Week 2 - Flow over a Cylinder.

Aim

1. To simulate the flow over cylinder and capture the phenomena of Von Karman vortex street
2. Study the effects of Reynolds number on coefficient of drag and lift
3. Calculating strouhal number

Introduction and Theory

We are simulating flow over cylinder and trying to capture the phenomena of Von karman Vortex Street.

Von Karman vortex street is the phenomena that is observed in the case of flow over cylinder due to the process of vortex shredding. It is also described as the repeating pattern of swirling vortices behind the cylinder.

Strouhal number (Sr) is the dimensionless number used to describe the oscillating flow.

vortex shredding frequency

d =diameter of cylinder

U =free stream velocity

Model used

We are using Laminar flow model and simple scheme is utilised for solving equations.

Geometry used

1. Diameter (d) of cylinder is 2m
2. Inlet is at a distance of 10d which is 20m
3. Outlet is at a distance of 20d which is 40m

Meshing

1. Meshing method is triangular with element size of 0.25m
2. Edge sizing is used with 36 number of divisions
3. Inflation layer is also used for body fitted meshing with first layer thickness of 5mm and 6 layers with inflation of 1.2

Material properties used

Density	1 kg/m3
Viscosity	0.02 kg/(m s)

Calculating Re

`Re=(ρUd)/μ`

S.No.	Density(kg/m3)	Velocity(m/s)	diameter of cylinder(m)	dynamic viscosity(kg/m s)	Reynolds no.
1	1	0.1	2	0.02	10
2	1	1	2	0.02	100
3	1	10	2	0.02	1000
4	1	100	2	0.02	10000
5	1	1000	2	0.02	100000

Part 1 Re=100

Steady Laminar model is used to get the following results

Unsteady Laminar model is used to get the following results

Part 2

Steady state laminar model used for different Reynolds number

Re=10

Re=100

Re=1000

Re=10000

Re=100000

Conclusion

From the above plots and contours the following inferences are drawn:

1. With increase of Reynolds number coefficient of drag and lift are increasing.
2. More wakes are formed as the Reynold number is increasing.
3. Von Karman vortex street is started to form after Reynold number 100.