Influence of the Reynolds number and the axial fan impeller blade angle on the turbulent swirling jet flow

Abstract

An axial fan impeller, in-built as the case A, after ISO 5801, defined as "free inlet, free outlet" with nine twisted blades, serves as turbulent swirling flow generator for this study. Three-component laser Doppler velocimetry (LDV) measurements have been performed in the jet flow at ten measuring sections downstream the axial fan impeller outlet. This paper discusses distributions of the circumferential velocity downstream, due to its importance in the analysis of the turbulent swirling flow phenomenon in the jet. Gradients of the radial velocity are also discussed. Influence of the Reynolds number (defined by the fan rotation speed n), as well as impeller blade angle on the circulation distribution is the focus of this paper. It was shown that the values of the circulation in the domain 0 < r/R < 1 decrease in hierarchical order from the initial (I) to the final (X) measurement section. However, this is not the case in the rest of the vortex jet flow, where the circulation changes are heterogeneous and chaotic, which is especially present in the domain 2 < r/R < 4. The influence of the Reynolds number on the distribution of the circulation varies depending on the measurement section and r/R domain. It is shown that in the region near the axis, circulation doesn’t depend on the impeller blade angle, while this influence is discussed in the rest of the flow region. Also, distribution of the angular velocity (Ω_W = W/r) is considered. The influence of the blade impeller angle in one measurement section is presented as well. All these discussions lead to better understanding of the production of the Reynolds stresses in the generated turbulent swirling jet by the axial fan impeller.