不同深度凹陷内湍流流动与传热性能的数值研究

采用标准k-ω湍流模型对具有不同深度的凹陷涡发生器表面湍流传热性能进行了数值计算,获得了雷诺数(Re)在8 500~60 000内不同深度的凹陷表面湍流传热、流阻和流动特征,并拟合了传热和摩擦因子关系式.凹陷表面平均传热性能和摩擦因子随着深度的增加而增大,并且Re越高传热性能和摩擦因子越高.在低Re值(Re=8 500)时深度比(σ,凹陷表面深度与截面直径之比)为0.1和0.3的凹陷传热相差不大,平均性能较光滑平板增强约40%左右;而在高Re值(Re=50 500)时后者比前者传热提高约11%,平均换热性能较光滑平板分别增强42.1%和51.6%,摩擦因子提高30%~120%.相对于光滑通道,凹陷表面综合热性能提高10%~35%,综合热性能随凹陷深度的增加而逐渐减小.详细的凹陷表面传热分布还表明,深度比为0.1和0.2的浅凹陷涡发生器局部传热分布对称,而深度比为0.26和0.3的深凹陷局部传热分布是非对称的,这主要是由于浅凹陷与深凹陷内部具有不同的涡流结构.

A Numerical Study of Turbulent Flow and Heat Transfer of Dimples at Different Depths

Abstract： Based on numerical simulations, the friction factors and heat transfer coefficients of four dimples with different depths were obtained by using the standard k ω turbulence model, and the relations for the heat transfer and friction factors were also presented when the Reynolds number (Re) varies from 8 500 to 60 000. The results showed that the average heat transfer coefficient and the friction factor gradually increase with the increasing of the depth. They also increase as the Reynolds number increases. In the case of Re=8 500 and σ=0.1 or 0.3 (σ: the ratio of depth to face diameter), the average heat transfer coefficient and the friction factor are almost invariant, the average heat transfer coefficient increases 40% to flat plate channel. Compared with the depth of σ=0.1, a dimple depth of σ=0.3 achieves a heat transfer enhancement of more than 11% at the Reynolds number of 50 500. Compared to the flat plate channel, the average heat transfer performances of the dimpled channels increase by about 42.1% and 51.6%, friction factors increase 30% and 120%, respectively; and also the overall heat transfer coefficients increase by 10% to 35%; the heat transfer coefficient decreases as the increase of the depth. The distribution of local Nusselt number in the flow direction of shallow dimpled channel at a dimple depth of σ=0.1 and σ=0.2 is symmetric. However, it becomes asymmetric in deep dimpled channel at a dimple depth of σ=0.26 and σ=0.3. The reason may be the different vortex structures in shallow dimples and deep dimples.