Mesh convergence studies are crucial for verifying the reliability and accuracy of analysis results. By systematically refining the mesh and observing the convergence of key aerodynamic parameters, such as lift and drag, you can establish confidence in the validity of your simulations. This guide will walk you through the steps of conducting a mesh sensitivity study in FlightStream, focusing on refining the mesh for a wing component.
Steps
- Establish initial conditions:
• Define relevant solver settings. Select a flight condition, such as altitude and velocity, that aligns with your study's requirements. It is recommended to set a non-zero angle of attack to ensure key physics are resolved during the simulation. Configure the solver to be inviscid, which means disabling viscous-coupling and separation models. This is because, in FlightStream, all downstream physics calculations (viscous effects, separation, etc.) are based on the inviscid pressure distributions. - Initial refinement in the U-Direction:
• Determine the direction exhibiting the greatest curvature. In most wing components, this corresponds to the U-direction, representing the chordwise direction. Construct a test matrix with varying mesh densities, starting with coarse settings and progressively refining them along the U-direction. - Iteration for convergence:
• Iteratively modify the mesh size and observe the convergence of forces, such as lift and drag.
a. Import your model with the selected mesh settings into FlightStream.
b. Run the solver with viscous coupling deactivated.
c. Document the forces after each simulation run.
d. Adjust the mesh size and repeat the process until the difference in forces between iterations is less than 1%. - V-Direction Refinement:
• Once convergence is attained in the U-direction, maintain the converged mesh density for that direction and proceed to refine the V-direction, typically the spanwise direction for a wing component. Adjust the mesh density in the V-direction and repeat the steps of importing, solving, and recording results until convergence is achieved. - Component-Wise Refinement:
• If necessary, apply this refinement procedure to all relevant components within your model.
Additional details regarding meshing in FlightStream:
Anisotropy: Users are encouraged to leverage the high level of anisotropy acceptable to the FlightStream solver, exceeding ratios of 50:1. This allows for independent refinement schemes in chordwise and spanwise directions for wing-like components.
Mesh Refinement Zones: Custom refinement zones can be defined along the spanwise or axial directions using parametric coordinates. These zones are beneficial for refining mesh density in areas such as nacelle-wing intersections, fuselage-wing junctions, and small gaps between components or control surfaces.
Attached are 3 files to help you perform a mesh convergence study on a simple wing.
sample_wing.csv - A component cross section (CCS) file of a simple wing (Note: remove the .txt extension on the attached file)
(Note: remove the .txt extension on the attached file)
script.txt - A Flightstream script file that allows you to run an AoA sweep.
Here is a helpful YouTube video that talks about how to perform the study. Note, that this is a legacy video and your version of FlightStream may differ.
Let us know in the comments below if you have success with these methods or are having any issues!
