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-   -   Help needed for calculating Specific Impulse (http://www.cfd-online.com/Forums/main/2617-help-needed-calculating-specific-impulse.html)

Dongsuk Chae September 20, 2000 23:30

Help needed for calculating Specific Impulse
 
Hi guys,

I recently work on nozzle flows of various geometries by CFD method. Reading related papers, I found that Isp(specific impulse) of nozzles is expressed by the ratio of an ideal specific impulse. I'm wondering how we obtain the idela specific impulse of a given nozzle. Plz, suggest me the method or related papers and books. Thanks in advance.

A. Taurchini September 21, 2000 03:44

Re: Help needed for calculating Specific Impulse
 
By definition specific impulse is

Isp=T/mf

where T is total thrust and mf is the mass of expelled propellent. Now the calculation of thrust depends on which kind of propulsion you use. For example if your nozzle is for a rocket system, then (in adapted condition : pext=pamb)

T= mf Vext

where Vext is the exhaust velocity that depends essentially from which kind of fuels and oxydizers you use. For this case is obviously

Isp=Vext

This is valid ONLY for rocket system. If you need more informations mail back. Bye.



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