K-Omega SST Turbulence Model

nvtrieu · July 19, 2010, 13:08

I'm doing simulation the flow over NACA0012 airfoil. In order to predict the lift/drag coefficient as long as the stall angle, the k-omega SST turbulence model is used.
The flow's specifications as follows:
-Velocity inlet: U=91.79 m/s
-Chord length: c=1 m
-Reynolds number: Re=6 million
-Fluid density: rho=1.2126 kg/m3
-Dynamic viscosity: muy=1.86x10^-5 Pa-s
Boundary conditions:
-Velocity inlet: inlet
-No-slip wall: foil
-Pressure outlet: outlet

When I selected the Turbulence specification is "k + omega" for Initial condition and for Inlet boundary condition, after running several iterations, I got this error:"Sever error: A floating point exception has occurred: floating point exception [overflow]. The specific cause cannot be identified. Potential causes may include: (a) solution divergence due to poor mesh quality, crude initialization, etc., or (b) errors in user-defined code or field functions."

This error also happened when I selected "Intensity + Length scale" for Initial condition.

Although, I used a very fine mesh with y+<1 (C-mesh). And I did not defined any field function.

However, when the Turbulence specification was turned into "Intensity + Viscosity ratio" for Initial condition, there was no error.

My first question is: Why I cannot change the Turbulence specification in Initial condition as I did?
The reason why I would select "k+omega" for Initial condition and for inlet boundary is I'm going to set the values of turbulent kinetic energy (k) and specific dissipation rate (omega).

Second: When the outlet boundary is set as Pressure outlet, do I need to change the Turbulence specification for outlet boundary into "k + Omega" as long as "Intensity + Length scale" or I just left it as "Intensity + Viscosity ratio"?

Thanks for any helps!

Trieu.
Email: trieuckgt@gmail.com
MSN: trieu.dut@live.com
YM: trieu_tme@yahoo.com

Maddin · July 21, 2010, 03:54

Initial conditions?

Velocity = 0? and inlet with 90+ m/s?
Drink some beer and think about that.

nvtrieu · July 21, 2010, 03:58

Hi Maddin,

Initial velocity=Inlet velocity.
I've solved for this problem.

Thanks!

Maddin · July 21, 2010, 06:05

Ok! What was the problem?

July 19, 2010, 13:08	K-Omega SST Turbulence Model	#1
nvtrieu Member Join Date: Jul 2009 Posts: 70 Rep Power: 17	I'm doing simulation the flow over NACA0012 airfoil. In order to predict the lift/drag coefficient as long as the stall angle, the k-omega SST turbulence model is used. The flow's specifications as follows: -Velocity inlet: U=91.79 m/s -Chord length: c=1 m -Reynolds number: Re=6 million -Fluid density: rho=1.2126 kg/m3 -Dynamic viscosity: muy=1.86x10^-5 Pa-s Boundary conditions: -Velocity inlet: inlet -No-slip wall: foil -Pressure outlet: outlet When I selected the Turbulence specification is "k + omega" for Initial condition and for Inlet boundary condition, after running several iterations, I got this error:"Sever error: A floating point exception has occurred: floating point exception [overflow]. The specific cause cannot be identified. Potential causes may include: (a) solution divergence due to poor mesh quality, crude initialization, etc., or (b) errors in user-defined code or field functions." This error also happened when I selected "Intensity + Length scale" for Initial condition. Although, I used a very fine mesh with y+<1 (C-mesh). And I did not defined any field function. However, when the Turbulence specification was turned into "Intensity + Viscosity ratio" for Initial condition, there was no error. My first question is: Why I cannot change the Turbulence specification in Initial condition as I did? The reason why I would select "k+omega" for Initial condition and for inlet boundary is I'm going to set the values of turbulent kinetic energy (k) and specific dissipation rate (omega). Second: When the outlet boundary is set as Pressure outlet, do I need to change the Turbulence specification for outlet boundary into "k + Omega" as long as "Intensity + Length scale" or I just left it as "Intensity + Viscosity ratio"? Thanks for any helps! Trieu. Email: trieuckgt@gmail.com MSN: trieu.dut@live.com YM: trieu_tme@yahoo.com

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July 21, 2010, 03:54		#2
Maddin Senior Member Join Date: Mar 2009 Posts: 260 Rep Power: 18	Initial conditions? Velocity = 0? and inlet with 90+ m/s? Drink some beer and think about that.

July 21, 2010, 03:58		#3
nvtrieu Member Join Date: Jul 2009 Posts: 70 Rep Power: 17	Hi Maddin, Initial velocity=Inlet velocity. I've solved for this problem. Thanks!

July 21, 2010, 06:05		#4
Maddin Senior Member Join Date: Mar 2009 Posts: 260 Rep Power: 18	Ok! What was the problem?