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Droplet Impact on Structured surfaces UDF — Ansys Learning Forum

Droplet Impact on Structured surfaces UDF

Best Answer

  • RobRob UKForum Coordinator Posts: 8,851
    Accepted Answer

    There's a transition depth so it the VOF level is high enough we resolve the film, as the depth decreases we switch to the film models.

Answers

  • usamausama Member Posts: 79

    The question is here

    Dear Ansys Community, hope you shall be in good health. i need help because i am facing some problem regarding droplet impact on the structured surface. 

    i am doing a 3D simulation for analysis of droplet spreading behavior on the structured surface. 

    i have written the udf is attached in the pictures. 

    To get spreading behavior/spreading factor/liquid-air interface the 

    "C_CENTROID(e,c0,t0);

    r[i]=e[0]; "

    is used in the udf.

    1) the problem i am facing right now when the droplet hits the structured surface the fluent crashes every time.

    2) if I remove that command mentioned above in the udf the fluent runs perfectly.

    can you help me to fix this issue?

    I need to use this command to get the spreading factor of the droplet impact.

    i also attached the udf pictures and geometry pictures in the form pictures.

    please reply urgently.

    i have a due date of the project in my University.

  • RobRob UKForum Coordinator Posts: 8,851

    Are you looking at DPM droplets or small amounts of VOF?

    There are the wall film models, and if you're wanting the surfaces you need to look at a surface thread (F...) rather than the cell thread (C...).

  • usamausama Member Posts: 79

    It is actually the large droplet that is spreading, I tried taking F_CENTROID also in that case also fluent is crashing

  • usamausama Member Posts: 79

    It is actually the large droplet that is spreading gently on the structured surface with 0.1m/s velocity (low weber number), I tried taking F_Centroid but the in that case also ansys fluent is crashing.

  • usamausama Member Posts: 79

    It is actually the large droplet that is spreading gently on the structured surface with 0.1m/s velocity (low weber number), I tried taking F_Centroid t

  • usamausama Member Posts: 79

    it is droplet is gently hitting the surface with 0.1 m/s. In the case of taking F_Centroid also it is crashing

  • usamausama Member Posts: 79

    Thanks rob on coming my post..

    its a long time not in touch with you hope you are fine.

    stay safe

    Usama

  • RobRob UKForum Coordinator Posts: 8,851

    I'm good thanks, hope all is well with you. I've also verified your account to try and stop the filters eating all of your posts.


    I'm not sure why you're getting the problems, but suspect you're trying to store data or do a calculation in the wrong form: not all data is available on F_ or C_ so you may have broken something. What I would suggest is having a look at the VOF to wall film models, that may mean you don't need a UDF.

  • YasserSelimaYasserSelima Member Posts: 929

    what is r and why it's defined [ND_ND]?

    Do you receive "sigsegv"


    add this before the two lines ...

    Message("i = %d", i);
    
  • usamausama Member Posts: 79


    Hi Selima,

    I am getting 999999: mpt_accept: error: accept failed: No error

    before it is getting crashed for each face loop all the cells having volume fraction interface will get stored in r[ND_ND] and then I am using for loop to get the maximum value stored in r array to get the spreading factor (i.e. maximum distance of cell having vof interface)

  • usamausama Member Posts: 79

    HI Rob,

    I have used VOF multiphase along with EWF activated with initial boundary conditions on the wall of impingement . I hve then initialized the solution and then went to EWF tab left the default and given water for film and surface tension coeff 0.072 and max thickness to 5mm and then clicked on initialize tab on EWF tab. But i am getting maxcfl 0 even after droplet impinged on wall

  • YasserSelimaYasserSelima Member Posts: 929

    ND_ND is 2 dimensions for 2D simulations and 3 dimension for 3 D simulation. so, with the fourth value you get "sigsegv". Declare r with a dimension larger than what you expect ... and initialise it with zeros, so when you get the maximum, you get an actual maximum

  • RobRob UKForum Coordinator Posts: 8,851
    Accepted Answer

    There's a transition depth so it the VOF level is high enough we resolve the film, as the depth decreases we switch to the film models.

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