Flow over a cylinder

Aim: Transient state fluid flow over a cylinder using Solidworks Flow Simulation.

Theory:

External Flow vs. Internal Flow

Fluid flow is classified as being internal or external, depending on whether the fluid is forced to flow in a confined channel or over a surface. The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe is external flow. The flow in a pipe or duct is internal flow if the fluid is completely bounded by solid surfaces. Water flow in a pipe, for example, is internal flow, and airflow over a ball or over an exposed pipe during a windy day is external flow.

Steady vs. Unsteady Flow

The terms steady and uniform are used frequently in engineering, and thus it is important to have a clear understanding of their meanings. The term steady implies no change at a point with time. The opposite of steady is unsteady.

The terms unsteady and transient are often used interchangeably, but these terms are not synonyms. In fluid mechanics, unsteady is the most general term that applies to any flow that is not steady, but transient is typically used for developing flows.

Laminar vs. Turbulent Flow

Some flows are smooth and orderly while others are rather chaotic. The highly ordered fluid motion characterized by smooth layers of fluid is called laminar. The word laminar comes from the movement of adjacent fluid particles together in "laminates." The flow of high viscosity fluids such as oils at low velocities is typically laminar. The highly disordered fluid motion that typically occurs at high velocities and is characterized by velocity fluctuations is called turbulent. The flow of low-viscosity fluids such as air at high velocities is typically turbulent. The flow regime greatly influences the required power for pumping. A flow that alternates between being laminar and turbulent is called transitional.

Problem Description: In this problem, we will solve for the Transient state condition and we will use a cylinder of diameter 0.05m and it would be better to take computational domain 10-15 times of the geometry so as to get a better plot of the pressure and velocity. We will take an external flow problem to calculate the flow over a cylinder. We will take Air as the fluid over the cylinder in which its density would be 1.225 Kg/m3 which is predefined and viscosity also as predefined.

The formula we will be using is: Re =(ρ.Vavg.D)/μ

The length of the Computational domain in the X-axis is 0.5m.

Case 1: When velocity is 10m/s the time should be: Time = Distance/Velocity 0.5/10 = 0.05 sec

Therefore, Simulation end time 2*0.05 0.1 sec

Case 2: When velocity is 12m/s the time should be: Time = Distance/Velocity = 0.5/12 = 0.042 sec

Therefore, Simulation end time 2*0.042 = 0.084 sec

Case 3: When velocity is 14m/s the time should be: Time = Distance/Velocity = 0.5/14 = 0.036 sec

Therefore, Simulation end time 2*0.036 = 0.072 sec

Case 4: When velocity is 20m/s the time should be: Time = Distance/Velocity 0.5/20 = 0.025 sec

Therefore, Simulation end time 2*0.025= 0.05 sec

From this, we can conclude that an increase in velocity-time decreases.

Procedure:

1. At first, we will open Solidworks part modelling to model our desired part for flow simulation over a body.
2. We will draw a cylinder of 0.05m and extruding up to 0.05m and then we will save the part and then we will go for flow simulation and click on new to start a new project.
3. Now we will select the external flow for the type of flow and fluid as air and then for velocity as 10 m/s.
4. Now we go running to calculate the solution. After the solution is being done we will go on for plots and results.
5. We will go to cut plot and hit on the XY plane and then distance as 0.025m which is the midplane distance and then we will create the pressure plot. Similarly, we will create another plot for the velocity
6. Now we will create a new parametric study and then the input will be velocity and output will be cut plots and then for scenario first one with velocity as 10 and then increasing by 20%, 40%, 100% and then we will hit on run to calculate for the results.
7. Now we will get the pressure and velocity plot to go for all the four problems.
8. Now we will close the parametric study and then we will go for the animation to animate the pressure and velocity plot.
9. We will calculate the pressure and velocity plot one by one and the record it so that it will get saved.
10. Now since it is done we will go for general settings and we can change the velocity and hit on solve or we can change it new calculation also but it will take some time. Doing it simultaneously will get all the results and hence it is done.

Results and Plots:

Case 01: Velocity at 10 m/s

Velocity Plot:

Pressure Plot:

Case 02: Velocity at 12 m/s

Velocity Plot:

Pressure Plot:

Case 03: Velocity at 14 m/s

Velocity Plot:

Pressure Plot:

Case 04: Velocity at 20 m/s

Velocity Plot:

Pressure Plot:

Observation:

1. As velocity increases Reynolds Number increases.
2. With an increase in Velocity, the Flow time decreases.
3. There is a formation of vortices at the back of the cylinder.
4. With the transient flow problem, we can calculate flow at each and every instance.
5. With this, we can also calculate stagnation pressure.

Simulation Results: https://www.youtube.com/playlist?list=PLgFSZcr_6YgyY0LfZJ1uhTeEG0bDpMkb_