August 10, 2018 at 12:30 pmAnanth NarayanSubscriber
Hello, I wanted to know how to display overall Reynolds number in CFD Fluent.
August 10, 2018 at 12:53 pmDrAmineAnsys Employee
You cannot input / output directly the device Reynolds number in Fluent.
As you know Re number is defined as: Re=rho*v*L/mu with Re=Reynolds number, rho=fluid density, v=fluid velocity, L=characteristic length, mu=dynamic viscosity.
Which flow configuration you have? The characteric length could be the hydraulic diameter of your Inflow boundary and for external aero might be the chord length
August 10, 2018 at 3:07 pmRaef.KobeissiSubscriber
It depends on the domain you're modelling. Imagine 2 pipes in series (3D), in that case the domain of each pipe has a different Reynolds Number. If it is 1 pipe, then it is calculated using the formule Re:= RHO.V.D/Mu, D is the characteristic length or in this case the hydraulid diameter which is the diameter of the pipe etc...
August 10, 2018 at 3:41 pmAnanth NarayanSubscriber
I calculated Re as 111896.7452 ~ 0.1189e5. I made 2d analysis with a circle(cutout) of diameter 0.1 m on rectangular surface with density and viscosity for air as 997 kg/m3 and 0.891e-3 kg/m.s respectively. On attached graph for the above mentioned re number, Cd-drag coeffcient is around 0.5, but on analysis with k omega sst scalable wall function I got drag coefficient as 0.27345. Where might be the mistake. Graph: Search on drag coefficient vs reynolds number sphere
August 10, 2018 at 4:20 pmKarthik RAdministrator
Couple of questions:
- Which turbulence model did you use when you got a Cd of 0.5?
- Could you elaborate a little on your mesh (especially the boundary layer mesh)? Did you ensure that your grid is suitable for the k-omega SST model by ensuring that your y+ ~ 1?
- Can you check the reference values for both the solutions and ensure they are the same?
- Have you performed mesh independence studies?
There is no attachment to your post. Could you please provide appropriate screenshots so we can have a look and help you?
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