Fluent Cd value isn’t correlating to Fd value

- April 21, 2021 at 1:33 pm
  
  jayjay_v
  Subscriber
  
  I am simulating a student solar vehicle for drag and lift and noticed that the Cd value output in ansys fluent did not match with the known dynamic pressure, known area, and drag force calculated in the simulation. When I saw this was happening I also simulated a cylinder in an enclosure to see if the same discrepancies would happen, they did, The drag coefficient is solving to be 1.632 times larger than the drag force which obviously does not make sense. The cylinder has an area of 0.785 m^2, velocity of 13.4 m/s, diameter of 1m, and length of 2m. The simulation produces a drag force of 75 N which makes sense since the Cd of a cylinder with the L/D ratio of 2 should be 0.86 but the simulation gives a coefficient of drag of 122.98. Anyone able to help explain why this is occurring? Thanks in advance!n
- April 21, 2021 at 2:54 pm
  
  Rob
  Forum Moderator
  
  The force is a calculated value based on flow, area etc. The coefficient is then based on some constants that you need to check are correct for your model. Have a look at the NACA airfoil examples and read up on the Reference Values in the manual. n
- April 21, 2021 at 4:15 pm
  
  jayjay_v
  Subscriber
  
  Hi Rob, thank you for the fast reply! Which manual could I find these references in? Can you link that directory or PDF here please?n
- April 21, 2021 at 4:20 pm
  
  DrAmine
  Ansys Employee
  
  Fluent Users Guide is my colleague referring to. Usually the frontal cross sectional area is used as reference area if one thinks of drag as flow resistance.n