180°矩形弯管流场的LDV测量

采用激光多普勒测速仪（简称LDV）对180°矩形弯管内流场进行了测量，得到时均速度、湍流强度等数据。除靠近内壁r^＋=0．1位置，弯管纵截面上的切向速度沿轴向基本不变，但靠近弯管上下壁面的切向速度逐渐减小直至为零。在弯管的主流区域，0°～60°之间的纵截面上，内侧切向速度增大，外侧切向速度减小；60°～180°之间的纵截面上，内侧切向速度减小，外侧切向速度增大。在整个弯管段内，内侧切向速度总是大于外侧的切向速度。由于受到边界层分离和二次流的影响，90°～180°纵截面上r^＊ =0．1位置的切向速度产生明显的变化。轴向速度值远小于切向速度值，并且沿轴向变化不大。轴向速度的正、负之分，说明了二次流的存在，并且二次流的旋转中心从外壁向内壁移动。切向和轴向湍流强度的数量级一样，基本在0．1V。左右。切向湍流度在150°～180°纵截面r^＊ =0．1位置的变化很大；但是轴向湍流强度分布比较平稳，其值沿轴向和径向变化不大。

Experimental measurement of flow field in 180° curved duct with rectangular cross-section by LDV

The flow field in the 180°curved duct with the rectangular section was measured by Laser Doppler Velocimetry （LDV）. The mean velocity and the turbulent intensity of the flow field were investigated. At the radial location, except for the r^＊ =0.1 location, the tangential velocity changed a little along the Z direction, and the tangential velocity decreased gradually until zero near the upper wall. The tangential velocity increased between 0° and 60°, while the tangential velocity decreased between 60°and 180° near the inner wall. On the contrary, the tangential velocity decreased between 0° and 60°, but the tangential velocity increased between 60° and 180°near the outer wall. In the 180° curved duct, the tangential velocity near the inner wall was larger than the tangential velocity near the outer wall. At the r^＊=0.1 location of 90°--180° longitudinal section, the tangential velocity had obvious fluctuation due to the boundary layer and secondary flow. The axial velocity was much less than the tangential velocity, and had a little change along the Z direction. The axial velocity showed significant positive and negative values, which indica- ted the existence of the secondary flow, and the center of secondary flow moved from the outer wall to the inner wall. The tangential intensity and axial turbulent intensity were about 0. lVi at with the same order of magnitude. The tangential turbulent intensity had an obvious fluctuation at the r^＊ =0.1 location between 150° and 180°. But the axial turbulent intensity changed a little along the axial and radial direction.