Measurements of Turbulent Flow Downstream from Elbow Pipe

Measurements of the longitudinal mean and fluctuating velocities downstream from a 90° elbow pipe of circular cross section were obtained using a laser-Doppler velocimeter at a Reynolds number of 5×104 and radius ratio of 1.1, 2, 4 and 8 in order to clarify the effect of the radius of curvature and the distance from the elbow exit on the behavior of turbulent flow. The turbulence intensity is large near the inner-radius wall of the elbow where flow separation occurs, and in the center of the pipe where velocity gradient is high. The increase of the cross-sectionally averaged value of the longitudinal component of the turbulent energy in the region more than 2 times the pipe diameter downstream from the elbow exit compared with that for fully developed turbulent flow is proporional to the -1.6 power of the radius ratio and decreases as an exponential function of the distance from the elbow exit.