粗糙表面不同粗糙元间局部流动与传热特性

Local flow and heat transfer characteristics among roughness ribs in rectangular channel

用规则微小横肋模拟固体表面粗糙度, 数值模拟和分析粗糙元间局部流动和换热特性. 结果显示, 在粗糙段各粗糙元间流动结构会发生变化, 大体上可分为入口区、中间区和出口区. 入口区流动变化比较快, 不同粗糙元间壁面涡结构显示出很大不同; 中间区则出现较稳定的单涡结构; 与入口区类似, 出口区流动结构又发生比较大的改变. 阻力曲线从入口处粗糙元间的“W”形, 逐渐演化到出口处正弦曲线形; 换热曲线基本呈中间高、边沿低的趋势. 研究表明, 特定粗糙段各粗糙元间流态变化导致局部阻力和换热特性有所不同.

The roughness was simulated by using regular transverse rectangle ribs on the bottom surface of a rectangular channel, and local flow and heat transfer characteristics among ribs along a roughened surface were numerically investigated. The results showed that various flow structures appeared in different rib spacing regions along the flow direction, according to which three flow regimes in the roughness section were generally classified into-entrance, middle and exit zone. In the entrance zone flow structures varied quickly, particularly vortex distributions close to the wall in the rib spacing region appeared quite different from each other. In the middle zone, the flow became relatively stable and the flow structure was a single vortex. Similar to the entrance zone, in the exit zone the flow experienced a significant change of flow structure. Flow resistance exhibited W-shape at the very beginning of the entrance zone, while it evolved into a kind of sine wave at the end of the roughness section. Generally, heat transfer coefficient tended to be high in the middle area of each rib spacing region. It was revealed that different characteristics of flow and heat transfer performance were determined by various flow structures in different rib spacing regions along the roughened surface.