Influence of the Axial Fan Blade Angle on the Turbulent Swirl Flow Characteristics

Abstract

U ovom radu je prikazano istraživanje turbulentnog vihornog strujanja u cevi na potisu aksijalnog ventilatora sa devet podesivih lopatica za uglove 22°, 26° i 30° i istovetni broj obrtaja (1500 min-1). Brzine su merene laser Dopler anemometarskom tehnikom u mernom preseku 3.35·D od ulaska u instalaciju. Postignuti su Rejnoldsovi brojevi Re=236784, 259151 i 277018. Prikazana je nehomogenost i anizotropnost izučavanog turbulentnog brzinskog polja. Profili vremenski osrednjenih obimskih brzina imaju karakter Rankinovog vrtloga, dok se u slučaju aksijalnih brzina primećuje povratno strujanje u oblasti vrtložnog jezgra za uglove 26° i 30°. Eksperimentalno određeni momenti drugog i viših redova prikazuju kompleksnost turbulentnog vihornog strujanja. Vizualizacija turbulentnog vihornog strujanja je prikazana za ugao 22°.

The paper presents the investigation of the turbulent swirl flow in a pipe behind the axial fan with adjustable nine blades for the angles of 22°, 26° and 30° for the same rotation number (1500 rpm). Velocities were measured with laser Doppler anemometry (LDA) in the measuring section 3.35·D from the test rig inlet. The achieved Reynolds numbers are Re=236784, 259151 and 277018. The non-homogeneity and anisotropy of the turbulent velocity field are shown. The time averaged circumferential velocity profiles have shown the Rankine vortex structure and revealed a reverse flow in the vortex core region for the blade angles of 26° and 30°. The experimentally determined moments of the second and higher orders reveal complex mechanisms in the turbulent swirl flow. In addition, the visualization of the turbulent swirl flow for an angle of 22° is presented.