Study on Dynamic Response Including Rotating Stall of a Rotor Blade Row

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In the project of improving the low flow rate characteristics of an axial flow fan and exploring the onset of rotatin stall, the followings are revealed:1. The low energy fluid accumulated toward the pressure side of rotor blased is responsible for the onset of rotating stall. The removal of this low energy fluid improves low flow rate characteristics of the fan perfectly.2. In a fan with relatively large tip clearance, the accumulation of the low energy fluid is caused by leakage vortices through tip clearance.3. In the near stall flow rate regime, the static pressure rise remains almost constant even if the fan flow rate is changed. The dynamic presure difference due to the deceleration of relative velocity through the rotor blade row is, on the contrary, sensitive to the change of fan flow rate. The difference becomes large with a small decrease in flow rate and causes much increase in blade row losses. The inlet velocity distribution is also sensitive to the screen in this flow rate regime.4. The instantaneous blade row losses calculated from the above data using the unsteady Bernoulli equation are plotted as a function of instantaneous inlet angle.5. In the initiation of rotating stall, it starts from the blade tip. The rotating speed of the cell remains constant throughout its development. The cell completely develops in four or five rotations of the rotor. The flow field in this stage is so changeable that it differs during the period of half pitch movement of the rotor.The instantaneous blade row losses obtained in 4. must be verified by using them in a numerical simulation of rotating stall which is going to be carried out hereafter.