圆孔射流核心区衰减对凹面冲击换热与流动特性影响数值研究

Numerical Study of Heat Transfer and Flow Characteristics of Nozzle Impingement Jet on Concave Surface by Jet Potential Core Analysis

凹面冲击射流流动与传热由于其在驻点处极高的换热能力而得到大量的关注及应用。但是冲击射流流动过程复杂,不同结构(如不同的壁面结构及冲击距离等)及流动参数都会对换热性能产生很大影响。本文通过数值仿真的方法验证了常用RANS湍流模型方案对凹面冲击射流流动与换热的影响,并和实验数据进行了对比。结果显示SST k-ω模型对于凹面冲击射流换热过程依然具有优势,尤其是在Nu第二峰现象的预测能力表现最优。本文研究了不同冲击距离H/d及Re下的流动与传热特性,并重点从射流核心区衰减的角度分析了不同冲击距离对冲击射流强化换热的机理。分析结果显示,射流核心区长度比ξ_(j)与壁面平均努塞尔数Nu有很大的相关性:ξ_(j)越小使得射流流体在核心区维持了足够的动能进入滞止区,得到的驻点处布局部Nu以及Nu越大,从H/d=4到H/d=1,在三种不同Re条件下,ξ_(j)分别下降了62%、61%和65%,而Nu相应增加了25%、22%及45%。

Impingement jet provides an effective method to enhance the heat transfer process because the heat transfer coefficient is much higher in the stagnation point than that in the forced convection flows.The heat and mass transfer of impingement jet are very complex,influenced by many structure parameters (impingement wall structure,distance between nozzle and target,etc.)and flow parameters.In this paper,commonly turbulence methods were simulated to verify the proper turbulence model based by RANS equation and compared with the experimental data.The results showed that the SST k-ωmodel has the advantage for concave impingement jet heat transfer process,especially the capacity to predict the phenomenon in the second Nu peak.In this article,the flow and heat transfer characteristics of different H/d and Re were studied,and the mechanism of heat transfer enhancement was analyzed from the point of the jet potential core region length.The analysis results show that the length of the jet core region has great correlation with the surface average Nusselt number.Smallerξ_(j)keep the jet fluid in the potential core region maintain enough energy into the stagnation zone,which causes the stagnation point and local both increase.From H/d=4 to H/d=1,at three different Re conditions,ξ_(j)decreases 62%,61%and 65%while the corresponding Nu increases 25%,22%and 45%,respectively.