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Sinha Wind Tunnel

General
In connection with his NASA project, Dr. Sinha has built a wind tunnel. It went into operation the week of 5/24/2004. His first task is to check out the tunnel itself and make adjustments as necessary to minimize turbulence and other flow disturbances. As wind tunnels go, this is a small one. Clearly, Reynolds numbers will be restricted and a lot of extrapolation will be needed to estimate actual flight conditions. Nevertheless, it should be very useful in speeding the progress of his deturbulator research.

Specifications

Entrance: 48” high by 36” wide
Test Section: 12” high by 9” wide
Contraction Ratio: 16:1
Airspeeds: 0 to 80 kts
Boundary Layer: about 0.75” in test section
Velocity Profile: flat within <1% in test section
Turbulence Level: 0.8%
Motor: 3-phase with solid state control
Propeller: 26”, 3-blade, balanced
Construction: Motor mount anchored to floor and isolated from tunnel.
The entrance section can be moved forward to accommodate
a longer test section, permitting longer chords with restricted
angles of attack.

Technical Issues
A primary issue is turbulence from the flow compression at the entrance. Measurements will be made using a hot wire anamometer to determine the turbulence levels. The design of the tunnel permits lengthining the entrance section as necessary to accommodate a flow straightener if needed.

Another problem in wind tunnel design is flow separation from the walls in the expanding transition section behind the test section. When this occurs, the high velocity flow flops about randomly within the section and strikes the propeller blades unevenly, causing them to alternately "fly" and stall. This puts a time varying load on the motor/propeller assembly, causing it to shake, and sets up flow pulsations that are felt upstream in the test section. There is some indication of this at the highest airspeeds in the present tunnel. Dr. Sinha is working on solving this problem. We'll have more to say about this later.

Utilization
Although this device is primarily for use in the deturbulator project, it could be made available, as a secondary priority, for outside projects. The details of such an arrangement would have to be worked out. For the moment, we can only say that this is a distinct possibility. If you wish to look into this, contact Dr. Sinha at or call 662-234-6248.

Credits
Our thanks to Robert Williams (Memphis Soaring Society, SparrowHawk owner) who worked out design issues and constructed the tunnel in his Memphis workshop. Thanks also goes to Ken Davis of Mid-America Prop in Wynne, Arkansas for balancing the propeller assembly.

(Click for larger image)


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