Study of the turbulent swirl flow in the pipe behind the axial fan impeller

¹ University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia
² University of Belgrade, Faculty of Architecture, Belgrade, Serbia

^a Corresponding author: djcantrak@mas.bg.ac.rs

Received: 27 May 2015
Accepted: 29 February 2016

Abstract

Experimental research of the turbulent swirl flow in the pipe behind the axial fan impeller is presented in this paper. Axial fan is inbuilt without guide vanes in the installation with a free inlet and ducted outlet, like it is widely used in the ventilation systems. One-component laser Doppler anemometry and stereo particle image velocimetry (SPIV) are used in two measuring sections on the fan pressure side and for three fan rotation numbers. Non-dimensional axial velocity profile is not significantly transformed downstream, while the circumferential is, although it preserves its character. Turbulence level is the highest in the vortex core in both measuring sections for all velocities. It increases downstream in the vortex core zone and decreases in the main flow region. Determined skewness and flatness factors point out the intermittent character of the generated turbulent swirl flow, as well as the existence of the organized coherent structure. Correlation curves indicate various dynamics of fluctuating circumferential velocity fields in measuring points. The Rankine vortex structure of the turbulent swirl flow is also revealed by the SPIV measurements. Analysis shows more dominant vortex core dynamics in the downstream section. Studied flow is characterized by extensive mass, momentum and energy transfer.