The Pre-Swirl Effect on the Efficiency of adjustable fan

The purpose of the work is to substantiate the choice of the estimated pre-swirl flow coefficient that ensures high efficiency of the fan regulated by turning the rotor blades in a wide range of rates. Radial clearances, incidence angles and theoretical total pressure rise dependencies on the pre-swirl flow coefficient are obtained analytically. It is shown that to change the theoretical pressure and flow coefficients by the same amount, the fan blades with a swirl of the flow along the rotation must be turned by a larger angle than the fan with a swirl against the rotation. This leads to a greater radial clearance changes when regulating the fan and an increase in pressure losses in the end regions. When regulating the fan by turning the rotor blades, pressure losses are associated with the stator and rotor flow mode mismatch, leading to a deviation of the incidence angles from the optimal values. Incidence angles in the fans with a pre-swirl against the rotation deviate less from the optimal values at flow rate changes, than the fans with a flow swirl along the rotation. Consequently, the flow swirl against the rotation increases the efficiency of fan regulation by turning the rotor blades. The analytical data obtained are verified by the examples of three fans with different pre-swirls: along rotation, against rotation and no pre-swirl). The characteristics of these fans obtained by numerical simulation in the ANSYS CFX software complex confirmed the derived analytical dependences.

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