Examining the Aerodynamic Performance of Commercial Bicycle Racing Wheels using CFD
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Examining the Aerodynamic Performance of Commercial Bicycle Racing Wheels using CFD

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Examining the Aerodynamic Performance of Commercial Bicycle Racing Wheels using CFD Examining the Aerodynamic Performance of Commercial Bicycle Racing Wheels using CFD Presentation Transcript

  • Matthew N. Godo, Ph.D.FieldView Product Manager, Intelligent LightDavid Corson,Program Manager - AcuSolve, Altair EngineeringSteve M. LegenskyGeneral Manager, Intelligent LightYves-Marie LefebvreSales & Support Engineer, Intelligent LightExamining the Aerodynamic Performance ofCommercial Bicycle Racing Wheels using CFD
  • Intelligent Light• Established in 1984 27 years in July 2011! Global Customer Base• Two components to our business: – FieldView Software – Applied Research Group • Customer-driven R&D • CFD & Post-processing Research • CFD for Wind Energy
  • Our MissionTo help our customers using CFD to do more with less and make better decisionsHow we accomplish our mission:• CFD post-processing products & methods• Workflow automation• Development of new CFD methodologies
  • The Right Wheel?
  • Background• Wind Tunnel testing used extensively in cycling for over 20 years – Typical for Zipp, 85h at $850/h, run 3 or 4 times per year• Benefits to cyclists from Wind Tunnels Advertisement ca – Improved rider positioning for lower drag 2007 – Significant performance improvements in equipment design• Current status – Still considerable component variations – UCI rule changes & enforcement can be rapid & unpredictable – Wind Tunnel reaching its limit today – Interpretation of results ‘controversial’ Zinn, L., “Spoked aero’ wheels catching up with discs”, Inside Triathlon, 1995, 10(4), p 36-37
  • How much does it matter? Tour de France 2008 Stage 20 Individual Time Trial 1 2 3.0% 3From Greenwell et.al. 4 5 Wheel drag is responsible for 10% to 6 Finish Position 7 8 15% of total aerodynamic drag 9 10  Rider makes up the drag majority 11 12 Improvements in wheel design can 13 14 reduce drag between wheels by as 15 0 1 2 3 4 5 Percentage Time Difference IronManTM Lake Placid Triathlon 2008 much as 25% Q 1 Male 45-49 Age Group Q 2 3.3% Overall reduction in drag can be on Q 3 Q 4 Q 5 the order of 2% to 3% 6 Finish Position 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 Percentage Time Difference
  • Boundary Conditions inner wheel (incl. spokes)hub mesh for inner wheel is created separately Realistic spoke rotation outer wheel (incl. tire) non-conformal interface Mesh Displacement (unsteady) Moving Reference Frame ground plane
  • Boundary Conditions Surrounding head tube domain top tube down tubeground planeground plane  Ground plane  no-slip surface  translational speed of 20 or 30mph yaw angle  Far Field  uniform velocity profile  yaw angles from 0o to 20o  Fork, frame, caliper, brake pads  no slip surface  zero relative velocity
  • Postprocessing ObjectivesPerformance Metrics Top View Turning Moment• Resolved Forces Wind Velocity (effective)• Turning Moments Axial Drag Force• Aerodynamic Torque Bike Velocity (relative) Side (Lift) Force = ∙ 0 Side View Vertical Force• Power to Overcome Aero Resistance Wind Velocity (effective) P = + ℎ Requirements Axial Drag Force• Quantitative & Qualitative Direction of Wheel Rotation• Easily automated & scalable• Batch compatible on remote clusters
  • CFD Results vs Wind Tunnel Data
  • Circumferential Variation, Side Force Direction of Flow
  • Turning Moments, All Wheels Turning Moment vs. Yaw Angle at 20mph Turning Moment vs. Yaw Angle at 30mph 1 0.2 0.4 2Moment [N·m] Moment [N·m] 0 0 0 0 -0.2 Rolf Sestriere -2 Rolf Sestriere Zipp 404 -1 Zipp 404 Zipp 808 -0.4 Zipp 808 Zipp 1080 Zipp 1080 HED TriSpoke HED TriSpoke Zipp Sub9 Disc Zipp Sub9 Disc (right axis) (right axis) -0.4 -4 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 Yaw Angle [degrees] Yaw Angle [degrees]
  • Wheel Only Studies Rolf Sestriere Zipp 404 Zipp 808• Configurations: 6• Speeds : 1 – 20mph• Yaw Angles: 1 – 10o• Design Points: 6• Time steps: 256 – For each design point• Total steps: 1536• ~1.2TB of data Zipp 1080 HED TriSpoke Zipp Sub9 – ~200GB per wheel Streaklines revealed strong periodic shedding, distinctive for each wheel studied
  • Strouhal No., All Wheels (20mph, 10 degrees yaw) 6.0Strouhal No. 5.0 3.0 2.0 1.0 Strouhal range obtained from resolved drag, side, vertical forces and moments
  • Expanding the Scope…• Configurations: 9 Zipp 404 Zipp 1080 HED TriSpoke• Speeds : 2 Wheel only – 20mph, 30mph• Yaw Angles: 5 – 0o, 5o, 10o, 15o, 20o• Design Points: 90 Reynolds Carbon• Time steps: 256 – For each design point• Total steps: 23040• Numbers of merit (for each step) Blackwell Bandit – Drag & Side Force – Turning Moment – Aerodynamic Torque – Total Power
  • Solver & CoprocessingAcuSolveTM Based on stabilized Galerkin/Least Squares Volume Mesh Second order accuracy  Time and space Equal order interpolation for all variables Globally & locally conservative Fully coupled pressure/ Parallel AcuSolve velocity iterative solver Processes Fully parallelized for Prism layers shared mem & clusters Socket Communication FieldView UNS file mini-grids User Requests Python (variables, elements, etc.) Script
  • Batch Postprocessing Workflow cluster or cloud system forces forces forces mini- grids Batch XDB XDBSolver Batch Postprocessing Parallel, 54 cores  FVXTM scripts used for all 4-6h elapsed per design performance metrics point  Concurrent, typically 40 Only mini-grids saved jobs in queue  Less than 1h per job
  • Batch Postprocessing Workflow cluster or cloud system Solver runs Batch XDB FTP XDBSolver Batch Postprocessing XDB Data Reduction Parallel, 54 cores  FVXTM scripts used for all  46X smaller files 4-6h elapsed per design performance metrics  Full numerical fidelity point  Concurrent, typically 40  FTP to local desktops for Only mini-grids saved jobs in queue interactive postprocessing  Less than 1h per job
  • Power vs Time vs Yaw Angle TriSpoke
  • Industrial Relevance “For Zipp, working with Matt on this paper [AIAA-2010- 1431] was largely what spurred the Firecrest rim shape development on the handling side. Before this, we had some super fast shape concepts, but realized from the data that there was just so much more to be done on the handling side, that we spent a few extra months in development chasing favorable handling characteristics (rearward center of pressure and shedding behavior). Ultimately we still cant replace the wind tunnel with CFD, but the ability to understand and predict so many aspects of performance and handling is pretty awesome! And thats just the beginning...” Zipp 404 Firecrestcross section profile Josh Poertner, Category Manager, Zipp Speed Weaponry, Indiana