Wind Tunnel: Flow Around a Cylinder



Axial Flow Fan

Objectives:

Investigate and report on the operation of an axial flow fan by determining the following:

• Determine the velocity profile in the tube.

• Determine the mass flow rate and power (rate of kinetic energy) exiting the system.

• Determine the efficiency of the motor/fan system.

• Investigate the effect of three flow restrictions on velocity profile, mass flow rate, power and efficiency.

Background:

The experimental apparatus, illustrated in Fig. 1, consists of a General Electric adjustable-blade, multistage axial-flow fan connected to a 7.5 HP DC cradled dynamometer. The rotor blade of the axial fan is on the outer perimeter of a disk that supports the fan blade.

According to its specifications, this fan has a maximum rated speed of 3000 RPM. It produces an air output of 2200 CFM at a static pressure of 3.75 inches of water when operating at 1800 RPM and a blade setting of 6425-6425. (This blade setting code indicates two stators and two rotors, with the stator blades set at an angle of 64 degrees and the rotor blades set at an angle of 25 degrees.)

Variable voltage control for the dynamometer is provided by a GE Speed Variator. The speed variator is a packaged all-electric drive operating from AC power. The power unit converts the incoming AC power to DC, which is used to supply a DC drive motor. Dynamometer scale readings and speed provide for direct measurement of the power required by the fan.

Downstream of the fan is a stainless steel circular duct with an inner diameter of 1.5 ft and length of 16.8 ft. Vertically and horizontally mounted 12 ft downstream of this duct are two pitot tubes that measure pressure heads at various positions across the duct diameter. The pressure heads are read directly from the water-filled inclined manometers connected to the pitot tubes through rubber tubing. A flow straightener is also placed in the duct before the flow reaches the pitot tube. In addition, a flow restriction disk can be clamped to the end of the duct in order to control the flow of air. Several disks, with different circular areas removed, are available. Use the method illustrated in Fig. 2 to find the centerline of the duct.

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