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

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A typical bobsleigh race … from inside!

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

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

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

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1.Evaluate aerodynamic performances (drag and lift forces) of italian team two-man bobsleigh using numerical analysis 2.Identify and test design modifications which may improve aerodynamic performances Motivation and Objectives

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

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

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1. From real object to design: reverse engineering

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Virtual Italian 2-men bobsleigh Wings Chute PilotBrakeman Nose Bumpers

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

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1.simulate the flow around the bobsleigh 2.evaluate the forces (drag/lift) acting on the solid surface 3. Discretization for CFD analysis 1.Steady state 2.Ideal gas 3.Turbulent flow (k-epsilon model + wall treatment) TARGET: ASSUMPTIONS:

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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) Inlet Free shear/wall outlet 4. Computational domain & boundaries Straight track Bends

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5. Results: velocity field & streamlines

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From qualitative analysis of flow…

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

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World championship 07 (Cortina dAmpezzo, Italy) Need ideas to improve design? Look at competitors!

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

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Speed140 km/h draglift H=50 mm142.9320.4 H=70 mm137.7303.7 - 4%- 5% h=50 mm h=70 mm Simulation results: Higher distance smaller drag …but drag reduction is not significant!

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*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 Observation 2: bobsleights have variable nose shapes USA GERMANY ITALIA Rounded noseTriangular nose Pentagonal nose Best performing!*

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

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Italian vs German bobsleigh GERMANY ITALIA Nose shapeBumpers and wingsShell curvature & Men position

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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) Inlet Free shear/wall outlet Computational domain & boundaries Straight track GER ITA Bends

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Results: velocity field & streamlines

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

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

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Speed140 km/h draglift H=50 mm142.9320.4 H=70 mm137.7303.7 H=70 mm133.8167.7 h=50 mm h=70 mm Comparison of performances …but we know we can do better! h=70 mm

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

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… 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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