绕流波动特性对不同区域流动传热影响

为研究换热设备后向台阶内置圆柱模型的强化传热机理,采用Fluent进行数值模拟,并通过PIV粒子图像测速方法验证模拟结果的可靠性.研究雷诺数为700后向台阶内置圆柱(Xc/S=0.6,Yc/S=1, d=6 mm)时,后向台阶流道不稳定流动的周期性,以及周期波动对流道不同区域传热的影响.研究结果表明:在过渡流状态下,流道周期速度波动受两基波频率影响,即台阶影响的频率f_s=7.25 Hz和受圆柱影响的频率f_c=14.10 Hz; f_c主要作用在流道上游局部区域,上游回流运动被破坏,努赛尔数瞬时峰值提高2.52倍; f_c促进台阶振动频率f_s提前产生,下游温度梯度减小,瞬时努赛尔数逐渐减小;台阶分离流体与圆柱尾流共同作用使得流道换热效果整体提升,同时壁面摩擦系数也增大.

Influence of flow fluctuation characteristics on flow and heat transfer in different regions

To study the enhanced heat transfer mechanism of the cylinder model built into the back step of the heat exchanger, Fluent was used for numerical simulation, and the reliability of the simulation results was verified by particle image velocimetry(PIV). When Reynolds number is 700 and the cylinder(Xc/S=0.6, Yc/S=1, d=6 mm)is inserted, the periodicity of the unsteady flow in the backward step passage and the influence of the periodic fluctuation on the heat transfer in different areas of the passage are studied. The results show that in the transitional flow state, the periodic velocity fluctuation of the flow passage is controlled by the frequency of two fundamental waves, that is, the frequency affected by the step f_s(f_s=7.25 Hz)and the frequency affected by the cylinder f_c(f_c=14.10 Hz). f_c mainly acts on the upstream of the flow passage, the upstream backflow movement is destroyed and the instantaneous peak value of Nusselt number is increased by 2.52 times; f_c promotes the generation of step vibration frequency f_s in advance; the downstream temperature gradient decreases and the instantaneous Nusselt number decreases gradually. The combined action of the step separating fluid and the cylinder wake improves the heat transfer effect of the flow passage as a whole, and at the same time, the friction coefficient of the wall increases.