Courant number and time step for compressible flow

- January 21, 2020 at 8:24 pm
  
  abd fs
  Subscriber
  
  Dear experts,
  
  I simulate a compressible transient flow with input conditions P = 0.25 MPa.
  
  This question relates to the courant number and the condition CFL (C <1) which determines the stability of many numerical methods.
  
  My question is: How to calculate the courant number and time step for compressible flow and inlet condition P = 0.25 MPa?
  
  I know there is a formula for an inlet velocity as shown below.:
  
  But for an inlet pressure, I don't know if there is a formula or a technique for the courant number?
  
  Best regards,
  
  SER
- January 22, 2020 at 5:53 am
  
  Amine Ben Hadj Ali
  Ansys Employee
  
  There is no formula for that. You need to solve first till pressure field is developed and then check the convective courant number value. Or you do some estimation based on pressure at the openings and the longest cell edge.
- January 22, 2020 at 9:50 am
  
  abd fs
  Subscriber
  
  Dear Amine,
  
  Thank you for your quick response I would be very grateful if you indicate a document or tutorial that can help me understand what you are explaining to me.
  
  it is the first time for me that I use this type of phenomenon, before asking this request I have searched a lot, but I have not found a document that can help me to solve this type of problem
  
  Best regards,
  
  SER
- January 22, 2020 at 12:04 pm
  
  Amine Ben Hadj Ali
  Ansys Employee
  
  User's Guide is good document. Also Check the theory guide when it describes pseudo time scale to have an idea how to estimate velocity from pressure fields. I think it is appropriate if you just run the case and then quantify the courant number and adjust accordingly.