[Julian K.]

Hi!

I am simulating the impaction of particles on a moving circular cylinder using Lagrangian particle tracking. I found out, that CFX does not consider the particle's radius while checking if a particle has collided with the cylinder's surface. Thus, the particle is captured, when its centre coordiantes of the coincide with the cylinder surface.
However, my case requires, that the particle is captured when the particle surface and the cylinder surface touch. Hence, I need to implement this simple algorithm:

if (x <= r_part + r_cyl)
then impaction
else no impaction

Where x is the distance between the centre coordiantes of the particle and the cylinder, r_part is the particle's radius and r_cyl is the radius of the cylinder.

I assume, that I need to implement the code via a User FORTRAN. Since I have absolutely no experience with this, I would like you to ask for some help. I found a file called 'pt_termination.F' (CFX\Samples\UserFortran) with the following code:

IF (DIST.GT.0.75) THEN
   FATE = DEAD
ENDIF

I wonder if this is the right point to start for me?! Do you have any other suggestions for me?

Thanks!

[Julian K.]

In the file <CFXROOT>/etc/VARIABLES I found the variable 'ptpos' with this description:

  VARIABLE: ptpos
    Option = Definition
    MMS Name  = CRD
    Long Name = Particle Position
    Quantity = Length
    Tensor Type = VECTOR
    Status = M
    User Level = 2
    Output to Postprocessor = No
    Output to Jobfile = No
    General Availability = PTM_UR
    Physical Availability = PARTICLE
    Component Short Names = \
       ptpos x, \
       ptpos y, \
       ptpos z
    Component Long Names = \
       Particle Position X, \
       Particle Position Y, \
       Particle Position Z
    Old Component Long Names = \
       Particle Position x, \
       Particle Position y, \
       Particle Position z
    Component MMS Names = \
       CRD-1, \
       CRD-2, \
       CRD-3
    Variable Scope = PARTICLE
  END

I guess, that I can use this variable to calculate x, the distance between the cylinder's and particle's centre coordiantes?!

Now, what's the name of the variable which gives me the centre coordinates of the cylinder? Btw, the cylinder is a moving rigid body, thus it's position is not constant.

[Julian K.]

By now, I found a way to determine if a particle touches the surface of an oscillating cylinder.

I use this User Fortran Code and put it into the file 'pt_termination.F':

#include "cfx5ext.h" 
dllexport(pt_termination) 
      SUBROUTINE PT_TERMINATION (NLOC,NRET,NARG,RET,ARG,CRESLT, 
     &                            CZ,DZ,IZ,LZ,RZ) 
CC 
CD User routine: template for particle user termination routine 
CC 
CC -------------------- 
CC        Input 
CC -------------------- 
CC 
CC  NLOC   - number of entities 
CC  NRET   - length of return stack 
CC  NARG   - length of argument stack 
CC  ARG    - argument values 
CC 
CC -------------------- 
CC      Modified 
CC -------------------- 
CC 
CC -------------------- 
CC        Output 
CC -------------------- 
CC 
CC  RET    - return values 
CC 
CC -------------------- 
CC       Details 
CC -------------------- 
CC 
CC====================================================================== 
C 
C ------------------------------ 
C     Preprocessor includes 
C ------------------------------ 
C 
#include "cfd_sysdep.h" 
#include "cfd_constants.h" 
C 
C ------------------------------ 
C        Argument list 
C ------------------------------ 
C 
      INTEGER NARG, NRET, NLOC 
C 
      CHARACTER*(4) CRESLT 
C 
      REAL ARG(NLOC,NARG), RET(NLOC,NRET) 
C 
      INTEGER IZ(*) 
      CHARACTER CZ(*)*(1) 
      DOUBLE PRECISION DZ(*) 
      LOGICAL LZ(*) 
      REAL RZ(*) 
C 
C======================================================================= 
C 
C --------------------------- 
C    Executable Statements 
C --------------------------- 
C 
C======================================================================= 
C 
C     Return variables: 
C     ----------------- 
C 
C     Particle fate                                        : RET(1,1) 
C 
C     Argument variables  
C     ------------------- 
C 
C     Particle mean diameter                               : ARG(1,1) 
C     Particle position                                    : ARG(1,2:4)
C     Cylinder x-position                   : ARG(1,5)
C     Cylinder y-position                   : ARG(1,6) 
C 
C     We know that NLOC is 1 for the particle user source routines!!!! 
C======================================================================= 
C 
C----------------------------------------------------------------------- 
C     Calculate the return variables 
C----------------------------------------------------------------------- 
C 
      CALL USER_FATE (RET(1,1),ARG(1,1),ARG(1,2),ARG(1,5),ARG(1,6)) 
C 
      END 
 
      SUBROUTINE USER_FATE (FATE,DIA,PPOS,CPOSX,CPOSY) 
C 
C --------------------------- 
C    Preprocessor includes 
C --------------------------- 
C 
#include "cfd_sysdep.h" 
#include "cfd_constants.h" 
C 
C ------------------------------ 
C        Argument list 
C ------------------------------ 
C 
      REAL               FATE, DIA, PPOS(3), CPOSX, CPOSY 
      REAL               CYLRAD, PRAD 
      REAL               CONTACT 
C 
C ------------------------------ 
C        Local variables 
C ------------------------------ 
C 
      REAL               DEAD, ALIVE 
C ------------------------------ 
C    Executable statements 
C ------------------------------ 
C 
      DEAD  = 0. 
      ALIVE = 1.  
C 
      CYLRAD = 0.005  
C 
C---- Particle starts as alive 
C 
      FATE = ALIVE 
C 
C---- Calc particle radius 
      PRAD = ((CPOSX-PPOS(1))**2 + (CPOSY-PPOS(2))**2)**0.5 
      CONTACT = CYLRAD - (PRAD - DIA/2.0) 
C 
C---- Check if user defined criterion was exceeded, stop particle 
C     --> Set particle mode to __dead__ 
C 
      IF (CONTACT.GT.0.0) THEN 
        FATE = DEAD 
      ENDIF 
C 
      END

In CFX I create a 'Particle User Routine', which uses the output of the F-file compilation. In case of an oscillating cylinder, you need to define the cylinder coordinates as two 'Additional Variables', called 'Xcyl' and 'Ycyl' (Varible Type = Unspecified, Units = [m], Tensor Type = Scalar). Now, these variables can be selected from 'Default Domain > Fluid Models > Additional Variable Models > Additional Variable'. You define both variables with an 'Algebraic Equation' with is for 'Xcyl'

rbstate(Position X)@Rigid Body Cylinder

and 'Ycyl'

rbstate(Position Y)@Rigid Body Cylinder

Now comes the crucial part: The in- and output arguments of the User Fortran need to be defined with a 'Particle User Termination Criteria', however, this can not be selected in the 'Particle Control' Panel of the CFX GUI. The 'Particle User Termination Criteria' needs to be defined using two seperate CCL-files, 'pt_term.ccl' and 'pt_extra.ccl'. There is the contents:
pt_term.ccl: (make sure the 'Library Path' is set corretly)

LIBRARY: 
  USER ROUTINE DEFINITIONS: 
    USER ROUTINE: termination 
      Calling Name = pt_termination 
      Library Name = pt_termination 
      Library Path = /work/simulations/test/part_capt/oscillation_capture 
      Option = Particle User Routine 
    END 
  END 
END 
FLOW:  
  SOLVER CONTROL:  
    Turbulence Numerics = First Order 
    ADVECTION SCHEME:  
      Option = High Resolution 
    END 
    CONVERGENCE CRITERIA:  
      Conservation Target = 0.01 
      Residual Target = 1.E-4 
      Residual Type = MAX 
    END 
    DYNAMIC MODEL CONTROL:  
      Global Dynamic Model Control = On 
    END 
    PARTICLE CONTROL:  
      PARTICLE INTEGRATION:  
        Option = Forward Euler 
      END 
      PARTICLE TERMINATION CONTROL: 
        Maximum Tracking Time = 10 [s] 
        Maximum Tracking Distance = 10 [m] 
        Maximum Number of Integration Steps = 100000 
        FLUID: Particle 
          PARTICLE USER TERMINATION CRITERIA: 
            Particle User Routine = termination 
            Argument Variables List = \ 
              Particle.Mean Particle Diameter,\ 
              Particle.Particle Position,\
          Xcyl,\
          Ycyl 
            Particle User Fate Return Variables List = \ 
              Particle Fate 
          END 
        END 
      END 
    END 
  END 
END

pt_extra.ccl:

RULES: 
  SINGLETON: PARTICLE TERMINATION CONTROL 
    Description = Sets details of the particle tracking integration \ 
                  algorithm. 
    Solver Name = PT_TERM_CTRL 
    Optional Parameter List = \ 
      Maximum Tracking Time, \ 
      Maximum Tracking Distance, \ 
      Maximum Number of Integration Steps, \ 
      Minimum Diameter, \ 
      Minimum Total Mass 
    Editable Option = True 
    Optional Child List = \ 
      MASS FRACTION LIMITS, \ 
     FLUID 
  END 
 
 OBJECT: FLUID 
   Description = This object encloses fluid-specific models and data. 
   # 
   # ...Context....   ...Allowed Contents......... 
   # DOMAIN           FLUID MODELS, SOLVER CONTROL 
   # SUBDOMAIN        SOURCES, BULK SOURCE DISTRIBUTION 
   # BOUNDARY         BOUNDARY CONDITIONS 
   # INITIALISATION   INITIAL CONDITIONS 
   # 
   Solver Name = FL 
   Object Name Restriction = CEL 
   Optional Child List =  \ 
     ADDITIONAL VARIABLE, \ 
     COMBUSTION MODEL, \ 
     COMPONENT, \ 
     DILATATIONAL STRESS, \ 
     ELECTROMAGNETIC MODEL, \ 
     FLUID BUOYANCY MODEL, \ 
     HEAT TRANSFER MODEL, \ 
     KINETIC THEORY MODEL, \ 
     SOLID PRESSURE MODEL, \ 
     SOLID BULK VISCOSITY, \ 
     SOLID SHEAR VISCOSITY, \ 
     THERMAL RADIATION MODEL, \ 
     TURBULENCE MODEL, \ 
     TURBULENT WALL FUNCTIONS, \ 
     WALL SLIP MODEL, \ 
     EROSION MODEL, \ 
     NUCLEATION MODEL, \ 
     INITIAL CONDITIONS, \ 
     BOUNDARY CONDITIONS, \ 
     SOURCES, \ 
     BULK SOURCE DISTRIBUTION, \ 
     SOLVER CONTROL, \ 
     INJECTION CONDITIONS, \ 
     PARTICLE ABSORPTION, \ 
     PARTICLE ROUGH WALL MODEL, \ 
     PARTICLE USER TERMINATION CRITERIA 
 END 
 
 SINGLETON: PARTICLE USER TERMINATION CRITERIA 
    Description = Controls user defined particle fate 
    Solver Name = USR_TERM_CTRL 
#   Context Rule = Option 
#   Allowed Option List = \ 
#     User Defined 
#   Essential Parameter List = \ 
#     Option 
#   CONTEXT: User Defined 
      Essential Parameter List = \ 
        Particle User Routine, \ 
        Argument Variables List, \ 
        Particle User Fate Return Variables List 
#   END 
  END 
 
  PARAMETER: Particle User Fate Return Variables List 
    Parameter Type = String List 
    Solver Name = CVAR_RET 
    Allowed String List = \ 
        Particle Fate 
  END 
END

These need to be added to the CFX solver call. From the command line, you add:

-ccl pt_term.ccl -ccl pt_extra.ccl

to your regular function call.

Now, after each time step. The solver writes the number of particles, which touched the surface of the cylinder in the 'Particle Diagnostics'.

[Julian K.]

Now, I know, that a particle touch the cylinder. However, I also would like to know on which side, lee- or windward, the particle was captured. I came up with two ideas:

1. open an external file from within the User Fortran call and write leeward, or windward in it
2. return the particle and cylinder coordinates in the 'Particle User Fate Return Variable List'

to 1.: I already tried this, using a very simple test code, which I added to the subroutine call of the User Fortran:

C---- Open and close file again to see if it works
    n = 0.005
      OPEN(UNIT=1, FILE='OUTPUT', STATUS='NEW')
    WRITE (1,'(F4.3)') N
      CLOSE(1)

The result is that the file 'OUTPUT' is being created an the value n=0.005 is written into it. However, eventually, an error occurs and the solver exits with return code 10.

Does anyone know, how why this error occurs?

to 2.: I haven't tried this, yet. But I suppose it won't work. I'll post my resutls, once I've tried it.