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Aerodynamic analysis of a two-man bobsleigh

Centro Interdipartimentale di Fluidodinamica e Idraulica Università di Udine. Aerodynamic analysis of a two-man bobsleigh. A.Soldati, S. Filippi, G. Miclet, M. Campolo, M. Andreoli, G. Moretti. Sport Aerodynamics- CISM course – Udine, 3-7 September 2007.

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Aerodynamic analysis of a two-man bobsleigh

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  1. Centro Interdipartimentale di Fluidodinamica e Idraulica Università di Udine Aerodynamic analysis of a two-man bobsleigh A.Soldati, S. Filippi, G. Miclet, M. Campolo, M. Andreoli, G. Moretti Sport Aerodynamics- CISM course – Udine, 3-7 September 2007

  2. A typical bobsleigh race … from inside!

  3. Push off stretch Starting area Main track Decelerating area Finish line …the track… Torino, Italy, Cesana Pariol track, 2006 Winter Olympics Course length: 1,435 m Difference in height : 114 m Bends: 19

  4. …the importance of men & bob aerodynamics… From 0 to 40 km/h Average speed: 50-110 km/h Top speed: 140 km/h

  5. …and typical performances What can we do to go faster?

  6. Motivation and Objectives • Evaluate aerodynamic performances (drag and lift forces) of italian team two-man bobsleigh using numerical analysis • Identify and test design modifications which may improve aerodynamic performances

  7. Steps of work CFD optimization & Virtual testing Model 1, …, Model n Reverse engineering CAD model Scaled Prototype & Wind tunnel testing Meshing technique CFD model CFD solver Full scale Prototype & field testing Performance index

  8. Research cooperation Aerodynamical optimization (M.V. Salvetti, UNIPI) Wind tunnel tests (G. Gibertini, PoliMi) Technical consultancy Design Rule/Constraint (I. Ferriani, Nazionale Italiana Bob) Multidisciplinary team University of Udine Coordination (G. Miclet) Fluid dynamic analysis/optimization (A. Soldati) Technical partners Reverse engineering/Prototyping (MarMax, UD) Reverse engineering/fast prototyping (S. Filippi) RANS CFD solver (CD Adapco, TO) Carbon/Kevlar shells (CS Canoe, PN)

  9. 1. From real object to design: reverse engineering

  10. “Virtual” Italian 2-men bobsleigh Pilot Brakeman Wings Chute Nose Bumpers

  11. 2. Virtual model: check of allowed dimensions (FIBT rules) Shape optimization of shell will be constrained by external vincula!

  12. 3. Discretization for CFD analysis TARGET: • simulate the flow around the bobsleigh • evaluate the forces (drag/lift) acting on the solid surface ASSUMPTIONS: • Steady state • Ideal gas • Turbulent flow (k-epsilon model + wall treatment)

  13. 4. Computational domain & boundaries Free shear/wall outlet Simulation data • Box dimensions (4.5m x 2.5m x 1.5m) • Height from bottom: 50 mm • Air relative velocity: 39 m/s (140 Km/h) • Wall velocity: 39 m/s (140 Km/h) Straight track Inlet Bends

  14. 5. Results: velocity field & streamlines

  15. From qualitative analysis of flow…

  16. … to quantitative evaluation of forces! Pressure/shear distribution over surface  Drag: 121 N (pressure) + 21.8 N (shear) (Lift : 320.4 N) Identification of “critical” regions

  17. World championship ’07 (Cortina d’Ampezzo, Italy) Need ideas to improve design? Look at competitors!

  18. Can we exploit any ground effect to improve performances? Observation 1: bobsleights have variable distances from bottom wall USA GERMANY RUSSIA Low “h” (50 mm) High “h” (70 mm) Airfoil Bobsleight International rules: h ≤ 100 mm

  19. h=50 mm h=70 mm - 4% - 5% Simulation results: Higher distance smaller drag …but drag reduction is not significant!

  20. USA GERMANY ITALIA Observation 2: bobsleights have variable nose shapes Rounded nose Triangular nose Pentagonal nose Best performing!* *Ref.: Advanced bobsleigh design: Part 2, aerodynamic modifications to a two-man bobsleigh, by F Motallebi, P Dabnichki* and D Luck, Department of Engineering, Queen Mary, University of London, London, UK

  21. Restart from good design to make it better: evaluation of German bobsleigh Reverse engineering from sequence of photos

  22. GERMANY ITALIA Italian vs German bobsleigh Nose shape Bumpers and wings Shell curvature & Men position

  23. Simulation data Box dimensions (4.5m x 2.5m x 1.5m) Height from bottom: 70 mm Air relative velocity: 39 m/s (140 Km/h) Wall velocity: 39 m/s (140 Km/h) GER ITA Computational domain & boundaries outlet Free shear/wall Straight track Inlet Bends

  24. Results: velocity field & streamlines

  25. GER ITA Streamline comparison H=70 mm, v=140km/h

  26. … and quantitative evaluation of forces! Pressure/shear distribution over surface  Drag: 113 N (pressure) + 19.8 N (shear) (Lift : 165.7 N) Identification of “critical” regions

  27. h=50 mm h=70 mm h=70 mm Comparison of performances …but we know we can do better!

  28. … other design modifications implemented Shape of wings Chute Aerodynamic profile of shell Better shape Rounded boumpers Flat bottom Rounded boumpers

  29. … and final result! Still to be tested • in lab to confirm results of CFD simulations • in the field … to win next bob championship

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