红外窗口不同冷却方式下的结构传热和热应力特性计算研究

Numerical study on heat transfer and thermal stress for infra-window with externally cooled and internally colled techniques

对外冷喷流和内冷管流等不同冷却方式下的红外窗口传热和热应力进行了数值计算研究。窗口结构传热和热应力采用有限元方法求解,带外部冷喷流窗口外表面气动加热率则通过对带冷源项的N-S方程求解给出,当采用管流冷却时,管流液体温度和窗口结构温度通过耦合迭代方式统一求解,管流和壁面间的换热系数采用工程关联公式估算。研究表明,在达到来流总温以前,窗口各点温度和热应力随加热时间单调上升,各时刻最大温度发生在外表面;而最大热应力则发生在合金材料内部。两种冷却方式对比表明,外冷方式对于窗口整体温度和热应力的降低十分有效,但具体到局部重要部位,外冷方式效果不如内冷,内冷方式对于管道附近部位具有更好的降温和降低热应力效果。因红外窗口尺度限制,冷却管道流动雷诺数偏小,流动为层流态,这限制了冷却管换热效率的提高,因此建议增加管道数目和管壁粗糙度来强化冷却。

The heat conduction and thermal stress problems for both externally cooled and internally cooled infra window in hypersonic flow are numerically simulated with finite element method. The N-S equations with volumetric heat sink are solved to give the convective heat transfer to window surface. When regeneratively cooled technique is used, the temperature of piped liquid coolant is strongly coupled with the window temperature, and an iterative procedure is needed to solve the coupled linear equations for temperature. The heat exchange coefficient between coolant and pipe is predicted by analytical correlation. It is shown that the window temperature and thermal stress increase monotonically as the time elapses. The maximum temperature is located at the window surface, while the maximum thermal stress at the interior of window alloy. The comparison demonstrates that the externally cooled technique is effective in reducing the window temperaure and stress on the whole, while the internally cooled technique is more efficient in reducing temperaure and stress in the vicinity of pipe. Limited by the window sizes, the flow Reynolds number based on the hydraulic diameter of pipe is so small that the pipe flow remains in laminar state, which has a comparatively small heat exchange coefficient. So more pipes with more rough surface are needed to enhance the heat exchange between the coolant and pipe.