单煤堆封闭煤棚内瞬态自然对流的数值研究

NUMERICAL STUDY ON TRANISENT NATURAL CONVECTION IN COAL SHED ENCLOSED OF SINGLE COAL PILE

近年来环境友好型的封闭式煤棚被广为采用,而煤堆放热会造成环境局部过热进而影响舒适度及作业人员身体健康,随之煤棚内对流换热问题成为关注重点。为了降低煤堆放热带来的危害,需要了解煤堆放热过程中传热流动机理,该文采用CFD数值模拟方法,对存储单煤堆的封闭式大跨度煤棚内的自然对流现象进行研究。在非定常条件下,研究了固定瑞利数下煤堆附近传热特点和流动转捩情况;研究了不同瑞利数下煤棚内流动结构的对称性和非对称结构出现时间,以及在充分发展阶段流动表现出的非定常特性。结果表明,煤棚内瞬态流动会经历三种不同发展阶段:初始阶段、演化阶段和充分发展阶段。在演化阶段,羽流分离脱落会推动煤棚内非对称流动结构形成,非对称现象出现的时间会随瑞利数增大而提前。在充分发展阶段,煤棚内流动呈现无规则的非定常湍流状态,且达到充分发展状态的时间随瑞利数增大而推迟。

In recent years,the environmentally friendly closed coal shed has been widely used in actual production and life.The heat released from the coal pile will cause local overheating of the environment,which will affect the comfort and health of workers.So the problem of convective heat transfer in coal shed has attracted extensive attention.In order to reduce the harm of coal heap heat release,it is necessary to understand the mechanism of heat transfer and flow in the process of coal heap heat release.CFD numerical simulation method is used to study the natural convection phenomenon in the closed large span coal shed with a single coal pile.Under unsteady conditions,the heat transfer characteristics and flow transition around coal pile with fixed Rayleigh number are studied.The emergence time of symmetric and asymmetric flow structures in coal shed under different Rayleigh numbers are studied.The unsteady characteristics of flow in full development stage are given.The results show that the transient flow in the coal shed will go through three different stages:initial stage,transitional stage and quasi-steady stage.During the transitional stage,the separation and shedding of the plume will promote the formation of asymmetric structure in coal shed,and the emergence time of asymmetric phenomenon will advance with the increase of Rayleigh number.In the quasi-steady stage,the flow in the coal shed presents the characteristics of irregular unsteady turbulent flow,and the time to reach full-development state is delayed with the increase of Rayleigh number.