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Problem 1
Problem
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Exercises
Exercise 1: Vertical Channel Flow
Problem Specification (pdf file)
Exercise 2: Laminar Flow within Two Rotating Concentric Cylinders
Contributed by Prof. John Cimbala and Matthew Erdman, The Pennsylvania State University
Problem Specification (pdf file)
The video below shows how to use ANSYS Fluent to set up and solve a problem like this.
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Exercise 3: Laminar Pipe Flow
Consider developing flow in a pipe of length L = 8 m, diameter D = 0.2 m, ρ = 1 kg/m3 , µ =2 × 10^−3 kg/m s, and entrance velocity u_in = 1 m/s (the conditions specified in the Problem Specification section). Use FLUENT with the "second-order upwind" scheme for momentum to solve for the flowfield on meshes of 100 × 5, 100 × 10 and 100 × 20 (axial divisions × radial divisions).
1. Plot the axial velocity profiles at the exit obtained from the three meshes. Also, plot the corresponding velocity profile obtained from fully-developed pipe analysis. Indicate the equation you used to generate this profile. In all, you should have four curves in a single plot. Use a legend to identify the various curves. Axial velocity u should be on the abscissa and r on the ordinate.
2. Calculate the shear stress Tau_xy at the wall in the fully-developed region for the three meshes. Calculate the corresponding value from fully-developed pipe analysis. For each mesh, calculate the % error relative to the analytical value. Include your results as a table:
3a) Consider the problem solved in this tutorial. At the exit of the pipe where the flow is fully-developed, we can define the error in the calculation of the centerline velocity as :
where Uu_c is the centerline value from FLUENT and Uu_exact is the corresponding exact (analytical) value for fully-developed laminar pipe flow. We expect the error to take the form :
where the coefficient K and the power p depend upon the method . Consider the solutions obtained on the 100x5, 100x10, and 100x20 meshesorder of accuracy of the discretization. Using MATLAB, perform a linear least squares fit fit of :
to obtain the coefficients p and K. Plot ϵ vs. ∆r (using symbols) on a log-log plot. Add a line corresponding to the least-squares fit to this plot.
Hint: In FLUENT, you can write out the data in any "XY" plot to a file by selecting the "Write to File" option in the Solution XY Plot menu. Then click on Write and enter a filename. You can strip the headers and footers in this file and read this into MATLAB as column data using the load function in MATLAB.
4. Let's see how p changes when using a first-order accurate discretization. In FLUENT, use "first-order upwind" scheme for momentum to solve for the flowfield on the three meshes. Repeat the calculation of coefficients p and K as above. Add this ϵ vs. ∆r data (using symbols) to the above log-log plot. Add a line corresponding to the least-squares fit to this plot. In all, you should have four curves on this plot (two each for second- and first-order discretization). Make sure you include an appropriate legend in the figure.
coefficients K and p. You can look up the value of Uexact from any introductory textbook in fluid mechanics such as Fluid Mechanics by F. White. Explain why your values make sense.b) Repeat the above exercise using the "first-order upwind" scheme for the momentum equation. Contrast the value of p obtained in this case with the previous one and the two cases and briefly explain your results briefly (2-3 sentences3sentences).
Hints
Note Hint: To interpret your results, you should keep in mind that the first first or second-order upwind discretization applies only to the convective inertia terms in the Navier-Stokes equationsmomentum equation. The discretization of the viscous terms are is always second-order accurate.
Go to Problem 2
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