Numerical investigation of flow and heat transfer in a swirl tube
Numerical investigation of flow and heat transfer in a swirl tube
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DOI：
10.1016/j.ijthermalsci.2014.12.001
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发表时间：
2015-10
影响因子：
4.5
通讯作者：
Christoph Biegger;C. Sotgiu;B. Weigand
中科院分区：
文献类型：
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作者：
Christoph Biegger;C. Sotgiu;B. Weigand
涡流管是一种很有前景的冷却方法，适用于涡轮叶片等热负荷较大的部件，因为它增加了周向速度，从而改善了流体的湍流混合。然而，这种旋流管内的流动和换热是相当复杂的，目前还没有完全了解。为了了解旋流管内的流动结构和冷却性能，我们采用分离涡模拟方法(DES)对旋流管进行了数值模拟，并与实验数据进行了比较。用数值模拟具有温度梯度的槽道湍流的文献数据验证了数值方法的有效性，得到的平均速度分布与实验结果吻合较好。数值模拟低估了进气附近的换热系数，但在下游的换热系数与数值模拟结果一致。结果表明，绕管轴方向的流场表现为一个涡系。在管壁附近，我们观察到向出口的轴向流动，具有较高的周向速度分量。相反，涡核由轴向回流组成。此外，湍流结构还表现为双螺旋涡旋，特别是在进气区。此外，换热结果表明，旋流进口处的努塞尔数最高，与光管相比，努塞尔数高达8倍。由于圆周速度的衰减，换热向管子出口方向减小，并变得更加均匀，但仍高于光滑管内的换热。壁面强梯度的周向速度是旋流管内高换热的主要机理。
A swirl tube is a promising cooling method for heavily thermally loaded parts like turbine blades due to the additional circumferential velocity and therefore improved turbulent mixing of the fluid. However, the flow and the heat transfer in such a swirl tube are quite complex and not yet fully understood. To gain understanding of the flow structure and the cooling capability, we simulated a swirl tube via Detached Eddy Simulation (DES) and compared it to own experimental data. The numerical method was validated with DNS literature data simulating a turbulent channel flow with a temperature gradient.DES and experiments agreed well for the mean velocity profile. The heat transfer coefficients are underestimated by the simulation near the inlet, but show an agreement further downstream. The results show that the flow field is characterized by a vortex system around the tube axis. Near the tube wall we observed an axial flow towards the outlet with a high circumferential velocity component. In contrast, the vortex core consists of an axial backflow. Additionally, turbulent structures showed double helix vortices especially in the inlet region. Furthermore, heat transfer results elucidate the highest Nusselt numbers at the swirl inlet which are up to eight times higher compared to a smooth tube. The heat transfer then decreases towards the tube exit due to the decay of circumferential velocity and becomes more uniform, but is still higher than the heat transfer in a smooth tube. The circumferential velocity with strong gradients in the wall region is the major mechanism for the high heat transfer in the swirl tube.