AFLR4 Example Cases Tutorial

Data files for a few AFLR4 sample cases are provided. Package archives with all of the example cases are provided in aflr4-examples.tar.gz (tar-gzip archive for Linux/MacOSX) and aflr4-examples.zip (zip archive for Windows). Additional small test cases of trivial geometry that can be used for debugging type work are provided in aflr4_caps-examples.tar.gz (tar-gzip archive for Linux/MacOSX) and aflr4_caps-examples.zip (zip archive for Windows). Copy the package archive files and unpackage them in a location of your choosing to run the example cases. All cases require minimal resources. AFLR4 takes the provided input geometry definition and automatically generates a surface mesh with spacings based on surface type, surface curvature and proximity of multiple components. AFLR4 as provided is capable of working with a discrete geometry definition or an EGADS CAD geometry definition. AFLR4 links in the Engineering Geometry Aircraft Design System (EGADS) from MIT and Open CASCADE from Open CASCADE S.A.S. for CAD functionality. Both EGADS and Open CASCADE are freely available and licensed under The GNU Lesser General Public License, version 2.1. EGADS and Open CASCADE libraries must be available to actually run the provided version of AFLR4.

Common AFLR4 options are listed below.

aflr4	[options]
	-i input_file	input file
	-o output_file	output file
	-log	generate a log file
	-ff_ids list_of_farfield_IDs	farfield surface IDs - if applicable
	-int_ids list_of_BL_intersecting_IDs	BL intersecting surface IDs (eg. symmetry plane) - if applicable
	-ref_len reference_length	should be physically based, e.g. chord length
	-er_all	use edge refinement based on surface to surface discontinuity on all surfaces
	-np number_of_processes	run in parallel with specified number of processes
	-min_ncell 1	reduce number of isotropic cells to one between BL regions - if applicable
	-BL_thickness BL_thickness	BL thickness - if applicable
	or
	-Re_l Reynolds Number	Reynolds Number based on reference length for estimating BL thickness

Note that the -BL_thickness, -Re_l, and -min_ncell options are only used during proximity checking between different bodies/components. Note that AFLR4 outputs a rerun argument file named case_name.aflr4.arg which contains all pertinent options. To rerun with the rerun argument file simply run aflr4 case_name.aflr4.arg. For EGADS CAD geometry cases the output EGADS geometry data file contains all the pertinent options included as attributes. To rerun an EGADS case use either the previous method for the rerun argument file or run with the output EGADS geometry data file and whatever output file name type is required.

See the AFLR4 documentation for information on all available options and usage. Alternatively, you can view text-based documentation at the command line with the following command.

aflr4 -help or aflr4 -help

An overview of AFLR4 example cases is provided in the following along with run parameters.

Nose (CAD geometry definition)

A simple nose cone in a farfield. Reference length is set equal to the minimum bounding box size of the nose cone only. Farfield IDs are are specified.

aflr4 -i nose.egads -o nose_new.surf -log -ff_ids 1-6

Wing and Nacelle (CAD geometry definition)

Edge refinement is added for resolution at the trailing edge and witng tip. Proximity checking automatically detects and reduces the spacing between the wing and each nacelle. Note that the farfield spacing has been increased to reduce the number of volume elements that will be generated by AFLR3 in the outer region.

aflr4 -i wingpod -o wingpod_new.surf -log -ff_ids 19-24 -er_all -ref_len 40 -Re_l 60e6

A compatible volume mesh can be generated using AFLR3.

aflr3 -i wingpod_new -blc -y+ 1 -refx 40 -Re_l 60e6 -blrm 1.3 -log

Multi-body generic cases 1 through 8 with discrete geometry definition

A set of simple multi-body generic cases. Reference length is set equal to the minimum bounding box size of the domain in each case. Proximity checking and spacing modification is automatically used in the regions where the components are in close proximity.

aflr4 -i case1.surf -o case1_new.surf -log -ff_ids 2,6

aflr4 -i case2.surf -o case2_new.surf -log -ff_ids 2,6

aflr4 -i case3.surf -o case3_new.surf -log -ff_ids 3,6

aflr4 -i case4.surf -o case4_new.surf -log -ff_ids 24,27

aflr4 -i case5.surf -o case5_new.surf -log -ff_ids 2, -int_ids 1,3,5,6

aflr4 -i case6.surf -o case6_new.surf -log -ff_ids 1,2

aflr4 -i case7.surf -o case7_new.surf -log -ff_ids 16,17

aflr4 -i case8..surf -o case8._new.surf -log -ff_ids 16,17

Bump disk with discrete geometry definition

A bump disk. Reference length is set equal to the minimum bounding box size of the domain. Without and with edge refinement on top surface only.

aflr4 -i bump -o bump_new.surf -log

aflr4 -i bump -o bump_new2.surf -log -erw_ids 3, -erw_list 1,

Plug with discrete geometry definition

A simple mechanical plug. Reference length is set equal to the minimum bounding box size of the domain.

aflr4 -I plug.surf -o plug_new.surf -log

Engine nacelle with discrete geometry definition

A jet engine nacelle in a farfield. Reference length is set equal to the engine core diameter. Farfield IDs are specified. BL thickness with minimal isotropic region thickness is also specified. Proximity checking and spacing modification is automatically used in the regions where the components are in close proximity.

aflr4 -i nacelle.surf -o nacelle_new.surf -log -ff_ids 53-56 -ref_len 100 -Re_l 110e6

A compatible volume mesh can be generated using AFLR3. For this case the proximity checking and spacing modification process provides spacing sufficient to support BL generation between nearby components.

aflr3 -i nacelle_engine_new -blc -y+ 1 -refx 100 -Re 110e6 -blrm 1.3 -nbldiff 2 -mblend 0 -log

A jet engine nacelle case with a symmetry plane is also provided. Other than the geometry all other parameters are the same.

aflr4 -i nacelle_engine_sym -o nacelle_engine_sym_new.surf -log -ff_ids 1,2 -int_ids 57, -ref_len 100 -Re_l 110e6

A compatible volume mesh can be generated using AFLR3. For this case the proximity checking and spacing modification process provides spacing sufficient to support BL generation between nearby components.

aflr3 -i nacelle_engine_sym_new -blc -y+ 1 -refx 100 -Re 110e6 -blrm 1.3 -nbldiff 2 -mblend 0 -log