Let’s cover Mach Diamonds today!

let’s start with the definition:

Mach Diamonds are are a formation of standing wave patterns that appear in the supersonic exhaust plume of an aerospace propulsion system, such as a supersonic jet engine, rocket, ramjet, or scramjet.

I know I know, you’re saying Toya, why did you throw so many words at me?

Don’t worry, I gotchu!

Let’s cover standing wave: You may have heard of a stationary wave!

It is a wave which oscillates in time but whose peak amplitude profile does not move in space.

Now what causes Mach Diamonds?

If you’re not okay with the word Mach, we can call em Shock Diamonds!

They occur when gas is exiting a nozzle at supersonic speeds (faster than the speed of sound) AT a different pressure than the one outside in the atmosphere!

At sea level, exhaust pressure might be lower than the thick atmosphere. & then at very high altitudes, the exhaust pressure might be higher than the thin atmosphere.

So these shock diamonds can appear just as a rocket is taking off, or at high altitude when it’s supersonic!

The "diamonds" are actually a complex flow field made visible by abrupt changes in local density and pressure as the exhaust passes through a series of standing shock waves and expansion fans

When a flow is overexpanded, the lower gas pressure within the exhaust compared to that of the external atmosphere causes the exhaust to be compressed or squeezed inward.

This compression increases the pressure of the exhaust.

Okay guys! There’s so much to do with Mach Diamonds! I got excited by last picture is the structure of Mach Diamonds in an overexpanded flow.

Mach Diamonds in the exhaust of a PW F100 engine

Isn’t this a beaut?

This situation, (in this picture) the pressure of the exhaust plume is lower than the atmosphere pressure.

We have a term for that! Overexpansion! It occurs at low altitudes where the atmospheric pressure is high