Activation of the Model

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4.1.5 Activation of the Model

TURMOD Command

The RSTM is activated by TURMOD(REYSTRS,DTFS,WALL1,WALL2,...). The 2nd argument defines the "false time step" relaxation to be applied to the SOLVEd variables. The remaining arguments are the wall PATCH names, up to a maximum of 18. The wall patches must already have been defined through laminar-wall PATCH settings for the velocity variables.

TURMOD(REYSTRS,DTFS,WALL1,WALL2,...) is equivalent to the PIL commands described below:

IRSMHM=0 Activates the default IP pressure-strain model. The IPY model is activated by setting IRSMHM=1, the QI model by IRSMHM=2, and the SSG model by IRSMHM=3. These settings must appear before TURMOD in the Q1 file.
IRSMSM=0 Activates the gradient-diffusion model for the Reynolds fluxes. The generalized gradient-diffusion model is activated by setting IRSMSM=1, and the Reynolds-flux transport model by IRSMSM=2. These settings must appear before the TURMOD command in the Q1 file.
SOLVE(EP,U2RS,V2RS,W2RS) Solve EP & the turbulent normal stresses.
STORE(KE,ENUT,LEN1)
SOLVE(UVRS) if U1 & V1 are stored |
SOLVE(UWRS) if U1 & W1 are stored | Solve turbulent shearing
SOLVE(VWRS) if V1 & W1 are stored | stresses.

If H1 or TEM1 are stored, and IRSMSM=0 or 1, TURMOD sets: STORE(UTRS) if U1 is stored STORE(VTRS) if NY > 1 STORE(WTRS) if NZ > 1 and .NOT. PARAB If IRSMSM=2 the procedure is the same excepting that SOLVE replaces STORE because transport equations will now be solved for each of the individual Reynolds flux components.

Likewise, if the scalars SC1, SC2, SCn, etc are STOREd, and IRSMSM=0 or 1: STORE(USC1,USC2,USCn);STORE(VSC1,VSC2,VSCn);STORE(WSC1,WSC2,WSCn) If IRSMSM=2 SOLVE replaces STORE because transport equations will now be solved for the Reynolds flux components. The maximum number of scalars that may be used in the RSTM is 9.

The first argument of the TURMOD may also be used to select a particular pressure-strain model, as follows:

TURMOD(RSMIPM, ...) selects the IPM model by setting IRSMHM=0.

TURMOD(RSMIPY, ...) selects the IPY model by setting IRSMHM=1.

TURMOD(RSMQIM, ...) selects the QIM model by setting IRSMHM=2.

TURMOD(RSMSSG, ...) selects the SSG model by setting IRSMHM=3.

For each wall boundary PATCH, the TURMOD command will: (a) set the COefficient to GRND2 for each COVAL of U1, V1 and W1;

(b) set the VALue to the appropriate wall velocity for each COVAL of U1, V1 and W1;

(d) create an additional PATCH and associated COVALs for the wall- reflection sources in the Reynolds stress and flux equations, as follows:
PATCH(WDMPi#, PHASEM, )
COVAL(WDMPi#, , FIXFLU, GRND1).
where i signifies N,S,E,W,H,L as appropriate and # is a 2-digit number assigned by TURMOD. COVALs are created for all SOLVEd stresses and fluxes, and the RSTM coding in subroutine UWDMP arranges that the sources are zero for those stress and flux components requiring no wall-reflection sources.

The wall-damping sources are created only for the pressure- strain models IRSMHM=0, 1 and 2. Wall damping is not required for IRSMHM=3, i.e. the SSG pressure-strain model.

If the user wishes to deactivate the wall-reflection terms, the user can: (a) not enter WAL1, WAL2 etc in the TURMOD command and define the wall-function PATCHes separately; or (b) use the SKIP facility after the TURMOD command so as to deactivate the wall- reflection PATCHes.

The default wall-boundary condition for mean-flow energy and scalar variables is zero flux. If the user wishes to prescribe a fixed wall enthalpy, temperature or scalar value, then this must be done explicitly, e.g. COVAL(WAL1,H1,GRND2,HWALL) would set a wall enthalpy of HWALL for the PATCH named WAL1. The turbulent and laminar Prandtl numbers, PRNDTL(H1) and PRT(H1) respectively, are used in the wall-function formulae with default values of unity.

As was discussed in Section 4 above, the default treatment for the turbulent stresses and fluxes is zero flux. Consequently, no COVAL statements are required for these dependent variables. However, if the user wishes to fix the near-wall turbulent stresses via equations (4.1), then the COVAL statements should be of the form:

COVAL(WAL1,U2RS,GRND2,GRND2); COVAL(WAL1,V2RS,GRND2,GRND2) COVAL(WAL1,W2RS,GRND2,GRND2); COVAL(WAL1,UVRS,GRND2,GRND2) COVAL(WAL1,UWRS,GRND2,GRND2); COVAL(WAL1,VWRS,GRND2,GRND2)

This practice may offer increased numerical stability, but is not recommended for general use for the reasons given earlier in Section 4.

Finally, TURMOD also makes the following settings:

RSTM=T ( LSGD(95)=T ).
UDIFF=T For modification of diffusion coefficients.
UCONNE=T For modification of convection neighbours.
USOURC=T For modification of source terms.
ENUT=GRND For calculation of ENUT in the RSTM coding.
EL1=GRND For calculation of the turbulence lengthscale LEN1 in the RSTM coding.

Assignment of Symmetry Planes

At symmetry planes, the appropriate turbulent shearing stresses and fluxes should be set to zero via the following PATCH and COVAL statements: PATCH(SMPLi, PHASEM, ) COVAL(SMPLi,,GRND1,0.0) where i signifies N,S,E,W,H,L as appropriate. These statements ensure that an i-direction diffusive link couples the in-cell value of the stress/flux component to the zero value assigned at the symmetry plane.

For example, for a 2-D hydrodynamic simulation in the Y-Z plane, the following PATCH and COVAL set VWRS to zero at the south boundary: PATCH(SMPLS,SOUTH,1,1,1,1,1,NZ,1,1) COVAL(SMPLS,VWRS,GRND1,0.0)

Storage and printout of auxiliary variables

The RSTM makes provision for users to store and print out the field values of various model parameters. The PIL command STORE can be used to create storage for the following variables:



      DUDX = dU/dx   ;   DUDY = dU/dy    ;   DUDZ = dU/dz
      DVDX = dV/dx   ;   DVDY = dV/dy    ;   DVDZ = dV/dz
      DWDX = dW/dx   ;   DWDY = dW/dy    ;   DWDZ = dW/dz
      PK   = 0.5*Pkk ;   EPDK = EP/KE    ;   PU2  = Puu
      PV2  = Pvv     ;   PW2  = Pww      ;   PUV  = Puv
      PUW  = Puw     ;   PVW  = Pvw      ;   DU2  = Duu
      DV2  = Dvv     ;   DW2  = Dww      ;   DUV  = Duv
      DUW  = Duw     ;   DVW  = Dvw      ;   FWAL = f
      U2DK = u2/KE   ;   V2DK = v2/KE    ;   W2DK = w2/KE
      UVDK = uv/KE   ;   UWDK = uw/KE    ;   VWDK = vw/KE
      DSDX = dC/dx   ;   DSDY = dC/dy    ;   DSDZ = dC/dz
      PUS1 = Puc,1   ;   PVS1 = Pvc,1    ;   PWS1 = Pwc,1
      PUS2 = Puc,2   ;   PVS2 = Pvc,2    ;   PWS2 = Pwc,2

Of course, once STOREd, the foregoing parameters can also be viewed via PHOTON or AUTOPLOT. The scalar derivatives and production terms correspond to the last-solved scalar or energy variable.

Empirical coefficients

The values of the various empirical coefficients are set in subroutine UST191 in the file GXRSTM.FOR. Users wishing to employ different values must make the necessary changes in this subroutine.

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