Trisonic wind tunnel

The Trisonic Wind Tunnel (TWT) was a wind tunnel in El Segundo, California. It was built by North American Aviation in the 1950s. The tunnel was so named because it was capable of testing in three speed regimes – subsonic, transonic, and supersonic, with a maximum speed of Mach 3.5.

The TWT was a blow-down type tunnel. In contrast to a continuous wind tunnel, a blow-down wind tunnel only provides air for short period. A continuous wind tunnel is driven by large fans and typically is only capable of subsonic speeds. Because a blow-down tunnel can build up pressure over a long period time, it can release air at faster speeds.

The TWT used two Westinghouse motors, totaling 10,000 hp and consuming 8 megawatts of electricity, that drove two compressors. TWT had its own substation to supply its high electrical demand. During the hot summer season, TWT ran on a night schedule to balance its load with public air conditioning.

The compressors pressurized eight large spheres totaling 214,000 cubic feet (6,100 m³). These spheres were connected to a single manifold that connected to a valve mechanism. When the valve was opened, the compressed air passed through the settling chamber, nozzle, and the test section, where instrumented aerodynamic models were mounted. A diffusing area that expanded in size slowed the air before it was exhausted vertically into the atmosphere. The diffuser area included a colander-like sieve made of 1-inch-thick (25 mm) steel to catch debris in the event of a catastrophic model failure.

The speed of the air was determined by the pressure of the spheres and the cross sectional area of the wind tunnel nozzle and diffuser. A smaller cross section in the nozzle caused the air to move faster. The TWT could change the shape of the nozzle by operating a series of hydraulic pistons that bend one-inch thick steel plates into the desired contour.

A distinguishing feature of the TWT was the size of its test section [7 by 7 feet (2.1 m × 2.1 m)]. Unlike most blow-down wind tunnels, the TWT test section had a so-called "walk in" test section that could accommodate very large aerodynamic models. Large models have several advantages:

• ability to model relatively small features, such as vortex generators
• ability to instrument the model with more pressure probes and sensors
• more surface area enabling more pressure sensors
• more interior space for instrumentation

Because of the "walk in" nature of TWT, the tunnel was designed with the possibility that someone could accidentally be locked in the tunnel. Two large emergency safety switches were provided. One was located at the test section, the other at the diffuser area. When either of these safety switches were activated, the valve could not be opened.

Another feature of TWT was the ability to visualize airflow over a model surface. By using optics built into the test section, an engineer could view air disturbance patterns as they were occurring during a test.

History

When Rockwell purchased North American Aviation, it also gained ownership of the TWT. The TWT was gifted to the University of California at Los Angeles (UCLA) in 1998, with the intention of TWT becoming a university research facility. It became known as the Micro Craft Trisonic Wind Tunnel. In 2007, UCLA decided to close TWT, citing environmental issues.

The last test to be conducted at TWT was completed on August 28, 2007. It was designated as test TWT 807.

TWT was demolished in 2009.

References

[1] American Institute of Aeronautics and Astronautics, Wind tunnels—an endangered species, May 2007

[2] El Segundo Wind Tunnel, 9/2007