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Propulsion system

  1. Jan 2, 2007 #1
    Propulsion system!!

    I am writing a report designing a propulsion system, ie a turbine to power an apu, and have various requirements such as a power demand for the apu of 400kW so the turbo-jet needs to have 421.05kN of power. i have various other information regarding the effiency's of the turbine.

    I believe the 1st thing i need to work out is the engine inlet area, but am having trouble finding an equation which would help me work this out. I do not have a value for mass flow rate which is the next thing i believe i will need to work out but am not sure how to work out in the inlet area A with out the mass flow rate!

    Can any one suggest some equations which might help or know of any useful websites or books on the subject!

    many thanks, happy new year

  2. jcsd
  3. Jan 2, 2007 #2


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    Why do you think that that is the first place to start in the design? Do you already have a compressor and turbine that you are building around or are those being designed as well? Those two components are going to be the main driving factors of required airflow and thus the required inlet area.

    I would be a bit careful with your terminology. Your power requirement is 440kW is a good start. The comment about 421.05 kN of power is not. Where did this come from? Usually, in rotating machinery, general loads like this are expressed as torques.

    There are no simple plug and chug equations that you can just plug in and voila. I'd say for starters look here: http://www.grc.nasa.gov/WWW/K-12/airplane/shortp.html

    This will give you a look into the basics. After that, you may want to look for books like Gas Turbine Theory by Cohen, Rogers and Sarvanamuttoo or Aircraft Engine Design by Mattingly, Heiser and Mattingly.
  4. Jan 2, 2007 #3
    Thanks for your help.
    Having looked back over what i was doing and being more awake, and after recovering from the new year! I have realised that when i said the first thing i need to work out is the inlet area, what i actually needed to be doing was using a number of estimated values for the inlet area and using matlab find the most apropriate value.
    I also forgot in the 1st post to insert a table of values which i allready have:

    Compressor inlet pressure: 1 bar
    Compressor inlet temperature: 15°C
    Turbine exit pressure: 1.2 bar
    Compressor isentropic efficiency: 93%
    Turbine isentropic efficiency: 95%
    Bleed flow from exit of compressor: 1.5% (of mass flow through compressor)
    Combustion pressure loss: 1% (of inlet combustor pressure)
    Combustion fuel to air ratio: 0.025:1
    Electrical generator efficiency: 95%
    Aircraft electrical power demand, Wg: 400kW
    Inlet dry air properties: [R=287J/kg/K, Cp=1005 J/kg/K, γ=1.4

    In regards to the 421.04kN of power yea you where correct i was getting confussed from my notes and what i actually meant was that i needed 421.05kW of power from the apu due to efficency so:

    400kW/95 x 100 = 421.05kW

    Am sure i will probally have some more questions which you guys can help me on later, but if any1 has any more useful web links it would be useful especially as my local libary has proved not to be!

    Thanks again

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