Gas turbine engines

[pcrispie]

Could someone please explain to me what is meant by a positive and negative stall in terms of stalls and surges within a gas turbine jet engine? I know what a stall is and the phenomena surrounding them, the relationships with surges but I am unsure about the positive and negative aspect. Thanks

 

[RPstress]

I've not heard the terms specifically. However, it's been a couple of days since you posted, so I'll put in a speculation as to what it might be about:

For a stall in a turbofan you get an initial pulse of high positive pressure travelling down the bypass duct which tries to burst it. This is then followed by a pulse of negative pressure so that you can get almost one atmosphere trying to crush the duct. We tend to refer to these as positive and negative pulses, but it could well be that people sometimes refer to the pressures as positive and negative stalls. It's important to note that you get both in the one stall, and because the negative follows the positive closely it's usually necassary to do a dynamic analysis of the pair.

-RP.