[mongya]

To use simple algorithm, is it right that I need to know the pressure gradient? How should I deal with the situation where all I know is just velocity source and absolute pressure at the inlet and outlet?

[praphul]

Hi Kim,

Can you provide more info ? Are you trying to code by yourself or are you relying on any commercial/opensource software ?

If you are using any CFD software, you need not have to know the pressure gradient. The software will perform the simple algorithm by itself. Assuming, incompressible flow, its always necessary to have atleast one pressure boundary for your problem. Its usually the relative pressure that counts in these kinds of flows. If its an enclosure (like Rayleigh Benard convection), you can fix pressure at a point to be zero.

I would recommend you to go through Suhas V Patankars text book for a simple explanation of SIMPLE alogrithm. Book name is 'Numerical heat transfer and fluid flow'

Regards,
Praphul T

[mongya]

Originally Posted by praphul

Hi Kim,



Can you provide more info ? Are you trying to code by yourself or are you relying on any commercial/opensource software ?



If you are using any CFD software, you need not have to know the pressure gradient. The software will perform the simple algorithm by itself. Assuming, incompressible flow, its always necessary to have atleast one pressure boundary for your problem. Its usually the relative pressure that counts in these kinds of flows. If its an enclosure (like Rayleigh Benard convection), you can fix pressure at a point to be zero.



I would recommend you to go through Suhas V Patankars text book for a simple explanation of SIMPLE alogrithm. Book name is 'Numerical heat transfer and fluid flow'



Regards,

Praphul T

Hi Mr.Praphul. I am high school student and am just trying to understand the algorithm of Finite volume method for 2D convection-diffusion problems. And the equations in the pictures is about doing surface integral to convection-diffusion governing differential equation and discretizing it. And what i want to know is whether there is any error in the expansion.

[praphul]

Hi Kim,

Yes. There will be slight errors in the numerical scheme. I would suggest you to also go through the numerical methods as well. Typically, there will be a slight errors in the approximation from the pde to the algebraic form.

Its very encouraging to know that you are a high school student and are exploring these topics already. I would also suggest you to get the proper base on mathematics as well. (You can refer to algebraic methods, methods to solve pde, ode is often what you need to be conversant with the topic).

Regards,
Praphul T

[mongya]

Originally Posted by praphul

Hi Kim,



Yes. There will be slight errors in the numerical scheme. I would suggest you to also go through the numerical methods as well. Typically, there will be a slight errors in the approximation from the pde to the algebraic form.



Its very encouraging to know that you are a high school student and are exploring these topics already. I would also suggest you to get the proper base on mathematics as well. (You can refer to algebraic methods, methods to solve pde, ode is often what you need to be conversant with the topic).



Regards,

Praphul T

Hi Mr.Praphul

I have a qeustion for you. So far i have studied vector calculus to understand Cfd for FVM textbook and governing equations in fluid dynamics textbook. In the cfd textbook i could see some calculations using matrix, but there had little difficulty in understanding the calculations because important main calculations are mostly conducted through partial differentiation. So is it okay to delay to study linear algebra? (i have heard that linear algebra is very important in cfd)

[FMDenaro]

Dear Kim
I really appreciate and encourage your curiosity about CFD, however since I have a long experience in teaching, I suggest to think about these points:


1) CFD is a science, it requires a strong background in math (I mean not only ordinary differential equations but PDE and integral equations), in physics, in fluid dynamics, in numerical methods and linear algebra.


2) Using a CFD software is a different matter than studying CFD.


3) Understanding linear algebra is relevant but it has to be considered a topic useful AFTER that the discretization methods of partial derivatives have been considered.


4) You can find many CFD textbooks but generally they require a knowledge superior than usually present in high school.


Could you detail the textbook you are using?
What do you know about differential equations?

[mongya]

Originally Posted by FMDenaro

Dear Kim
I really appreciate and encourage your curiosity about CFD, however since I have a long experience in teaching, I suggest to think about these points:


1) CFD is a science, it requires a strong background in math (I mean not only ordinary differential equations but PDE and integral equations), in physics, in fluid dynamics, in numerical methods and linear algebra.


2) Using a CFD software is a different matter than studying CFD.


3) Understanding linear algebra is relevant but it has to be considered a topic useful AFTER that the discretization methods of partial derivatives have been considered.


4) You can find many CFD textbooks but generally they require a knowledge superior than usually present in high school.


Could you detail the textbook you are using?
What do you know about differential equations?

Dear Mr. FMDenaro
the textbooks i am using are 돌맹이 which is calculus textbook, fluid dynamics by White, and Korean translation of An introduction to computational fluid dynamics the finite volume method by H K versteeg.
And what i know about differential equations is just how to solve or expand ODE and PDE, and i can understand what specific PDE actually means in physical aspect even if it contains some dell operators, like diffusion term in Navier-stokes equation.

Additionally, the reason why i have come to study cfd is because of the strong longing to understand cfd itself.
When i was in the first grade of high school( 16 in American age / 17 in Korean age) (now, i am 18 in American age) i was taught how to use cfd commercial software like Autodesk by myself and simulated lots of objects with it and also i thought cfd is something fun and attractive. but one day, i realized all i know about cfd is just how to it and not itself and this is i think just a superficial understanding of cfd. But i wanted deeper understanding of cfd because then i thought to simulate one accurately needs more extensive knowledge of cfd and one of my dreams is to simulate one with les or dns or in-house code. So thats why i have come to study cfd theory.

[FMDenaro]

Originally Posted by mongya

Dear Mr. FMDenaro
the textbooks i am using are 돌맹이 which is calculus textbook, fluid dynamics by White, and Korean translation of An introduction to computational fluid dynamics the finite volume method by H K versteeg.
And what i know about differential equations is just how to solve or expand ODE and PDE, and i can understand what specific PDE actually means in physical aspect even if it contains some dell operators, like diffusion term in Navier-stokes equation.

Additionally, the reason why i have come to study cfd is because of the strong longing to understand cfd itself.
When i was in the first grade of high school( 16 in American age / 17 in Korean age) (now, i am 18 in American age) i was taught how to use cfd commercial software like Autodesk by myself and simulated lots of objects with it and also i thought cfd is something fun and attractive. but one day, i realized all i know about cfd is just how to it and not itself and this is i think just a superficial understanding of cfd. But i wanted deeper understanding of cfd because then i thought to simulate one accurately needs more extensive knowledge of cfd and one of my dreams is to simulate one with les or dns or in-house code. So thats why i have come to study cfd theory.

I strongly encourage you to go to university, you need to learn mathematical and numerical analysis and fundamental of fluid dynamics, then you can attend a course in CFD.


Be aware, CFD is general but you have to know what is FDM, FVM, FEM, SM that are different formulations used in CFD.


You can find useful to read first a simple textbook about FDM like Computational Fluid Dynamics by J. Anderson and only after read about the FVM. Your aim to do LES/DNS with your in-house code requires years of studies.

[mongya]

Originally Posted by FMDenaro

I strongly encourage you to go to university, you need to learn mathematical and numerical analysis and fundamental of fluid dynamics, then you can attend a course in CFD.


Be aware, CFD is general but you have to know what is FDM, FVM, FEM, SM that are different formulations used in CFD.


You can find useful to read first a simple textbook about FDM like Computational Fluid Dynamics by J. Anderson and only after read about the FVM. Your aim to do LES/DNS with your in-house code requires years of studies.

Thank you for your encouragement and thank you for letting me know such great information. Actually probably I will enter university next year (probably SNU or Korea university or Hanyang university). Before I get 30, I will try at my best to do the LES simulation with in-house code.