body fitted coordinates
DESCRIPTION
BODY FITTED COORDINATES. BFC grid type ‘O’ for na airfoil. BFC grid for a rectangular to circular nozzle. DOCUMENTATION. BFC phoenics online documentations: Introduction , Boundary Conditions and GCV (general colocated velocity method) Tutorials (look for BFC tutorials) - PowerPoint PPT PresentationTRANSCRIPT
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BODY FITTED COORDINATES
BFC grid for a rectangular to circular
nozzle
BFC grid type ‘O’ for na airfoil
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DOCUMENTATION
• BFC phoenics online documentations: – Introduction, – Boundary Conditions and – GCV (general colocated velocity method)
• Tutorials (look for BFC tutorials)• Browse at the phoenics input library cases for:
BFC and Multblock
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When To Use BFCs• BFCs are particularly suitable for internal or external flows with
smoothly-varying non-regular boundaries.
• For such flows, BFCs provide: – Good geometric representation, – Possibility of economical grid refinement close to the surface, – Good representation of surface boundary layers, and hence of wall
friction and heat transfer. – BFCs can also be used to reduce numerical "false-diffusion" errors, by
aligning the grid with the local flow direction where possible, e.g., for angled jets (inclined fan heater in a room)
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BFC grids• The task of the BFC grids is to map a physical domain
into a cartesian computational domain. • The actual areas and volumes are transmited into the
computational domain by means of area and volume multipliers deduced from the physical domain.
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Coordinate Systems
• Columns of cells must continue from one end of the grid to the other, i.e., the mesh is structured.
• The cells are counted using the same conventions as in Cartesian and polar geometries:
• 1 to NX in the IX-direction• 1 to NY in the IY-direction• 1 to NZ in the IZ-direction• The grid corner points must be
prescribed by the user, via a Cartesian frame of axes, (XC, YC, ZC).
• The alignment of the Cartesian axes - and the origin - can be chosen arbitrarily.
• NOTE: The Cartesian coordinates (XC,YC,ZC) must NOT be confused with the cell-indices (IX,IY,IZ).
• Note how the Cartesian and grid axes only coincide for the first few cells.
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Structure of the Grid File• XC, YC and ZC are the Cartesian co-
ordinates of the nodes.• Note that: I goes from West to East,
J goes from South to North, and K goes from Low to High.
• I, J & K count nodes (cell corners), • IX, IY & IZ count cells. • NX, NY and NZ are the numbers of
cells in the I (IX), J (IY) & K (IZ) directions.
• The total no of nodes along x is NX+1, the same applies to the other directions. I=1 I=6
IX=5IX=1
EAST
WEST
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Velocity Components• Q is the total velocity vector.
• U1, V1 (and W1) are the SOLVEd velocity resolutes.
• UCRT, VCRT (and WCRT) are the deduced vector components in the Cartesian coordinate system.
• UC1, VC1 (and WC1) are the deduced vector components in the grid line directions (the co-located velocities)
IY
IX
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The Steps In BFC Grid Generation
1. Specify POINTS - provide the Cartesian coordinates of key features of the geometry to be meshed
2. Specify LINES - join the points by lines, which are divided into segments corresponding to the number of cells which lie along the line. Lines may be straight, arc segments, or spline curves through defined points.
3. Create FRAMES - link the lines to make 2-D FRAMES. Frames always have four corners.
4. MATCH Grid to Frames - match the grid plane to appropriate frames.
5. Form the 3-D Grid - link 2-D grid planes to form a 3-D grid.
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POINTSLINES
EACH LINE IS DIVIDED IN POINTS WHICH WILL FORM THE VOLUMES
FORMING THE FRAMESEACH FRAME HAS ALWAYS 4 CORNERSEXTRUDING TO FORM VOLUMES
SEE ADDITIONAL INFORMATION AT: Introduction,
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WORKSHOP#1: SETTING A BFC GRID
a. Set to view plane (XY); b. click on mesh togle;c. Select BFC grid
Y
X
5 10
5
5
DIMENSION: NX = 15 & NY = 10
• The points cartesian coordinates are defined on
the problem data sheet
* Edit your q1 file to Set points XPO= 0.0;YPO= 0.0;ZPO= 0.0; GSET(P,A) XPO= 4.0;YPO= 0.0;ZPO= 0.0; GSET(P,B)
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WO
RKSH
OP#
1 –
STEP
2 Se
tting
: poi
nts,
line
s, a
nd n
umbe
r of n
odes
RESCUE Q1
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WO
RKSH
OP#
1 –
STEP
2 ½
Se
tting
: dim
ensio
n, li
nes a
nd c
ells
RESCUE Q1
• Dimension declares the total number of volumes along each direction. Set NX = 15 and NY = 10
* Edit your q1 file to Set lines/arcs GSET(L,L1,A,B,5,1.0) GSET(L,L2,B,C,10,1.0) GSET(L,L3,C,D,5,1.0) GSET(L,L9,B,H,5,1.0,ARC,1)
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WORKSHOP#1 – Step 3FRAMES always have 4 corners only
Frame#1: cornersGSET(F,F1,A,-,B,-,H,-,G,-)
Frame#2: cornersGSET(F,F2,B,-,C,-,D,-,H,-)
Frame#4: cornersGSET(F,F4,G,H,D,-,E,-,F,-)
Number of Cells on each side of the Frame
has to match!
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WORKSHOP#1 – Step 3Setting a Frame
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WORKSHOP#1 – Step 4 Match a grida. Pick the first corner of a Frameb. Match the corner with the NODES coordinatesc. Specify the first corner direction to the next points. All frames
have right-handed axes. Ex: B->C +I & C->D +J
(I,J,K)(6,1,1)
(I,J,K)(1,1,1)
(I,J,K)(1,6,1)
RESCUE Q1
* Match a grid mesh GSET(M,F1,+I+J,1,1,1,LAP5) GSET(M,F2,+I+J,6,1,1,LAP5) GSET(M,F4,+I+J,1,6,1,TRANS)
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WORKSHOP#1 – Step 4 Match a grid
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WORKSHOP#1 – Step 5 Volumea. Grid along (XY) planeb. To create volumes is necessary to extrude the grid along the K
direction
* Copy/Transfer/Block grid planes GSET(C,K2,F,K1,1,15,1,10,+,0,0,1,INC,1)GSET(C,pln2,F,pln1,i1,i2,i3,i4,+,dx,dy,dz,INC,pwr) shift grid plane by a distance and include the internal planes
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Inlet Boundary Conditions• It is a special b.c. because
the mass fluxes are related to the U1, V1, W1 resolute and not to the UCRT, VCRT and WCRT.
• In general the required angles will vary from cell to cell. • Subroutine GXBFC has been provided to calculate the inlet
conditions automatically, for the case of uniform inflow.• UCRT, VCRT, WCRT and density is non-standard, and simply
provides a mechanism for transmission of UIN, VIN, WIN and RHOIN to GXBFC
SEE ADDITIONAL INFORMATION AT: Boundary Conditions
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Use Of Cyclic Boundaries
• The default setting in PHOENICS is no cyclic conditions, and a symmetry condition is assumed.
• Cyclic (or periodicity) boundary conditions applies only along the east and west boundaries of XZ plane.
• The provision for BFCs is intended for turbomachine (and airfoil) applications in which cyclic conditions are needed at the entrance to and exit from the blade passage.
• To activate x-cyclic boundaries: Group 6, Q1 file:• XCYIZ(1,NZ,T) (switches XCYCLE on for all IZ slabs) • XCYIZ(1,9,T) (switches XCYCLE on for IZ=1 to 9)
case B523 exemplifies the use of x-cyclic boundary conditions for the flow through a cascade
of wedges
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WORKSHOP#1: SET UP A CASE USING BFC
• Models: – elliptic GCV and,– solution for Vel & P– KECHEM
• Numerics: 200 iter.• Props: Fluid: air(0)• Create objects: – inlet size: (10,1,1) & -2 m/s, – outlet size (5,1,1) – blocakge.
• Note: case B116 has 15x15 volumes.
inlet
outlet
plat
e
plat
e
plate
RESCUE Q1
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Real world is not so simple
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Automatic Block Links• The GCV solver uses
overlapping cells at block joints. These cells must exist in the individual block grid files.
• Link automatic is when the blocks share the same IJK orientation and same number of cells
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A Natural Link• A natural link is when the blocks share the same IJK orientation but
not the same number of cells
• B1 share the north face of L3 with the south face of B2
B2
B1
S
N
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Basic steps for Multi-Block Setupa. Plan the decomposition of domain
into individual blocks. A possible configuration is shown. Block 1 is to be 5 x 15 x 1, and Block 2 is to be 15 x 5 x 1.
b. Generate the grid for each individual block. The grid for each block will be generated in a separate mesh-generator session.
c. Combine the grids to form the multi-block grid and define inter-block links. This step involves hand-editing the input Q1 file.
d. Define remainder of the problem (variables, boundary conditions, etc).
B2
B1
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Block linksa. The GCV solver uses overlapping cells
at block joints. These cells must exist in the individual block grid files.
b. Only the linked faces of a block require an extra layer of dummy cells.
c. Block B1 has an extra plane of nodes at J =17 with thickness DY=0.
d. Similarly B2 has an extra plane of nodes at J = 1 with thickness DY =0
e. These extra nodes are most conveniently copied exactly from the 'real' edge nodes, so that they are invisible to any viewing program.
f. See further examples at GCV
(15,6)
(16,5)
J=1
J=16J=17 DY=0
J=1J=2
J=6B2
B1
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Linking the blocks in Q1 • TALK=T;• RUN( 1, 1) • BFC=T• NUMBLK=2• READCO(GRI+)• MPATCH(1,MBL1-2,
NORTH,1,NX,NY-1,NY-1,1,NZ,1,1)• MPATCH(2,MBL2-1,
SOUTH,6,10,2,2,1,NZ,1,1) • STOP• See additional information on
linking blocks at GCV
(15,6)
(16,5)
J=1
J=16J=17 DY=0
J=1J=2
J=6B2
B1
Y
X
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WORKSHOP#2 – Flow in a bifurcation; a natural link
• Each block’s grid is developed and then linked together.
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WORKSHOP#2 - Flow in a bifurcation;
• We will follow the workshop on how to assemble natural links in a pipe bifurcation: wksh multiblock 1.
• To short the drilling time, please download the q1 file which contains the Points and Lines.
• After UPLOADING the file start from section: ‘Set grid for first block’ on wksh multiblock 1.
Block 2Bl
ock
1
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WORKSHOP#2 – Blocks’ construction;
• Hint: before building MGRID2 (left) erase: the volume, the frame and the cells of MGRID1 (right) leaving only the lines.
• Rescue q1 files at the links: MGRID1 and MGRID2.
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WORKSHOP#2 – Assembling the case
• Rescue q1 files at the links: MGRID3, GRI1, GRI2. Save these files at your working directory.
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Unnatural Block Links• Link is unnatural when the blocks do not share the same IJK
orientation
Y
X
B1B2
B3
SN
E W
WN
Blocks 1&2 and 1&3 are linked 'naturally' - West to East and South to north, whilst the link between 2&3 is 'unnatural' - a North face is linked to a West face. The instructions are in the tutorial: workshop multblock-2; also visit the links: READCO , MPATCH and link the three blocks.
E
N
E
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Basic steps for Multi-Block Setup a. Plan the decomposition of domain
into individual blocks. A possible configuration is shown above. Each block is to be 5 x 5 x 1.
b. Generate the grid for each individual block. The grid for each block will be generated in a separate mesh-generator session.
c. Combine the grids to form the multi-block grid and define inter-block links. This step involves hand-editing the input Q1 file.
d. Define remainder of the problem (variables, boundary conditions, etc).
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WORKSHOP#3 - Flow in a disk sector;
• We will follow the workshop on how to assemble un-natural links in a disk sector: workshop multblock-2
• To short the drilling time, please download the q1 file which contains the Points and Lines.
• After UPLOADING the file start from section: ‘Set grid for first block’ on workshop multblock-2
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WORKSHOP#3 – Blocks’ extrusion parameters
UGRID1.q1 UGRID2.q1 UGRID3.q1
B1
B3
B2WE
N
S WN
B1 B2 B3
BLOCK # B1 B2 B3 Length plane plane plane from/to from/to from/to Direction K 1 to 2 1 to 2 1 to 2 dZ = 1Direction J 6 to 7 6 to 7 2 to 1 dY = 0Direction I 2 to 1 6 to 7 2 to 1 dX = 0
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TALK=T;RUN(1,1) BFC=T GCV=T NUMBLK=3 READCO(UGRI+)MPATCH(1,MBL1.2,WEST,2,2,1,NY-1,1,NZ,1,1) MPATCH(2,MBL2.1,EAST,NX-1,NX-1,1,NY-1,1,NZ,1,1) MPATCH(1,MBL1.3,NORTH,2,NX,NY-1,NY-1,1,NZ,1,1) MPATCH(3,MBL3.1,SOUTH,2,NX,2,2,1,NZ,1,1) MPATCH(2,MBL2.3,NORTH,1,NX-1,NY-1,NY-1,1,NZ,1,1) MPATCH(3,MBL3.2,WEST,2,2,2,NY,1,NZ,1,1) SPEDAT(SET,GCV,MBL3.2,C,WNL) STOP
B1
B3
B2WE
N
S W
N
• If the blocks are rotated relative to each other in IJK space (B3 to B2), the block alignment must be specified through SPEDAT command.
• This string defines how the N, E and H faces of the first block link to the second block. The default, natural, link would be S W L; i.e. North to South, East to West and High to Low, see B1 to B3 and B2 to B1.
WORKSHOP#3 - Matching Blocksq1 code lines
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The string defining the block rotation consists of three letters, which may be any of E W N S H L. The individual characters define the relative orientation between the N, E and H faces of the first block (B2) of the pair of blocks, and the current block (B3) respectively.
B1
B3
B2WE
N
S W
N
y
x
x
yB2 EW
N
S
B3N S
W
E B3 is rotated 90º
from B2
Blocks’Linkages
WORKSHOP#3 - SPEDAT COMMAND & BLOCK ROTATION
SPEDAT(SET,GCV,MBL3.2,C,WNL)BLOCK#2 -> N E H BLOCK#3 -> W N L
B3N S
W
E
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WORKSHOP#3 – Case setting;
• Properties: air (0)• Model: laminar, activate
velocities, CGV• Numerics: 100 iteractions• Objectcs: Inlet (V = 1,0 m/s) &
Outlet
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WORKSHOP#3 – Results
• Rescue q1 files at the links: UGRID123, UGRI1, UGRI2, UGRI3. Save these files at your working directory.
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Multblock Application in Complex Geometry
• The selected figures come from the cases available in the phoenics input library ( Multiblock)
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Phoenics BFC Generator
• The Phoenics built-in BFC Generator is helpful for simple problems.
• If an application demands several ‘natural or unnatural’ links the mesh generation process becomes very complex.
• In this scneario phoenics BFC generator is not recommended. There are specific software for mesh generation recommended such as: ICEM,
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• This is a ‘O’ type grid where the airfoil upper section is mapped into the computational domain for reference.
Physical Domain Computational Domain
Airfoil Grids: ‘O’ grid
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Airfoil Grids: ‘C’ gridshttp://courses.cit.cornell.edu/fluent/airfoil/step1.htm
• The domain size is expressed in terms
of the airfoil thickness.
• Airfoil with finite thickness (present
illustration) require Natural and/or
Unnatural links, unfortunately. It is not
an easy task to do using Phoenics BFC
grid generator!
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C Grids for Finite Thicknes Airfoil ( represent the frames’ corners)
• Blocks B1, B2, B3 have natural links• B4 is 180o rotated in regard to B1.• Multi Block grid.• Provide extra Y cells to B1 and B4 • SPEDAT(SET,GCV,MBL4.1,C,NEL)
(A) (B) (C)
(D)
(E)(F)(G)
(H)(L)B1 B2
B3B4
xy
xy
xy
x
y
zero thickness trailing edge
B1 B2
B3
(A) (B) (C)
(D)
(E)(F)(G)
(L)B4
finite thickness trailing edge
• Blocks B1, B2, B4 have natural links• B3 is 180o rotated in regard to B4.• Multi Block grid.• Provide extra Y cells to B4 and B3• SPEDAT(SET,GCV,MBL4.3,C,NEL)
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Finite x Small Thickness Airfoil• The small thickness airfoil is gives an approximated solution.
• The thin airfoil consists
of a line and it is easily
setup on the BFC mesh
generator in phoenics.
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Natural links for airfoil: frames
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Natural links for airfoil: grid
This grid would be a 2nd choice for the C grid. It still can be improved by changing the inclination of lines L23 & L24 an designing a better number of cells to result in a more orthogonal mesh. One can also design a similar grid for a zero thickness airfoil
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Axis symmetric flow in a sector• Choose the XY plane to work• Set NX = 20, NY = 10 and NZ = 1• Once a XY frame is done a copy of it will be made rotating x axis by 1 rad (57º)
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Set Points – GSET, GSET(P,…)P X Y ZA 0 0 0B 10 0 0C 10 1 0D 9 10 0E 6 4 0G 0 1 0
B
A
C
E
D
G
* Edit your q1 file to Set points XPO= 0.000000E+00;YPO= 0.000000E+00;ZPO= 0.000000E+00;GSET(P,A ) XPO= 1.000000E+01;YPO= 0.000000E+00;ZPO= 0.000000E+00;GSET(P,B ) XPO= 1.000000E+01;YPO= 1.000000E+01;ZPO= 0.000000E+00;GSET(P,C ) XPO= 9.000000E+00;YPO= 1.000000E+01;ZPO= 0.000000E+00;GSET(P,D ) XPO= 6.000000E+00;YPO= 4.000000E+00;ZPO= 0.000000E+00;GSET(P,E ) XPO= 0.000000E+00;YPO= 1.000000E+00;ZPO= 0.000000E+00;GSET(P,G )
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Set Lines/arcs – GSET(L,…)
* Edit your q1 file to Set lines/arcs GSET(L,L1,A,B,10,1.0) GSET(L,L2,B,C,10,1.0) GSET(L,L3,C,D,10,1.0) GSET(L,L4,D,G,20,1.0,ARC,E) GSET(L,L5,G,A,10,1.0)
Number of volumes Grid Power
L2
L1
L3
L4
L5
B
A
C
E
G
D
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Set Frames – GSET(F,…)
* Edit your q1 file to Set frames GSET(F,F1,A,B,C,-,D,-,G,-)
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Match a frame – GSET(M,…)
* Edit your q1 file to Set frames GSET(F,F1,A,B,C,-,D,-,G,-)
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Copy/Transfer/Block grid planes– GSET(C,…)
* Copy/Transfer/Block grid planes GSET(C,K2,F,K1,1,20,1,10,RX,1,0,0,INC,1)
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Inlet
Outlet
plate
plate
• Inlet: set an inflow of 1m3/s• Properties: Air (0)• Model: GCV + LVEL (turbulence)• Numerics: 500
Edit Objects
Rescue q1