# Could compressor stalls be caused by air in supercritical conditions?

It is likely that in compressors of jet engines appear conditions that cause the intaken air to become supercritical, cf Is the air in a jet engine supercritical? .
Is it possible that supercriticality of the fluid (air) is one of the causes for compressor stalls or compressor surge ?

Is it possible that supercriticality of the fluid (air) is one of the causes for compressor stalls or compressor surge ?

...is definitely no.

Stall is caused by an excessive angle of attack of the incoming air, relative to the blade. It can happen on the first stage (first row of rotating blades), where the pressure is no where near high enough to be supercritical. Surge occurs when the stall is very severe, so it’s the same phenomenon, just worse.

While the likelihood of a stall occurring is determined by measuring the total pressure distortion across the compressor face, it is the angle of attack that is the critical factor. Regions of low total pressure indicate the flow is likely to be turbulent in these regions, and therefore the angle of attack is not steady, and can exceed the ability of the air to follow the surface of the blade. Once it separates, it becomes turbulent, which means the blade does not perform its function of compressing it well. This is a big problem, as the compressor is trying to get the air to flow “uphill”. Stall generally starts as a phenomenon involving a few blades on one or more stages. It can then develop and cover a large section of the compressor. If the axial velocity of the flow through the compressor starts to vary, faster and slower, then faster again, it is called surge. The engine “chugs”.

• stall can also be caused by ingestion of objects so i think the root cause of stall and surge is a non-equidistribution of pressure, flow velocity, ... on the surface of the first stage and following stages of the compressor that also occurs in a high angle of attack Aug 27, 2018 at 12:40
• @ralfhtp No, if the distribution of pressure and flow velocity is uniform, but the pressure gradient is too large/the flow too slow, it will also stall (all at once). This is basically what could happen in pre-FADEC engines if you added power too quickly—the pressure would increase too fast, the flow would slow below what is appropriate for the compressor speed, the compressor would stall, and the engine would usually flame out as it burned out all the oxygen without fresh air coming in. The reason is really that the flow is too slow, which is usually because the pressure gradient is too high. Aug 29, 2018 at 19:24

Supercritical liquid–gas boundaries are lines in the p–T diagram that delimit more liquid-like and more gas-like states of a supercritical fluid.

(Source: wikipedia.org)

Due to the high temperature of the gas in a jet engine, it will behave like a gas, and never liquid-like. The only way to have the gases behave liquid-like and cause compression issues, is by cooling the gas close to its critical point, which is very cold for a jet engine.

You need the gas to be near the [cold] critical point to exhibit both gas and liquid and/or move seamlessly between the gas and liquid states.