Chapter 8	RUNNING THE STAR SOLVER
	Running in Serial Mode

Chapter 8 RUNNING THE STAR SOLVER

The following tutorial data files are used in this chapter:

mvmesh.sh
star.evn
star.ccmg
star.mdl			(Created in Chapters 6 and 7)
star.prob
param.prp
save_ice_after_map
es-ice.inp

star.drp (required for cases that include fuel injection)

This chapter describes the necessary steps for running a CFD analysis using the STAR solver. Instructions for running STAR are provided for the following scenarios, depending on your available computing resources:

•Running the analysis in a serial mode — used when you have limited resources and only one CPU

•Running the analysis in parallel mode — used when you have multiple CPUs

•Running the analysis in parallel on multiple nodes — used when you have access to multiple CPUs on multiple machines

•Running the analysis in batch — used when you intend to submit the analysis job to a queuing system

•Running a restart analysis — used when your analysis was interrupted before completion

Note that STAR runs in double precision by default. If you are running STAR-CD on Windows, use the STAR-CD PowerShell Prompt supplied with the STAR-CD installation.

Running in Serial Mode

If you have limited computing resources and only one CPU is available, your only option is to run STAR in serial mode. However, as a typical engine simulation is a transient analysis involving complex physics and a relatively large number of cells, this mode results in large processing times.

Note that, in a serial analysis, STAR and Ice share the CPU. Therefore, STAR can only begin calculating the CFD solution once Ice has provided the mesh for the current time step.

To run a serial analysis:

•In a Linux terminal or PowerShell prompt, enter the following command: star

Running in Parallel Mode

If multiple CPUs are available, you can run STAR in parallel (the recommended mode of operation). The number of processes you assign for running the analysis

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are divided between STAR and Ice, depending on various settings in the mvmesh.sh file. By default, one process is assigned to Ice and the remaining ones to STAR. However, note that there are occasions during the analysis when Ice requires additional computer resources, so STAR and Ice may share the same process. For more information on running in parallel and how Ice uses computing resources see Chapter 10 in the User Guide.

To run a parallel analysis:

•In a Linux terminal or PowerShell prompt, enter the following command: star <N>

where <N> is the number of processes you wish to use

Running in Parallel on Multiple Nodes

If multiple nodes are available, you can run STAR across all nodes and assign a specified number of processes to each node. For example, if you have two nodes, each with eight CPUs, you could assign eight CPUs from the first node and four from the second.

To run on multiple nodes:

•In a Linux terminal or PowerShell prompt, enter the following command: star nodename1,N nodename2,M ...

where:

•nodename1 is the name of the first node, nodename2 the name of the second node, and so on

•N is the number of processes assigned to the analysis on the first node, M the number of processes assigned to the analysis on the second node, and so on

Running in Batch

If you intend to submit the analysis to a queuing system and run on a cluster, you can run STAR in batch by generating a batch script called batch.sh. When the queuing system executes batch.sh, the batch file runs the analysis on the cluster.

To generate the batch script:

•In a Linux terminal or PowerShell prompt, enter the following command: star -batch

You can then submit the batch script to the queuing system via an appropriate command. For example, the PBS command is:

qsub -l nodes=N ./batch.sh

where N is the number of nodes you wish to assign to STAR.

Restarting the Analysis

If your analysis is interrupted for any reason, you can perform a restart run to

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	Restarting the Analysis

resume operations. The analysis resumes from the last time step that was written to the star.ccmp file. To avoid STAR repartitioning the mesh, use the same number of processes as the initial run.

To restart an analysis:

•In a Linux terminal or PowerShell prompt, enter the following command: star -restart <N>

where <N> is the number of processes you wish to use

Restarting an analysis creates a subdirectory containing the output files from the previous run. Note the location of these files when post-processing the results in es-ice and pro-STAR.

Note that the -restart option adds a flag to the star.prob file. Thereafter, each time STAR is run, the analysis restarts from the last time-step in the star.ccmp file, even if the -restart option is not supplied. Therefore, to run the analysis from the first time step after using the -restart option:

•In a Linux terminal or PowerShell prompt, enter the following command: star -norestart <N>

The -norestart option removes the flag from the star.prob file

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