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Old   June 17, 2005, 12:49
Default Thrust calculation
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I simulated the operation of a small engine with an inlet, a combustor, and an outlet. The engine is sitting on the ground so the thrust is static. I monitored the average velocity-u and mass flow rate at the exit. At the inlet, velocity and mass flow rate is known constant. Thrust is calculated from momentum force only: (mdot* mass flow rate) @ outlet ĘC (mdot*mass flow rate) @ inlet. If the exit velocity is sometimes negative (opening boundary), is this still right? (negative exit velocity*negative exit mass flow rate=positive thrust, which is not phyisic)

Is there a more accurate way to calculate thrust in this case? Thanks.
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Old   June 17, 2005, 12:52
Default Re: Thrust calculation
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sorry, the thrust is (mdot*velocity) @ outlet -(mdot*velocity)@ inlet. where mdot=density*area*velocity
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Old   July 5, 2012, 16:53
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Ajinkya Desai
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hey, I am simulating an oscillating/flapping fin in FLUENT. I plotted the cd vs the flow time and if the time averaged Cd comes out negative then it amount to a net THRUST rite? I need to know if this is the best way of calculating thrust. Also i should tell you, that for this oscillating fin, the average drag is coming out positive, contradictory to our hypothesis. Some one please help me with this.
Thank you.
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Old   July 5, 2012, 18:24
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Try the fluent forum.
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Old   July 9, 2012, 11:48
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Julio Mendez
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In the report of the CFFX solver, you see the forces and moments at walls, try to look at them.
You can define a Result vector from this report and you will have the real force!!
Good luck!
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