Solve divergence for the PISO algorithm in unsteady solution (ANSYS FLUENT)

- November 21, 2020 at 11:52 am
  
  Ruk
  Subscriber
  
  hello to allnnI'm doing an unsteady simulation for the delta wing in the Fluent. I compared PISO and SIMPLE-C algorithms in this investigation. Since Fluent offers to use the PISO algorithm for transient flow but the solution was diverging for this algorithm and the system gave a floating-point error. In contrast, the solution was convergent in the SIMPLE-C method. I don't know why the PISO algorithm is inefficient at this unsteady project (Contrary to Fluent's suggestion). Time step adjusted about 0.0002 s. I used to see the same question in a different place but I did not get the right answer.nnAlso, when I used Extrapolate Variables the solve was diverging for both algorithms.nnplease guide me.nnThanksn
- November 23, 2020 at 1:13 pm
  
  Amine Ben Hadj Ali
  Ansys Employee
  
  Might be due to the fact that URF's of SIMPLEC are bit conservative. Which version are you using?n
- November 23, 2020 at 2:55 pm
  
  Ruk
  Subscriber
  
  I'm using ANSYS 17.2. I checked the URF values of SIMPLE-C and PISO. There isn't any different between them.n
- November 23, 2020 at 5:12 pm
  
  Amine Ben Hadj Ali
  Ansys Employee
  
  Piso has two pressure corrections steps. So even if using same exposed URFs the numerical method is different: can u check if the behavior is reproducible with a supported version. What else are you modeling?n
- November 23, 2020 at 5:19 pm
  
  Amine Ben Hadj Ali
  Ansys Employee
  
  Also what happens if you disable skewnes corrections?n