Flow over a cylinder - Solidworks Flow Simulation

1. AIM:

- To simulate the flow over a cylinder for the conditions mentioned below:

1. Random initial velocity and thus obtain the Reynolds number.
2. 120% of initial reynolds number.
3. 140% of initial reynolds number.
4. 200% of initial reynolds number.

2. INTRODUCTION:

- The flow of a fluid is transient or unsteady if its flow parameters (i.e. velocity and pressure) are dependent not only on the position in the coordinate system used to describe the field of flow, but also on time. As far as the current project is concerned, we are dealing with the analysis of system as a function of time thus instead of a steady state analysis, a 'Time Dependent' analysis is chosen.

- External analysis is used when we need to understand the fluid behavior around our model based on the environment conditions. Wind Turbines, Airplanes, ships, heat sinks, and automobiles would all be studied using external flow analysis. In External studies, the computational domain acts as our virtual wind tunnel with boundary conditions, heat sources, and transient behavior all applied through the user friendly setup wizard.

3. OBJECTIVES:

- To create Pressure-Velocity animations for all the above mentioned cases.

4. FLOW SIMULATION SETUP:

1. A CAD model of a cylinder of dimension 50D(mm) and 100L(mm) is created in Solidworks.
3. Enable Flow Simulation in add-ins.
4. 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. Since this is an external flow, we will not be specifying any boundary conditions.

6. Here, since velocity is not given, we can assume it to be 1`m/s` in the X-direction.
`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 air [`Pa.s`] = `1.516 X10^-5`

7. After putting the values and solving for `R_e`, we get `R_e` = 3298.
- (For case 1), `R_e` = 1.2*3298 = 3958, `rho` = 1 `(kg)/m^3`, `D` = 0.05 `m`, Length = 0.1`m` and `mu` = 1.516x`10^(-5)` `Pa.s`. Hence we get V = 1.1999`m/s`

- (For case 2), `R_e` = 1.4*3298 = 4618, `rho` = 1 `(kg)/m^3`, `D` = 0.05 `m`, Length = 0.1`m` and `mu` = 1.516x`10^(-5)` `Pa.s`. Hence we get V = 1.3999`m/s`

- (For case 3), `R_e` = 2*3298 = 6596, `rho` = 1 `(kg)/m^3`, `D` = 0.05 `m`, Length = 0.1`m` and `mu` = 1.516x`10^(-5)` `Pa.s`. Hence we get V = 1.9999`m/s`

8. 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.

The mesh can be refined to a greater extent but the current project is set up on a laptop with lower specifications. Thus mesh refinement is limited to third setting for balanced calculation time.

5. OBSERVATIONS, RESULTS AND CONCLUSION:

Initial case: for determining the reynolds number -

Case 1: Reynolds number = 120% of initial Reynolds number. Velocity calcuated as per the new Reynolds number = 1.1999`m/s`

Case 2: Reynolds number = 140% of initial Reynolds number. Velocity calcuated as per the new Reynolds number = 1.3999`m/s`

Case 3: Reynolds number = 200% of initial Reynolds number. Velocity calcuated as per the new Reynolds number = 1.9999`m/s`

Conclusion:

1. As the Reynolds number increases, the pressure right before the cylinder wall (facing area) also increases.
2. As the Reynolds number increases, the pressure near the top and bottom surfaces reduces, i.e. inversely proportional.
3. There is on notable change in pressure even though above observations can be drawn. We can cay that changing reynolds number as little to no effect on the pressure near the surface of the object.
4. Also, in case of velocity, as reynolds number goes beyond 4000, the flow becomes turbulent. The velocity attained by the fluid after hitting and getting deflected from the cylinder continues to remain for a long time than that flow where Reynolds number is less.
5. We thus can say that while Reynolds number is less, viscous forces are dominant and as Reynolds number increases, inertial forces become more dominating.