封闭空腔中多相流振荡传热特性的数值模拟

Numerical simulation of oscillating heat transfer characteristics in cavity partly filled with cooling liquid

振荡强化传热在内燃机活塞和气门中得到广泛应用,但是其热量输运机理了解还不够深入,目前仍然主要基于经验进行活塞和气门冷却结构的设计,这无疑使得系统传热量难以准确确定。采用CFD动网格技术和VOF多相流模型,对封闭空腔中填充部分冷却介质的振荡传热进行了数值计算,分析了对流传热系数随转速、冲程以及填充率的变化规律。结果表明:振荡能够明显地强化传热,转速是影响振荡强化传热的主要因素,强化传热的效果随着转速以及活塞冲程的增大而增强;当冷却介质填充率在30%～60%范围内时,强化传热效果明显,但当冷却介质填充率超出此范围时,传热效果变差。分析结果对内燃机活塞及气门的冷却设计具有指导意义。

Oscillating heat transfer has been widely used in engine pistons and valves, but the mechanism of heat transport is still not clearly understood, so the design of liquid cooled pistons and valves is mostly based on empirical knowledge and it is difficult to achieve appropriate heat transfer rate. In this study, a numerical simulation on oscillating heat transfer characteristics in a cavity partly filled with cooling liquid was performed by using CFD dynamic mesh method and volume of fluid （VOF） model. The relations of heat transfer coefficient to the speed and stroke of piston and fill ratio of liquid were obtained. The results indicate that the oscillation enhances the heat transfer significantly. The rotation speed is the major factor affecting heat transfer, and the heat transfer enhancement is reinforced with the increase of rotation speed and piston of stroke. When the fill ratio range of liquid is 30%--60%, the enhancement of heat transfer is remarkable, otherwise the effect of enhancement pistons and valves. is unsatisfactory. The results are helpful to the design of pistons and valves.