Gas turbine performance vs ambient temperature question 2

[HRTesla]

Dear engineers,

I've got a second question

Does anyone know why the isentropic and the polytropic compressor efficiency increases when the ambient temperature increases? Many thanks in advance for your replies

Kind regards,

HR

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[davefitz]

I am not certain of the correct answers. Normally when modelling a combustion gas turbine for different ambient temperatures , I would assume:

for each site elevation , constant compressor inlet P and constant turbine outlet P

constant RPM and blade geometry ( duh)

constant turbine inlet temperature ( TiT)- but this can be calculated different ways depending on the means of cooling the combustor

constant volumetric flow entering the compressor- but this simplification assumes any bypass piping and throttling dampers are in a fixed optimum positions- this may be one reason that the isentropic and polytropic efficiency is varying in your performance review- modern CTG's fiddle with these vanes, dampers and bypasses to minimize NOx and maximize TiT.

If the turbine has a known and fxed "flow factor" for the gases entering the first row of blades, and it runs at a fixed TiT, then the combustor pressure must vary with gas flowrate. Its not clear if this implies a constant pressure ratio across the compressor for various ambient temperatures.

But I am sure there are books and papers that will rpvide simple thermodynamic models to explain the issues you found.