Influence of the Circumferential Forward Skew Angle of Blades on the Blade Tip Leakage Flow Field of a Low-pressure Axial Flow Fan

An experimental and numerical study was performed of a low-pressure axial flow fan installed with blades of four different circumferential forward skew angles (1.27,6.1,8.3 and 12 degrees).By utilizing Reynolds Number averaged Navier-Stokes (N-S) equation group and a turbulent flow model of Spalart-Allmaras (S-A) No.1 equation,a numerical calculation was conducted of the three-dimensional viscous flow field of the impeller at steady operation points.Under the precondition of the numerical calculation results being identical with the measured ones,analyzed was the axial distribution of blade surface pressures at the blade tip.The calculation results show that with an of the circumferential forward skew angle of the blades,the initial location of the blade tip leakage vortex will gradually shift toward the blade trailing edge.By employing a particle image velocimetry (PIV) system,the blade tip leakage flow field of the impeller was tested and measured,explicitly showing the evolution of the blade tip leakage vortex.It has been found that with an of the circumferential forward skew angle of the blades,the stability of the blade tip leakage vortex will first become greater and then weaker ,the axial displacement of the vortex in question will first decrease and then increase while its circumferential displacement will first and then decrease.