REYNOLDS NUMBER INFLUENCE ON INTEGRAL AND STATISTICAL CHARACTERISTICS OF THE TURBULENT SWIRL FLOW IN STRAIGHT CONICAL DIFFUSER

Abstract

Results of experimental investigations of the turbulent swirl flow in straight conical diffuser are presented in this paper. Diffusers have the inlet diameter 0.4 m and total divergence angles 8.6°. The incompressible swirl flow field is generated by the axial fan with outer diameter 0.397 m. Measurements are performed in one measuring sections downstream the axial fan impeller, i.e. in conical diffuser (z/R0 = 1) with one-component laser Doppler anemometry (LDA) system, for four flow regimes. Axial and circumferential velocities are measured. Reynolds numbers calculated on the basis of the average axial velocity, ranges from 149857 to 216916. Integral parameters, such as volume flow rate, average circulation and swirl number are determined. Statistical characteristics are calculated such as level of turbulence, skewness and flatness factors. The highest levels of turbulence for axial velocity are reached in the region 0.4 < r/R < 0.6, where D = 2R. The highest levels of turbulence for circumferential velocity are reached in the region around r/R = 0.4 for lower values of circulation, respectively in the core region for higher values of circulation.