Transient flow simulation of flow over a cylinder at different Reynolds numbers

Objective:

• Calculate the baseline case Reynolds number.
  • Re = rho*U_inlet*D/mu
  • D = cylinder diameter
  • mu = dynamic viscosity
  • rho = density
• Run a baseline simulation and then calculate the Reynolds number. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.
  • For example
    • If the Reynolds Number value for the baseline simulation is 100. Then it should be increased( as a factor of 20%, 40%, and 100%) to 120, 140 and 200
• Simulation end time should be calculated properly
  • If the inlet velocity is 1m/s and if the length of the domain is 5 m then the flow through time is 5 seconds. That is, it takes 5 seconds for the flow from the inlet to go to the outlet.
  • This 5 second is called the flow through time
  • Make sure that end time is set to 2 times flow through time. According to the previous example, the end time would be 10 seconds.
• Create animations for pressure-velocity for all the three Reynolds number.
• Explain your observations

Procedure:

1. Create a new part file and change the unit system to MKS System.

2. In front view normal to the plane draw a circle of 0.02m dia and extrude it to 0.04m to obtain a cylinder geometry

3. Save the file and set parameters in wizard section set simulation as external because we are interested to perform simulation outside the component.

4. working fluid is Air and Baseline simulation parameters are set as follow

Properties of Air 1atm pressure @30 degree celsius

Density = 1.164Kg/m^3

Dynamic viscosity =1.872*10^-5 kg/m-s

Kinematic Viscosity 1.608*10^-5m^2/s

Velocity =1m/s @ Re =1240

Increasing Reynolds number by Factor of 20,40 and 100 resp.

Velocity =1.2m/s @ Re = 1492

velocity =1.4m/s @ Re = 1741

Velocity = 2m/s @ Re = 2487

Simulation End time :

Velocity =1m/s @ Re =1240 and length is 0.04m simulation end time 0.08seconds

So for ,

1.Velocity =1.2m/s @ Re = 1492 simulation end time 0.066 seconds

2.velocity =1.4m/s @ Re = 1741 simulation end time 0.057seconds

3. Velocity = 2m/s @ Re = 2487 simulation end time 0.04seconds

By Setting up Calculated parameters results are obtained and animations are created to visualise the simulation.

Velocity @ 1m/s

Pressure @1m/s

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Pressure @1.2m/s

Velocity @1.4m/s

Pressure @1.4m/s

Velocity @2m/s

Pressure @2m/s

Observations :

we can conclude from the study with the increase in Reynolds number flow tries to converge and pressure doesn't showcase any significant changes