Chapter 13 MESH REPLACEMENT

The following tutorial files are used in this chapter:

save_es-ice.4-final es-ice.inp es-ice.PNL GRID_MOVE.NULL MAKE_EV.BAT

make_ev.tab

mvmesh.sh (Created in Chapters 3 - 6)

READ_TMP.BAT save_ice_after_map template.bnd template.cel template.cpl template.vrt

MESH_REPLACEMENT/save_es-ice.dense

This chapter demonstrates the es-ice mesh replacement feature, whereby the starting mesh is replaced by any number of alternative meshes at user-specified crank angles. In general, the replacement meshes are finer than the starting mesh, thus providing a better representation of changing and more complex engine geometries. This technique can be used to improve solution accuracy during certain stages of the engine cycle where in-cylinder conditions change rapidly (e.g. combustion, squish, valve opening, valve closing). Therefore, it is often beneficial to use a dense mesh when the piston approaches TDC. The STAR solver completely handles the transition between meshes and solution mapping.

In the following example, a coarse mesh (save_es-ice.4-final) is replaced by a dense mesh (save_es-ice.dense) between 340 degrees CA and 380 degrees CA, and also between 700 degrees CA and 740 degrees CA. This strategy employs mesh replacement at TDC between the exhaust and intake phases, and TDC between the compression and expansion phases, as illustrated in Figure 13-1:

Figure 13-1 Diagram of mesh-replacement time line

The necessary steps for setting up mesh replacement are outlined in the following list:

1.Prepare the file structure, with the coarse-mesh model located in the working directory and the dense-mesh replacement model in a subdirectory

2.Write data files for the replacement model within its own directory

3.Create Ahead Files for the dense mesh

4.Define the mesh replacement operations with respect to crank angle and write the required files

5.Set up a mesh replacement simulation in pro-STAR. This process requires

creation of an events file, plus changes to under-relaxation factor and analysis controls for both meshes.

Preparing the File Structure

If the tutorials in Chapters 3 - 6 of this volume have been completed consecutively, the model and data files for the coarse mesh will be present in your current working directory.

•Create a subdirectory called dense within your working directory using your computer’s operating system facilities

•Place the dense model file (save_es-ice.dense) in the newly created dense subdirectory

Figure 13-2 illustrates the required file structure:

Figure 13-2 Required file structure

Rebuilding the Dense Mesh

When working with a model file from an older version of es-ice, we recommend that you rebuild the case in order to take advantage of the latest changes to the code. In addition, certain data files must be present in the dense subdirectory for use as input into pro-STAR (see Chapter 8, “Write Data” in the User Guide).

To begin rebuilding the case, you must first resume the dense model as described below:

•Make the dense subdirectory your current working directory and then launch es-ice in the usual manner

•In the Select panel, click Read Data

•In the Read Tool, click the ellipsis (...) button next to the Resume file box and select the dense model file (save_es-ice.dense) from the file browser. This action loads the model and displays the dense mesh in the Template window.

The meshing pipeline in es-ice generates the 2D and 3D templates, trims and assembles the mesh, and executes the Star Setup process. Entering the following es-ice command will run the meshing pipeline and rebuild the mesh with the latest version of the code:

Pipeline, TrimmedModel, StopAt, StarControlsLoad

As the pipeline re-runs Star Setup, you must reload the model into Star Controls, redefine the interface between manifolds and ports and redefine the boundary patches. For convenience, the Star Controls panel settings are already correctly defined. If you are unfamiliar with these settings or the Star Controls panel, please consult Chapter 6 of this volume.

To redefine the model in Star Controls:

•In the Select panel, click Star Controls

•In the Load model view of the Star Controls panel, click Load Model

•In the Assembly view of the Star Controls panel, redefine the interface between the manifolds and ports as follows:

•In the Plot Tool, deselect the Fill toggle button and click CPlot

•In the Star Controls panel, select the Partial toggle button and click CP

Match

•In the Controls Workspace window, click an interior face between the intake manifold and port, as shown in Figure 13-3

Interior Face

Figure 13-3 Interior face between intake port and manifold

•In the Star Controls panel, deselect the Partial toggle button and click

CP Match

•In the Controls Workspace window, click an interior face between the exhaust manifold and port

•Click CPTransform

•Click Finish

•In the Boundary Conditions view of the Star Controls panel, redefine the boundary patches as follows:

•For the Cylinder domain, under Extra Regions > Spark Plug, click Define

•In the Plot Tool, select the Fill toggle button

•In the Boundary Tool, click Display All

•Click Keep Picked and select the patches that define the spark plug in the Controls Workspace, as shown in Figure 13-4

Figure 13-4 Spark Plug patches

•In the Boundary Tool, click Define

•For the Port and Valve 1 domain, under Extra Regions > Intake Flow

Boundary, click Define

•In the Boundary Tool, click Display All

•Click Keep Picked and select the patches that define the intake flow boundary in the Controls Workspace, as shown in Figure 13-5

Figure 13-5 Intake flow boundary

•In the Boundary Tool, click Define

•For the Port and Valve 2 domain, under Extra Regions > Exhaust Flow Boundary, click Define

•In the Boundary Tool, click Display All

•Click Keep Picked and select the patches that define the exhaust flow boundary in the Controls Workspace, as shown in Figure 13-6