# Help needed for calculating Specific Impulse

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 September 20, 2000, 23:30 Help needed for calculating Specific Impulse #1 Dongsuk Chae Guest   Posts: n/a 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.

 September 21, 2000, 03:44 Re: Help needed for calculating Specific Impulse #2 A. Taurchini Guest   Posts: n/a 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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