Getting started with Flow Simulation in SolidWorks

1. AIM:

- To run a pipe flow simulation with an inlet Reynolds number of 100,1000 and 10,000.

2. INTRODUCTION:

- Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by boundary conditions.

- CFD is applied to a wide range of research and engineering problems in many fields of study and industries, including aerodynamics and aerospace analysis, weather simulation and environmental engineering, industrial system design and analysis, fluid flows and heat transfer, and engine and combustion analysis.

- Solidworks Flow Simulation is an intuitive Computational Fluid Dynamics (CFD) solution embedded within SOLIDWORKS 3D CAD that enables you to quickly and easily simulate liquid and gas flows through and around your designs to calculate product performance and capabilities.

- How a problem is approached and solved?

• Initial processing includes:
  
  • The geometry of the problem can be defined using CAD model. From there, data can be suitably processed (cleaned-up) and the fluid volume (or fluid domain) is extracted.
  • The volume occupied by the fluid is divided into discrete cells (the mesh). The mesh may be uniform or non-uniform, structured or unstructured, consisting of a combination of hexahedral, tetrahedral, polyhedral elements.
  • Boundary conditions are defined. This involves specifying the fluid behaviour and properties at all bounding surfaces of the fluid domain. For transient problems, the initial conditions are also defined.
• The simulation is started and the equations are solved iteratively as a steady-state or transient.
• Finally a postprocessor is used for the analysis and visualization of the resulting solution.

3. OBJECTIVE:

For above mentioned Reynolds numbers,

1. Place line probes at 95%, 90% and 85% of the pipe length.

2. Compare the normalized velocity profile at each of these locations

3. Normalize the velocity profile by the inlet velocity.

4. FLOW SIMULATION SETUP:

1. A CAD model of a tube of appropriate dimension is created in Solidworks.
2. After enabling Flow Simulation in add-ins, 2 lids are created at each end of the tube which act as inlet and outlet markers.
3. After that, the flow simulation wizard is used to set up all the properties.

4. Steps for wizard: (Note that gravity is unchecked, i.e. there is no gravity in this study)

5. After wizard setup, boundary conditions are set up which include inlet conditions, outlet conditions and wall of the pipe by right clicking on boundary condition entry in left side tree.

6. Boundary conditions:

7. Here, since velocity is not given, we need to calculate it using reynolds number which is given.
`R_e = (rho.V.D)/mu` where `R_e` = reynolds number
`rho` = density of the working fluid [`(kg)/m^3`]
`V` = velocity of the fluid [`m/s`]
`D` = diameter of the pipe through which flow is going to happpen [`m`]
`mu` = Dynamic viscosity of water [`Pa.s`]

8. After putting the values and solving for V, we get V = 0.00178`m/s`
(For case 1), `R_e` = 100, `rho` = 1000 `(kg)/m^3`, `D` = 0.05 `m`, Length = 0.5`m` and `mu` = 8.9x`10^(-4)` `Pa.s`

9. For the mesh, right click on global mesh and see whether automatic mesh is selected or not. You can also set manual mesh so that you can increase no. of cells in any direction.

For case 1, with reynolds number as 100, we got velocity = 0.00178 m/s.

thus for case 2 and case 3 with reynolds numbers 1000 and 10000, we get velocity as 0.0178m/s and 0.178m/s respectively.

5. OBSERVATIONS, RESULTS AND CONCLUSION:

At 85% of the total length of the pipe,

We can say that as reynolds number increases, the turbulance of the flow also increases and the working fluid is mixed more and more and thus the effect of viscosity and the effect of friction near the walls gets lesser and lesser. Thus we can see less of the blue color in the third image and more of blue color in the first image indicating low velocity.

At 90% of the total length of the pipe,

At 95% of the total length of the pipe,

After comparing velocity plots between 85%, 90% and 95% of length of the pipe, we can surely and safely say that there is not much difference between these plots as the length of our pipe is only 0.5m and the values of 85, 90 and 95% of 0.5m are very close to each other. Thus no notable change is observed. But after observing the trend we can say that as length increases, the velocity near the walls decreases.

Plots according to Reynolds number:

`R_e` = 100 (Sketch 3,4,5 are nothing but line probes at 85, 90 and 95% of the length of the pipe)

We can see that the velocity profiles at all the line probes are overlapping each other with a higher accuracy. Thus we can say that at a low reynolds number, the velocity is not affected much at closer distances. Notable thing is that velocity at walls is "equal to" Zero.

`R_e` = 1000

We can see that the velocity profiles at all the line probes are overlapping each other with a higher accuracy. But velocity in the middle section or at the centre of the pipe is varying. That velocity is directly proportional to the distance from the inlet of the pipe. Thus we can say that at a middle ground laminar flow, the velocity is not affected much starting from the pipe wall upto a distance of approximately `D/4`. The red region is affected and as mentioned above, the velocity changes (increases). The red region approximately covers a distance of `D/2`. Notable thing is that velocity at walls is "equal to" Zero.

`R_e` = 10000

Similar reasoning as above. Only a major difference is that the region of highest velocity (red region) is much more wider than that of Reynolds number 100 and 1000. It is due to turbulence and continuous mixing of fluid.