Why turbulence-model at very high Re-numbers?

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thschrader
Posts: 1363
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Why turbulence-model at very high Re-numbers?

Postby thschrader » Sat Apr 14, 2018 4:51 pm

Hi,
did some cfd test-runs with my little house.
goal: compute the resulting drag-force at 115 km/h wind-speed
according to german DIN-manuals. When using cfmesh/mesh-refinement and
k-omega turbulence model, I get a resulting drag force of approx 37,4 kN.
When doing the same with snappyhexmesh/mesh-refinement and NO turbulence model,
I get nearly the same force. Checking the results "by hand" gives a good accordance.
In reality there is turbulence (turbulence-intensity behind house approx 20%), but
in the models there is practically no difference. So why should I use time-consuming
turbulence calculations?
Comments welcome.
Thomas
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cfmesh.JPG
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oliveroxtoby
Posts: 219
Joined: Fri Dec 23, 2016 9:43 am

Re: Why turbulence-model at very high Re-numbers?

Postby oliveroxtoby » Sun Apr 15, 2018 5:17 pm

thschrader wrote:
Sat Apr 14, 2018 4:51 pm
Hi,
did some cfd test-runs with my little house.
goal: compute the resulting drag-force at 115 km/h wind-speed
according to german DIN-manuals. When using cfmesh/mesh-refinement and
k-omega turbulence model, I get a resulting drag force of approx 37,4 kN.
When doing the same with snappyhexmesh/mesh-refinement and NO turbulence model,
I get nearly the same force. Checking the results "by hand" gives a good accordance.
In reality there is turbulence (turbulence-intensity behind house approx 20%), but
in the models there is practically no difference. So why should I use time-consuming
turbulence calculations?
Comments welcome.
Off the top of my head: Turbulence modelling will mostly influence how accurately the friction drag is calculated. However, for a big blunt body like a house, the force will mostly be composed of a pressure drag component, with the friction drag being less significant. That would typically not be the case for a car or an aircraft.