Insight into the Turbulent Swirl Jet behind the Axial Fan

Abstract

Swirl flow occurs in various technical systems, nature, biomedical application, and etc. Turbulent swirl flow in ventilation systems occurs in turbomachines, as well in ventilation channels behind them, in pipes, diffusers and jets. In this paper is presented experimental investigation of the turbulent swirl flow behind the axial fan in free jet. Experiments have been performed in measuring sections downstream the axial fan impeller by use of the three-component laser Doppler velocimetry (LDV) technique. Axial fan is installed after the ISO 5801 standard, category A - free inlet and free outlet. Flow inlet conditions were varied by fan rotation speed and outlet blade angle. Axial impeller generates Rankine swirl in all cases. Distributions of the time averaged velocity components revealed all characteristic fluid flow zones. Transformation of these velocities downstream was also analyzed. It was shown the character of the circumferential velocity maxima downstream decrement. Evolution of the statistical moments of the higher order is also presented. It is shown that skewness and flatness factors differ from normal Gaussian distributions. The highest turbulence levels are reached in the shear layer zone and in the injection zone. Turbulence swirl flow anisotropy states are calculated on the basis of the three-component LDV measurements and presented in the invariant maps. Most of the turbulence states are positioned in the region, i. e. vicinity of the three-component isotropic turbulence and axisymmetric expansion states.