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

Enthalpy

Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.Enthalpy is a...

, 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

Mach

Mach may refer to:* Mach , a lunar crater* Mach disk, diamond pattern seen in rocket exhaust* Mach number, a measure of speed* Gillette Mach3, a manual razor with three blades* Mach bands, an optical illusion...

 3 to Mach 30 to create testing conditions that simulate hypersonic

Hypersonic

In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...

 to re-entry

Re-Entry

"Re-Entry" was the second album released by UK R&B / Hip Hop collective Big Brovaz. After the album was delayed in May 2006, the band finally release the follow-up to "Nu Flow" on 9 April 2007...

 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 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
  Flow chemistry
  In flow chemistry, a chemical reaction is run in a continuously flowing stream rather than in batch production. In other words, pumps move fluid into a tube, and where tubes join one another, the fluids contact one another. If these fluids are reactive, a reaction takes place...
  
  

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

• Durability

The ability to withstand deterioration.

• Turbulence
  Turbulence
  In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
  
  

The disordered movement of fluids.

• Heat transfer
  Heat transfer
  Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change 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
  Vibration
  Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
  
  

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.

• Force -Moment Balance

Used to measure three or six components, three forces (lift, drag, and side) and three moments (pitch, roll, and yaw), to completely describe the conditions on the model. Forces on the model are detected by strain gauges located on the balance. Each gauge measures a force by the stretching of an electrical element or foil in the gauge. The stretching changes the resistance of the gauge which changes the measured electric current through the gauge according to Ohm's law. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.

HYPULSE

NASA's Hypersonic Pulse Facility (HYPULSE) is operated by the General Applied Science Laboratory

General Applied Science Laboratory

The General Applied Science Laboratory is an American aerospace company, known as a pioneer of hypersonic propulsion.-Description:The General Applied Science Laboratory was founded in 1956 by Antonio Ferri and became a developer and testing house for advanced propulsion systems.Another early...

 (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