axial compressor design

[salah]

hi guys:
thanks for the interaction
and since we are talking about diffusion in rotor and stator , or as some call degree of reaction, i have a question which is :
what would happen if the diffusion (100%)takes place fully in the diffuser,allowing the rotor for velocity increase only? we would end up with higher flow velocity at rotor outlet and then the diffusion takes place fully in the diffuser?


and can we run the turbine engines with pressure ratios less than 3.5 which i found to be the smallest PR ?
I mean ,would it be practical to run turbine engines with pressure ratio of say 2.5 or or 2 or even less see 1.7?
what is the thermodynamics or aerodynamics related to such design,?

[racket]

Hi

If all the"compression" is done after the wheel the losses will be higher , the overall stage efficiency will be lower .

Our engines will operate from quite low PRs of ~1.3 :1 , the lower the PR the lower the power output, and the worse the fuel consumption for output , its basic thermodynamics , we have to do work on the air ,to get work out of it.

Cheers
John

[salah]

hi guys:
would it be possible to increase the impeller tip speed by increasing the length of the axial part of the impeller (if you like expanding the distance between inlet and outlet,not by increasing the impeller tip D but by increasing the axial part of the impeller.?

in other worlds,making the impeller divergent passages between inlet and outlet mostly axial.?
would we end up with high tip speed?

[racket]

Hi Salah

NO ,.................... tip speed is a function of diameter and rpm

Cheers
John

[salah]

hi guys:
you stated that the pressure ratio in your design is 1.3:1 ,if you please provide additional info such as the mass flow rate ,TIT and the the TOT and the exit temp,
thank you.

[smithy1]

No...John said they can run as low as 1.3:1 The higher the PR the better the power output/efficiency...

[racket]

Hi Salah

A 1.3 : 1 PR is only an idling pressure ratio , mass flow will only be around 1/3rd of full rpm levels and there will be negligible power output obtainable , T I Ts will be ~600 deg C with a TOT of ~550 deg C

Cheers
John

[salah]

thank you guys:
I read that the PR is responsible for highest temp in the engine cycle. but what about the mass flow?
what i mean is , assuming 2 different turbine engines with same pressure increase (no matter what rpm or fuel needed ),but one is running with mass flow twice as much.(by twice mass flow i mean by using larger inlet area,not increasing the PR) would we have same TIT?
I do not think so?
what i am trying to see is, can we run the turbine engine with low PR put compensating for that with high mass flow?

[racket]

Hi Salah

We can run a VERY LARGE turbine engine at a low PR and produce some usable power , but specific burn rates would be horrendous , several pounds of fuel per horsepower per hour :-(

T I T can be influenced by a number of factors , so its not possible give you an answer .

Cheers
John

[salah]

hi guys;
regarding that stator vanes in the turbine stage.it there to have the turbine run at high speed required by the compressor.and also some temp drop should be made in the stator as part of the whole stage temp drop .this is made by accelerating the air through that convergent path .
and i have been doing some reading and regarding the fuel high rate that match low comp PR ,can be solved by a heat-exchanger upstream of combustor.

now assuming that P03=3.018 BAR,the TIT=1200 K,AND temp drop required=207.7 k and assuming the turb eff=.9 ,in COHEN book the T04=1200-207.7=992.3K
and then another temp was find which is T04'=1200-(207.7/.9)=969.2 K..
my Q IS WHAT IS THE IDEAL AND ACTUAL TEMP DROP THROUGH THE STAGE ?

[racket]

Hi Salah

The "ideal" temperature drop is without any efficiency loss , that is, the actual temperature drop is exactly the same as required to power the comp, actual temp drop is whats required .

The "ideal" temp drop T04'in Cohen and Rogers is used for calculation purposes.

Could you give me a page reference to the Cohen calcs you need explaining and I'll go through it with you

Cheers
John