PHOTON USE
  p;  parphi;;;
 
  msg        PLANE JET
  msg
  msg        longitudinal-velocity contours and vectors
  msg            -
  msg Press  to continue
  gr ou x 1;con wcrt x 1 fi;0.2;vec x 1;pause;vec off;con off;red
  msg        Temperature contours:
  con temp x 1 fi;0.2;  pause;  con off;red
  msg        Eddy-viscosity contours:
  con enut x 1 fi;0.2
  msg            -
  msg Press e to END
  enduse
 
    GROUP 1. Run title and other preliminaries
TEXT(Plane Jet;Mixing Length Model;Para
TITLE
  DISPLAY
  A free turbulent plane jet is formed when fluid emerges steadily
  from a wide slot into a reservoir of the same fluid at rest.
 
  Downstream of a 'development length', of about 8 slot widths, the 
  flow becomes self-similar.
 
  In the self-similar region of the jet, both the velocity and
  temperature half-widths vary in proportion to z, and the centre-
  line velocity and temperature excess decay as z**(-0.5).
 
  The calculations are started at z = 0, where the velocity is
  supposed to have a "top-hat" shape, with a uniform value from
  y = 0 to y = half the slot width, and a much smaller value for
  larger values of y.
 
  The grid width and forward step are set to increase linearly 
  with z.
  
  
  ENDDIS
#pause 
  The locally-defined variables are as follows:
 
     WJET     Jet velocity at the slot                  (m/s)
     REYNO    Reynolds number
     HSLOT    The width of the jet slot                 (m)
     TJET     The jet temperature at the inlet          (C)
     TFREE    The temperature of the free stream        (C)
 
  The experimental data indicate velocity and temperature half-width
  spreading rates of 0.11 and 0.14, respectively, in the self-
  similar region of the jet. The present calculation predicts values
  of 0.11 and 0.14, respectively, which are in very good agreement
  with the experimental values. The sensitivity of the solution to
  grid-size may be assessed by increasing NY and reducing the
  forward step size DZW1 ( and consequently increasing NZ ).
 
REAL(WJET,REYNO,HSLOT,TJET,TFREE)
REYNO=5.E5; HSLOT=0.2; WJET=10.; TJET=1.0; TFREE=0.0
    GROUP 4. Y-direction grid specification
NY=20; YVLAST=HSLOT*0.5
YFRAC(1)=-20.;YFRAC(2)=1.0/20.
   *** Linear grid expansion with slope DYGDZ
AZYV=1.0               ! this dictates that yvlast is linear in z
REAL(DYGDZ); DYGDZ=0.3 ! dygdz is  d(yvlast)/dz
ZWADD=YVLAST/DYGDZ  ! so YVLAST = YVLAST at the inlet
                                + DYGDZ * (ZWLAST + ZWADD)
    GROUP 5. Z-direction grid specification
PARAB=T
NZ=100    ! 100 z intervals
   see grex3
  ** The z-direction step size is made proportional to YVLAST in
     GROUND by setting AZDZ=PROPY and DZW1 here
AZDZ=PROPY     ! propy = grnd2; means dz is proportional to y
DZW1 = 0.1     ! the proportionality factor; so dz=0.1 * yvlast
    GROUP 7. Variables stored, solved & named
NAME(H1)=TEMP;STORE(ENUT,LEN1)
SOLVE(P1,V1,W1,TEMP)
    GROUP 8. Terms (in differential equations) & devices
  **Built-in source term in TEMP equation is de-activated.
DIFCUT=0.0; TERMS(TEMP,N,Y,Y,Y,Y,Y)
 
    GROUP 9. Properties of the medium (or media)
ENUL=WJET*HSLOT/REYNO;PRT(TEMP)=0.65
  **Select formula for the length scale
  ** Prandtl=mixing-length constants
  ** EL1A = mixing-length constant for mixing-layer zone
     EL1B =   ''     ''      ''    for jet zone
     EL1C = velocity fraction for jet-width calculation
     EL1D = free-stream velocity for jet-width calculation
     EL1E = jet-discharge velocity ( mixing-length constant
            is switched from EL1A to EL1B, when centre-line
            velocity falls below EL1E )
EL1=MIXLENJET; EL1A=0.07; EL1B=0.1; EL1C=0.01; EL1D=0.0; EL1E=WJET
  **Select Prandtl mixing-length formula supplied in GXENUT for
    the turbulent kinematic viscosity.
ENUT=MIXLEN
    GROUP 13. Boundary conditions and special sources
     1. Outer Boundary-- free stream
PATCH(HIGHY,NORTH,1,1,NY,NY,1,NZ,1,1)
COVAL(HIGHY,P1,FIXVAL,0.0);COVAL(HIGHY,W1,ONLYMS,0.0)
COVAL(HIGHY,V1,ONLYMS,0.0);COVAL(HIGHY,TEMP,ONLYMS,TFREE)
     2. Inlet Boundary-- uniform velocity and temperature at slot
PATCH(SLOT,LOW,1,1,1,NY/2,1,1,1,1)
COVAL(SLOT,P1,FIXFLU,RHO1*WJET);COVAL(SLOT,W1,ONLYMS,WJET)
COVAL(SLOT,TEMP,ONLYMS,TJET)
     3. Inlet Boundary-- uniform velocity and temperature
PATCH(OUTSIDE,LOW,1,1,NY/2+1,NY,1,1,1,1)
COVAL(OUTSIDE,P1,FIXFLU,0.001*RHO1*WJET)
COVAL(OUTSIDE,W1,ONLYMS,0.001*WJET)
COVAL(OUTSIDE,TEMP,ONLYMS,TJET)
    GROUP 14. Downstream pressure for PARAB=T
IPARAB=1
    GROUP 16. Termination of iterations
LITHYD=30
RELAX(V1,FALSDT,(1/NY)*ZWLAST/WJET)
RELAX(W1,FALSDT,ZWLAST/WJET)
    GROUP 19. Data communicated by SATELLITE to GROUND
  ** Select strain-rate for use in Mixing-Length model
DWDY=T
    GROUP 21. Print-out of variables
OUTPUT(P1,Y,Y,Y,Y,Y,Y);OUTPUT(V1,Y,Y,Y,Y,Y,Y)
OUTPUT(W1,Y,Y,Y,Y,Y,Y);OUTPUT(TEMP,Y,Y,Y,Y,Y,Y)
    GROUP 22. Monitor print-out
IZMON=10;IYMON=1;ITABL=1;NPLT=1;IPLTL=LITHYD;TSTSWP=-3
  ** parabolic file dumping
TSTSWP=-5;IDISPA=5;IDISPB=1;IDISPC=NZ
    GROUP 23. Field print-out and plot control
 
ORSIZ=0.4;PATCH(IZEQNZ,PROFIL,1,1,1,NY,NZ,NZ,1,1)
PLOT(IZEQNZ,W1,0.0,0.0);PLOT(IZEQNZ,TEMP,0.0,0.0)
PLOT(IZEQNZ,ENUT,0.0,0.0);NZPRIN=NZ
PATCH(IYEQ1,PROFIL,1,1,1,1,1,NZ,1,1)
PLOT(IYEQ1,W1,0.0,0.0);PLOT(IYEQ1,TEMP,0.0,0.0)
PLOT(IYEQ1,ENUT,0.0,0.0);NZPRIN=NZ