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Fatih Kalay

VWT and Turbulence Models

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Hello, I am new with the AcuSolve, started with Fluent and now trying to improve my works on AcuSolve,

 

My problem is; I can't calibrate the program. In the attachment you can find a work i prepared. Using a smooth sphere, which is big as a golf ball (d=0.042 m) I analysed over and over with the conditions you can see. After that i prepared a chart and compared it with the literature. According to literature, it should decrease after turbulence zone. However my values always increased. They are even not equal to ampirical values in laminar zone for sphere.

 

After this I changed my analysis type to transient (when I learned transient analysis option of VWT runs with DES instead of Spalart-Allmaras)

And re run some specific values to see the general characteristic of the curvature (Reynolds number to Cd)

 

I can't catch the characteristic, which I see in the literature.

 

For some values like Re= 4e5, 6e5, 1e6... I can't even reach closer to the ampirical values.

 

Also It happens on another geometries like Ahmed Body, I analyse and I always get different values from literature.

 

1. I wonder if I am able to change the turbulence model of VWT.

2. How can I use k-omega and k-epsilon turbulence models ( I get error: kinetic energy and dissimilation must be non-zero) (Even I enter values, I get the same error)

3. Why my values have high error ratio, even i prepare my problem with high quality ( Blockage ratio, element value, refinement zones etc...)

 

Thank you.

ahmedbody.JPG

golfball.JPG

vwtAnalysis_transient_ahmedbody.pdf vwtAnalysis_steady_ahmedbody.pdf vwtAnalysis_velocity25_ahmedbody.pdf

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You most likely have a very coarse mesh - with around 3 Million volume elements - way to few for this type of study.  (Maybe those runs with 12 Million could be enough - but very likely still too coarse...)  You'll need to have very fine resolution on the body to capture the separation point(s) as well as very fine in the wake region to capture the recirculation and shedding zones properly.  You'll also need to run transient with likely very small time steps.  Perhaps it's better to work with your local Altair support team - as this is not a trivial study...

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