Mesh Effects for CFD Solutions
Sponsored by the Meshing, Visualization, and Computational Environments Technical Committee

Mesh Effects for CFD Solutions: Overview

The AIAA Meshing, Visualization, and Computational Environments Technical Committee invites abstract submittals for a special session on Mesh Effects for CFD Solutions. The goal of this special session is to quantify how changes in the mesh affect solution accuracy and convergence for a CFD flow solver. Presentations from these special sessions will be used to update the gridding guidelines for future AIAA CFD workshops.

These special sessions will build upon the mini-symposium held at 2019's GMGW-2: Mesh Effects on CFD Flow Solutions.

All papers in these sessions will describe simulations on systematically varied meshes of a 2-D multi-element airfoil from the NASA High Lift CRM.

Not a Workshop - Submit Your Abstract to AIAA

Mesh Effects for CFD Solutions is not a workshop in the style of GMGW-1 and GMGW-2 for which special registration was required. Instead, it will consist of special sessions during the AIAA Aviation conference.

The normal AIAA process for submitting an abstract, review, acceptance, submission of a full manuscript, and presentation at the conference applies. For more details, see the AIAA Aviation 2020 Call for Papers.

IMPORTANT: After you submit your abstract to AIAA, email your control number and paper title to meshingworkshop@gmail.com so we can ensure it gets assigned to the special session.

Objectives

Participants in the special session are asked to perform a systematic investigation of what mesh characteristics constitute a best practice mesh for a 2-D multi-element airfoil for their flow solver using a Spalart-Allmaras (SA) or Spalart-Allmaras Negative (SA-Neg) turbulence model.

Papers should describe how the mesh was varied and correlate those mesh characteristics with solution accuracy and convergence.

The resulting best practice mesh should be documented in sufficient detail for another practitioner to replicate the results.

Examples of mesh characteristics that could be investigated:

• Cell Type
• Number of constant cell height mesh layers normal to wall
• Stretching ratio normal to wall
• Stretching ratio rate normal to wall
• Edge length
• Edge length ratio
• Aspect ratio
• Area ratio
• Maximum included angle
• Farfield distance

Note that these examples are not required nor is this a comprehensive list. Feel free to choose characteristics or parameters that make sense for your meshing technology and flow solver.

For the characteristics you choose, we recommend that their influence on lift and drag for an alpha sweep from -2 to 26 degrees (CL vs alpha and drag polar for angle-of-attack every 2 degrees) is investigated. A grid convergence study with the final best-practice mesh for the nominal angles of 8 and 16 degrees should be included and participants are encouraged to conduct grid convergence studies at additional angles if time permits.

Geometry

All participants in the special session are asked to use the supplied geometry below for their studies.

• The units in the geometry model files are meters.
• The local chord (measured with the flap and slat stowed as shown above) is 1 meter.
• The slat and flap deflection angles are 30 and 37 degrees, respectively.

A 2-D cut of the HL-CRM wing is provided in IGES and STEP formats. (Right click and use “Save link as”.)

• IGES File: crmhl-2dcut.igs
• STEP File: crmhl-2dcut.stp
• EGADS File: crmhl-2d.egads

Flow Conditions

Simulations should use the following flow conditions which are based on standard sea level conditions. Note that conditions marked in italics are optional settings.

If you choose or need to use different values for these optional conditions, please provide evidence of the sensitivity of your results to any assumptions you make.

Mach Number	0.2
Reynolds Number	5 million
Cref	1.0
Angle of Attack	8 degrees
Ref Pressure	101 KPa
Ref Temp	272.1 K
Prandtl Number	0.72
Turbulent Prandtl Number	0.9
Ratio of Specific Heats	1.4
Wall Boundary Condition	Adiabatic
Farfield Boundary Condition	Riemann Invariant
Farfield Distance	1000 chord-lengths

We recommend that Sutherland’s law is used for viscosity. If you choose to use a different model, please note what was used and why in your paper and presentation.

Turbulence Models and Verification

A Spalart-Allmaras (SA) or Spalart-Allmaras Negative (SA-Neg) turbulence model is should be used for all simulations.

Your paper and presentation should note whether and how you have verified your implementation of SA or SA-Neg using the NASA Turbulence Modeling Resource.

Presentation and Deliverables

Participants are asked to include the following data in their paper and presentation.

• Mesh size (cell and node counts)
• Mesh spacing normal to wall
• Cell stretching ratio
• Lift, drag, pressure drag, viscous drag and pitching moment coefficients and pressure coefficient distributions for (a) each element and (b) the total configuration
• All coefficients should be non-dimensionalized using the clean wing chord (Cref above)
• The moment reference point to be used for all pitching moment coefficients is (0.25, 0,0), i.e. the quarter-chord point of the clean wing
• Location of separated flow and stagnation points
• Relevant a priori mesh metrics
• Velocity Profiles
• Any error estimations or relevant solution metrics used in investigation

The presentation template provides information on the slides and type of data we would like to see in each participant's presentation. Please use this reference to present as much of this data as possible within your allotted presentation time. Note that 5-10 minutes will be reserved at the end of your time slot for a question and answer period.

• GMGW2.5-presentation-template.pdf (PDF)