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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


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


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

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