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 ve-locity 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. 1Vi 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.