Grid required in x and z calculation in LES/DES

quarkz · October 30, 2018, 07:23

Hi,

I am trying to perform DES simulation after completing my RANS simulation. My y+ = 1 but I am not sure how to estimate and compute the grid required in the x and z directions. I will be running my simulations in OpenFOAM.

I read from some papers that delta x+ and z+ are ~ 100 and 30. So from this info, how can I estimate my grid number in x and z?

Thanks

LuckyTran · October 30, 2018, 08:48

It's really simple. Don't overthink it. From your RANS, figure out first layer thickness needed to get y+ = 1. Now multiply that length by 100 and that's the spacing you need in x direction, and 30 to get the spacing in z. Your target y spacing far from walls should also be y+ ~ 30.

quarkz · October 30, 2018, 19:23

Hi Lucky Tran,

Thanks for the clarification.

Btw, I am simulating flow pass a cone. Is the criteria the same in the z direction too ?

October 30, 2018, 07:23	Grid required in x and z calculation in LES/DES	#1
quarkz Senior Member TWB Join Date: Mar 2009 Posts: 400 Rep Power: 19	Hi, I am trying to perform DES simulation after completing my RANS simulation. My y+ = 1 but I am not sure how to estimate and compute the grid required in the x and z directions. I will be running my simulations in OpenFOAM. I read from some papers that delta x+ and z+ are ~ 100 and 30. So from this info, how can I estimate my grid number in x and z? Thanks

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October 30, 2018, 08:48		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,665 Rep Power: 65	It's really simple. Don't overthink it. From your RANS, figure out first layer thickness needed to get y+ = 1. Now multiply that length by 100 and that's the spacing you need in x direction, and 30 to get the spacing in z. Your target y spacing far from walls should also be y+ ~ 30.

October 30, 2018, 19:23		#3
quarkz Senior Member TWB Join Date: Mar 2009 Posts: 400 Rep Power: 19	Hi Lucky Tran, Thanks for the clarification. Btw, I am simulating flow pass a cone. Is the criteria the same in the z direction too ?