Thrust calculation from cfd data(Numerical Integration)

balkrishan · April 23, 2018, 06:18

I am doing CFD analysis on the supersonic nozzle, I need to calculate the thrust of the nozzle from CFD data. I don't know how to calculate the thrust numerically. The equation for thrust calculation is
$T = \int \rho u (u.n) dA$

please help

AliE · April 23, 2018, 11:57

Hi,

If you use a particular software, maybe you have the integration option somewhere in the post processor. However, in order to evaluate that surface integral numerically, you consider constant the integrand over each cell face composing the patch where you need to evalute the momentum fluxes. Doing this your integral will be: \sum_{1}^{N} mf*Uf*Af, where Uf is the face center value for the velocity, Af the face area while mf is the mass flow rate throught the patch.The sum extends to all the patch faces. Hope this help.

piu58 · April 23, 2018, 13:34

Numerical integration is simple, because it can be reduced to a summation (as Ali mentioned). The problem here is to define a appropriate surface for the integral. If it encompass a too large volume, some of the thrust is transformed in heat (via turbulence) and your value gets too low.

steve_podleski · April 23, 2018, 15:03

take the gage pressure at the nozzle interior surface and element area normal to thrust direction and add the momentum of the flow of the upstream boundary of the nozzle. (the viscous forces on parallel surface may be insignificant....depends on the level of accuracy that your require).

balkrishan · April 24, 2018, 05:45

thanks for suggestions I will look and get back if some problem comes.

April 23, 2018, 06:18	Thrust calculation from cfd data(Numerical Integration)	#1
balkrishan Member Bal Krishan Join Date: Jul 2017 Posts: 43 Rep Power: 8	I am doing CFD analysis on the supersonic nozzle, I need to calculate the thrust of the nozzle from CFD data. I don't know how to calculate the thrust numerically. The equation for thrust calculation is $T = \int \rho u (u.n) dA$ please help

April 23, 2018, 13:34		#3
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	Numerical integration is simple, because it can be reduced to a summation (as Ali mentioned). The problem here is to define a appropriate surface for the integral. If it encompass a too large volume, some of the thrust is transformed in heat (via turbulence) and your value gets too low. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

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April 23, 2018, 11:57		#2
AliE Senior Member Join Date: Dec 2017 Posts: 153 Rep Power: 8	Hi, If you use a particular software, maybe you have the integration option somewhere in the post processor. However, in order to evaluate that surface integral numerically, you consider constant the integrand over each cell face composing the patch where you need to evalute the momentum fluxes. Doing this your integral will be: \sum_{1}^{N} mfUfAf, where Uf is the face center value for the velocity, Af the face area while mf is the mass flow rate throught the patch.The sum extends to all the patch faces. Hope this help.

April 23, 2018, 15:03		#4
steve_podleski New Member Join Date: Mar 2018 Posts: 11 Rep Power: 8	take the gage pressure at the nozzle interior surface and element area normal to thrust direction and add the momentum of the flow of the upstream boundary of the nozzle. (the viscous forces on parallel surface may be insignificant....depends on the level of accuracy that your require).

April 24, 2018, 05:45		#5
balkrishan Member Bal Krishan Join Date: Jul 2017 Posts: 43 Rep Power: 8	thanks for suggestions I will look and get back if some problem comes.