PCG solver

pthcvn1990 · December 27, 2016, 01:12

Dear all Foamers,

To simulate the nozzle flow with steady state condition, I am finding difficulties. I already have utilised more number of days than usually required to solve such problem. Finally I changed my solver from smooth to PCG with DIC conditioning and my problem ran for 500 iterations.

I simply changed my solver from smooth to PCG. I want to know what is Preconditioned Conjugate Gradient regarding CFD and where I can employ these solvers.(in short I would like to know the applications of solvers present in openFoam)

Any help will be much appreciated.

Thanks.

openfoam_aero · May 20, 2022, 10:04

Conjugate gradient solvers are typically an accelerated gradient descent solver. It is used for solving the system of linear equations Ax = b which is encountered after discretisation of the domain and applying boundary conditions. The pre-conditioning is sort of a way to ensure faster convergence. Basically the pre-conditioner is useful for systems that have a large condition number (condition number is the ratio of the largest to the smallest eigenvalue of a system of equations). Having a large condition number means that the magnitude of the gradient in each step is small thereby requiring a lot of iterations to converge. Actually for a steady state problem, you can use the GAMG (geometric agglomerated algebraic multi grid solver).

December 27, 2016, 01:12	PCG solver	#1
pthcvn1990 New Member parth chavan Join Date: Jul 2015 Posts: 5 Rep Power: 10	Dear all Foamers, To simulate the nozzle flow with steady state condition, I am finding difficulties. I already have utilised more number of days than usually required to solve such problem. Finally I changed my solver from smooth to PCG with DIC conditioning and my problem ran for 500 iterations. I simply changed my solver from smooth to PCG. I want to know what is Preconditioned Conjugate Gradient regarding CFD and where I can employ these solvers.(in short I would like to know the applications of solvers present in openFoam) Any help will be much appreciated. Thanks. openfoam_aero likes this.

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May 20, 2022, 10:04		#2
openfoam_aero Member Uttam Join Date: May 2020 Location: Southampton, United Kingdom Posts: 34 Rep Power: 5	Conjugate gradient solvers are typically an accelerated gradient descent solver. It is used for solving the system of linear equations Ax = b which is encountered after discretisation of the domain and applying boundary conditions. The pre-conditioning is sort of a way to ensure faster convergence. Basically the pre-conditioner is useful for systems that have a large condition number (condition number is the ratio of the largest to the smallest eigenvalue of a system of equations). Having a large condition number means that the magnitude of the gradient in each step is small thereby requiring a lot of iterations to converge. Actually for a steady state problem, you can use the GAMG (geometric agglomerated algebraic multi grid solver).