Change the discretization form in fluent

Abhinand · August 9, 2020, 00:16

Is it possible to modify the diffusion term in the momentum equation and discretize it differently?
For eg: D d^2 u/dy^2 is discretized as (u_(i+1)-2u_i +u_(i-1))/dy^2

I want to write it as ((du/dy)_(i+1) - (du/dy)_(i))/Dy

Where and how can I accomplish this in fluent?

AlexanderZ · August 10, 2020, 02:57

as far as I know, you can change the scheme for all momentum equation only
what you need is in
Solution Methods -> spatial discretization, Momentum -> First order Upwind

other option is to define your own diffusion equation using user-define scalars
In that case you may select spatial discretization separately

Abhinand · August 14, 2020, 21:44

AlexanderZ,

Thanks for your reply. Do you mean to say, I can add a separate UDS equation and add to the velocity to get my new discretization.
Lets say I discretize the diffusion term by B, and fluent by default discretizes by A

The net momentum equation should be something like Fluent - A + B right?
But how do I modify or write in the discretization equation, since modification only in that form will affect the velocity calculation and using UDF I can affect only the values of velocity.

Please let me know your thoughts

August 9, 2020, 00:16	Change the discretization form in fluent	#1
Abhinand Member Abhinand Join Date: Jun 2016 Posts: 75 Rep Power: 10	Is it possible to modify the diffusion term in the momentum equation and discretize it differently? For eg: D d^2 u/dy^2 is discretized as (u_(i+1)-2u_i +u_(i-1))/dy^2 I want to write it as ((du/dy)_(i+1) - (du/dy)_(i))/Dy Where and how can I accomplish this in fluent?

August 10, 2020, 02:57		#2
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	as far as I know, you can change the scheme for all momentum equation only what you need is in Solution Methods -> spatial discretization, Momentum -> First order Upwind other option is to define your own diffusion equation using user-define scalars In that case you may select spatial discretization separately Abhinand likes this. __________________ best regards ****************************** press LIKE if this message was helpful

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August 14, 2020, 21:44		#3
Abhinand Member Abhinand Join Date: Jun 2016 Posts: 75 Rep Power: 10	AlexanderZ, Thanks for your reply. Do you mean to say, I can add a separate UDS equation and add to the velocity to get my new discretization. Lets say I discretize the diffusion term by B, and fluent by default discretizes by A The net momentum equation should be something like Fluent - A + B right? But how do I modify or write in the discretization equation, since modification only in that form will affect the velocity calculation and using UDF I can affect only the values of velocity. Please let me know your thoughts