## Fluids

#### Instantaneous turbulent fluctuating velocity in DPM’s DRW model

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• Shuvo Chowdhury
Subscriber

Hello..
I am calculating particle deposition in a simple 2D turbulent channel flow.

In DRW model , it is said that Instantaneous turbulent fluctuating velocity is calculated from rms fluctuating velocity of the flow , multiplied by a normal distributed random number.

My question is, where do DPM's DRW get this RMS flow fluctuation velocity from? Is there any specific variable for RMS fluctuating velocity?

I am using RSM turbulence model , where we calculate these fluctuating velocities from Reynolds Stress ( sqrt( reynold stress). Am I right?

Do DPM do the same ?

Please Help. I need this information because I have to change one of the flow RMS flutuating velocity near wall region.

Thanks

• SRP
Subscriber

Hi,

Discrete Random Walk (DRW) model includes the effect of turbulent dispersion on particle tracks by adding a perturbation or a fluctuating velocity component to every track emanating from the injection locations

For more details, please refer to theory guide: 12.2.2. Turbulent Dispersion of Particles (ansys.com)

If you are not able to access the link, please refer to this forum discussion: Using Help with links (ansys.com)

Thank you

Saurabh

• Shuvo Chowdhury
Subscriber

I think you are mentioning the formula below

I want to where u'rms is taken from by DRW. There is no such field variable . Does it take from reynolds vv stress ?

• SRP
Subscriber

Hi,

The local rms value of fluctuating component is taken from the kinetic energy of turbulence.

Thank you

• Shuvo Chowdhury
Subscriber

Hello SRP , Thanks for the reply .

Turbulence model like k-e and k-w, where isotropic turbulence fluctuation is assumed, these fluctuating velocities is calculated as sqrt(2k/3).

But, since the RSM model which allows anisotropic turbulence fluctuation , will it be applicable too?

• SRP
Subscriber

Hi,

Yes it is applicable but fluctuating velocity is multiplied by the extra term when RSM model is used.

Thank you