Numerical Results

Contour plots of Axial Velocity

Note that there are two types of velocities in an LES simulation - instantaneous velocity and mean velocity. The instantaneous velocity is the actual velocity at any time instant in the domain. When we collect the statistics, the instantaneous velocity is time-averaged to obtain the mean velocity. Let us make a mid-plane in the domain to look at the contour plots of instantaneous axial velocity and the mean axial velocity.

(Click) Graphics and Animation > Contours > Set Up.. as shown in the figure below.

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In the Contours window, click on New Surface > Plane... as shown below.

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In the Plane Surface window, click Point and Normal. Under Points, choose (x0 (m), y0 (m), z0 (m)) = (0,0.0635,0) and under Normal choose (ix (m), iy (m), iz (m)) = (1,0,0). Name the surface as midplane_les under New Surface Name. Click Create. The plane can be viewed using Graphics and Animations > Mesh > Set Up....

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Go back to Contours window and select Velocity... and Y Velocity under Contours of and under Surfaces choose midplane_les and click Display. The figure below shows the contour plot of instantaneous axial velocity.

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For the contour plot of the mean axial velocity, select Unsteady Statistics... and Mean Y Velocity under Contours of and under Surfaces choose midplane_les and click Display

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From the two plots we can clearly see the difference between the two velocities.

XY plot of Axial Velocity

Let us make a line across the pipe at the center of the domain to look at the mean axial velocity and compare it with the solution from k-e model in the next section.

(Click) Plots > XY Plot > Set Up.. as shown in the figure below.

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In the Solution XY Plot window, click on New Surface > Line/Rake... as shown below.

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In the Line/Rake Surface window, under End Points choose (x0 (m), y0 (m), z0 (m)) = (0,0.03175,0) and (x1 (m), y1 (m), z1 (m)) = (0,0.03175,0.00635). Name the surface as midline_les under New Surface Name. Click Create. The line can be viewed using Graphics and Animations > Mesh > Set Up....

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Go back to Solution XY Plot window and select Unsteady Statistics... and Mean Y Velocity under Y Axis Function and under Plot Direction choose (X,Y,Z) = (0,0,1). Choose midline_les under Surfaces and click Plot. The figure below shows the contour plot of instantaneous axial velocity.

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To save the line plot, select Write to File in the Solution XY Plot window and click Write. Select a location and save the file as MeanYVel_LES.xy.

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Save the project and close FLUENT.

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