Flow over a cylinder
Theory-
In this challenge we have to run a baseline simulation of a cylinder in which external flow takes place. And also calculate the Reynolds number. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation. Also create animations for pressure-velocity for all the three Reynolds number.
CAD model-
- Select a top plane and make a circle of 4 m.
- Then extrude it to 5 m to make a cylinder.
- Select external amalysis type and give total analysis time is 5 sec and output time step is 0.5 sec.
- Select air as working fluid.
- Thermodynamics parameters remains same as default.
- As per this drawing, give the value of velocity is Y direction - 1 m/s (as per question) and in other direction = 0 m/s.
Mesh-
- Create a cut plot in XY plane in middle of cylinder.
- Then run the simulation.
- Then click on Animation.
- Then click on Wizard and give animation time is 10 sec.
- Since we want to animate development of flow field distribution in time to see transient animation of time dependent analysis and hence select the Scenario type of the animation.
Calculation-
We know,
- Re = rho*U_inlet*D/mu
- D = cylinder diameter
- mu = dynamic viscosity
- rho = density
At given Thermodynamics parameters-
mu = 0.001003 kg/m-s
rho = 1.225 kg/m^3
D = 4
U_inlet = 1m/s
Hence, we can calculate the value of Reynolds number (Re) = 4,885.34
In Case 2- When Reynolds number is increased by a factor of 20% - Then value of Re_2 = Re*1.2 = 5,862.41
Hence velocity = 1.2 m/s
In Case 3- When Reynolds number is increased by a factor of 40% - Then value of Re_3 = Re*1.4 = 6,839.48
Hence velocity = 1.4 m/s
In Case 4- When Reynolds number is increased by a factor of 100% - Then value of Re_4 = Re*2 = 9,770.68
Hence velocity = 2 m/s
- We just change the value of velocity in each case for each animation and other parameters remains same.
Result ( YouTube link for each 4 cases)-
Case 1 ( Reynolds number when velocity = 1 m/s) - https://youtu.be/0VR3M2tTBJc
Case 2 (Reynolds number is increased by a factor of 20%)- https://youtu.be/1gWz8yuKdD4
Case 3 (Reynolds number is increased by a factor of 40%)- https://youtu.be/cWgh9NfU1WY
Case 4 (Reynolds number is increased by a factor of 100%)- https://youtu.be/m_3VVzRODtY