ENC_Q.HTM

Encyclopaedia Index

Q1PIN file

Q1QUIT

---------- PIL logical, default F -------

When set to T in a Q1 file, Q1QUIT will suppress the interactive session regardless of the setting of TALK.
If set to T interactively, it will act as if END had been entered. In either case, the Q1 file will also be unconditionally overwritten by the instruction stack or the COPYQ1 file, depending on the setting of DMPSTK.

Q2

When the PHOENICS Satellite module has finished processing all the information which it has read from the Q1 file and/or received interactively from the user, but before it writes the Q1EAR, EARDAT and FACETDAT files, it looks for a file called Q2 in the working directory.

If the file does not exist, it proceeds to write the files; however, if Q2 does exist, it processes any PIL, In-Form or > OBJ and, if they are legitimate, appropriately modifies what it subsequently writes to Q1ear etc.

For example, if the Q2 contains the single line:

restrt(all)

inspection of the subsequently-written Q1EAR will reveal that the FIINIT values of all variables have been set equal to READFI.

Similarly, if the Q2 contains object-introducing lines such as:


> OBJ,    NAME,        CYL
> OBJ,    POSITION,    xposcyl, yposcyl, zposcyl
> OBJ,    SIZE,        xsizcyl, ysizcyl, zsizcyl
> OBJ,    GEOMETRY,    cylinder
> OBJ,    ROTATION24,        1
> OBJ,    TYPE,        BLOCKAGE
> OBJ,    MATERIAL,    198,Solid with smooth-wall friction

the presence of the new object will be recognised by the following lines in Q1EAR:

 SPEDAT(SET,CYL,DATFILE,C,cylinder)
 SPEDAT(SET,OBJNAM,^OB3,C,CYL)
 SPEDAT(SET,OBJTYP,^OB3,C,BLOCKAGE)
 SPEDAT(SET,CYL,MATERIAL,R,198.)

the following in EARDAT:

 CYL       DATFILE        Ccylinder
 OBJNAM    ^OB3           CCYL
 OBJTYP    ^OB3           CBLOCKAGE
 CYL       MATERIAL       R198.

and the following in FACETDAT:

OBJECT=     3  NFACETS=   300  OBJNAM = CYL      IOBJTYP =      7  OBJCLASS = VOL-OBJECT

A distinction should be observed however between these two examples, namely:

the first, being concerned with PIL variables over-writes the previously-set (or default) FIINIT values; but
the second, being object-related, is allowed only for introducing new items. Indeed, if an object with the name CYL existed already in the Q1 file, the Satelite would issue a warning about the illegitimacy of using the same name twice; and the second object would not be accepted.

QCOM

-------------- Command ----------------

QCOM(....This command writes anything to the right of the left parenthesis to COPYQ1, which can later be dumped to the Q1 file.

For example, QCOM(BFC=T will write the line: BFC=T to COPYQ1, and QCOM(SOLUTN(P1,Y,Y,Y,Y,Y,Y) will write the line: SOLUTN(P1,Y,Y,Y,Y,Y,Y) to COPYQ1.

However, QCOM does not cause the SATELLITE to interpret what is written to COPYQ1, for example, QCOM(BFC=T will not set BFC to TRUE.

Q-Criterion

The Q-criterion [1,2] is popular in the CFD community as a useful criterion for detecting vortices. The Q value is defined as the relative difference between the magnitude of the rate of rotation and strain tensors (and is the second invariant of the rate of deformation tensor). Therefore,

Q = 1/2(Ω_ijΩ_ij - S_ijS_ij)

where Ω_ij and S_ij are the magnitudes of the mean rotation and rate of strain tensors, respectively:

Ω_ij = 1/2(∂u_i/∂x_j-∂u_j/∂x_i)

and

S_ij = 1/2(∂u_i/∂x_j+∂u_j/∂x_i)

The rotation tensor is related to the vorticity tensor ω_ij by

Ω_ij=1/2ω_ij

and the tensors Ω_ij and S_ij are the antisymmetric and symmetric parts of the deformation tensor

D_ij= ∂u_i/∂x_j = S_ij + Ω_ij.

Hunt et al [1] defined a vortex as a spatial region where Q > 0, which means where the vorticity tensor dominates the rate of strain tensor. Locations in the flow with positive Q values are defined as vortices using this criterion, as they contain local rotational motion.

In the post-processor the idea is to visualise vortices by generating isosurfaces of Q for several positive values. The recommendation is to use an isosurface at a positive value near zero. Some adjustment will then be required to find the right value to see the vortices.

The Q-criterion can be stored and written to the RESULT and solution files by putting STORE(QCR1) into the Q1 file. For two-phase applications, STORE(QCR2) elicits storage and printout of the Q-criterion for the 2nd phase.

At present it is necessary to also necessary store the mean rates of strain GEN1 and GEN2, and the vorticity magnitudes VOR1 and VOR2. The latter require storage of all ij-velocity derivatives excepting i=j, i.e:

STORE(QCR1);STORE(GEN1,VOR1,DUDY,DUDZ,DVDX,DVDZ,DWDX,DWDY)
STORE(QCR2);STORE(GEN2,VOR2,DU2Y,DU2Z,DV2X,DV2Z,DW2X,DW2Y)

For turbulent flow, usually storage of GEN1 & GEN2 is provided automatically by the turbulence model.

Hunt,J.C.R., Wray,A.A. and Moin,P., "Eddies, stream, and convergence zones in turbulent flows", Center for Turbulence Research Report CTR-S88, p.193, (1988).
Haller,G. "An objective definition of a vortex", J. Fluid Mech, vol.525, pp1–26, (2005)

Quadratic sources and sinks

See COVAL for information about how to create patches which provide sources which are proportional (VAlue - Phi) **2

QUIT

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[Quit] the current PHOTON session.

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