How to plot and calculate species velocity individually?

Member

Hi,

Sorry, it is me again...

I just have another problem. In my case, it is a 3d particle located in the origin point with reaction. So, there is reactant coming in and products coming out.

First question is should I use radial velocity to present direction and magnitude? Because the velocity magnitude can not give me direction. But why I get plot like this? Should it be all positive value since all narrows are going out  in the vector plot.

The second question is how to plot and calculate species velocity individually? once I calculate flow rate on the surface by "surface report" - "flow rate" - "mass fraction of XX", I will get the value with same positive sign for both reactant and product which seems unreasonable.

Thanks!

• UKForum Coordinator
edited July 3

Radial, axial & tangential velocity are all referenced against the axis of rotation as set in the fluid cell zone. Depending on what it's set as you can get all sorts of interesting post processing results that are meaningless.

Species are attached to the phase they're in, there is no species velocity.

• Member
edited July 3

I think I did not express my question clearly... What I want is the velocity for each species, like if there is a reactant/product going in / out, there should be a velocity for the reactant/product. And the direction of these velocities is the opposite. therefore, the flow rate direction should also be the opposite. otherwise how to calculate the flow rate for each species? And it seems not right by using "surface report" - "flow rate" - "mass fraction of XX" because I get same direction for reactant and product.

So, there is any way to calculate the velocity for each species in fluent?

Thanks!

• UKForum Coordinator
edited July 6

There will but then is the particle moving into fresh reactant material and then emitting products?

• Member
edited July 6

Glad to hear that. But the particle is not moving. There is no forced velocity.

• UKForum Coordinator
edited July 7

In which case you'll need to look at diffusion flux to and from the surface, check the gradients and you may need a mix of Custom Field Functions and a UDF.

• Member
edited July 7

In my case, the surface I am interested in is a 3D shell-like surface, which means it contains both negative and positive axis of X, Y, Z. Is that possible to calculate diffusion flux for such a surface if I only want to get one "general" value not three value for dY/dx, dY/dy, dY/dz? if so, how?

Also, do you mean the existed data report method for velocity can not give me a correct answer?  I understand for custom field function. But what should I do for the UDF?

Thanks!

• UKForum Coordinator
edited July 8

You'll need the surface facet normals and then look at the species gradients. Beyond that and I'm unable to advise as this is considered a public forum.