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Raven CFD – Agenda (March 10-11 th 2004)
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  1. Raven CFD – Agenda (March 10-11th 2004) March 10th, 2004 • 10:00 Welcome / Introduction • 10:30 Raven CFD Overview • 11:00 Inset Body Approach • 11:30 Raven Domain Refinement • 12:00 Lunch • 12:30 MSDACS Status Report • 13:00 Open Discussion March 11th, 2004 • 09:00 Raven Training • 09:30 General Description • 09:45 Overview of Tools • 10:15 Suggested Approaches (Re: MSDACS) • 10:45 Job Deck / Raven Inputs • 11:15 Boundary Conditions • 11:45 Directory Structure / Outputs • 12:15 Post-Processing • 12:30 Lunch • 13:30 Review / Open Discussion

  2. Outline • Aletheon Technologies • Capabilities • Example Analysis • Raven Flow Solver • General Overview • Development in Support of SDACS Program • Future Developments • Inset Body • Raven Domain Refinement • Inset Bodies • A Review of Standard CFD Techniques • Inset Body • Examples • Overview (Benefits/Limitations) • Applications • Raven Domain Refinement • An Overview of Grid Adaption • Raven Domain Refinement • Methodology • Use w/ Inset Bodies • Flowfield Feature Resolution

  3. Computational Capabilities • Super-Computer • 210 processors • 105 Rack-mounted nodes • 140 Gigabytes RAM • 2.4 Terrabyte RAID Storage System • High-speed backbone switch • SGI Workstations • 64-Bit Workstations • Graphics Processing • Pre-Processing • Class “A” CAD Generation • Large-Scale Comp. Analysis • 15,000,000 –45,000,000 elements • ~100 Full-scale calculations annually

  4. Raven CFD

  5. Raven CFD • Internally Developed (2001) to Fill Gap w/ Existing Commercial Flow Solvers • Commercially Available July 2003 • Unstructured Arbitrary Element Flow Solver • General Polyhedral Elements (Prism for Accurate BL Resolution) • Parallel Implementation • Superlinear Performance (demonstrated on thousands of procs.) • Optimized for Linux clusters (also works on SGI, HP, Sun, Cray, etc.). • Low communication overhead (Fast-Ethernet Sufficient). • Unconditionally stable. • Able to run CFL of 1 million. • Problems started with CFL of nearly 1 million. • Temporal damping used to start “difficult” problems, or high time step. • Solution updates restricted to allow startup transients. • Time accurate. • Uses global time step for all calculations (including valves). • Implicit algorithm used for time step advancement. • Cell centered, finite volume. • Dependent variables stored at cell centers. • Faced based processing (no elements formed).

  6. Raven CFD • Euler/RANS Equations • Spalart-Allmaras and k-w turbulence models • DES available to solve large regions of separations • Implicit integration scheme. • Gauss-Seidel sweeps used for implicit algorithm. • Newton sub-iterations to recover accuracy. • Second order accurate (Runge-Kutta required for higher order). • Higher order fluxes. • Approximate Reimann scheme of Collela. • Least squares used to form higher order flux interfaces. • Limiter used to prevent oscillations (TVD).

  7. Raven CFD • Cost effective option for solution of large scale problems. • Developed to be massively parallel to solve large scale problems. • Significantly less expensive than other solutions (Fluent, Star-CD, etc.). • Designed to accurately solve “real world” problems. • Specialized design for solution of specific problems. • Not designed to solve all fluid problems. • No support for multi-phase, reacting flows, etc. • Specialized design enhances performance and reduces cost. • Provides higher fidelity at a lower cost. • V1.4 Release March 2004. • V1.5 Scheduled for Mid 2004 • Inset Body Method • Raven Domain Refinement (RDR)

  8. Raven CFD – Development (In Support of SDACS) • Algorithm Enhancements • Wall-heat transfer • Lift/Drag Calculation • Improved Convergence Rates • Increased Stability • Immersed Boundaries • Blocked / Flow-through (switching w/out re-gridding) • Eliminated Wall-distance Calculation • 4-8 hours  10 seconds • Reduced Restart File Size ; Improved I/O Performance • Split Flow Visualization Data • Rapid transient Analysis Post-Processing • Usability Enhancements • External Tool Development • RSplit, RMap, RPFix, HexGrid, FVToDomain, STLToRaven, etc… • Solution Analysis Tool (Transient Histories, Convergence History, Performance, etc…) • Parametric Analysis Tool • Multiple Run Comparison (50-concurrent solutions) • Component Based Comparisons • Details to be provided in Training Class

  9. CFD Overview – CAD Geometry • Simplify Geometry (fill holes, join surfaces, remove features) • Water-tight Surfaces • Trim all surfaces (wheel to road, control arms to wheel) • Export to Grid Generation Package

  10. CFD Overview – Surface Grid • Generate Body-Fitted Grid (BC’s) • 100,000 Surface Tris • Element Impingement (Wheel/Road BC) • Similar Difficulties MSDACS Ball Seats

  11. CFD Overview – Volume Grid • Generate Volume Mesh • Fixed Body / Rotating Body • BC ??? (Solid Disk)

  12. CFD Overview – Boundary Layer • Viscous Layer Generation • 18 Layers x 100,000 surface tris • 1,800,000 per wheel (x4) • 0.0001” from Surface • Timestep/Convergence Issues • Fixed Geometry (No True Rotation) • Rotation Applied Through BC • No Camber/Toe/Turning w/ Re-gridding • No Suspension Changes w/out Re-gridding • Excessive Cell Count

  13. Inset Body – Propeller Demo

  14. Inset Body – Wheel Demo • Transient Movement • Rotation/Translation • Fixed & Dynamic • Direct CAD Insertion • No Geometric Simplifications • No CAD Cleanup Required • No Watertight requirement • Accurate Inviscid Results • Imposed Turbulent Profile • 10% of 10% ~ 1% • 10% of 10% (of 10%)

  15. Inset Body – Methodology – Standard CFD • Standard CFD Approach (Body Fitted) • Benefits • Accuracy • Near-wall region resolution • Viscous Effects • Surface Heat Flux • Deficiencies • CAD requirements • Timing for body-fitted grid generation • Cell counts for viscous resolution • Post-processing • Convergence Rate < due to viscous layer resolution (Relative Measure) • Geometric Simplification Needed

  16. Inset Body – Methodology – GLS Approach • Fully Inset or GLS Approach • Benefits • CAD to CFD in minutes • Rapid Convergence • Minimal CAD Effort • No CAD cleanup, surface trimming, stitching; No Water-tight requirement • Geometric Protrusion Allowed; No Gometric Simplifications • Fully Automated • Analyst Independence ; Automated Feature Resolution • No A-Priori Limitations • Simplified Post-Processing • Purely Hex Mesh (conformal/non-conformal) • Design Tool • Rapid Geometry Change; No Grid Requirements; Self-Automated • DOE Studies (Thousands of Cases) • Full-Matrix Mapping • Design/Trend-Analysis Tool • Limitations • Less accurate near-wall region??? • Separated Region Locations/Extent??? • Surface Heating??? • Assuming Standard Approach Resolved Near Wall Region Appropriately • Rarely achieved for realistic engineering problems • Otherwise, possibly just as accurate, possibly more accurate (extensive testing required)

  17. Inset Body –Applications • MSDACS • Fixed Ball, Multiple Positions (no re-gridding) • Shutoff valves • Offseat leakage parametric studies ; Single Grid • Moving Components (Ball/Flapper Valve) • MTA Manufacturing Defects (Inertial Separator/Throat Diameters) • Sensitivity Analysis • Rapid (No Re-Gridding) • Limited by Computational Resources; Not Human-Resources • Numerous Defects Structures Examined • Independent / In-Parallel • Eliminate Grid Sensitivity • Store Separation • Rotating Propulsion Devices • Propellers • Helicopter Blades • Internal Engine Simulations • Valves • Cylinder Heads • Deforming Bodies • Large Particulate Tracking

  18. Inset Body – Applications • Multi-body simulations (Mixed or GLS) • Vehicle Drafting Studies • Multi-car simulations • Dynamic movement • Wake Interaction Studies • Fixed or dynamic (transient) • Vehicle Ride-Height Mapping • Full-matrix map • Vertical Launch Systems • Wheel Steer/Camber/Toe-In • Rapid CAD to CFD Capability • Surface Deformations • Optimization Studies / Parametric Techniques • No re-gridding Required • No Grid Movement Required • No Cell Quality Degradation; Element Crossover; Numerical Instabilities; • Rapid Solution Analysis/Convergence

  19. Grid Adaption Overview • Fixed Domain Approaches • A-Priori Grid Generation Required • Difficult to Optimize Cell Placement • Curved Shocks, Vortex Locations, Shear Layer Boundaries, Blunt Body Wakes, Wing Upwash Angles, etc… • Result • Excessive cell counts around primary flow features • Under-resolved regions of flowfield • Parametric Studies Very Difficult w/ Single Grid • Grid Resolution Studies • Required for nearly all problems • Rarely implemented in practice • Difficult, Time-consuming, Typically Neglected • Common Grid Adaption Approaches • Increase cell count around “weighting function” • Difficult determination of appropriate wf • Pressure, Entropy, Vorticity, Density, Mixed Functions, …etc • A-priori knowledge of flowfield required • CFD / Grid Adaption Specialist • Multiple Analyst / Multiple Results • Knobs/Knobs/Knobs • Inefficient for Extremely Large Problems • Serial or Parallel Inefficiencies • Non-integrated approach (start/stop solution) • Time Accuracy • Integrated Approach w/ grid speed terms, implicit formulation, and Efficient/Accurate Interpolation • Difficult to maintain conservation and accuracy

  20. Raven Domain Refinement • Raven Methodology • Unified / Generally Applicable Approach • Minimal Inputs • Final Cell Count, Minimum Cell Size, Start/Stop Iteration Counts • No Knobs (No wf specification) • Analyst Independence (Goal) • Multiple Users / Single Result • Grid Resolution Studies • Can be fully Automated • Easily Integrated into all calculations • Results Automatically Highlight Grid Dependent Results • Combined Approach • Utilizes H/P/R Refinement Techniques • Practical versus Academic Implementation • Fully Integrated, Easy of Use, Generally Applicable, Improves Analyst Independence • Inset Bodies • Automatically Refines Volume Mesh After Inset Body Insertion • Coarsening Under Development • Movement Clusters to Inset Body Surface (Minimize Cell Counts) • Follows Inset Body • Translation/Rotation • Single Starting Grid / Multiple Parametric Studies • Minimal Inputs • Characteristic Cell Size on Surface of Inset Body • No A-Priori Knowledge (i.e. refinement) of Insertion Points Required • Simplified Geometric Resolution • No Geometric Accuracy/Interface with NURBS/Surface Smoothing/Thin-baffle cross-over, etc… problems • Flowfield Feature Resolution • Subsonic, Transonic, Supersonic • Shocks, Vortices, Shear Layers

  21. Raven Domain H/P-Refinement

  22. Raven Domain H/P-Refinement

  23. Inset Body R-Refinement

  24. Inset Body – Minimize Internal Pt. Count

  25. Flowfield R/H/P Refinement

  26. Flowfield R/H/P Refinement

  27. Flowfield R/H/P Refinement

  28. Flowfield R/H/P Refinement

  29. Unified Solution Approach

  30. State of Development • PDE Modifications • N-S recast for Inset Body Approach • Updated Momentum Equations • Updated Implicit Terms • Transient Insertion of Geometry • Mixed Standard/Inset Approach • Pre-Defined User-Specified Motion • Translation/Rotation (Static + Dynamic) • Pressure Forces Interpolated To Inset Surface • Direct CAD Insertion (STL data format) • GLS Approach • Base model completed • Feature Resolution In Progress (Geometry + Flowfield) • Post-processing Development Nearing Completion • Raven Domain Feature Detection/Resolution • Inset Body (Refinement/Clustering) • Flowfield Features (shocks, vortices, separated regions, etc…) • Generalized Approach • Minimal Inputs • Unified Method • Subsonic, transonic, supersonic, Inset Body • “Analyst Independence” • Time-Accurate Grid Resolution • Inset Body w/ Movement (Propeller) • Grid Coarsening • Error Bounding Studies Underway

  31. Ongoing Development Efforts • Higher-Order Interpolation Schemes • Improved Accuracy for Inset Forces • Extend to Energy Equation • Body heating on Inset Bodies • Inset Movement Capabilities • Compound Motion • Rotation + Translation Combined • 6-DOF Model Development • Surface Deflections • GLS Approach • Fully-Automated Design Studies • Surface Deformations • NURB Mapping • Control Point Movement • User controlled or fully automated • Optimization Techniques • Fully Transient Grid Resolution • Grid Speed Terms • Re-Cast NS • Temporal Sub-Iterations • Non-Equilibrium Air • Transition (Inset + Raven Domain Refinement) from Pre-release to Production Tool • Expand Scope Testing • Documentation • Error bounding studies

  32. Conclusions • Research Phase Concluded • Efficacy/Feasibility of Methodology Proven • Generalized Development Underway • Widely Applicable Approach • Problem Scope Expanded • Reduced Analyst Time • Improved Accuracy (RDR) • 1-step Closer to Analyst Independence • Applicable to a wide range of DoD Related Problems • Funding Driven Development Efforts • Development Efforts Primarily Automotive Driven To Date • Continue Development for DoD Problems • Transition To General Release Status • Expansion of Capabilities • Funding Required for Next Phase of Development (BAA, SBIR, etc…)