Week 2 - Flow over a Cylinder.

Simulate the flow over a cylinder

PART-I

1. Simulate the flow with the steady and unsteady case and calculate the Strouhal Number for Re= 100.

PART-II

1. Calculate the coefficient of drag and lift over a cylinder by setting the Reynolds number to 10,100,1000,10000 & 100000. (Run with steady solver)
2. Discuss the effect of Reynolds number on the coefficient of drag. [ Results should be validated with any standard literature and error should be within 5 %]

Geometry creation in SpaceClaim

Aim: Simulation of flow over the pipe

Karman vortex street: When fluid flow towards the body, flow around a bluff body produces a regular pattern of alternating vortices called as Von Karman vortex street.

Introduction: Flow over the pipe simulation helps to determine the behaviour of air flow velocity over the pipe geometry. As soon as the Reynold number is increasing the flow velocity decreases.

Theory:

1. Boundary layer: Gradient in mean velocity and temperature is steep normal to the wall.
2. Inflation layer: To solve the gradient, cell need to be smaller normal to the wall than along the wall.
3. Y + : The behaviour of flow near the wall is complicated phenomenon and to distinguish the different regions near the wall, the concept of wall has been formulated.

Modelling Approach: Here we have to use viscous model for the analysis.

Meshing: the meshing is used is triangular type 2d element. Here we use unstructured mesh with giving proper element size defined in the length parameter.

The number od elements and nodes are 40149 and 20531 respectively.

Here we also used the inflation layer for getting proper results near the cylinder wall boundary.

The above images define the boundary condition the cfd analysis. Here we define the line geometry as inlet, outlet, cylinder wall and symmetry.

Here we use laminar model for the cfd analysis.

For the user define material, here we define the density is 1 kg/m3 and viscosity is 0.05 kg/ms

Fluid domain fro the above region is air with user define material

Outlet pressure here we consider is normal atmospheric pressure value. It means that the gauge pressure is 0.

Reference value for the above model

Area: 2m^2

All calculation starts from inlet.

Report and results

For this project, main results are interested in lift and drag.

The residual plot graph is showing whether the solution is converged or not. As the every line shows respective velocity values, these lines when in straight, it means that the solution is converged.

The report plot is for lift coefficient.

The contour plot for the velocity distrubuition plot for the flow velocity having 0.25 m/s

For Re – 10

For Re – 100

For Re – 1000

For Re – 10000

For Re – 100000

Conclusion

Sr.No.	Reynolds number	cl	cd
1	10	1.44 x 10^9	-1.72 x 10^9
2	100	1.34 x 10^7	-1.06 x 10^7
3	1000	1.81 x 10^5	-4.68 x 10^4
4	10000	2638.36	-473.32
5	100000	45.55	0.212

From the above results, as the Reynold number is increases the values of flow velocity calculated is decreases and results which is obtained in terms of coefficient of lift and coefficient of drag is also affected.

In the major sense, as higher the velocity value the lift force is also more and vice versa.