Global courant number exceeds 250 for constant heat flux bcs.

- February 7, 2023 at 5:12 am
  abhnv_01
  Subscriber
  I am trying to simulate a heat pipe in (2D) which has three sections:
  1. Evaporator - Constant heat flux (boundary conditions)
  2. Condensor - Constant temperature (boundary conditions)
  3. Adiabatic section - Zero heat flux (boundary conditions)
  I am using VOF multiphase model -> Evaporation - condensation model -> Lee model.
  Transient simulation with gravity and implicit body force formulation.
  Time step size = 0.0001 (1E-04).
  The simulation works well for first 10000 time steps (1 seconds of flow time) and then this error where global courant number exceeds 250.
  
  But here is a mystery, the simulation runs well with constant temperature boundary condition at the evaporator.
  
  I want results with constatn heat flux, I am not able to track the error, any help will be highly appreciated.
- February 7, 2023 at 6:05 am
  
  SRP
  Ansys Employee
  
  Hi,
  I suggest to try variable time stepping in order to automatically change the time-step. It is better to use the variable time stepping method to control the CFL under limit. The solution will be stable with the variable time stepping method.
  Thank you
  Saurabh