Mixing length
 

Hay people

i have one rectangular duct 50mm*50mm*4500mm, for the boundary condition at the inlet i have choose the turbulent intensity 5% but the problem what i have how i can choose the turbulent mixing length in the entrance of the duct, have somebody some suggestion or literatur for that Thanks

Re: Mixing length
 

I have seen in manuals for different CFD programs that a fully developed turbulent flow has turbulence intensity of 5% (as you use) and a mixing length of 0.1 times the hydraulic diameter.

Regards

Bo

Re: Mixing length
 

Hay jensen

you mean 0.1 times the hydraulic diameter is 10% von Hydralic diameter in the entrance( i have a circular entrance von 100mm diameter. thanks

Re: Mixing length
 

Hi sabatini,

If the values of the turbulent viscosity are more than one or two orders of magnitude grater than the molecular viscosity, then the you should thoroughly review the assumption and/or data used to calculate turbulence at the boundaries.

Regards,

AK Balasubramanian