均直巷道通风能量耗散机理

Mechanism of ventilation energy dissipation in homogeneous roadway

为了深化对风流能量耗散的认识,基于流体力学相关原理,以均直巷道内稳定流动的风流为研究对象,首先分析了巷道风流分别为层流和湍流时的能量耗散,并指出了两者的异同,然后分析了平板间流体和圆筒壁间流体能量耗散,找到了无旋流动和有旋流动的本质,最后从细观角度对巷道风流层流流动和湍流流动(通风)的能量耗散产生原因及形成机理进行了分析,建立了巷道各项参数与通风能量耗散间的关系,特别分析了涡在湍流核心区能量耗散中的作用。发现单位长度巷道的层流能量耗散率与平均风速的平方及风流的动力黏度成正比,与巷道半径无关;单位长度巷道的湍流能量耗散率与平均风速的立方、沿程阻力系数、巷道半径及空气密度成正比。不论何种流体运动,从局部来看,其单位体积能量耗散率等于流体动力黏度与剪切速度梯度的平方的乘积。湍流流动与层流流动的本质区别在于,湍流中存在的涡旋使得局部剪切速度梯度增大,能量耗散率随之增大。湍流核心区能量耗散与巷道平均风速的立方成正比关系,是由于涡的初始动能与速度平方成正比,产涡频率与速度成正比。随着巷道壁面粗糙度的增大,层流底层边界上产生的涡的半径、初始动能及湍流核心区能量耗散也随之增大。

The essence of roadway ventilation resistance is energy dissipation.In order to study the ventilation energy dissipation,the steady flow in homogeneous roadway is taken as research object and the principle of fluid mechanics is used as analysis basis.Analysis is firstly carried out for energy dissipation as the ventilation in laminar and turbulent flow respectively,and the similarities and differences between them are identified.Then the essence of non-rotational and rotational flow are analyzed by the energy dissipation of fluid between plates and cylindrical walls.Finally,the formation and mechanism of ventilation energy dissipation are analyzed from a microscopic perspective.The relationship between various parameters of roadway and ventilation energy dissipation is established and the effect of vortex on the energy dissipation in turbulent core region is analyzed.It is found that the energy dissipation rate of laminar flow per unit length of roadway is directly proportional to the square of average velocity and the dynamic viscosity,and independent of roadway radius.The turbulent energy dissipation rate of roadway per unit length is directly proportional to the cubic of average velocity,frictional resistant coefficient,radius and air density.Locally,the energy dissipation rate per unit volume is equal to the product of the shear velocity gradient squared with dynamic viscosity for any fluid motion.The essential difference between turbulent flow and laminar flow is that the vortex existing in turbulence increases the local shear velocity gradient leading to an increase in energy dissipation rate.The energy dissipation in the turbulent core area is proportional to the cube of the average velocity in the roadway,because the initial kinetic energy of the vortex is proportional to the square of the velocity,and the frequency of vortex generation is proportional to the velocity.With the increase of wall roughness,the radius and initial kinetic energy of the vortex generated on the bottom boundary of laminar flow and turbulent core energy dissipation rate also increase.