1. Automated CFD Preprocessing
G/Turbo
Automated CFD Preprocessing
for
Turbomachinery

2. Agenda Overview of G/Turbo Basic Operations Tip gaps & Spinners
CCAD-GAMBIT Filter
Demos

3. Overview of G/Turbo

4. What is G/Turbo?
Automated tools built upon GAMBIT for blade-row preprocessing
Blade and flowpath generation
Topology decomposition
Edge, face, boundary layer, and volume meshing
Application-specific views
Cascade (viewing in the spanwise direction)
Add-on to GAMBIT/Fluent 6 bundle

5. Applications Automotive Pumps & Fans Turbochargers Torque Converters
Gas Turbines
Steam Turbines
Industrial Pumps & Compressors
Industrial & Domestic Fans/Blowers (HVAC)
Sewage Pumps
Hydraulic Turbines
Pharmaceutical pumps
Electronics Cooling Fans
Marine Propulsion
Aircraft Propulsion
Vacuum Cleaner Impellers
G/Turbo is intended to be flexible enough to deal with a wide variety of geometries

6. User Interface
Tools
Turbo
User can switch to full GAMBIT interface with click of a button
Geometry and Meshing tools co-located for ease of use

7. Terminology
tip clearance
casing
inlet
outlet
blade
hub

8. Geometry Input Many options for definition of blades, hub, casing
Point data input file (formatted or raw)
All curve import formats supported by GAMBIT e.g. Parasolid, ACIS, IGES, STEP etc.
Creation within GAMBIT

9. Automatic Periodics
Blade mean lines automatically computed, copied, and revolved to form periodics
User can interactively adjust (drag) where periodics meet inlet and outlet, adjusting all spanwise curves as a linked group, or individually

10. Automatic Volume Generation
Optional tip gap by fixed distance or user specified edge for non-uniform definition

11. Rapid Linking & Boundary Zoning
Links both meshing and geometry for decomposition
Applies boundary zones
Enables import of predefined turbo topologies from CAD

12. Automatic, Flexible Meshing
Structured
Predefined H-grid template
User-defined alternative strategies using standard GAMBIT tools
Unstructured
Hexahedral
Tetrahedral
With or without hex/wedge boundary layers

13. Mesh Topology Examples
H-pave
H-grid
Tri-pave
Quad-pave

14. G/Turbo: Unique Advantages
Unstructured hex, wedge, and tet meshes
Full GAMBIT geometry and meshing tools available for special needs
Add geometry details to automatically-generated model
Fine-tune mesh
Import Parasolid, ACIS, STEP, IGES, and other formats
Complete journaling for parametric studies

15. Basic Operations

16. Import / Create Design Curves
The starting point for G/Turbo is a set of basic design curves for the machine, comprising:
Blade profile sections
Hub definition
Casing definition
Any number of blade profiles may be used, but each blade profile must consist of 2, 4 or 6 curves as indicated below:
1 pressure side curve & 1 suction side curve
2 pressure side curves & 2 suction side curves.
3 pressure side curves & 3 suction side curves.
Profile definitions must be consistent.
Hub and Casing definitions can be made up of any number of connected edges.

17. Example - Six Edge Blade Profile
3 suction side edges
3 pressure side edges

18. Importing Design Curves
Point data import
Native “.tur” format (curves created automatically)
ProE “.ibl” format (curves created automatically)
ICEM-input format (curves created automatically)
Plain vertex data
Edge import
Parasolid
ACIS
STEP
IGES
STL
Mesh
Note that these edges must be “real” so STL and Mesh must be converted after import.
Creation of geometry within GAMBIT

19. Native “.tur” format Easy to read, ASCII text format which includes:
Axis of rotation
Cylindrical or cartesian coordinates
Point data for hub, casing and tip clearance edge
Number of blades
Number of profiles
Number of edges per profile
Continuity information
Blade profile data
Comments as required

20. Turbo Blade Row Topology Creation
Two components required to define blade row
Flowpath annulus via hub and shroud curves
Airfoil sections from hub to shroud
G/Turbo assumes a single blade passage topology (i.e. flow is circumferentially periodic and thus periodic boundaries can be employed)
Periodic boundary shape is derived from
Blade meanline (determined automatically by the blade geometry)
User-adjustable upstream and downstream curves
Combination of blade meanline and upstream/downstream curves called “medial edges”

21. Turbo Profile User Inputs
Hub inlet vertex
Casing inlet vertex
Axis of rotation
Leading edge vertices of the blade profiles
Optionally a splitter blade may also be included (also specified by it’s leading edge vertices).
Note that the order of picking of the blade profiles IS important.
Blade leading edges must be specified in order from hub to casing.

22. Turbo Profile Result Revolved rails – two per blade profile
Set of “medial” edges – one per blade profile, based on the meanline of each profile.
Used to create the periodic cutting plane
Note – For cases involving splitters, the periodic is based on the main blade alone

23. Adjust Inlet & Exit Points
Inlet and Exit positions for the periodics not prescribed by the blade profiles
User can adjust the medial edge inlet/exit positions as desired.
Positions may be moved together as a set, or individually (with links toggle)
Note - If the angle between the medial edges and the rails is too acute ( <30 degrees) this may create difficulties for subsequent volume creation and/or mesh skewness.

24. Turbo Volume Creation – User Inputs
The final step of the geometry creation requires specification of:
Number of blades in the row (or explicit sector angle definition)
Tip Gap definition - may be either:
Uniform distance from the casing, or
User specified as a “tip cutting edge”
Defined using inlet vertex as for hub & casing in profile definition.
Number of Spanwise Sections
Topology can be split into a number of hub-to-casing sections on creation, which can help subsequent meshing for twisted blades.

25. Volume Creation - Mechanics
Periodic faces extended* and revolved by required angle to form sector volume.
Hub and Casing curves revolved into faces and sealed to form annular volume.
Sector and annulus volumes intersected and resulting volume rotated by appropriate angle.
Blade surfaces formed from profile definitions, extended* and used to split volume giving flow passage and blade volumes.
Tip gaps and spanwise sections split volumes and clean-up of geometry performed as required.
*Extension factor controlled by TURBO.GENERAL.BLADE_EXTENSION_FACTOR default

26. Turbo Volume Creation – Outcome I
Single blade with no tip clearance
Single turbo volume – topological annulus

27. Turbo Volume Creation – Outcome II
Single blade with uniform tip clearance
Turbo volume (a) consists of 3 sub-volumes (b), (c) & (d)
Note: Option in the Turbo defaults to retain the “solid” blade –useful when considering conjugate heat transfer e.g. cooled turbine blades.

28. Turbo Volume Creation – Outcome III
Single blade with user defined tip clearance
Similar 3 sub-volumes, plug, outer-plug & outer-blade
Only the cut is different.

29. Turbo Volume Creation – Outcome IV
Blade and splitter
Including tip gap will give 4 sub-volumes (2 plugs instead of 1)

30. Turbo Volume Creation – Outcome V
With Spanwise Sections
Sections evenly spaced from hub to casing

31. Define Turbo Zones
User selects the faces that make up the different parts of the topology.
Links periodic faces for both geometry decomposition and meshing
Sets solver and assigns appropriate boundary zones
“Pre-decompose” options
Link spanwise faces (e.g. hub & casing)
Split edges for manual positioning
Allows turbo topologies defined externally using CAD packages to take advantage of automated decomposition and meshing tools.

32. Automatic Decomposition
Decomposes turbo volume based on standard templates for H grids

33. Decomposition Mechanics
The automatic decomposition works by:
Merging,
Pressure side Faces
Suction side Faces
Hub faces
Casing faces.
This results in a standard topology to which we can apply the above templates.
Split Positions for the decomposition are based are based on the %length of each edge and the TURBO.P2P_DECOMPOSE defaults.

34. Single Blade Split Position Defaults1 2 3 4

35. Double Blade Split Position Defaults1 3 5 2 4 6 8 7

36. Single Blade Mesh Interval Defaults8 7 9 5 1 2 4 6 3

37. Single Blade Mesh Grading Defaults3 2 1 1 2 3 1 3 1 3
Note – Mesh grading is by Successive Ratio

38. Double Blade Mesh Interval Defaults13 16 2 1 6 7 17 5 14 3 8 4 11 9 12 15 10

39. Double Blade Mesh Grading Defaults4 2 1 1 3 3 4 4 1 4 3 1 1 4 1 4 3 1 1 4

40. Shaped Edge Decomposition
Splits may be created using “shaped” edges such that the edge remains normal to the blade/periodic surface.
The split behavior is controlled using the TURBO.GENERAL.DECOMPOSE_WITH_SHAPED_EDGE default

41. Flat Leading/Trailing edges
If these faces are included in the pressure/suction side definition at the Turbo Zone step, they will become merged and the sharp edge definition will be lost.
Neglect them in the Turbo Zone definition and the decomposition tool recognizes this and uses the discontinuous point as a split point, ignoring the default for this position.

42. Manual Decomposition
Should the geometry not suit the “standard” decomposition H templates, the user may decompose manually
Linking Spanwise faces at the Turbo Zone stage enables fast manual decomposition.
Spanwise linked faces are split together and the associated volume is also split
Disadvantages of manual decomposition:
Edge meshing is not controlled by the defaults and consequently bunching must be applied manually.
Face Vertex Types may need to be set manually to achieve the desired outcome.

43. Face Vertex Types
The first four vertex types are all used in regular quad face meshing.
They can be described by the number of grid lines that are connected to the vertex.
The last two (Tri- and Notrielement) are
used in special cases.
Type: End Side Corner Reverse
Internal grid lines
Example C R E S

44. Manual Decomposition - Example
Mapped Mesh
Quad Tri-primitive Cooper Mesh

45. Meshing
The full set of Gambit2.0 meshing tools is available for use with G/Turbo including:
3D Boundary Layers
Structured / Unstructured Hex
Tetrahedral
Triangular Prisms
Hybrid combining any of the above

46. Boundary Layers Create Boundary Layer Form
Show Option: toggles display of temp. boundary layer
Useful for complicated models
Definition (3 of 4 inputs required)
First row: height of first row of elements (a)
Growth factor: factor for geometric series (b/a)
Rows: total number of element rows
Depth: total height of boundary layer (D)
Internal continuity and Wedge corner shape
Transition Pattern (2d only)
Reduces number of elements in ‘flow’ direction.
Not to be used with tets; watch for highly skewed cells.
Attachment
to edges (associated with face)
to faces (associated with volume)
Note – True 3D Boundary Layers must be applied to Faces NOT Edges

47. True 3D Boundary Layers High quality meshes adjacent to the surfaces
Works with Tetrahedral, mapped/sub-mapped & Coopered meshes !

48. Edge Meshing
Control mesh density and distribution in a face or volume by meshing the edges first.
Edge mesh distribution is controlled through the spacing and grading parameters.
Using the Edge meshing form
Picking
Temporary graphics
Links, Directions
Grading/Spacing
Special characteristics
Apply and Defaults
Invert and Reverse
Options
Apply without meshing

49. Picking Edges for Meshing
Temporarily meshed edges
When you pick an edge, the edge is temporarily meshed using white nodes
Displayed edge mesh is based on current grading and spacing parameters
If you modify the scheme or spacing, the temporary mesh will be immediately updated
When you Apply, the mesh nodes will turn blue
Sense
Sense is used to show direction of grading
Every picked edge will show its sense direction using an arrow
The sense can be reversed by a shift-middle click on the last edge picked (this is in addition to the “next” functionality) or by clicking on the Reverse button

50. Grading Controls mesh density distribution along an edge.
Grading can produce single-sided or double-sided mesh
Doubled-sided mesh can be symmetric or asymmetric.
Symmetric schemes produce symmetric mesh about edge center.
Asymmetric schemes can produce asymmetric mesh about edge center.
Single-sided grading:
Uses a multiplicative constant, R, to describe the ratio of the length of two adjacent mesh elements, i.e.,
R = l(i+1) / li
R can be specified explicitly (Successive Ratio) or determined indirectly
Gambit also uses edge length and spacing information to determine R.
Single-sided grading
Symmetric grading
Asymmetric grading

51. Face Meshing Upon picking a face
GAMBIT automatically chooses Quad elements
GAMBIT chooses the Type based on the Solver/face vertex types
Available element/scheme type combinations
Quad
Map
Submap
Tri-Primitive
Pave
Quad/Tri
Wedge
Tri

52. Face Meshing - Quad Examples
Quad: Map
Quad: Submap
Quad: Tri-Primitive
Quad: Pave

53. Face Meshing - Quad/Tri and Tri Examples
Quad/Tri: Map
Quad/Tri: Pave
Quad/Tri: Wedge
Tri: Pave

54. Linking Periodic & Spanwise Edges/Faces
Mesh Links
Mesh linked entities are instantaneously updated so that the mesh is identical
Mesh links exists in the Edge, Face, and Volume forms
Option specific to periodic boundary conditions
Simultaneous linking of both periodic and spanwise faces is possible
Reverse orientation is needed since Edge directions on corresponding vertices are opposite + + + +
Note: Mesh linking is performed automatically if topology is defined
using Define Turbo Zones

55. Volume Meshing Volume Meshing Form: Upon picking a Volume
GAMBIT will automatically choose a Type based on the solver selected and the combination of the face Types of the volume.
In ambiguous cases, GAMBIT chooses the Tet/Hybrid: TGrid combination
Available element/scheme type combinations
Hex
Map
Submap
Tet-Primitive
Cooper
Stairstep
Hex/Wedge
Tet/Hybrid
TGrid

56. Volume Meshes - Hex Examples
Hex: Map
Hex: Submap
Hex: Tet-Primitive
Hex: Cooper
Hex: Stairstep

57. Hex/Wedge and Tet/Hybrid Examples
Hex/Wedge: Cooper
Tet/Hybrid: TGrid

58. Examining the Mesh Examine Mesh Form Display Type Display Mode
Plane/Sphere
View mesh elements that fall in plane or sphere.
Range
View mesh elements within quality range.
Histogram shows quality distribution.
Select 2D/3D and Element Type
Select Quality Type
Display Mode
Change cell display attributes.

59. Cascade View 2D development view of a 3d spanwise surface.
3D surface is “unwrapped” onto a 2d plane without stretching
Limited to viewing only – entity picking not possible
Used in conjunction with 2d mesh quality to quickly spot problems
Multiple sections may be viewed simultaneously in adjacent windows

60. Cascade View - Example 3d view of radial machine
2d “cascade” view of boundary layer on hub face

61. Tip Gaps & Spinners

62. Tip Gaps
Easily created using the G/Turbo automated construction tools.
No automatic decomposition is provided
May be meshed unstructured
Beneficial to decompose when boundary layers are attached
Greater control over bunching
Only necessary to decompose source face and Cooper mesh volume
Short projection distance
Turn off autosmooth
set MESH.COOPER.SMOOTH_PROJECTED_FACE_MESH default to 0.

63. Tip Gaps – Example “butterfly” mesh
Leading Edge
Trailing Edge

64. Spinners
Often pumps have nosecones or “spinners” upstream of the blade passage instead of a hub which extends all the way to the desired inlet of the domain.
Spinner
G/Turbo requires a well defined hub curve at a positive radial distance in order to construct the Turbo Volume.

65. Spinners - approach
To construct a geometry which includes a spinner it’s necessary to first create an artificial hub curve effectively splitting off the front portion of the spinner.
New hub curve (+ve radius)
Original hub curve (on axis)
The remaining geometry can then be constructed manually after the Turbo Volume is complete the two connected together.

66. CCAD-GAMBIT Filter

67. Motivation
There is a need to provide a link between geometry generated with the Concepts/NREC AGILE suite and Fluent 6
Geometry created by CCAD module
CCAD generates geometry files called “machining files”
denoted by file extension “.mch”
Initial efforts have focused on developing a simple filter to convert the machining file into a format which can be processed by GAMBIT and G/Turbo
GAMBIT’s “Native turbo” format
denoted by file extension “.tur”
A filter has now been written in C to do the conversion (mch2tur.c)
Can be compiled on multiple platforms (e.g. PC/Windows, Linux, UNIX)

68. Machining File Format
CCAD 7.2 D:\public\hoover\_pump\pump.mch 03:11:03PM, Monday, March 04, 2002
# OF POINTS= 100 (shroud to hub) = 2
TOTAL # OF BLADES= 6 # OF MAIN BLADES= 6
UNITS=INCHES
Total meridional distance = e+000 (SHROUD) e+000 (HUB)
impeller (Main Blade) SHROUD
I R THETA Z TN BETA %M
e e e e e
e e e e e
e e e e e
e e e e e
e e e e e .
e e e e e
e e e e e
e e e e e
e e e e e
impeller (Main Blade) HUB
e e e e e
e e e e e
e e e e e
e e e e e
e e e e e
e e e e e
e e e e e
e e e e e
e e e e e
Polygon points for inlet extension
4 --- # of polygon points for shroud
e e+000
e e+000
e e+000
e e+000
4 --- # of polygon points for hub
e e+000
e e+000
e e+000
e e+000
Polygon points for exit extension
e e+000
e e+000
e e+000
e e+000
e e+001
e e+001
e e+001
e e+001

69. “Native” Turbo Format / TIP CLEARANCE EDGE / FILE TRANSLATED FROM CCAD
/ NUMBER OF BLADES 1
/ NUMBER OF PROFILES 2
/ NUMBER OF EDGES PER PROFILE 3
/ PROFILE EDGE CONTINUITY
/ SECTION #1
/ Pressure Side
e e e+000
e e e+000
100
e e e+000
e e e+000
e e e+000
e e e+000
e e e+000 .
/ FILE TRANSLATED FROM CCAD
/ FILE VERSION
2 0 4
/ ROTATIONAL AXIS
/ COORDINATE TYPE
/ HUB EDGE 1
361
e e e+000
e e e-002
e e e-001
e e e-001
e e e-001
e e e-001 .
/ CASING EDGE 1
328
e e e+000
e e e-002
e e e-002
e e e-001
e e e-001
e e e-001 .

70. Analysis Procedure CCAD mch2tur.c Fluent 6 GAMBIT, G/Turbo .mch file
.tur file
Fluent 6
GAMBIT,
G/Turbo
.msh file

71. Near-Term Plans
Provide stand-alone filter to Concepts/NREC - Fluent clients
Enhance and refine the existing filter
support for splitter blades
Incorporate the filter into GAMBIT
.mch file will be a supported turbo format along with existing .tur and .ibl formats

72. G/Turbo Demos