tg-intro_14.0_l03_geometry.pdf

© 2011 ANSYS, Inc. April 19, 20121 Release 14.0

14. 0 Release

Introduction to ANSYSTurboGrid

Chapter 3Geometry


Geometry

Geometry Definition in TurboGridImport

Geometry

Generate Topology

Analyze Mesh

Generate Mesh

Impr

ove

Mes

h


Geometry Input

• ANSYS TurboGrid takes advantage of the periodic nature of the flow in turbomachinery components, and creates a mesh for only one bladeset (blade passage).

• Theta extent of one blade passage is calculated as 360 degrees divided by the number of main blades.

• Side surfaces of the blade passage are declared periodic and interfaced with corresponding surfaces of neighbouring blade passages


Geometry ‐ Convetion

• In ANSYS ‐ TurboGrid, the hub is coloured in blue and the shroud is coloured in grey.

• The blade leading edge (LE) is coloured in green and the trailing edge (TE) is coloured in red.


Geometry Input

• ANSYS ‐ TurboGrid requires basic data that describe one blade passage:

• Meridional flow path:• Series of points along hub and shroud surfaces, from inlet to outlet

• Blade profiles:• Continuous loop of points defining blade profiles at as many spanwise locations as necessary to accurately represent the blade

• The same is needed for main as well as splitter blades.


Schematic of Input Curves

BladeProfiles

Hub curve

Shroud curve


Input Requirements

Point data input

- information file (blade.inf) (optional)

- hub curve (blade_hub.curve)

- shroud curve (blade_shroud.curve)

- blade profiles (blade_profile.curve)

Format

-ASCII input file

-(points given in (x,y,z) or (r,,a))


TurboGrid Input as an Export from BladeGen

‐ TurboGrid input curves can be generated as an export from BladeGen

‐ TurboGrid File Export Dialog shows the export of four files: hub.curve, shroud.curve, profile.curve, as well BladeGen information file (“.inf” file)

‐ The information file “.inf” file contains geometry units, leading and trailing edge types and *.curve filenames


BladeGen Information File (.inf)

!====== CFX‐BladeGen Export ========

Axis of Rotation: Z

Number of Blade Sets: 11

Number of Blades Per Set: 1

Blade Loft Direction: Streamwise

Geometry Units: IN

Coordinate System Orientation: Righthanded

Blade 0 LE: EllipseEnd

Blade 0 TE: CutOffEnd

Hub Data File: Blade1_hub.curve

Shroud Data File: Blade1_shroud.curve

Profile Data File: Blade1_profile.curve


Point Data Input for Single Blade • hub.curve / shroud.curve• points for a curve ordered from inlet to outlet• must extend upstream of the leading edge (LE)and downstream of the trailing edge (TE)• determines the axial extent of the domain

• profile.curve• must have at least two blade profiles

‐ first is blade/hub intersection‐ last is blade/shroud intersection

• each profile consists of:‐ a name: # curvename‐ closed loop of points

• NOTE that dummy numbers in the examples on the

right serve only to show the format of the file arrangement

Hub Curve

Shroud Curve

Profile Curve


Splitter Blades

• Splitter blades are secondary and tertiary blades which are placed between the main blades.

• A bladeset contains one main blade and optional splitter blades which repeat cyclically around the axis of the rotating machine component.

• For rotating machine components without any splitter blades, the number of bladesets equals the total number of blades.


BladeGen Information File (.inf) forBlade Set with Splitter Blades

!====== CFX‐BladeGen Export ========

Axis of Rotation: Z

Number of Blade Sets: 11

Number of Blades Per Set: 2

Blade Loft Direction: Streamwise

Geometry Units: IN

Coordinate System Orientation: Righthanded





Hub Data File: Blade1_hub.curve

Shroud Data File: Blade1_shroud.curve

Profile Data File: Blade1_profile.curve


Arrangement for hub.curve and shroud.curve is the is the same as in the case of single blade

Arrangement for profile.curve must include information about the main blade and all splitter blades

NOTE that dummy numbers in the example on the right serve only to show the format of the file arrangement.

Point Data Input for Splitter Blades


Import of Geometry

• To start a new case the options are:

• Load BladeGen …

‐ File > Load BladeGen…

or click on a Toolbar.

Select .inf file for that geometry

• Specify multiple geometry objects at once:

‐ File > Load Curves…

or click on a Toolbar

• Load a cfg file

‐ File > Load CFG…

( For TurboGrid 1.6 simulation setup)


Geometry ‐Machine Data

• Pitch Angle:Method: Bladeset Count# of Bladesets

• Rotation: Method: ‐ Principal Axis: Z, Y, X, ‐Z, ‐Y, ‐X ‐ Custom Axis by two Cartesian coordinates of points on the axis

• Units:‐ Base Units: cm (default)


Import of Splitter Blade from File• Splitter Blade geometry can be imported from a

separate file after the main blade has already been imported.

• Right click on Blade Set and select: Insert > Blade

• In the Details of BLADE: Blade 1, in File Name, select the name of the file of the splitter blade


Import of Splitter Blade Geometry

• This import (left) is equivalent to that via BladeGen.inf file (right)


Machine Data ‐ Base Units

• The base units are necessary because the geometry kernel has an optimal range for storing numbers between 0.2 and 200.

• If the geometry data are given in mm, but the machine is on the order of 10m in size (e.g. Francis Turbine), the numbers stored in mm would be outside the optimal range. In this case the base units should be m to reflect the scale of the machine.

• The base units specified in the Machine Data object are used only to adjust the range of numbers to suit the geometry kernel.

• They are not used to interpret geometric data contained in the files (i.e. the hub or shroud curve file), nor are they used to specify the units of the exported mesh.

• When this requirement is violated, WARNING is generated.


Machine Data ‐ Base Units

• Warning should not be taken lightly • Consequences may be errors in: surface trimming, surface intersection, projection and mesh generation

• No need to restart TurboGrid ‐ simply reset Base Units in Machine Data

• Default Base Units are [cm] – appropriate for most machines. Hydraulic machines may require Base Units of [m]


Rotation Axis Visibility

• By turning on the visibility of the Machine Data object, the rotation axis (coloured in red) and a sample radial direction vector (coloured in blue) become visible in the viewer.

• The visibility of the Machine Data object is off by default.


Load TurboGrid Curves

• Geometry

‐ # of Bladesets

• Rotation:

‐Method:

‐ Principal Axis: (Z, Y, X, ‐Z, ‐Y, ‐X)

‐ Custom Axis by two points

• Coordinates and Units:

‐ Coordinates : Cartesian or Cylindrical

‐ Length Units: cm (default) (mm, m, in, ft)

• TurboGrid Curve Files

‐ Hub ./hub.curve

‐ Shroud ./shroud.curve

‐ Blade ./profile.curve

• Leading Edge Definition on the Blade

• Trailing Edge Definition on the Blade

‐ Cut‐off or square

‐ Line of rotation on hub and shroud


Details of Blade Set• Coordinate System and Blade File Definition

‐ File Name:

‐ Coordinates: Cartesian, Cylindrical

‐ Length Units: cm (default), mm, m, in, ft

• Geometric Representation: Method:

‐Method: BladeModeler, Frank Milled, Specify

‐ Lofting: Spanwise, Streamwise, Specify

‐ Curve Type: Bspline, Piecewise linear

‐ Surface Type:

• Leading Edge Definition

• Trailing Edge Definition

‐ Cut‐off or square

‐ Line of rotation on hub and shroud

• Bias of Blade towards High Periodic

‐ Factor


Geometric RepresentationANSYS TurboGrid generates blade surfaces using a two‐step process:

1. Curves are generated2. A surface is created by lofting across the set of curves (i.e.

sweeping from one curve to the next

The Method setting allows two preset methods and one general method, for controlling the settings that govern the geometric representation of blade surfaces (i.e. the Lofting, Curve Type and Surface Type

Method Lofting Curve Type Surface TypeBlade Modeller Spanwise Bspline RuledFlank Milled Streamwise Piecewise linear RuledSpecify User specified User specified User specified


Geometric Representation Rules

• The following rules are followed for selecting the geometric representation method:

• If the blade is loaded from a BladeModeler .inf file, the BladeModeler option will be selected automatically.

• If the BladeModeler option is selected and there are only two blade profile curves (for the applicable blade), the selected option will change to Flank Milled (which is equivalent, in this case).

• If the Flank Milled option is selected and there are more than two blade profile curves (for the applicable blade), the selected option will change to BladeModeler and a warning message will be issued.


Surface Creation by Lofting• The direction in which lofting occurs is set by the Lofting setting. The available

Lofting options are: The available Surface Type options are:

(1) Streamwise and (2) Spanwise

• In the process of streamwise lofting, the curves that are swept are

formed by connecting corresponding points between adjacent blade

profiles. For this method of lofting, one must ensure that:

‐ each blade profile has the same number of points

‐ the points are ordered in the same direction

‐ the first, nth, and last point of each blade profile are at similar

locations around the blade

• In the process of spanwise lofting the curves that are swept are the blade profile curves


Curve Type Settings• The set of curves that are used to loft the blade surface may be constructed in

one of two ways, as determined by the Curve Type setting. The available Curve Type options are:

(1) Piece‐wise linear and (2) Bspline

• Piece‐wise linear method causes the points listed for each profile

in the blade file to be connected to one another with straight lines.

• Bspline curve generation method results in the interpolation of a

smooth curve for each profile using points listed in the blade file.

This method may be necessary if the profile curves are defined with

a small number of points.

The Bspline option is default.


Bspline vs. Piecewise Linear

Hub curve: Bspline Hub curve: Piecewise Linear


Surface Type Settings

• The manner in which the set of curves is lofted is controlled by the Surface Type setting. The available Surface Type setting options are:

(1) Ruled and (2) Bspline

• A ruled surface is created by sweeping along linear paths that connect one curve to a corresponding place on the next curve. The Ruled method for surfaces is similar to the Piece‐wise linear method for curves, but is done in 2D manner instead.

• A B‐spline surface is created by sweeping along curvilinear paths that connect one curve to a corresponding place on the next curve. The Bspline method may be necessary if the blade is defined with a small number of profile curves.


Hub and Shroud Tip Clearance

• By default TurboGrid assumes the blade extends from hub to shroud

• To create shroud tip or hub tip, the Shroud Tip or Hub Tip object should be selected.

• Tip options:

‐ None

‐ Constant span:

‐ Normal distance

‐ Variable Normal Distance

‐ Profile number


Bias of Blade towards High Periodic

• The Bias of Blade towards High Periodic setting, is available in the Blade Set object

• It is expressed via Factor which controls the location of the periodic surface in the passage with respect to the first blade of the blade set.

• The value of the Factor is between 0 and 1 (default 0.5). A higher value of this Factor brings the high periodic surface closer to the blade (causing the low periodic surface to move further from the blade). A lower value brings the low periodic surface closer to the blade.

• The main purpose of this feature is to avoid having a periodic surface too close to (esp. touching), the blade surface. Such a situation can occur for some blade geometries.

• This is useful for:• Nozzles where periodic location may not be ideal• Unequally spaced blades


Importing Periodic Surfaces

• TurboGrid creates periodic surfaces based on the blade meanline

• Periodic surfaces can be imported from a file• Useful for 360° analyses where blades are not the same• Example: damaged blade


Periodic/Interface Surfaces

• Periodic surfaces and Interface surfaces can be exported and read into other TurboGrid sessions

• Saved as point data


Auto‐Adjust Interface Between Stages

• Automatically adjust s a stage interface between adjacent stages

• Click the Interface button in Inlet or Outlet editor

• In the Open Blade File dialog box, select and open the file that defines the blade in the adjacent stage

• Note that the hub and shroud curves are required to extend past this blade



• ANSYS TurboGrid will do the following:• Adjust the stage interface location according to the shape of a new blade• Add a graphical presentation of the new blade to the Inlet or Outlet object• Turn on the visibility of the Inlet or Outlet object, as applicable• Make the Points generated using adjacent stage check box available and initially selected. This option will override the Curve setting, forcing them to be computed based on the blade from the adjacent stage



• Basic Guidelines:• Use the same hub (and shroud) curves that extend through both stages, and the same Curve Type setting: Bspline or Piece‐Wise Linear.

• If hub (shroud) curve for each stage is used, the curves should meet at a point, and not overlap. There is a risk of a discontinuity in slope where the curves meet.

• Use the same interface points for stage interfaces. Do this by saving the interface (inlet or outlet geometry object, as applicable), then loading the interface for the adjacent stage.

tg-intro_14.0_l03_geometry.pdf

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