Flow over a cylinder

INTRODUCTION TO COMPUTATIONAL FLUID DYNAMICS:

It is a branch of fluid mechanics that uses numerical analysis and algorithms to solve fluid flow situations. High-performing computers are used to conduct the calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions. It has fascinated researchers, as it is a fast, accurate, and reliable method of analyzing the variation of hydrodynamic properties of the flow over and within a body.

ABOUT REYNOLD'S NUMBER:

Reynolds number can reveal whether the flow is laminar or turbulent. It is defined as,

Re = ρVD/μ

Where

V - average velocity at the inlet of a diffuser,

D - Diameter of the inlet,

ρ - Density of the test fluid

μ - Viscosity of the test fluid.

AIM:

To perform the Flow simulation of flow through a cylinder using SolidWorks flow simulation.

OBJECTIVE:

• To analyze the fluid flow over a cylinder by calculating Reynold's number for baseline simulation
• To increase the calculated Reynolds number to a factor of 20%, 40%, & 100%.
• To perform the simulation for all values of Reynold's number and to create an animation file for velocity-pressure.

PROCEDURE:

3D MODEL:

Here to perform the flow simulation of flow through a pipe, a cylinder is been sketched and extruded in the front plane with the below parameters (MKS System):

Diameter of the cylinder = 0.04m

Length of the cylinder = 0.2m

BASELINE SIMULATION PARAMETERS:

To perform the flow simulation over the cylinder, let us assume the velocity of air to be 5m/s to calculate the Reynolds for the baseline simulation:

INPUT PARAMETERS	VALUES
Analysis Type	External Flow
Fluid	Air
Global Mesh Level	5
Initial Velocity	5 m/s
Density	1.125 kg/m^3
Diameter	0.04 m
Dynamic Viscosity	18.14*10^-6 Ns/m^2
Time-dependent	Total Analysis Time: 0.16 s Output time step: 0.016 s

Re = ρVD/μ

Where

V - average velocity at the inlet of a diffuser,

D - Diameter of the inlet,

ρ - Density of the test fluid

μ - Viscosity of the test fluid.

By substituting the known values we get, the baseline Reynolds number is calculated as,

Re = 13,506.06

Similarly, Reynold's number at 20, 40 and 100 % is been calculated below,

Reynolds number by a factor of 20%:

To perform the flow simulation over the cylinder, let us take the Reynolds number factor as 20%:

Re = 13506.06 + (20% of 13506.06)

Re = 16,207.27

Reynolds number by a factor of 40%:

To perform the flow simulation over the cylinder, let us take Reynolds number factor as 100%:

Re = 16,207.27 + (40% of 16,207.27)

Re = 18,908.48

Reynolds number by a factor of 100%:

To perform the flow simulation over the cylinder, let us take Reynolds number factor as 100%:

Re = 27,012.12+ (40% of 27,012.12)

Re = 27,012.12

SIMULATION END TIME:

We know that Velocity = Distance/time, on rearranging we get end time for the baseline simulation as:

Since the length of the domain along the X-axis is 0.4 m. Then,

Time = Distance / velocity

= 0.4/5

= 0.08 s

Given that the end time should be 2 times the flow-through time. Then Simulation End Time = 0.16 s

	Velocity	Reynolds Number	Simulation End Time (2 times the flow-through time)
Baseline	5 m/s	13,506.06	0.16
At 20%	6 m/s	16,207.27	0.133
At 40%	7 m/s	18,908.48	0.114
At 100%	10 m/s	27,012.12	0.08

From the above study, the Velocity increases with a decrease in time.

RESULT:

1) Flow over a cylinder | Baseline Simulation:

Velocity = 5m/s

Re = 13,506.06

Simulation end time = 0.16 (2 times the flow-through time)

Velocity contour | cut plot:

Pressure contour | cut plot:

2) At 20% of Reynolds Number | Flow over a cylinder:

Velocity = 6m/s

Re = 16,207.27

Simulation end time = 0.133 (2 times the flow-through time)

Velocity contour | cut plot:

Pressure contour | cut plot:

3) At 40% of Reynolds Number | Flow over a cylinder:

Velocity = 7m/s

Re = 18,908.48

Simulation end time = 0.114 (2 times the flow-through time)

Velocity contour | cut plot:

Pressure contour | cut plot:

4) At 100% of Reynolds Number | Flow over a cylinder:

Velocity = 10m/s

Re = 27,012.12

Simulation end time = 0.08 (2 times the flow-through time)

Velocity contour | cut plot:

Pressure contour | cut plot:

CONCLUSION:

As a result, the above flow simulation study clearly shows that:

	Velocity	Reynolds Number	Simulation End Time (2 times the flow-through time)
Baseline	5 m/s	13,506.06	0.16
At 20%	6 m/s	16,207.27	0.133
At 40%	7 m/s	18,908.48	0.114
At 100%	10 m/s	27,012.12	0.08

1. The Velocity increases with a decrease in time with respect to the Reynolds number
2. When Reynold’s number increases, the flow over the cylinder becomes a steady flow.
3. The velocity plot at 20% & 40% is slightly an unsteady flow plot whereas, at 100%, the flow is steady.
4. In terms of Pressure, there is no significant change in the flow.

Thus the Flow simulation of flow through a cylinder is been simulated using the Solidworks flow simulation.