Flow over a cylinder

Introduction:this assignment is about making a cfd simulation of flow over a cylinder, which shows us how fluids will behave, when it comes in contact with the surface so the plots of the simulation would give us the necessary information about the boundary layer formation and other physical parameters associated with it at the end of the simulation calculation we can make an animation of the transient condition which gives us a better visual understanding.

Theory:

The simulation is set up in a rectangular box like wind tunnel where the box size is chosen such that the end time is set to 2 times flow through time ,i.e. the air take 10 seconds to flow from one end to the another.but we must understand this is an experiment so there will be always some disturbance rebounding from the wall of the tunnel,so it is necessary to choose a optimum size such that the disturbances are at their minimum.the calculation of the Reynolds number is done using the hydraulic diameter, velocity and kinematic viscosity.

Explanation:

>make a cylinder by drawing a circle and extruding it(500cmdia,1000cmlength)

>the click on to the cfd simulation wizard enter all the essential condition, make it a as external flow,transient condition and also set the intlet velocity(1m/s).

>resize the computation domain meeting our reqirements

>the set the size of mesh we need (i used the default mesh),since it was a external flow i made mesh redefinment and made the mesh finer at the curved surface area of the cylinder by this we can get much acccurate results.

>then make a parametic study set the input parameters as the boundry condition initial velocity(1,1.2,1.4,2 m/s) the select the out parameters as cut plots of the velocity and pressure.

>then make the design study as a seperate study and make the animation for transient condition of velovity and pressure profile inthe cut plots

results:

velocity profile

1 m/s 2 m/s

1.4 m/s 2 m/s

Pressure profile

animation:

All the velocity and pressure transient animation are enclosed.

Reynolds number calculation:

Reynolds number for air flowing inside the wind tunnel of area(3mx3m)

hydraulic diameter=4*area/wetted perimeter

re=v*dh/γ

kinematic viscosity

1 m/s of air=2.027x10^5

1.2 m/s of air=2.432x10^5

1.4 m/s of air=2.8378x10^5

2 m/s of air=4.054x10^5