Shock diamond

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Shock diamond (also known as Mach diamond , Mach disk , Ring Mach , donut tail or a diamond thrust ) is the formation of a standing wave pattern that appears in a supersonic exhaust system of aerospace propulsion, such as a supersonic jet engine, rocket, ramjet, or scramjet, when it is operated in the atmosphere. Diamonds are formed from complex and visible flow fields due to sudden changes in local densities and pressures caused by standing shock waves. Mach diamond (or disk) is named after Ernst Mach, the physicist who first described them.

Video Shock diamond

Mekanisme

The diamond shock is formed when the supersonic exhaust from the push thrust is slightly over-expanded, meaning that the static pressure of the gas coming out of the nozzle is smaller than the ambient air pressure. This pressure increases the adiabatic flue gas flow, and the decrease in speed causes the static temperature to increase substantially. This leads to the reignition of unburned burning products in the engine exhaust. The exhaust is generally over-expanded at low altitudes, where the air pressure is higher.

When the outflow from the nozzle, ambient air pressure will suppress the flow. External compression caused by tilted shock waves tends to angle to the flow. The compression flow is alternately extended by Prandtl-Meyer expansion fans, and each "diamond" is formed by the pair of oblique surprises with an expansion fan. When the compressed stream becomes parallel to the center line, the shock wave is perpendicular to the flow form, which is called the normal shock wave. The first surprise diamond is located here, and the space between it and the nozzle is called "silent zone". The distance from the nozzle to the first surprise diamond can be approached by

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂxÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â0.67Â\; Â\; Â\; Â\; Â\; Â\; Â}$ Â Â Â Â Â Â ÂÂ << Â »D Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Â Â Â Â Â Â ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Â

                                0        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â    Â       Â Â

                      Â 1        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â      ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                          ,               {\ displaystyle x = 0.67D_ {0} {\ sqrt {\ frac {P_ {0}} {P_ {1}}}},}  Â

where x is distance, D ₀ is the nozzle diameter, P ₀ is flow pressure, and P ₁ is atmospheric pressure.

When the exhaust passes through normal shock waves, the temperature increases, triggering excess fuel and causing the light that makes the shock diamond visible. The well illuminated areas appear as discs or diamonds, giving them their names.

Eventually the flow extends so that the pressure returns below the ambient, where the expansion fan point reflects from the contact discontinuity (outer edge of the stream). The reflected wave, called a compression fan, causes a compressive flow. If the compression fan is strong enough, another oblique shock wave will form, creating a second shock diamond. The disk pattern will be repeatable indefinitely if the ideal gas and friction, however, the turbulent shear on the contact discontinuity causes the wave pattern to disappear with distance.

Diamond patterns can also form when the nozzle is under-expanded (exit pressure is higher than ambient), in low atmospheric pressure at higher altitudes. In this case, the expansion fan is first formed, followed by an oblique shock.

Maps Shock diamond

Alternate sources

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

Blowdown natural gas pipeline

Surprise diamonds can be seen during blowdown of the gas pipeline because the gas is under high pressure and out of the blowdown valve at extreme speed.

Artillery

When the artillery pieces are fired, the gas escapes from the muzzle of the cannon at supersonic speed and produces a series of surprise diamonds. Diamonds cause bright muzzle flash that can expose the location of gun cannons to enemies. It was found that when the ratio between flow pressure and atmospheric pressure is close, the shock diamond is greatly minimized. Adding brake snout to the tip of the muzzle balances pressure and prevents surprise diamonds.

Radio jets

Some radio jets, powerful jets from plasmas derived from quasars and radio galaxies, are observed to have radio emission nodes that are periodically upgraded. The jet runs at supersonic speed through a thin "atmosphere" of gas in space, so it is hypothesized that this knot is a surprising diamond.

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See also

• Afterburner
• Flue gas
• Plume (hidrodynamics)
• Machine rocket nozzle
• Shock waves

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Note

src: qz.com

External links

• "Methane explosion" - the formation of a shock diamond in a NASA methane engine built by XCOR Aerospace, the NASA website, May 4, 2007

Source of the article : Wikipedia