Propelling nozzle design
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Joined: Apr 2008
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From: England
Propelling nozzle design
Does anyone know of a book, or fully worked example, for designing a propelling nozzle for a turbojet? Google is not proving helpful.
I have borrowed a few books on gas turbine design but they seem exclusively concerned with the design of the gas generator not the nozzle!
This is for practical application on my Rolls Royce Nimbus thrust conversion. Although I've been given some dimensions I want to run the design myself to ensure it's correct!
Edit: Or, if I'm asking the wrong questions can anyone give me any pointers at all on design? Even some keywords would be very helpful, I'm aware of things like nozzle choking but I'm struggling to understand what it actually means when the nozzle pressure ratio causes this critical point to be reached, as an example.
I have borrowed a few books on gas turbine design but they seem exclusively concerned with the design of the gas generator not the nozzle!
This is for practical application on my Rolls Royce Nimbus thrust conversion. Although I've been given some dimensions I want to run the design myself to ensure it's correct!
Edit: Or, if I'm asking the wrong questions can anyone give me any pointers at all on design? Even some keywords would be very helpful, I'm aware of things like nozzle choking but I'm struggling to understand what it actually means when the nozzle pressure ratio causes this critical point to be reached, as an example.
Last edited by Jon Starr; 14th February 2013 at 22:03.
Joined: Feb 2005
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From: flyover country USA
Once the nozzle pressure ratio (Pt/Ps) reaches critical (~1.89), the nozzle throat is choked, and no further velocity (i.e. thrust) is available.
So what you need for designing the nozzle are the gas parameters - Temp, pressure (probably determined by noise limits), gas mass flow... and these will set the nozzle area. The geometry will probably be determined by the position of the gas turbine (aircraft CG considerations) and the distance to the nozzle exit plane. Sometimes there is a smooth ramp of flow area to the exit, and sometimes a constant tubular section back to a convergent section right at the aft end; The former is probably lighter.
So what you need for designing the nozzle are the gas parameters - Temp, pressure (probably determined by noise limits), gas mass flow... and these will set the nozzle area. The geometry will probably be determined by the position of the gas turbine (aircraft CG considerations) and the distance to the nozzle exit plane. Sometimes there is a smooth ramp of flow area to the exit, and sometimes a constant tubular section back to a convergent section right at the aft end; The former is probably lighter.
Joined: Dec 2010
Posts: 291
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From: Europe
Try this:
AIAA-2004-3923
NOZZLE SELECTION AND DESIGN CRITERIA
Eric Gamble*
Dwain Terrell, P.E.
Rich DeFrancesco
SPIRITECH Advanced Products, Inc.
You can use equation (2) to calculate the nozzle area you require with or without afterburner - just plug in the appropriate flow quantities.
AIAA-2004-3923
NOZZLE SELECTION AND DESIGN CRITERIA
Eric Gamble*
Dwain Terrell, P.E.
Rich DeFrancesco
SPIRITECH Advanced Products, Inc.
You can use equation (2) to calculate the nozzle area you require with or without afterburner - just plug in the appropriate flow quantities.
Last edited by CliveL; 17th February 2013 at 05:02.
Thread Starter
Joined: Apr 2008
Posts: 15
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From: England
barit1: Thank you very much for information and the explanation of nozzle choking, I think I actually understand it when put that way.
CliveL: Thanks for that document, I'm going to have to read that very carefully. I have the pressure, temperature and velocity at the turbine face and the area of the turbine face and center-body so that looks like enough information to use the equations.
CliveL: Thanks for that document, I'm going to have to read that very carefully. I have the pressure, temperature and velocity at the turbine face and the area of the turbine face and center-body so that looks like enough information to use the equations.
