Transient flow over a cylinder using Solidworks Flow Simulation

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 challenge 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 from the add-ins menu.
4. After that, the flow simulation wizard is used to set up all the parameters of the mathematical model.

5. Steps for wizard: (Note that gravity is unchecked, i.e. there is no gravity in this study)
   1. Give a suitable project name.
   2. Select a proper unit system, preferably SI system.
   3. Select a flow type. In our case, the flow is over the cylinder. Hence, it is an external flow.
   4. Select the proper fluid that is used in the simulation. In this case, the fluid is air. Also, select the proper flow type, depending on the nature of the flow i.e laminar, turbulent or mixed.
   5. Set wall conditions as it is. Do not make any changes as far as the challenge is considered.
   6. Now, set the velocity of the flow of the fluid along the proper direction, in X direction in our case.

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 1.5`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` = 4940.
   - (For case 1), `R_e` = 1.2*4940 = 5928, `rho` = 1.225 `(kg)/m^3`, `D` = 0.05 `m`, Length = 0.1`m` and `mu` = 18.6x`10^(-6)` `Pa.s`. Hence we get V = 1.8001`m/s`

- (For case 2), `R_e` = 1.4*4940 = 6916, `rho` = 1.225 `(kg)/m^3`, `D` = 0.05 `m`, Length = 0.1`m` and `mu` = 18.6x`10^(-6)` `Pa.s`. Hence we get V = 2.1002`m/s`

- (For case 3), `R_e` = 2*4940 = 9880, `rho` = 1.225 `(kg)/m^3`, `D` = 0.05 `m`, Length = 0.1`m` and `mu` = 18.6x`10^(-6)` `Pa.s`. Hence we get V = 3.0002`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 -

Pressure plot animation

Velocity plot animation

Case 1: Reynolds number = 120% of initial Reynolds number. Velocity calculated as per the new Reynolds number = 1.8001`m/s`

Pressure plot animation

Velocity plot animation

Case 2: Reynolds number = 140% of initial Reynolds number. Velocity calculated as per the new Reynolds number = 2.1002`m/s`

Pressure plot animation

Velocity plot animation

Case 3: Reynolds number = 200% of initial Reynolds number. Velocity calculated as per the new Reynolds number = 3.0002`m/s`

Pressure plot animation

Velocity plot animation