CFD Online Discussion Forums - Why I cannot calculate the thrust of my nozzle?

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Why I cannot calculate the thrust of my nozzle?

Guys
I have an axisymmetric domain that there is a nozzle in there. Here is a sketch of my domain

https://www.cfd-online.com/Forums/at...1&d=1536249090

"Outlet-1" and "Outlet-2" is "Pressure-farfield" boundary condition and "Outlet-3" is "Pressure outlet" boundry condition. The inlet of this domain is also zoomed up and showed. I heard that I can use the properties of the domain to calculate the thrust but my effort failed. Here is the information of my domain that I got from Fluent:

Code:

  Mass Flow Rate (kg/s)

  -------------------------------- --------------------

  inlet 0.3848487

  outlet1 1.5579536

  outlet2 20.835326

  outlet3 -22.802237

  ---------------- --------------------

  Net -0.024108255

  









  Mass-Weighted Average

  Velocity Magnitude (m/s)

  -------------------------------- --------------------

  inlet 173.49819

  outlet1 6.1609674

  outlet2 11.367706

  outlet3 110.55185

  ---------------- --------------------

  Net 62.176956

  





  Area-Weighted Average

  Static Pressure (pascal)

  -------------------------------- --------------------

  inlet 228198.8

  outlet1 111876.66

  outlet2 110103.08

  outlet3 101325

  ---------------- --------------------

  Net 109679.36

Here is one of my calculation:

https://www.cfd-online.com/Forums/at...1&d=1536249619

I should've been made mistake to calculate the thrust.

Any idea to calculate the thrust would be appreciated!

Thank you Alexander for your response,
There is a point about my problem.
To calculate the thrust of a Bell nozzle you can calculate its thrust easily using mass flow rate of the nozzle inlet and velocity at the exit of the nozzle (even you can get avarage pressure to calculate pressure thrust) but calculating the thrust of an Aerospike nozzle is challenging. You remember this topic:

https://www.cfd-online.com/Forums/fl...le-fluent.html

Now I'm thinking to calculate the thrust using my domain not the nozzle.

Any idea?

Hi, Roh, you have set a very good example of asking questions. It makes rather easy for others to understand your point. well done!

Note that the momentum flux is a vector, so you have to use mass-averaged velocity component (axial-velocity in this case since you only interested in thrust) instead of velocity magnitude.

Quote:

Originally Posted by Roh (Post 705590)

Hey Roh,

Did you find the answer to the question you posted? I'd appreciate your response.

Thanks

I believe the geometry is from the work of Prasanth P Nair on conical aerospike and bleed effect. Im also working on a project for my undergrad on linear aerospikes and we essentially used the thrust equation of an aerospike from the Rocket Propulsion Elements Textbook by Sutton to compute thrust coefficients.

Refer to the authors paper above and check out the equation used for thrust. Itll provide more clarity.