Studies On Flow Characteristics In Axial Gap And Rotor's Hollow Regions Of Axial Fan

In consequence of the advantages such as installing convenience, compact structure, favorable performance in inverting flow and so forth, contra-rotating fans have been widely adopted in mines. However, on account that the fan's two rotors rotate in opposite directions and the unsteady interaction between two stages is resultantly intense, this kind of fans has gradually shown the drawbacks of high noise and disappointing safety of rotor. As for axial turbomachinery, the axial gap between two stages is the main factor affecting the intensity of the unsteady interaction, based on which and also aimed at reference instructing the axial gap selection advisably related to efficient, silent, safe and compact fans, unsteady computations were implemented on a contra-rotating mine fan, No FBDCZ36, to investigate the variations of aeroacoustic performance, rotor safety and aerodynamic performance with the axial gap. It is showed that aeroacoustic performance and rotor safety all improve as the axial gap increases, but over the axial gaps of 80 percent and 60～70 percent of the first mean span chord(b) respectively, their improvement tendencies slow down, so no meaning could be found to enlarge the axial gap further; optimum aerodynamic performance is observed at the axial gap of 55 to 60 percent of b, in which the 2nd rotor's inlet flow angle and the mixing between wake and main flow are two main factors influencing the variation of aerodynamic peformance. For the fan investigated in the research, it is found that favorable overall properties appear with the axial gap of about 70 percent of b.Considering structural strength and material saving, blades and hubs of large and medium axial fans are all hollow. When fans are working, there are relative eddies existing in the hollow regions as a result of the air's inertia. With friction, energy loss could be found in the regions. In this investigation, unsteady computations were carried out on the hollow regions of a large axial mine fan's rotor. It is found that owing to spacing size limitation, turbulent fluctuation and air's small inertia, no obvious relative eddies are observed in the regions and the air's relative velocity value is ensuingly limited. Combined that the air's dynamic viscosity has only the order of 10-5, energy loss in the regions could be negligible. Thus, it's of no concern to implement further investigation or dispose in the hollow regions.