High-Order Overset for Moving Grids · Flux points on arti cial boundary faces - Arti cial Boundary...
Transcript of High-Order Overset for Moving Grids · Flux points on arti cial boundary faces - Arti cial Boundary...
Introduction Overset Method Results
High-Order Overset for Moving Grids2017 Aero/Astro Industrial Affiliates Meeting
J. Crabill, A. Jameson
Aerospace Computing Laboratory, Stanford University
April 19, 2017
J. Crabill, A. Jameson 2017 Aero/Astro Affiliates Meeting 1/20
Introduction Overset Method Results
Outline
1 Introduction
2 Overset Method
3 Results
J. Crabill, A. Jameson 2017 Aero/Astro Affiliates Meeting 2/20
Introduction Overset Method Results
Outline
1 IntroductionMotivationWhy High-Order?(Direct) Flux Reconstruction Basics
2 Overset Method
3 Results
J. Crabill, A. Jameson 2017 Aero/Astro Affiliates Meeting 2/20
Introduction Overset Method Results
Background: Overset-Grid CFD
Problem: Complex geometries in relative motion
Solutions:
Constant re-meshingMesh DeformationOverset Grids: One grid per body of interest
Well-established approachSimplifies mesh generationNot conservative - Introduces error withinter-grid interpolation
[DARCorp]
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Introduction Overset Method Results
Why Use High-Order?
Higher accuracy per DOF
Less dissipative: Better at preservingunsteady, vortex-dominated flows
Better suited for utilizing modernhardware
[NASA]
Previous work has shown high-order + overset retainshigh-order accuracy [1] [2]
Current work: Show high-order overset is accurate and efficient onmoving grids and complex geometries
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Introduction Overset Method Results
Direct Flux Reconstruction (DFR) Basics
Similar in concept to many finite-element methods
Solution defined at multiple solution points inside each element
Solution point values used to construct element-wide polynomials
Conservation enforced at flux points with common flux functions(i.e. Riemann solvers)
J. Crabill, A. Jameson 2017 Aero/Astro Affiliates Meeting 5/20
Introduction Overset Method Results
Outline
1 Introduction
2 Overset MethodOverset Hole CuttingArtificial Boundary (AB) Method
3 Results
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Introduction Overset Method Results
Hole Blanking / Boundary Creation
Example CFD application: Flow around airfoil
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Introduction Overset Method Results
Hole Blanking / Boundary Creation
With overset method, only small grid local to airfoil required
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Introduction Overset Method Results
Hole Blanking / Boundary Creation
Remainder of domain filled in with background grid
(Typically a structured or pseudo-structured grid)
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Introduction Overset Method Results
Hole Blanking / Boundary Creation
Must remove elements from background grid where airfoil isAll nodes within solid boundary marked as hole nodes
Remaining overlapping points marked as fringe/receptor nodes
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Introduction Overset Method Results
Traditional Hole Cutting
Traditional finite-volume: interpolate to nodes (dual-cell centroids)
(Volume Interpolation)
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Introduction Overset Method Results
High-Order Hole Cutting
High-Order Overset: No fringe/receptor nodes neededOnly require that grids have a continuous overlapping boundary
(Surface Interpolation)
J. Crabill, A. Jameson 2017 Aero/Astro Affiliates Meeting 11/20
Introduction Overset Method Results
Hole Blanking / Boundary Creation
Flux points on artificial boundary faces - Artificial Boundary FluxPoints - are only points requiring data interpolation
Less interpolation required than for volume approachNatural extension of discontinuous finite-element methods
J. Crabill, A. Jameson 2017 Aero/Astro Affiliates Meeting 12/20
Introduction Overset Method Results
Fringe Point Connectivity
Donor cells found using fast search algorithm (i.e., binary tree)
Iterative method used to find reference position
For moving grids, search + iteration required at every time step
Connectivity for all points done in parallel on accelerator
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Introduction Overset Method Results
Artificial Boundary Method
Data interpolated to faces as external / “right” state
Interface flux / Riemann solver used as normal
Grids ”unaware” of any special computation occurring
Dubbed the Artificial Boundary approach [2]
1D Example
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Introduction Overset Method Results
Outline
1 Introduction
2 Overset Method
3 ResultsTaylor-Green VortexPerformance ComparisonConclusion and Future Work
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Introduction Overset Method Results
Taylor-Green Vortex
High-Order Workshop “difficult”-level test case [3]
3 overset grid computations performed for comparison:
1 Inner grid static2 Inner grid translating in 3D figure-8 pattern3 Inner grid rotating around arbitrary axis
Elements added/removed from background grid as inner grid moves
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Introduction Overset Method Results
Taylor-Green Vortex
Comparing to 5th-order reference solution generated by PyFR [4]
Excellent agreement even with continual blanking/unblanking
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Introduction Overset Method Results
Performance Comparison
Overhead less than 2x over single, static grid
(P=4)
Run using the Taylor-Green test case
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Summary
High-order overset code developed
High-order accuracy retained
Minimal overhead for complex, dynamic calculations
Future Work:
Develop high-order-specificconnectivity algorithms
Near-Term Case: Golf Ball
Reynold’s Number: 180,000Mach Number: .2Difficult Re to modelPlan to utilize overset to simulatespinning golf-ball trajectory
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Questions?
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References I
Crabill, J., Sitaraman, J., and Jameson, A., “A High-Order OversetMethod on Moving and Deforming Grids,” AIAA AviationConference, 2016.
Galbraith, M. C., A Discontinuous Galerkin Overset Solver , Ph.D.thesis, University of Cincinatti, 2013.
“2nd International Workshop on High-Order CFD Methods,” 2013.
Witherden, F. D., Farrington, A. M., and Vincent, P. E., “PyFR: AnOpen Source Framework for Solving Advection-Diffusion TypeProblems on Streaming Architectures using the Flux ReconstructionApproach,” Computer Physics Communications, Vol. 185, 2014,pp. 3028–3040.
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