# Discussion Forum

## Turbulence model of hydraulic valve

 Topics: 4.3
RSS feed   |   Turn on email notifications   |   3 Replies   Last post: October 16, 2012 8:42am UTC

Mikael Noerregaard Nielsen

October 15, 2012 1:13pm UTC

Turbulence model of hydraulic valve

Hello everybody

I really hope you can help me with this:-)
I'm currently trying to simulate a flow of hydraulic oil through a valve however, I keep getting the following error:
Failed to find a solution.
In segregated group 1:
Divergence of the linear iterations.
Returned solution is not converged.

I'm relatively new at using Comsol but this forum has giving me a lot of information and I've solved many of my previous poblems using your answers although I couldn really find anything about my current problem. I've tried to fix the stated problem by increasing the Factor of error estimate which did'n do anything.
It's a rather simple geometry at 220x160x140 [mm] and Im having enough elements for the boundary layer mesh to be without errors or problems which leaves me at 271206 degrees of freedom.

I've included the convergence plot.

Best regards

Mikael

Ivar Kjelberg

October 15, 2012 6:14pm UTC in response to Mikael Noerregaard Nielsen

Re: Turbulence model of hydraulic valve

Hi

CFD is tricky indeed, often the initial conditions are too far off, then try to refine them or make a first steady state at lower flow, then ramp up from there, or you need to increase drastically the number of max iteration (default 25) or sometimes, you are missing a complete BC such as a gauge pression settings.

Also if you have enough RAM you could try to run a direct solver, sometimes they work better, depends on the model there is no single answer.

CErtainly plotting velocity and pressure helps often to see what is happening. Not to say in case of turbulent flow its trickier ^n ;)

--
Good luck
Ivar

Amir Fadel

October 16, 2012 6:16am UTC in response to Mikael Noerregaard Nielsen

Re: Turbulence model of hydraulic valve

Hi,

First of all in your graph Segregated group 1 does converge, it is Segregated group 2 not to converge in time. However, if you need help you need to upload yoru model, this piece of information is not enough.

Cheers

Mikael Noerregaard Nielsen

October 16, 2012 8:42am UTC in response to Amir Fadel

Re: Turbulence model of hydraulic valve

Hey Ivar and Amir

Thanks a lot to both of you for the fast replies!
The solution to my problem was actually very simple = direct solver.
Again, thanks a lot

Best regards

Mikael

PS. Amir, I found that odd as well. Segregated group 1 seemed to converge however, I got the error stated above. No explanation that one though:-/

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