Stall and surge in cold air unit
 

Hi, how stall and surge occur in cold air unit.? why it occurs?, what are the factors effects the stall in compressor? how it will reduce mass flow rate? please give proper explanation for compressor stall

Thank you

Sounds like homework....:=

Suck, Bang, Boom! Normally the "Boom" exists in the exaust. When the compression fails to be less than that in the "boom" section of the motor (compressor stall) the bang section sends the boom FWD...

That is the most superb and succinct description of adverse pressure gradient and reverse flow I have ever seen. :E

With fire out of the front hole (sometimes).

You're going to have to spend a few hours of learning on this to understand all the contributors in a multistage multispool compressor system. Way beyond internet postings

Basically it has to do with angle of incidence on the airfoils (changing with speeds and air flows) and, turbulent flow (airfoil damage or clearance).

How and where these get into the act is what takes the time to learn the answers to your question. Any stall means some stages are not working fully, hence mass flow rate falls off.

The surge part of it is when the engine simply gives up breathing in a full stage stall for a second and tries to catch its breath.

mnatesh

Compressor Stall – Turbine Engine

That's a nice summary.

Also, be sure to read the additional points at the bottom of that summary article:

1. Turbine engine
2. Centrifugal flow compressor
3. Axial flow compressor
4. Engine pressure ratio (EPR)
5. Compressor pressure ratio

Suggestion. Read the compressor stall article. Then, go to each of the other five to expand your understanding. Then, go back and read the compressor stall article again, and it will probably make more sense.

Cheers.

Stalls & Surge - Axial Compressors
 

mnatesh,

A little more insight into compressor stalls or surge...

Stall (rotating stall more accurately) is a flow breakdown at one or more rotating compressor blades. Typically, a rotating stall is a stagnated region of air which moves in a circumferential direction of rotor rotation, but a fraction of rotor speed. At a given throttle setting it does not move axially in either direction, although it may cause pressure waves to move upstream (compression waves) or down stream (rarefaction waves).

Surge is a response of the entire engine which is characterized by flow stoppage or reversal in the compression system. Upon surge, a compression component will unload by permitting the compressed fluid in downstream stages to expand in the upstream direction, forming a more or less planar wave which at high speeds leads to flow reversal. The compressor can recover and begin again to pump flow. However, if the surge inducing cause is not removed, the compressor will surge again and will continue the surge/recovery cycle until some relief is provided. Surge may be initiated by a rotating stall.

There are two types of stall one can distinguish. Blade (rotating compressor component) stall is a two-dimensional type of stall, where a significant portion of the blade airfoil has large wakes due to substantial thickening or separation of the suction surface (convex surface, i.e., up-side of an aircraft wing) boundary layer. Wall stall is an end-wall boundary layer separation (airfoil tip area).

Stall margin is a measure of the operating range between the design point and the in-stall point. Typical design values of stall margin range from 15 to 25%. For each compressor design, a compressor performance map can be drawn to assure there is an adequate stall margin built in for the total engine operating envelope.

Mass Flow...
As mass flow is decreased (throttle closed), pressure increases and the compressor will operate along the unstalled operating line. Further reduction in mass flow will bring about rotating stall. If the mass flow is increased (throttle opened), the compressor does not jump back to original point on the operating line but along a stalled characteristic line until such time additional mass flow causes it to revert to the unstalled operating line.

Hope this answers your questions regarding stalls, surge and mass flow.

For :mad: sake guys, the original Troll post asked about the cold air unit!!!!

He is not asking about engine compressors. :ugh:

Methinks you lot of experts now need to research cold air units. Try Goggling Bootstrap systems. :):)

(btw, I lecture this at professional level....)

Alternatively, ignore the Troll and do something useful. :ok:

I can lecture this in 50 minutes IN ENGLISH!

As a suggestion for CAU stall: malfunctioning mass flow control valve (pack valve opening rapidly) or a by-pass valve oscillating, damaged impeller blades, semi blocked heat exchangers/intercoolers or ducting thereby causing a back pressure which could also be caused by icing in a downstream water separator.On B727's a unit similar to a CAU was used as a flow multiplier when the APU supplied air con on the ground, this could stall if the system ambient air inlet was blocked or crosswinded.

Speaking of lecturing

it's downright rude to critize those who are only trying to offer help :=

5 paragraphs in 50 minutes! Most people would have fallen asleep by the time you got to the second sentence.

@ Lightning Mate

Better yet, Google the "English" version, aircraft cold air unit, otherwise you get a lot of stuff about boots, UGG's!:p

7968 posts ago (your first), you were probably considered a troll as well.:suspect: Somewhere along the line, you have gotten grumpy! :E

Self-explanatory based on "Goggling Bootstrap systems.;)

thanx
 

Thanx for your reply

I gotta say..... I've seen this sort of thing on these pages many times and I wonder if the OP has ANY clue what kind of "help" he's getting.....?

There are folks here who's expertise is so far beyond the "thanx for your reply" that I doubt it's ever been possible before in history.... Ask any aviation related question here in the Prune, and you might even get some input from the fella who designed it (whatever "it" is). ...it's truly amazing the collection of knowledge here! (BTW Lightning Mate, Turbine D did a far better job than you so far.... what have you got to show for that? :p)

Cheers all....
Mnatesh... Listen up dude... good stuff comes in these packages... ya just haveta learn to sift the wheat from the chaff. ;)