Multiblock Method

The Multiblock method is used to smooth multiblock mesh. This smoother works on the base of the (structured) blocks of the pre-mesh.

The Multiblock smoother is used to obtain smooth grid lines. It is specially optimized for blade configurations. The mathematical basis is that an elliptical differential equation of the form , where is the "control function", will be solved. It can be proved that by using the elliptical operator , smoothness of the mesh will be achieved. The control function will be specified so that the smoothed mesh will obtain certain characteristics, such as orthogonality and layer height of the first layer.

The following parameters are available for this method.

Relaxation Block(s)

allows you to select/deselect blocks. Click the appropriate selection icon to select or deselect blocks.

Block Display Off

if enabled, the selected blocks will not be displayed on the screen.

Smoothing Direction
3D Direction

smoothes all the blocks of the pre-mesh independently.

Select direction

allows you to select the smoothing direction.

Reference Edge

specifies the edge defining the smoothing direction. To select the smoothing direction click the Edge selection icon. A block will be highlighted in the display. Click the edge that defines the desired smoothing direction.

If I, J, or K is selected, and no Global vertices are selected, then the blocks of the pre-mesh will be smoothed in planes starting and ending at the indices specified, and with the increment specified. The planes in between will be interpolated and smoothed, if Volume iterations is set greater than 0. If directions I, J, or K is selected, and the Global Vertices option is selected, then the pre-mesh will be smoothed globally over selected edges defined by its end vertices, in planes starting and ending at the indices specified, and with the increment specified. The planes in between will be interpolated and smoothed, if Volume iterations is set greater than 0.

For example, if you select a smoothing direction I, Start Index = 1, End Index = 20, and Increment = 5, the nodes on the planes I = 1, 6, 11, 16, and 20 would be smoothed with the remaining nodes interpolated. It is also possible to define a list of planes by specifying the plane numbers separated by spaces in the Planes field. In this case the plane numbers have higher priority than the Start and End Index fields.

Note:  To identify planes, use the Blocking Display Tree > Pre-Mesh > Scan Planes function.

Auto Setup

When Auto Setup is selected, all subfaces which fulfill the following conditions will be selected as Non-Relaxation Faces and Hold Cell Height Faces:

  • Subfaces that belong to the selected blocks.

  • Subfaces that are not perpendicular to the selected smoothing direction.

  • Boundary subfaces with respect to the selected blocks. For example, they cannot be block interfaces between two selected blocks.

  • Subfaces that are not periodic.

Additionally, all vertices which are connected to the selected blocks will be defined as Global Vertices.

Layer Options

These options allow you to select layer options when smoothing.

Start Layer

is the index plane in smoothing direction at which the smoothing should start. The value should be between 1 and less than or equal to the maximum index. If plane numbers have been set under Planes then this field will not be used.

End Layer

is the index plane in smoothing direction at which the smoothing should end. The value should be between 1 and less than or equal to the maximum index. If plane numbers have been set under Planes then this field will not be used.

Increment

specifies the increment to smooth the planes between the Start and End Layers. The nodes will be interpolated in between the layers.

Volume iterations

if set to greater than, 0 then only the nodes between the planes selected for smoothing will be smoothed with this number of iterations after interpolation.

Planes

specifies the index planes in the smoothing direction for smoothing. The values should be between 1 and less than or equal to the maximum index, and should be separated by blanks. If specified then it will overwrite the values for Start and End Layer, and Increment.

Face Options

allows you to choose from the following options for selected subfaces:

Non-Relaxation Faces

freezes subfaces.

Hold Cell Height Faces

orthogonality and first cell height will be obtained on all grid lines perpendicular to the selected subfaces.

Face Display Off

if enabled, then the selected faces will not be displayed.

Face Icons

enables the display of the selected faces by icon. Otherwise the selected faces will be shown in solid display, at 90% of their full size.

Face Filters

allows you to filter the selected faces using the Use All Selected Faces, Use Only Block Interfaces, and Use Only Boundaries options.

Remove periodic faces

if enabled, the periodic faces will be removed from the selection.

Select or deselect faces by clicking on the appropriate selection icon.

Vertices Options
Global Vertices

If any end vertices of a block edge have been selected, and a smoothing direction is selected, then the pre-mesh will be smoothed globally in planes. It is recommended that all vertices be selected as Global Vertices and that the real (not periodic) boundaries be frozen.

Layer Vertices

This option is intended to be used for Ogrid vertices. For neighbor nodes, the bisector will be calculated placing the neighbor nodes on the bisector line in a distance specified as the First Layer Distance. If the First Layer Distance is smaller than 0.0, the selected vertices will not be used. Vertices can be added or removed from the selection list, and the First Layer Distance can be changed for the selected vertices.

Layer Vertices are only used in global edge smoothing. To access this option, a smoothing direction must have been selected.

Vertices Display Off

if enabled, the selected global or layer vertices will not be displayed.

Select or deselect vertices by clicking on the appropriate icon.

Clear all selections

resets all selections.

Advanced Options

contains the following advanced options:

Number of Iterations / Steps
Iterations in equation solver

specifies the number of iterations for the equation solver (default is 25). An equation solver (SOR method) is used to solve the elliptic equation method.

Steps in global edge smoothing

specifies the number of smoothing steps in the global-edge smoothing method. In each step the Pre-Mesh will be smoothed globally and the output will be used as input in the next step (default is 25).

Parameters
Projection limit

is useful for near-wall layers. This parameter is used for node distribution whose first spacing from the surface is less than the geometry tolerance. A value greater than 0.0 will define a distance normal to the surface up to which the nodes will be interpolated. A single value of projection limit is used at all locations on the model.

Relaxation factor

is a factor to stabilize the smoothing value. Reasonable values should be between 0.0 (exclusive) and 1.0 (inclusive). The default value is 0.5.

Residual factor

is used during global edge smoothing. Starting from the 2nd global edge step, the average change compared to the previous step will be calculated by dividing this value by the value calculated in the 2nd step. If this relative value gets lower than the Residual factor, a stop criterion has been reached. The default value is 0.05.

Surface fitting

constrains boundary nodes to the true geometry surfaces. With this option disabled, the boundary nodes will be projected to the triangulation of the geometry surfaces.

Use projection

enables smoothing steps to be performed, allowing nodes to move away from constraints (curves, surfaces), and then the nodes are finally projected back to the curve or surface. By default, this option is disabled.

Use orthogonal positioning

is used during global edge smoothing or plane smoothing. If Hold Cell Height has been set on a subface, a special method will be used to calculate the control function values in a way that the first layer nodes will be placed to hold the original or user defined (layer vertices) cell height and to be orthogonal (bisector) to the boundary. By default, this option is enabled.

Use fractional positioning

is used during global edge smoothing or plane smoothing. If Use orthogonal positioning has been set, the first layer nodes will not be moved in one step to the orthogonal position but in a certain amount of steps (10). This is mainly to stabilize the orthogonal positioning algorithm in highly clustered meshes. By default, this option is disabled.

Methods

In the structured smoother, several elliptic relaxation methods are available both for the volume and faces (subface boundaries). The default method is Sorenson - Laplace. In the case of global edge smoothing, this parameter is not relevant.

  • Sorenson-Laplace

    Sorenson methods attempt to maintain node distributions (bunching) near the surface boundaries while improving orthogonality. This hybrid method attempts to improve orthogonality at the boundary while maintaining the first layer height from the boundary surface and making a uniform node distribution in the interior

  • Sorenson-Thomas & Middlecoff

    This method improves orthogonality at the boundary while maintaining the first layer height from the boundary surface and holding the original clustering on the interior.

  • Thomas & Middlecoff

    This method generally improves the orthogonality of grid lines across boundaries while holding the original clustering in the interior.

  • Laplace

    This method attempts to give a uniform mesh size for all selected elements or to give a uniform transition.

  • Interpolation

    This uses an algebraic transfinite interpolation method with Soni interpolants to generally improve internal angles.

  • Hilgenstock - Thomas & Middlecoff

    Hilgenstock methods maintain orthogonality. This hybrid method maintains orthogonality between block boundaries (subfaces) to give a smooth transition across subfaces, while maintaining the first layer height from the boundary surface.

  • Hilgenstock - Laplace

    This attempts to improve orthogonality and uniform node distribution within the mesh.

Grid expansion rate

is the exponent for the exponential decay of Sorenson terms from the boundary to the interior of a face. Reducing this factor will cluster the elements closer to the boundary. Default values are 3.5 for faces and 4.6 for the volume.

Multiblock Settings
Load Settings

allows you to load previously saved Multiblock settings.

Save Settings

allows you to save the current Multiblock settings in a file.

Run in sequence

allows you to load different Multiblock settings files and run them in sequence. Click Start sequence to begin running the sequence of files.

Convert old settings

allows you to convert Multiblock settings which were created with the Ansys ICEM CFD 4.3 version.

Convert file

specifies the old settings file.

Save as file

specifies the new settings file.

Convert

starts the conversion.