且中心区外缘的对流换热系数呈现波瓣状分布;而在大冲击间距比下(H/d=6和8),波瓣射流趋向冲击靶板附近的速度分布更为平缓且中心速度低于圆形射流,波瓣射流在驻点区的冲击对流换热弱于圆形射流冲击。

Numerical simulations of the jet impingement heat transfer on a flat target were performed under typical jet Reynolds numbers ranging from 10 000 to 20 000 and dimensionless impinging distances ranging from 2 to 8 by using the Realizable k-ε turbulence model. Particular attention was paid to explore the differences between the lobed jet and conventional or round jet impingements at different impinging distances. The results show that the lobed nozzle produces array streamwisevortices downstream the nozzle outlet to enhance the mixing of jet with the surrounding air,resulting in distinct features of jet development and impingement heat transfer with the round jet. The effect of nozzle shape is tightly associated with the impinging distance. At a small impinging distance（such as H/d = 2 and 4）,the peak approaching velocity of lobed jet close to the target is found to be greater than the round jet,producing higher stagnation convective heat transfer and a lobe-shaped convective heat transfer distribution around the stagnation zone. While at a large impinging distance（such as H/d = 6 and 8）,the lobed jet is found to achieve more smooth velocity profile and less peak velocity related to the round jet approaching closely to the target,resulting in weaker stagnation convective heat transfer than the round jet.