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Old   April 17, 2011, 12:33
Default Froude Number CFX
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John
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hi,

Could anyone help me to determine Froude Number using CEL in CFX,
Fn=V/sqrt(g*l).

my problem is that Im working on a multiphase (water+air) flow over an obstacle and i dont know the fluid depth (water) what length scale should I consider and where could I find this specific variable?

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Old   April 17, 2011, 20:03
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The length scale depends on what you are doing. For instance a ship is the length of the ship, wave models use the depth of water. So what are you modelling?
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Old   April 18, 2011, 08:11
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Quote:
Originally Posted by ghorrocks View Post
The length scale depends on what you are doing. For instance a ship is the length of the ship, wave models use the depth of water. So what are you modelling?
I would like to monitor a point using CEL calculating the Froude number for the entire length specifically before and after the bump... I have the velocity as 0.26 m/s but what Im not sure how to find the fluid level in this case,what i mean by "l" is the Hydraulic depth (cross sectional area of flow / top width)

Fn=V/sqrt(g*l).



Table 3. Domain Physics for CFX
Domain - Default Domain Type Fluid Location Primitive 3D Materials Air at 25 C Fluid Definition Material Library Morphology Continuous Fluid Water Fluid Definition Material Library Morphology Continuous Fluid Settings Buoyancy Model Buoyant Buoyancy Reference Density DenRef Gravity X Component 0.0000e+00 [m s^-2] Gravity Y Component -g Gravity Z Component 0.0000e+00 [m s^-2] Buoyancy Reference Location Automatic Domain Motion Stationary Reference Pressure 1.0000e+00 [atm] Heat Transfer Model Isothermal Fluid Temperature 2.5000e+01 [C] Homogeneous Model True Turbulence Model k epsilon Turbulent Wall Functions Scalable
Table 4. Boundary Physics for CFX
Domain Boundaries Default Domain Boundary - inflow Type INLET Location INFLOW Settings Flow Regime Subsonic Mass And Momentum Normal Speed Normal Speed 2.6000e-01 [m s^-1] Turbulence Intensity and Length Scale Eddy Length Scale UpH Fractional Intensity 5.0000e-02 Fluid Air Volume Fraction Value Volume Fraction UpVFAir Fluid Water Volume Fraction Value Volume Fraction UpVFWater Boundary - top Type OPENING Location TOP Settings Flow Regime Subsonic Mass And Momentum Entrainment Relative Pressure 0.0000e+00 [Pa] Turbulence Zero Gradient Fluid Air Volume Fraction Value Volume Fraction 1.0000e+00 Fluid Water Volume Fraction Value Volume Fraction 0.0000e+00 Boundary - outflow Type OUTLET Location OUTFLOW Settings Flow Regime Subsonic Mass And Momentum Static Pressure Relative Pressure DownPres Boundary - back Type SYMMETRY Location BACK Settings Boundary - front Type SYMMETRY Location FRONT Settings Boundary - bottom Type WALL Location BOTTOM3, BOTTOM1, BOTTOM2 Settings Mass And Momentum No Slip Wall Wall Roughness Smooth Wall
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Old   April 18, 2011, 08:23
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Probably the easiest way to get the depth is to define a tall, thin rectangular region from the bottom to the top of your domain. Then if you do something like volumeInt(Volume Fraction)@region/volume()@Region this will give you a percentage height of the column in your region.

You will need to do a small edit to your mesh to do this.
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