陷窝强化对流换热机理数值模拟分析

Numerical mechanism analysis of heat transfer enhancement by dimple

为了给后续优化陷窝设计提供参考,本文采用RANS数值模拟了底板布置典型深宽比为0.2的陷窝的两组光滑平板间充分发展对流换热流动的情况,分析了陷窝强化对流换热的机理。为验证数值模拟方法的可靠性,建立了与已有文献中的实验一致的模型,与实验结果对比,数值结果误差小于6%,验证了本文数值模拟方法的可靠性。本文通过此数值模拟方法研究表明：陷窝背风面动量输入小、流速低、对流换热弱、类龙卷风涡对壁面螺旋型焦点处对流换热最多减弱50%;陷窝尖后缘的高速绕流、冲击、边界层不连续发展和湍流强度增强等强化了对流换热;陷窝后缘处对流换热最大增强25%;尾流诱导达两倍陷窝表面直径距离的纵向涡对,由于纵向涡对在对称面上诱导向上的速度,对流换热减弱;由于纵向涡对两侧诱导向下的速度,对流换热较强;尾流区换热增强5%~25%。从整体来看,陷窝强化了对流换热。

To provide reference for dimple optimization design, the fully developed convective heat transfer between two planes, with a single dimple of depth to print diameter ratio of 0.2 placed on the below plane, is simulated with RANS in Fluent, to analyze heat transfer enhancement mechanism. Comparisons with experiment data show a good agreement; this proves the reliability of numerical method. It is found by simulation that: the convective heat transfer in leeward side of the dimple is decreased, because of where a low momentum region occurs. The lowest Nu/Nu0 is located at the focus point and is decreased by 50%. The sharp edge acceleration, impingement, boundary layer break and increased turbulence instability all act to enhance heat transfer, and the highest heat enhancement is in the dimple rear rim by 25%. Dimple wake induce counter rotate longitudinal vortex pairs, which induce upward velocity in middle and downward velocity in two sides, and enhance heat transfer more at two sides and less at middle. The dimple wake enhances heat transfer from 5% to 25%. In the average of the whole plane, the dimple enhances heat enhancement.