Flow Uniformity and Turbulence Level Measurements by LDA in the Wind Tunnel for Anemometers Calibration

Abstract

Existing wind tunnel in the Laboratory for Hydraulic machinery and energy systems, Faculty of Mechanical Engineering, University of Belgrade, is redesigned, by adding axial fan regulated by the inverter at the tunnel inlet and flow straightener in the pipe before the carefully profiled Witoshinsky nozzle. Various anemometers could be calibrated in the axisymmetric uniform jet after the nozzle with inner diameter of 145 mm. In this paper are presented experimental results of the flow uniformity and turbulence levels, as well as skewness and flatness distributions for various flow regimes in the wind tunnel measurement section by one-component laser Doppler anemometry (LDA) along the horizontal radius in 27 points. Time-averaged axial velocity profiles have been obtained for twenty Reynolds numbers in the interval Re = 1780 to 148869, determined for point on the jet axis r/R =0. Uniform velocity profiles are obtained in the jet core region, i.e. up to r/R = 0,9 for all Reynolds numbers except the lowest one. Turbulence levels have been also reported for all these cases and achieved turbulence levels were below 2% in the free jet core region for almost all measuring points and regimes, what follows standard ISO 17713-1 requirements. Achieved validation was high. Sampling rate varied and in most of the cases was in average 250-400 Hz. Thermal fog seeding was applied at the calibration tunnel inlet, i.e. at the axial fan suction side.