y+ estimation
 

Warm Greetings to all,

I need to plot a graph between friction factor and Reynolds no. So for that can anyone help me find out, what will be the appropriate model to be used, the appropriate y+ value, and the wall spacing needed for 'turbulent' simulation of the fluid flow having different Reynolds no which has the following details:

• modelling in ansys cfx11.0
• cuboid fluid domain (flow is normal to the cross section)
• cross section area= .3 x .037 m*m and height= 1.652 m
• fluid: air at 25 c (isothermal)
• Reynolds no: 4000, 6000, 9000, 12000, 15000, 18000
• boundary type: wall with no slip (on 4 faces connecting the cross section area)
• boundary type: inlet (on one of the cross sectional area)
• boundary type: outlet with (on the opposite cross sectional area)
• pressure at the outlet= atm pressure
• turbulence: medium intensity
• keeping all other parameters as default while modelling

Looking forward for a reply.
Thanks

I realise asking this sort of question seems to be the simple way to an answer but really you are not going to learn much.

A far better thing to do would be to look in CFD textbooks and the academic literature on this type of flow and work these things out for yourself. Then you will know why you chose the models and what issues or compromises there are in using them.

This is a very basic flow which is a standard benchmark case in CFD. There will be zillions of people using this scenario in the academic literature.

But to answer your questions:
* What turbulence model - SST
* What y+ - around 50 if you are happy using wall functions, 1 if you want to integrate to the wall.
* Wall spacing - there is a wall spacing calculator in the CFX documentation

Thanks a lot ghorroks for your precious time.
Also, I will definitely look into your suggestions.