多孔仿生射流表面减阻特性数值模拟

Numerical simulation of drag reduction characteristics of a bionic jet surface with multiple holes

利用RNGk-ε湍流模型对流体在多孔仿生射流表面上的流动特性进行了数值模拟。结果表明:减阻率和流速比呈线性关系,流速比越大减阻效果越好,最大减阻率为59.02%;单孔射流表面中心线上的摩擦阻力系数先减小后增大,局部减阻率最大为111.8%;射流孔越多,减阻效果越好。探讨了仿生射流表面减阻机理:射流通过改变其表面附近的流场结构,使得边界层黏性底层的厚度增加,垂直于壁面的法向速度梯度减小,达到了显著的减阻效果;同时产生稳定的流向涡结构,并在壁面处形成小的二次涡,抑制了流体间的动量交换,减小了摩擦阻力。

Numerical simulation is carried out to study the drag reduction characteristics of porous bionic jet surface according to RNGk-εturbulence model.The results show that there exists a linear dependency of the drag reduction on the rate of velocity,that is,the higher the rate of the velocity,the better the effect of drag reduction.The maximal efficiency of drag reduction is 59.02%.Friction coefficient decreases at first,and then increases along with the central line of the bionic jet surface with single hole.The efficiency of drag reduction in local region can be up to 111.8%.Furthermore,the more the number of jet holes,the better the drag reduction effect.The mechanism of the drag reduction of the bionic jet surface is studied.It is found that the jet-flow increases the thickness of the viscous sublayer in the boundary layer by changing the structure of the flow field in the vicinity of the jet surface.As a result,the gradient of normal velocity,perpendicular to the surface,is decreased,which contributes to remarkable drag reduction.Meanwhile,the gradient of normal velocity generates streamwise vortex structure and develops small secondary vortex on the surface,which results in inhibiting momentum exchange between fluids,thus,reducing the friction on the jet surface.