Abstract
It is of great value to study the impact of abnormal blade installation angle on the inducement mechanism of rotating stall to achieve the active control of rotating stall in an axial fan. Based on throttle value function and SST k-ω turbulence model, numerical simulations of the unsteady flow process in stall condition of an axial flow fan with adjustable vanes were carried out, and the influence mechanism of abnormal stagger angle of a single blade in the second stage rotor on induced position and type of stall inception and evolution process of rotating stall were analyzed. The results show that compared with synchronous adjustment of blade angle, the blade with abnormal stagger angle will cause the increase of flow rate at the beginning of stall and make the fan fall into an unstable condition in advance. The existence of blade with abnormal angle does not cause the change of the induced position and type of stall inception and the inducement mechanism of rotating stall, which are the same as the axial fan with normal blade angle. Moreover, the single blade with abnormal deviation angle has important impacts on the 3D unsteady evolution process from stall inception to stall cell formation in two rotors.
Highlights
With the wide application of the two-stage variable pitch axial fan, its safety and reliability has become increasingly vital in engineering applications
Rotating stall is the instability phenomenon that occurs when the fan operates at flow rates below the design conditions, which can deteriorate the flow field, generate noise [1], and threaten the service life of rotor blades owing to the alternating stress, but even cause fan blades to break and endanger the operation of the fan seriously
The mechanism of rotating stall in a centrifugal fan has been experimentally studied by Hou [5], who found the intermittent phenomenon of energy exchange when the fan works under weak rotating stall and the stall on the pressure side of the G4-73 fan blades; he further pointed out that stall at the pressure side of blades requires two conditions, i.e., the actual inlet
Summary
With the wide application of the two-stage variable pitch axial fan, its safety and reliability has become increasingly vital in engineering applications. Bianchi S et al [15] conducted an experimental study on stall inception patterns under different installation angles of rotor blades in a low-speed axial fan. Domestic researches on stall inception patterns and the influence factors mainly focus on the tip clearance, the axial spacing, the rotating speed [24] and so on now. Domestic researches on stall inception patterns and the influence factors mainly focus on the tip clearance, the axial spacing, the rotating speed [24] and so on It has been showed in the literature that an abnormal regulation of the stagger angle may have an important impact on the fan performance and the stability control. Through simulations in the inception patterns, starting positions mechanism studied presence of an abnormal deviation of a second-stage blade angle in a two-stage axial fan.
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