Week 2 - Flow over a Cylinder.
Flow over a Cylinder
Aim:
To Simulate the flow over a cylinder and explain the phenomenon of Karman vortex street.
Part 1:-
- Simulate the flow with the steady and unsteady case and calculate the Strouhal Number for Re= 100.
Procedure
Geometry :-
A plate with the dimension of 20*60m is created using spaceclaim.
Now,we want to simulate effect of fluid flow over cylinder, select the circle and delete it.
Meshing:
1.select the edges of geometry and named them as inlet,outlet ,wall and symmetry.
2.Now select the body and go to mesh and click on generate To ensure triangular mesh, go to mesh > insert > select triangular mesh type.
3.After generating mesh,it is seen that size of cirle looks distoreted.
go to mesh > sizing > select circular edge > deffinition >type > no,of divisions >36.
3.Setting up Ansys fluent
Before opening the set up we should update the mesh. Then we should change the viscous flow to laminar
Open Materials and create a fluid that is to be used for the simulation for this case, it is air and also inputs the density and kinematic viscosity values.
Open Zones and input the inlet velocity as per the reynolds number and check if the fluid is updated.
Update the reference values which is located inside set up at the right-hand side.
Fluent details/procedure:
a. laminar model
b. fluid: Air
c. Method of discretization: Simple
d. Density/kinematic viscosity: 1/0.05
e. Creating a monitor point behind the cylinder by selecting point under surfaces in the results bar.
f. After creating the monitor point, create reports/plots for drag, lift, velocity wrt cylinder.
g. Create plots for the velocity at the monitor point to analyze the vortex shedding.
h. Use hybrid initialization for steady-state and standard for transient state simulations
part 1:-
(i) Simulate the flow with the steady case and calculate the Strouhal number for Re=100 and velocity 10m/s
- Velocity and pressure contours
- residual plot :-
- velocity at the monitor point
- Drag and lift Coefficient:-
(ii) Simulate the flow with the unsteady case and calculate the Strouhal number for Re=100 and velocity 10m/s.
- Velocity and pressure contour
- residual plot :-
- velocity at the monitor point
- Drag and lift Coefficient:-
Part-2
(1) Simulate the flow with the steady-state solver for Re=10.
For Re=10 velocity v=1m/s
- Velocity and pressure contours
- residual plot :-
- velocity at the monitor point
- Drag and lift Coefficient:-
(2)Simulate the flow with the steady case and calculate the Strouhal number for Re=100 and velocity 10m/s
- Velocity and pressure contours
- residual plot :-
- velocity at the monitor point
- Drag and lift Coefficient:-
(3) Simulate the flow with the steady-state solver for Re= 1000.
For Re=1000 velocity v=100m/s
- Velocity and pressure contours
- residual plot :-
- velocity at the monitor point
- Drag and lift Coefficient:-
(4) Simulate the flow with the steady-state solver for Re= 10000.
For Re=10000 velocity v=1000m/s
- Velocity and pressure contours
- residual plot :-
- velocity at the monitor point
- Drag and lift Coefficient:-
(5) Simulate the flow with the steady-state solver for Re= 100000.
For Re=100000 velocity v=10000m/s
- Velocity and pressure contours
- residual plot :-
- velocity at the monitor point
- Drag and lift Coefficient:-
Conclusions:
- In the first case, the flow over a cylinder is simulated for both Steady and unsteady cases with Re=100, and with the results generated the phenomena of Von Karman Vortex Street are also observed.
- Necessary plots are plotted in order to observe that the flow is converged and the vortex shedding is happening.
- Contours are generated in order to observe the flow over a cylinder.
- By plotting Power Spectral Density vs Frequency, the Strouhal number is calculated.
- In the second case,
- six different simulations i.e (Re = 10,100,1000,10000,100000,1000000) are simulated to observe the behavior of the drag and lift coefficients by changing the Reynolds number.
- In order to observe the behavior of the drag coefficients for the simulations, the velocity of the flow is varied to change the Reynolds number and the rest of the parameters are kept constant.
- As we know if the Reynold number is less than 2000, then flow in a pipe is Laminar. Hence we use the Viscous model = Laminar.
- For Re=10, it is observed that there is no formation of vortex shedding and in the rest of the cases, it is clearly observed.
- As per the basic conditions and parameters, the results are validated from the literature.
- As we refine the mesh we need to run more iterations.
- From the above table, it can be concluded that the error percentage is less than 5%