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Component Meshing

The vehicle meshing is performed by providing necessary geometry information (such as surfaces) and related parameters. It mainly includes parameters pertaining to Tunnel surfaces, Vehicle surfaces, Grill surfaces, Heat exchangers and Fan.

Tunnel

Any wind tunnel used for the vehicle simulation is modelled using Tunnel Definition. The tunnel defined using Vehicle template should be of rectangular shape.

Tunnel Definition can be specified using three available options: Provide Surfaces Provide Margins Provide Vector & Point

Figure 7.15 - Tunnel definition

1. Provide Surfaces: In this method, the outer surfaces of the wind tunnel can be directly provided. This option is typically used when tunnel surfaces are already created using other CAD packages and imported into Simerics-MP+.

Tunnel Surfaces: The surfaces of the wind tunnel are selected under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon for Tunnel Surfaces. Flow Direction: This is the direction of the wind in the tunnel. Typically, this should be aligned with the tunnel inlet. The direction is specified with the coefficients of flow direction unit vector in coordinates. Cross Direction: Cross direction is explained using the vector right hand rule as shown in the Figure 7.16. The direction is specified with the coefficients of cross direction unit vector in coordinates.         Figure 7.16 - Cross directions

Figure 7.17 - Provide surfaces

2. Provide Margins: In this method, margins are specified by a fraction of vehicle dimension in that direction. The and directions correspond to the flow and cross directions and direction is determined by right hand vector rule.

Flow Direction. Cross Direction. Bounding Box Margin: Two types of margins are available under this option which are Nonuniform and Diagonal Positions. Nonuniform: This defines a bounding box that has different dimensions in , and directions. The values of the Minimum Side Sizes and Maximum Side Sizes are calculated based on the ratio of, the distance the car is in each direction from the walls of the wind tunnel, to the car size in that direction. So the values are all relative to the length, width and height of the car. The calculation procedure is explained in virtual wind tunnel. Diagonal Positions: This defines a bounding box that has different dimensions in , and directions. The values of the Minimum Corner Position and Maximum Corner Position are provided to calculate the wind tunnel dimension.

Figure 7.18 - Provide margins

3. Provide Vector and Point: In this method, tunnel surfaces are created by specifying the following parameters:

   Flow Direction. Cross Direction. Floor Point: This is the coordinate of one point through which the floor of the wind tunnel passes. Reference Front Tire Surfaces: Select the front tire surfaces under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Front Tire Center: Specify the center of the front tire in co-ordinates. This is auto-populated with default value once the surface is selected. Reference Rear Tire Surfaces: Select the rear tire surfaces under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Rear Tire Center: Specify the center of the rear tire in co-ordinates. This is auto-populated with the default value once the surface is selected. View Tunnel details: This displays the dimensions of the wind tunnel upon the selection of Yes. Details of the wind tunnel are Length, Width, Height and Wheelbase Center To Front.

   Figure 7.19 - Provide vector and Point

Vehicle Vehicle Surfaces: Select all the surfaces of the vehicle, except the outer casings for the heat exchangers and fans under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Grille Refinement Surfaces: Select all the surfaces that define the grille under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Grille Min Cell Refinement: This has three ways of refining the grille mesh cells: Refine One Level, Refine Two Levels and Refine Three levels. The default cell refinement for grille surfaces is Refine Three Levels. Mesh Size: Allows to choose between three types of mesh i.e., Course, Normal or Fine from the drop-down list.   Note: The surfaces, Grille refinement surfaces, reference tires and other refinement surfaces, are specified elsewhere and need not be added along with vehicle surfaces.

Figure 7.20 - Grill min cell refinement

Heat Exchangers Heat exchangers are added by selecting Heat Exchanger Template for Add Heat Exchanger. Specify the following parameters for heat exchanger template. Heat Exchanger Name: Provide name of the heat exchanger such as condenser or radiator. Tolerance: Depending on the accuracy of the cuboid shape, which is used to represent the heat exchanger, the Tolerance value is changed. Heat Exchanger Surfaces: Select heat exchanger surfaces under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. The surfaces must represent/define a rectangular cuboid box (normally extruded rectangle). View Point Information: Specify the coordinates of the Reference Point, Length Point, Width Point and Thickness Point. Mesh Parameters: Default mesh parameters are automatically set for Grid in Length, Grid in Width, Grid in Thickness and these can be changed.

Figure 7.21 - Heat exchanger

Fans

Fans can be added by selecting one of the following in the Add Fan drop-down list. Plane Blades Blades and Outer Surface Fan Mesh Name: Provide the name.

Figure 7.22 - Fan definition

1. Plane: This option is used to define the fan using fan curves.

Fan Surfaces: Select the surface for the fan plane under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Once selected, fields such as Axis, Center, Hub Radius and Outer Radius are auto-populated. The Axial Margin is a user input. Create Outer Preview: This creates preview surfaces for the outer casing. Cell Size Option: This is used to change the number of cells for meshing. Default: The number of cells are determined automatically. Custom: The number of cells in each direction can be changed using this option.

Figure 7.23 - Fan plane

2. Blades: If the fan geometry is available, use this option to model the fan using MRF approach.

Fan Surfaces: Select blade surfaces under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Fan blade center and axis are user input. The Outer Radius is automatically calculated based on the center and axis provided. The axial and radial margins are used to create the outer casing of the MRF zone. Preview surfaces can be created to check MRF casing. Cell Size Option.   Note: Preview surfaces created are not used for mesh creation directly and may be deleted.

Figure 7.24 - Fan blades

3. Blades and Outer Surface: This feature is used when the fan blade geometry and casing are available.

   Fan Surfaces: Select blade surfaces under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Outer Surfaces: Select outer casing surfaces under CAD Surfaces in the Geometric Entities Panel and click Add Surfaces icon. Cell Size Option.         Figure 7.25 - Components mesh on Y plane section

   Figure 7.26 - Blades and Outer surfaces

Flow Monitor Surfaces

Specify the surfaces on which the flow rate is to be monitored, as shown in Figure 7.11.

Internal Volume Definition

This feature is available for Underhood Thermal meshing mode. Specific components that need to be retained for temperature prediction and internal volume analysis can be added by selecting one of the following in the drop-down list.

• Volume Surfaces: This option allows adding all the surfaces that define a component, which need to be retained.

  New Volume Surfaces: Select all the surfaces of components under CAD Surfaces in the Geometric Entities Panel.

• Identifying Boundaries: This option allows adding only one surface that defines a component which need to be retained.

  Boundaries: Select all the boundaries that correspond to specific components under CAD Surfaces in the Geometric Entities Panel.

Internal Volume Options

This feature controls the number of volumes that need to be retained by selecting one of the following.

• Biggest Identified Volumes: This option allows to retain all the biggest volumes that are connected to selected surfaces. Smaller volumes that get split due to meshing will not be retained.
• All Identified Volumes: This option allows to retain all the volumes that are connected to selected surfaces.
• All Volumes: This option allows to retain all the neighboring volumes apart from the volumes that are connected to the selected surfaces.

Fan Solid Volumes

Fan solid volume can be retained by selecting Yes or No from the drop-down list.

Split Interface

Interfaces are separated automatically, if Split Interface (see, Figure 7.12) is set as Yes.