Visualization of tip vortex flow in an open axial fan by EFD

Abstract

The behavior of tip vortex in an axial fan without casing wall (called open axial fan) was discussed and analyzed. The velocity measurement was performed by using two-compon ents Laser Doppler Velocimetry (LDV) system. The detailed velocity and vorticity distribution inside blade passage and downstream of rotor were obtained. Thus the structure of tip vortex and its behavior were graphically visualized by experimental fluid dynamics (EFD). The tip vortex flow trace was indicated with the calculation of vorticity. As a result, it was found that tip vortex was generated at blade tip region near leading edge and it extended to downstream of blade exit with its core tending inward to hub direction. In addition, leading edge vortex was also found at the forepart of the experimental open fan.

Measurements of aerodynamic noise and wake flow field in a cooling fan with winglets

“…9(a), the traces of the vorticity are generated from the suction side of rotating blades and develop to the peripheral direction, but incline 12° to the axial direction. Similar vorticity traces were obtained without the shroud of a fan by Cai et al (2002) by analyzing the velocity data from the LDV measurements.…”

Visualization of aerodynamic noise source around a rotating fan blade

“…With this method, however, it is impossible to identify the flow structure regarding the noise generation with high spatial resolution. On the other hand, as for the flow field around the fan blade, the flow field is visualized by oil film and smoke (Nashimoto et al, 2000), and the velocity field is measured by laser doppler velocimetry (Nash, 1999;Cai et al, 2002) and particle image velocimetry (Nashimoto et al, 2004). Although these studies on flow field around the fan blade allow for the understanding of flow phenomena, such as separation, reattachment and vortex shedding, these techniques are not suitable for identifying the noise source distribution.…”

Flow fields with tip leakage vortex in a small axial cooling fan

“…For the cooling fan of the outer unit in room air conditioner, Jang et al [7,8] outer casing, Kato et al [9] have numerically analyzed the relationship between vortices and noise level using LES. Also, Cai et al [10] and Shiomi et al [11] have experimentally clarified the tip vortex behavior inopen-type axial rotor without outer casing using LDV measurement. These researches have mainly been done for relatively large rotor whose diameter is larger than 300mm.…”