一种低流阻表面的流动与传热特性

采用数值模拟方法对流体在有圆孔表面的流动及传热特性进行研究。研究中分别对四种不同的工况进行数值模拟。数值模拟结果所得换热面努塞尔数Nu与采用迪图斯—波尔特(Dittus-Boelter)公式计算所得Nu数进行比较,计算误差均小于5%。研究结果表明,在四种工况下,圆孔表面由于圆孔的存在改变其表面附近流动边界层的流动结构,使得边界层内垂直于壁面的法向速度梯度变小,进而使得边界层厚度增加,且由于圆孔表面下方流体可吸收部分来自边界层以外的动量传递,降低壁面附近的湍流扰动,从而减少损耗,达到明显的减阻效果。计算结果显示:四种工况下圆孔表面的存在使得流动均有不同程度的减阻效果,四种工况中减阻效果最大可达14%;但是随着流动减阻效果的改善,圆孔表面的换热性能均有所降低。

Flow and Heat Transfer Characteristics of Low Flow Resistance Surface

The flow and heat transfer characteristics of surface with circular holes are studied by numerical simulation method.Four different conditions are simulated.The simulation results of heat transfer surface nusselt numbers are compared to the nusselt numbers which are calculated by Dittus-Boelter equation.The differences are less than 5%.The research results manifest that,in the four conditions,the model with circular holes surface has obvious effect on drag reduction.Because the circular holes change the flow structure of boundary layer near the surface which makes the normal velocity gradients perpendicular to the surface smaller and makes the boundary layer thickened.And because of part of momentum transfer from the outside of boundary layer is absorbed by the fluid under the circular hole surface,the turbulent disturbance near the wall and the wastage reduces.The calculation results show that the existence of surface with circular holes make the flow models have different effects of drag reduction and the best effect of drag reduction obtained in the simulations of four conditions is 14%,but as the drag reduction increasing,the heat exchange performance gradually weaken.