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Overset Mesh and Related Technologies in CFD++ from
a User Perspective
Prasanth Kachgal and Nili Bachchan Metacomp Technologies, Inc.
14th Symposium on Overset Composite Grids and Solution Technology
October 1st, 2018 University of Maryland
College Park, MD
© 2018 Metacomp Technologies, Inc. 1
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• Two example cases set up from beginning to end using ICFD++
• Introduction to general case setup in new ICMP infrastructure
• Advanced User Interface (AUI)
• Overview of overset mesh approach in CFD++
• Concatenation of grids
• Cutting and Blanking (New Visualization Features)
• Boundary conditions
• Overview of coupled Six-DOF and general mesh motion
© 2018 Metacomp Technologies, Inc.
Goals
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Company Background
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• Founded in 1994
• Key staff members are pioneers in CFD research
• CFD++ is 7th generation CFD software by founder, each one
state-of-the-art when introduced
• Strong algorithm to applications experience
• Provides complete CAE solutions for its customers
MIME Mesh Generation
CSM++ Structural Mechanics
CAA++ Computational Aero-acoustics
CFD++ Computational Fluid Dynamics
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Company Focus
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© 2018 Metacomp Technologies, Inc.
CFD++ Capabilities
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CFD++ is a comprehensive software suite that includes a rich collection of tools to help increase the end users’ effectiveness.
External and Internal flows Sliding/Moving/Overset Meshes Rotating Machinery 6DOF/Moving Bodies Conjugate Heat Transfer Porous Media Modeling High-Speed and Low-Speed Reacting flows Multi-Speed Problems Supercritical Fluids Dispersed Phase Models (particles and droplets) Multiphase Mixture Models Phase Change Modeling (evaporation/condensation) Free Surfaces and Fronts (flames, shocks, etc.) Radiation Heat Transfer Unique Propeller and Helicopter Blade Model
Turbomachinery
Propulsion High- and low- Speed combustion
External Aerodynamics
Wind energy – terrain verification
Unsteady flow with Hybrid RANS/LES
Under-hood flows
6DOF/moving bodies
Exhaust gas infiltration
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CFD++ Numerical Features
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Coupled density or pressure-based solvers
Realizable physical, mathematical & numerical models
Agglomeration (algebraic) multi-grid accelerated solver for fast convergence to steady state
Multi-dimensional TVD framework for truly 2nd order accuracy on all meshes
Up to fourth order accuracy (temporal) in explicit mode
Second order accuracy in time in implicit mode
Specialized low-diffusion schemes for transient phenomena
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© 2016 Metacomp Technologies, Inc.
Metacomp Overset Philosophy
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Same multidimensional least squares interpolation everywhere
Very intuitive geometric approach (same for 2D and 3D)
Flexibility via sequential cutting (reduces number of overlap cells)
Fully integrated
Cutting can be performed (if necessary) completely within the run
Coupled with Rigid Body Motion and 6DOF computation
No re-meshing after cutting/blanking
Perfect conservation via flux-stitching
© 2018 Metacomp Technologies, Inc.
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CFD++ Key Attributes
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Internal unstructured book-keeping Allows for all cell types within same grid
Multiple blocks OK (structured and unstructured)
Wall distance free turbulence models and fast wall distance re-computation
Allows for transient computation with grid blanking
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The Integral Way
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ICFD++ Advanced User Interface (AUI)
• Integral Computational Multi-Physics (ICMP) concept and infrastructure
• Common interfaces across all products in series • Intuitive and simple guided process: setting up problem
definition analyzing and understanding results
• Helps user make the best choices for the problem and decreases risk of error
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© 2018 Metacomp Technologies, Inc.
AUI
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Notebook Pages
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© 2018 Metacomp Technologies, Inc.
AUI
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Action Tree – Navigates through setup
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© 2018 Metacomp Technologies, Inc.
AUI
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Action Panel
Action Item
Confirmed item X Unconfirmed item
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AUI
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• Dependency based options in Action Panel
• “Thinking Engine” adapts Action Tree items based on selections
If it’s not relevant, you don’t see it!
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Overset Blanking Procedure
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Marking cells intersecting the cutter surface (“cut cells”)
Blanking cells enclosed by the layer of “cut cells” and non-live boundaries
Retain or not retain “cut cells”
Cutter Boundary
Live Boundary
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© 2018 Metacomp Technologies, Inc.
Overset Blanking Procedure
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Marking cells intersecting the cutter surface (“cut cells”)
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© 2018 Metacomp Technologies, Inc.
Overset Blanking Procedure
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Marking “live” cells – recursively marching to adjacent cells until “cut” cell or non-live boundary is encountered
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Overset Blanking Procedure
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Retain/Blank “cut” cells – additional boundary created after cutting (overset/patched)
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Sequential Cutting/Blanking
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Allows multiple sequential cuts of varying types, retain options, live BC/cell designations
Multiple “Ranks”(each utilizes regular cutting procedure)
Allows “BC created by cutting” to subsequently act as cutter
Useful for complex overlapping geometries, robust cutting procedures for evolving transient solutions, 3+ overlapping bodies
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© 2018 Metacomp Technologies, Inc.
Sequential Cutting
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Original Grid Rank 1
Rank 2
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Cutting/Blanking Visualization
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• Visualize grid blanking before launching simulation
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1. 2D Ball Drop into Water
Demo Cases
6DOF
Volume of Fluid
Buoyancy
Cutting and Blanking
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Case 1: Concatenation of Grids
Background (Group 1) Ball (Group 2)
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Case 1: Concatenation of Grids
Concatenated Grids
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Case 1: Cutting and Blanking Goals
Remove Background Grid
Minimize Overlap Cells
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Case 1: Rank 1
Cutter: Ball Zonal BC
Live: Background outer BCs
Blank: Background Group
Live: Background outer BCs
Overlap: Retain Cut Cells
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Case 1: Ball Drop Solution
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3D Capsule Drop
• Same cutting/blanking settings as 2D Ball
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2. 2D Store Separation with Fin Deployment
Demo Cases
Multiple body 6DOF
Thrust from exhaust
Prescribed motion RBD
Multiple rank Sequential cutting
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Case 2: Concatenation of Grids
Background (Group 1) Store (Group 2)
Fin 1 (Group 3) Fin 2 (Group 4)
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Case 2: Concatenation of Grids
Concatenated Grids
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Case 2: Cutting and Blanking Goals
Remove Background Grid
Remove Fin Grids
Remove Store Grid Minimize Overlap Cells
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Case 2: Sequential Cutting Rank 1
Blank: Background Group Live: Background BCs
Overlap: Retain Cut Cells
Cutter: Store Zonal
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Case 2: Sequential Cutting Rank 2
Blank: Store and Fin Groups
Live: Store exhaust and Fin tops
No Overlap: Do Not Retain Cut Cells
Cutter: All Wall BCs
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Case 2: Fin Deployment Solution
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Examples
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Bullet Leaving Gun Barrel
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To simulate the detonated propellant a region
of very high temperature and pressure air was
imposed behind the bullet
2-D axisymmetric computation simulates about
2.5e-4 s (when bullet reaches end of domain,
about 0.1 m from barrel exit) - grid was 81,000
cells
Propellant races ahead of bullet and exits
barrel at about 6.25e-5 s
1.5 hours on 2 CPUs, required 2500 global
time-steps with 9900 total iterations
Each animation frame is 2.5e-6 s
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3D Ball Valve
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Incompressible Flow
Perfect mass balance achieved through flux stitching
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3D Store Separation
38 Aerodynamic forces on store Aerodynamic moments on store
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F18 Fuel Tank Separation
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Localized cutting, zonal connection, force
integration and localized 6DOF
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Grain Burning: Overset + Mesh Morphing
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Grain Burning: Overset + Mesh Morphing
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Grain Burning: Overset + Mesh Morphing
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Thank you!
Questions?