Any Turbine Experts out there?

[Aheli]

Im sitting a Turbine exam tommorow, and I got a couple of questions.

What is the diference between surging and choking in the compressor?
What do these actually do?

[helimutt]

Just a question. If you don't know that already then I wouldn't take the exam!!

[Aheli]

thanks for your "help" helimutt

it is hard learning on these correspondence courses especially while you are working.

The notes i have are not that great

smartarse

[helimutt]

Hopefully you'll have passed the exam when you read this. The point I was trying to make was if people start to tell you stuff which is fairly simple, then the hard stuff is going to be even harder to absorb. I'm doing a correspondence course right now and know exactly what it's like.(the CPL Techs.) If you haven't got a complete set of notes for corespondence course, I wish you luck in the exams.You really need complete notes.

Me a smart arse? I wish!!

[IHL]

Aheli:
I am not a turbine expert but I have operated 5 or 6 different types.
I have never heard of the expression choking with a turbine engine, but I have seen the term “acceleration surging” also more commonly know as compressor stall. Referring to my notes from years past: A compressor stall is an imbalance between to vector quantities ,inlet velocity and compressor RPM. Caused by 1) Turbulent or disrupted airflow to the inlet area.2)Excessive fuel flow caused by abrupt acceleration. 3)Excessively lean fuel mixture caused by abrupt engine deceleration .Compressor stall is indicated by; popping/banging sound, fluctuating rpm, and increased EGT/ITT/TOT/MGT ect.

In other words it’s a problem with airflow, as the engine accelerates the pressure rise at the exit from the compressor is greater than what can be handled by the combustion section and 1st stage nozzle. As the pressure builds the airflow is forced out through the front of the compressor causing the popping sound and possibly damaging compressor blades in the process.

Engine manufacturers employ airflow control devices such as : bleed valves, variable inlet guide vanes and variable stator vanes, and bleed bands to avoid stalls. On some aircraft a compressor stall can shock load the drive train in addition to damaging the compressor, on others it is just a nuisance popping noise.

Some Rolls Royce Allison engines in some applications are particularly prone to stalling, and when they are installed there is a procedure used where the throttle is rapidly advanced to check for stalling. Should stalling occur maintenance is performed to eliminate it.

Hope this may be of some use.

IHL