Learning Forum

[N. M.]

Hello Everyone,

I am perforing a series of simulation about a micronozzle.
There is a way to compute the thrust directly in Fluent by using the thrust equation with the values of velocity, pressure and mass flow rate reached at the nozzle outlet and make it an output parameter?

 

In other terms, I want that at the end of the simulation, Fluent calculate the thrust by using an equation written by me, using the value of velocity, pressure and mass flow rate at the outlet for each point of the outlet,

 

Thank you 😀

[Rob]

Have a look at Expressions and Custom Field Functions. Then how surface integrals of those may work. 

[N. M.]

Hello Rob,

I attempted this operation by writing the equation shown in the attached Figure 1. However, I believe that "Amag" is not the correct variable. I want the equation to be computed for each point on the outlet surface (in other words, for each cell), but "Amag," as I understand it, represents the area of the entire surface to which the equation is applied, not the area of a single cell. How can I define this equation to calculate it for each cell of the outlet surface and then sum all the results to obtain the overall thrust?

In the attached Figure 2, you can see how I tried to apply this equation (Figure 1) to the outlet surface. I went to Report Definitions → New → Surface Report → Sum, and then selected my expression under "Field Variable" and applied it to the outlet by selecting it under "surfaces." However, I am sure that "Amag" is not the correct area.

Thank you 

 

 

[Rob]

If you want the value on each facet you'll need to view a contour or export the data. I'd favour Custom Field Functions for that, although as Expressions are being continually developed they may be suitable too. 

[N. M.]

So I have to do that in post processing. My idea is to obtain the searched value at the end of a simulation as an output parameter, because I have to performa a certain number of simulations and I want to avoid to post process each of them to calculate the thrust.

[Rob]

Do you want an area (or mass) average value or the point (facet) values?