[yaseen wsu]

Hello every one
I simulated flown over the weir using SST and k-e turbulence model but both results are similar (inlet and outlet mass flow rate. and wall function, is a straight line. Is that possible.
Regards
https://www.cfd-online.com/Forums/at...1&d=1501611800
https://www.cfd-online.com/Forums/at...1&d=1501611819
https://www.cfd-online.com/Forums/at...1&d=1501611844

[ghorrocks]

Yes, this is possible, in fact it is normal. CFX uses an iterative approach to work out the wall distance and it usually converges after a few iterations, and much quicker than the CFD solver. So it frequently looks like what you show.

[yaseen wsu]

Originally Posted by ghorrocks

Yes, this is possible, in fact it is normal. CFX uses an iterative approach to work out the wall distance and it usually converges after a few iterations, and much quicker than the CFD solver. So it frequently looks like what you show.

Thanks for you reply
Also I used RNG k-e, but after 800 iteration it doesnot reach convergence, and its accuracy is less than k-e and SST, while SST and k-e after 150 or less iterations reach the convergence, can you tell me the reason.
Regards

[ghorrocks]

RNG is very similar to k-e, but has subtle differences. Have a look at the CFX documentation or a turbulence textbook for more details.

It looks like in your case the subtle differences are enough to make it not converge. But remember for other cases it works better, so it will depend on exactly what you are modelling to determine the best turbulence model.

[yaseen wsu]

Originally Posted by ghorrocks

RNG is very similar to k-e, but has subtle differences. Have a look at the CFX documentation or a turbulence textbook for more details.

It looks like in your case the subtle differences are enough to make it not converge. But remember for other cases it works better, so it will depend on exactly what you are modelling to determine the best turbulence model.

Thanks a lot for your explanation
I am modelling of flow of water over weir like flow over bump but the difference is in my case jump was occur when the water reach downstream of the weir.
Yes this is my job, to find a turbullence that can well simulate all flow variables, k-e worked for fully turbullent flow, but near walls flow is almost laminar, and at the jump there is swirling for this reason I want to use RNG
Regards