User:Dbs11tdl/Expansion Tunnel

Expansion and shock tunnels are aerodynamic testing facilities with a specific interest in high speeds and high temperature testing. Shock tunnels use steady flow nozzle expansion whereas expansion tunnels use unsteady expansion with higher enthalpy, or thermal energy. In both cases the gases are compressed and heated until the gases are released, expanding rapidly down the expansion chamber. The tunnels reach speeds from Mach 3 to Mach 30 to create testing conditions that simulate hypersonic to re-entry flight. These tunnels are used by military and government agencies to test hypersonic vehicles that undergo a variety of natural phenomenon that occur during hypersonic flight.

Expansion Process

Expansion Tunnel

Expansion tunnels use a dual-diaphragm system where the diaphragms act as rupture discs, or a pressure relief. The tunnel is separated into three sections: drive, driven, and acceleration. The drive section is filled with high pressure helium gas. The driven section is filled with a lower pressure desired test gas, such as carbon dioxide, helium, nitrogen, or oxygen.. The acceleration section is filled with an even lower pressurized test gas. Each section is divided by a diaphragm, which is meant to be ruptured in sequence causing the first diaphragm to rupture, mixing and expanding the drive and the driven. When the shock wave hits the second diaphragm, it ruptures casing the two gases to mix with the acceleration and expand down the enclosed test section. Operation time is approximately 250 microseconds.

Shock Tunnel

Reflected shock tunnels heat and pressurize a stagnant gas by using shockwaves that are redirected back into the center; this excites the gases and produces movement, heat, and pressure. The gases are then released and expanded through the nozzle and into the test chamber. Operation time is approximately 20 milliseconds.

Testing

During the expansion process, a variety of test are run to analyze the aerodynamic and thermal properties of the test vehicle.

• Skin friction

The drag that is created when an object travels through a fluid, such as a liquid or gas.

• Flow chemistry

The analysis of reactions that take place during a continuous flow.

• Durability

The ability to withstand deterioration.

• Turbulence

The disordered movement of fluids.

• Heat transfer

The thermal energy transfer from one system to another.

• Aero elastic

The forces created by the movement of air and the manner in which air bends around the object.

• Thermal protection

The ability to withstand heat transfer, reducing the temperature.

• Vibration

The oscillation, or shaking, of the molecules.

Testing Instruments

• Thin-film Heat Transfer Gauge

When the gauge is heated, the resistance changes; this causes a change in voltage, which is used to calculate the amount of heat transferred into an object.

• Piezoelectric Pressure Transducer

Under pressure, crystals became electrically charged, proportional to that of the pressure exerted.

• Laser Diode Spectrograph

Measures the properties of the refracted light, generated by the laser traveling through the turbulent gas around an object.

Facilities

HYPULSE

NASA's Hypersonic Pulse Facility (HYPULSE)is operated by General Applied Science Laboratory (GASL) in New York. The HYPULSE facility was developed for the testing of re-entry vehicles and air-breathing engines. The specifications of the HYPULSE include a diameter of 7 feet and a 19 foot length. This facility was upgraded to have two modes, Reflected Shock Tunnel (RST) and Shock-Expansion Tunnel (SET). HYPULSE-RST generates speeds from Mach 5 to 10, where as the HYPULSE-SET produces speeds from Mach 12 to 25.

Vehicles tested at HYPULSE:

• Hyper-X
• X-34
• HYPLUSE Scramjet Model(HSM)

LENS-I,II

Large Energy National Shock tunnels (LENS) were constructed over the past 15 years at the Aerothermal/Aero-optic Evaluation Center (AAEC) at Calspan-University of Buffalo Research Center (CUBRC). The LENS facilities were developed for the testing of advanced missile seekerheads and scramjet engines. LENS I and LENS II have similar control, compression and data acquisition systems. LENS I facility has an 11-inch diameter by 25.5 foot long drive tube that is electrically heated with an 8-inch by 60 foot driven section capable of reaching Mach 7 to 18. Test models can have a maximum length of 12 feet and a diameter of 3 feet. The LENS I heats up the drive gas to 750 degrees F to operate at a maximum 30,000 psi. The LENS II facility integrates a 24-inch diameter to both the 60 foot drive and also the 100 foot driven tubes, which runs between Mach 3 and 9.

Vehicles tested at LENS-I:

• HyFly
• X-34
• Orbiter model
• National Aerospace Plane(NASP)

Vehicles tested at LENS-II:

• HyFly
• BLK IVA
• X-43
• ARRRMD
• HyCause
• RRSS

LENS-X

LENS-X is an 8 foot diameter by 100 foot expansion tunnel with a top speed of Mach 30. The drive chamber, filled with helium or hydrogen gas, is compressed to 3,000 psi at 1000 degrees Fahrenheit; this breaks the first diaphragm, causing the driven chamber to experience an influx of hot gas, generating pressures over 20,000 psi before the second diaphragm is ruptured.

Vehicles tested at LENS-X:

• Orion
• DARPA Falcon