[ma_martinez]

Hi,

I want to know the gradient of pressure of my fluid. I want to know when the pressure is negative but I don´t know how I can chage the range of the pressure to set one parameter in 0 as you can see in the image. How can I change the range?

Captura.JPG

Thanks beforehand,

[vinerm]

To change Range, change from Global to User-Specified. As far as gradient is concerned, that won't be available in CFDPost if you ran simulation in Fluent. Open the case and data file in Fluent and plot pressure gradient there.

[ma_martinez]

I have done what you have said but when I plot the gradient of pressure in X axis the program represents it as if there are any changes, the grandient of pressure that is represented is 0 in all the volume of control as you can see in the image. But it is not like this. Why this is happening?

Captura.jpg

Thanks beforehand,

[vinerm]

I suppose you are plotting in CFDPost. As I mentioned, CFDPost may not have this data available. You have to plot it in Fluent if the simulation was done in Fluent or you have to write a cdat file from Fluent with dp-dx selected as a variable, load that file in CFDPost, and then plot dp-dx.

[ma_martinez]

No, I have plot it in Fluent as you can see in the image.

Captura.jpg

The things is that I dont know how to write a cdat file from Fluent with dp-dx selected as a variable and that can be the problem.

[vinerm]

If you are plotting it in Fluent and it still doesn't show the gradients, then, it probably didn't save any gradient or the gradient is 0. To check if the gradient is saved or not, issue the following command

sol set exp

in Fluent's text user interface. Look for the question regarding keeping the memory from being freed. Answer yes to that question and run 1 iteration. Then plot the gradient.

[ma_martinez]

Perfect, I have done what yo say and I think that it works. Why was happening this?

Captura.jpg

So, If I want to know de gradient for all the iterations, I have to do again all the simulation?

[vinerm]

Fluent does not store gradients by default so as to save memory. If you want gradients to be reported, just enable it using the command mentioned in the previous post and run 1 iteration.

[ma_martinez]

Okey, but my question is, this pressure gradient of one iteration is the same for the whole simulation? For example, in my case, I have done 10000 iterations in this simulation, so my question is, this result of the grandient can be extrapolated to the whole simulation?

And another question, how I can set the range of the pressure manually?

[vinerm]

For a steady-state simulation, any field, whether pressure, velocity, or their gradient, have no significance until and unless the solution is converged. It means that only the final field and its gradient is the correct one, provided the solution has converged.

[ma_martinez]

That was what I was thinking. So, I may do the whole simulation.

And another question, how I can set the range of the pressure manually?

[vinerm]

What do you mean by manually? Pressure range is what is reported in Contours when Node values are not selected.