Week 2 - Flow over a Cylinder.

Aim :-Flow Over a Cylinder

Objective :- in this case we have to perform the follow cases.

→Performing 2D Simulation

→Modyfyning Reyonlds Number

→Creating Custumize fluids.

→Creating Run Time Animation

→Visulizing Vortex Shadding

→ Adding Moinitor Points

→Numerical Diffusion.

→Steady State and transient analysis

→Post Prpcessing.

Problem to solve-

Reyonlds No   100

                      1

step 1

open the Ansys Workbench.

Select Fluid Flow (Fluent) And Give Name -- Flow Over a Cylinder

Double Click on the Geometry (Space Claim) & Set the units in meter.

Select the Y axis and start the sketch.

After that the Genrate the mesh Box Right Click and update and after that double click on mesh,

click on mesh, it will  show the Quaderatel mesh but we need the triangles mesh.

follow the steps

Right Click on Mesh→ Insert → Method→Click on Automated Method→for select the body → select the triangles →ok→genrate mesh

 

Create the infliation (its  Helps to the Body fitted mesh.)

Steps to apply infliation.

Right Click On Mesh→ Input→Method→Select the body→Select the boundary (only Edges selected)→apply →ok→Infliation option(First layer thickness)→height-5e-3

Genrate the mesh ok,

Create the Inlet 

outlet 

cylinder wall

symmetry both side wall

Update all 

Go to the Setup Physics

Domain:- Steady →Absolute→Viscous model ( Laminar)

Check the material

create the point. give the distance 4x diameter ,y-0

Solving :-Definitions → Surface  Report → Vortex Avarage →Name&Report File.

Create The Contours:-

Solving  Check on Hybrid ok → Hit I-0 start → then go to results → Contours →New →filled opton (Velocity)→Velocity Magnitude → select all inlet ,outlet ,boundary →Save & Display → Compute → click on Graphics Check the results.

Change the pressure intial contour

.

Uncheck the solving residuals for better result.

Create the animation activites.

Steady Condition.

Unsteady Case Condtion.

Drag & Lift

Lift coefficient decreases rapidly and drag coefficient increases rapidly when Reynolds number is decreased below critical range. This occurs due to change in flow pattern near Gurney flap at low Reynolds numbers.

 

Strauhall number:

 Strouhal number is a dimensionless number describing oscillating flow mechanisms.

The Strouhal number is often given as

      St = f*d/u

Here,we have calculated staruhal no.using ansys fluent.

1.Go to fluent solver > results > fft analyser > load lift coefficient fiel > select plot FFT

Here, x axis denotes strauhal number and y axis denotes magnitude.

2.To get the magnitude of strauhal number,

go to results > fft analyser > click on write fft to file > click on write fft.

open the file in excel and 1st coloumn denotes the frequncy and 2nd coloumn denotes strauhal number.use the command max and select 2nd row and find the magnitude of strauhal number.

Conclusion:

1.When fluid flows over cylinder, wake region is formed next to cylinder due to decrease in pressure and recirculation of flow occures and hence flow separation occures.