Integral and statistical characteristics of the turbulent swirl flow in a straight conical diffuser

Abstract

The results of the experimental investigations of the turbulent swirl flow in a straight conical diffuser with inlet diameter 0.4 m and total divergence angle 8.6 • are presented in this paper. The incompressible swirl flow field is generated by the axial fan with outer diameter 0.397 m. The measurements were performed in one measuring section downstream the axial fan impeller in the conical diffuser in position (z/R 0 = 1) with original classical probes and an one-component laser Doppler anemometry (LDA) system, for four flow regimes. The comparative measurements of axial and circumferential velocities are presented. The Reynolds number, calculated on the basis of the average velocity, ranges from 149857 to 216916. Integral parameters, such as volume flow rate, average circulation and swirl number, are determined. Statistical characteristics, such as level of turbulence, skewness and flatness factors, are calculated. The highest levels of turbulence for axial velocity are reached in region 0.4 < r/R < 0.6, where D = 2R. The highest levels of turbulence for circumferential velocity are reached for the regimes with lower circulation in r/R ≈ 0.4, i.e., in the vortex core region for the cases with higher circulation.