Measurements of turbulent flow downstream from an elbow

Measurements of the longitudinal mean and fluctuating velocities downstream from a 90° elbow of circular cross section and 1.1 radius ratio were obtained using a laser-Doppler velocimeter at Reynolds numbers of 50,000, 500,000 and 1,000,000 in order to clarify the behavior of the turbulent flow downstream from the elbow. The turbulence intensity increases in the region of steep velocity gradients and on the inside of the elbow due to the flow separation, and the former is larger than the latter. The maximum value of the cross-sectionally averaged value of the turbulence intensity is located at 1 pipe diameter downstream from the elbow. At this distance, the power spectrum of the fluctuating velocity has a distinct peak at a reduced frequency of about 0.4. No marked dependence is observed on Reynolds number for the turbulence intensity or the power spectrum downstream near the elbow.