Analysis of vortical flow field in a propeller fan by LDV measurements and LES - Part I: Three-dimensional vortical flow structures

Three-dimensional structures of the vortical flow field in a propeller fan with a shroud covering only the rear region of its rotor tip have been investigated by experimental analysis using laser Doppler velocimetry (LDV) measurements and by numerical analysis using a large eddy simulation (LES) in Part I of the present study. The propeller fan has a very complicated vortical flow field near the rotor tip compared with axial fan and compressor rotors. It is found that three vortex structures are formed near the rotor tip: the tip vortex, the leading edge separation vortex, and the tip leakage vortex. The tip vortex is so strong that it dominates the flow field near the tip. Its formation starts from the blade tip suction side near the midchord. Even tit the design condition the tip vortex convects nearly in the tangential direction, thus impinging on the pressure surface of the adjacent blade. The leading edge separation vortex develops close along the tip suction surface and disappears in the rear region of the rotor passage. The tip leakage vortex is so weak that it does not affect the flow field in the rotor.