Project

Simulation of flow over a cylinder using Ansys Fluent

OBJECTIVE:

To perform the steady and transient simulations of flow over a cylinder using Ansys-fluent.

METHODOLOGY:

fig.geometry model for the simulation

Diameter of the cylinder - 2m
Plane surface area-60mx20m
Distance between the left face domain and centre of cylinder-20m
Distance between the right face domain and centre of cylinder-40m
Distance from the centre of the cylinder to the top as well as bottom face of the domain is 10m.

2. Mesh:

Traingle element is generated with element size of 0.5m.
Created a 6 inflation layer around a circle to get a body fitted mesh in order to get accuracy of results.
Inlation first layer height is given as 0.005m and growth rate is given as 1.2.
Naming the selection such as inlet-left face domain ,outlet-right face domain, symmetry-top and bottom,wall-edge of circle.

fig.inflation layer around a circle.

fig.Mesh with element size as 0.5m

3. Setup:

Performed mesh check.
Solver > type-pressure based >velocity formulation-absolute > Time-steady >2D space- planar.
physics >models>viscous>laminar model is chosen
air with density of 1 kg/m^3 and viscosity-0.02 kg/ms is chosen to get Re=100
Boundary conditions-inlet velocity -1 m/s and pressure outlet-0(gauge pressure).
Solution > Definitions were made to see the vertex average velocity at the monitor point which is pointed 8m(x-axis) from the centre of the circle.
Results > contours >velocity and pressure.

4. Solution:

Steady state :

fig.Residual plot

fig.vertex average velocity at monitor point.A

As we see from the above two graph,the residuals are constant after the 200 iteration and doesn't converge a solution for the velocity at monitor point.
vertex average velocity at the monitor point starts fluctuating at 100 iteration as it gradually increases and after 200 iteration it gives a constant fluctuating velocity magnitude that means von carmen vortex street is visible in this range.

fig.velocity contour

with this velocity contour ,we can see the von karmen vortex street clearly with fluctuation.
velocity is maximum at the boundary layer separation and minimum at behind the cylinder.

fig.pressure contour

High pressure value is seen at front edge of a cylinder where the fluid impinges.
creates a low pressure region at the boundary layer separation.

Solution Animation:

Transient state:

fig.Residual plot

fig.vertex average velocity plot at monitor point

1000 time step,0.1s time step is given for the unsteady calculation.we see from the above graph,the velocity magnitude starts fluctuating after 25 seconds and it gradually inceases.
After 100 seconds the velocity magnitude constantly fluctuating.

fig. velocity contour

with this velocity contour,we can see a clear image of how the velocity magnitude fluctuates compared to steady state.

fig.pressure contour.

fig.velocity vector contour plot

from this plot, we can visually see that how the velocity vector behaves once the fluid is impinging the cylinder and form the vortex shedding.

Solution Animation:

Strouhal number:

St=fd/V

f-shedding frequency d- characterstic diameter v-velocity of the flow impinging the obstruction.

for this case it is found out to be 0.15m

st=0.3

CONCLUSION:

In both steady and transient simulation,we observed the vortex shedding for reynolds number Re=100 and plots and calculations were done.

Ship work like this
in your own course.