LDV Measurements of Three Dimensional Turbulent Flow Field in a Centrifugal Impeller

A Laser Doppler Velocimeter (LDV) and shaft encoder was used to measure velocities at the design flow of the shrouded centrifugal backswept impeller.Measurements of the three-dimensional velocity field were acquired at several main planes through the passage.The measurements described both the through flow velocity field along circumferential measurement planes and the velocity vector at radial planes.It was found that the high velocity flow was held near the hub side on the suction surface of blade passage and shifted from the hub to the shroud side on the pressure surface as the fluid approached the exit.The results also provided the evidence of the development of a "wake" of low momentum fluid near the shroud at midpitch at the exit.The velocity vector plots showed that the flow angles on the hub were very differential from those on the shroud side because of the fluid viscosity.The results indicated that the secondary flow generated in vertical direction of the main flow velocity was related to curvature and rotating of impeller.The secondary flow velocity vector plots were also presented at the middle passage and exit.The development of the secondary vortex along impeller blade passage has been clearly observed and recorded.