Analysis of velocity profile measurements obtained by different methods in low-speed, small-scale wind tunnel

Abstract

A low-speed small-scale wind tunnel was designed for spray investigation under cross and co-flow conditions. Precisely defined profiles of mean velocity and turbulent intensity in the wind tunnel test section are crucial parameters for any rigorous flow study. Different velocity measurement techniques were used to evaluate the velocity and turbulent intensity profiles in the test section. Two non-intrusive techniques, Phase-Doppler Anemometry and Laser-Doppler Anemometry (PDA, LDA), and two intrusive techniques, Constant Temperature Anemometry (CTA) and pitot static tubes of S and L-type were applied. The velocity was measured in 19 equidistantly spaced positions in a centrally placed horizontal plane. The data were obtained for four different mean velocities in the test section (7, 14, 21, 28 m/s). Results of different measurement techniques were mutually compared, and repeatabilities and uncertainties of PDA and CTA measurements were assessed. Turbulent velocity spectra measured by the CTA were analysed. The effect of declination of the pitot static tubes (L-type and S-type) was briefly discussed and compared with an industrial velocity probe QuadraTherm® 640i In-Line Mass Flow Meter with a measuring range of 5–300 m/s. Velocity and declination of pitot static tubes were analysed only in the central point of the test section. The results show that a fully turbulent and uniform flow is developed 15 mm upstream the test section area. Mean velocity and turbulent intensity profiles obtained by different techniques are in a good agreement. Uncertainties of type B of PDA and CTA measurement method are below 5%. Turbulent intensity in the main stream is under 5%. Advantages and drawbacks of the presented measurement techniques were discussed. The PDA was found to be the most suitable measurement technique due to its precision and non–intrusive flow probing.