Shock diamond

Shock diamonds (also known as Mach diamonds or thrust diamonds) are a formation of

Shock diamonds form when the supersonic exhaust from a

The distance from the nozzle to the first shock diamond can be approximated by

$${\displaystyle x=0.67D_{0}{\sqrt {\frac {P_{0}}{P_{1}}}},}$$

where x is the distance, D₀ is the nozzle diameter, P₀ is flow pressure, and P₁ is atmospheric pressure.[3]

As the exhaust passes through the normal shock wave, its temperature increases, igniting excess fuel and causing the glow that makes the shock diamonds visible.

Eventually the flow expands enough so that its pressure is again below ambient, at which point the expansion fan reflects from the contact discontinuity (the outer edge of the flow). The reflected waves, called the compression fan, cause the flow to compress.

Diamond patterns can similarly form when a nozzle is under-expanded (exit pressure higher than ambient), in lower atmospheric pressure at higher altitudes. In this case, the expansion fan is first to form, followed by the oblique shock.[2]

Alternative sources

Shock diamonds are most commonly associated with jet and rocket propulsion, but they can form in other systems.

Natural gas pipeline blowdowns

Shock diamonds can be seen^{[by whom?]} during gas pipeline blowdowns because the gas is under high pressure and exits the blowdown valve at extreme speeds.^{[citation needed]}

Artillery

When artillery pieces are fired, gas exits the cannon muzzle at supersonic speeds and produces a series of shock diamonds. The diamonds cause a bright muzzle flash which can expose the location of gun emplacements to the enemy. It was found that when the ratio between the flow pressure and atmospheric pressure is close, which can be achieved with a flash suppressor, the shock diamonds were greatly minimized. Adding a muzzle brake to the end of the muzzle balances the pressures and prevents shock diamonds.^[1]: 41

Radio jets

Some

• Index of aviation articles
• Plume (hydrodynamics)
• Rocket engine nozzle

References

External links

Wikimedia Commons has media related to Shock diamonds.

• "Methane blast" - shock diamonds forming in NASA's methane engine built by XCOR Aerospace, NASA website, 4 May 2007
• "Shock Diamonds and Mach Disks" - This link has useful diagrams. Aerospaceweb.org is a non-profit site operated by engineers and scientists in the aerospace field.