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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
A typical bobsleigh race … from inside!
…the track…
Torino, Italy, Cesana Pariol track, 2006 Winter Olympics
Course length: 1,435 mDifference in height : 114 mBends: 19
Push off stretch
Starting area
Main track
Decelerating area
Finish line
…the importance of men & bob aerodynamics…
From 0 to 40 km/h Average speed: 50-110 km/h
Top speed: 140 km/h
…and typical performances
What can we do to go faster?
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
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
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)
1. From real object to design: reverse engineering
“Virtual” Italian 2-men bobsleigh
Wings
Chute
Pilot Brakeman
Nose
Bumpers
2. Virtual model: check of allowed dimensions (FIBT rules)
Shape optimization of shell will be constrained by external vincula!
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:
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
5. Results: velocity field & streamlines
From qualitative analysis of flow…
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
World championship ’07 (Cortina d’Ampezzo, Italy)
Need ideas to improve design? Look at competitors!
Can we exploit any ground effect to improve performances?
High “h” (70 mm)
USA GERMANY RUSSIA
AirfoilBobsleight International rules:
h ≤ 100 mm
Observation 1: bobsleights have variable distances from bottom wall
Low “h” (50 mm)
Speed 140 km/h
drag lift
H=50 mm 142.9 320.4
H=70 mm 137.7 303.7
- 4% - 5%
h=50 mm
h=70 mm
Simulation results: Higher distance smaller drag
…but drag reduction is not significant!
*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
USAGERMANYITALIA
Rounded nose
Triangular nose
Pentagonal nose
Best performing!*
Restart from good design to make it better:evaluation of German bobsleigh
Reverse engineering from sequence of photos
Italian vs German bobsleigh
GERMANY
ITALIA
Nose shape Bumpers and wings Shell curvature & Men position
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
Results: velocity field & streamlines
H=70 mm, v=140km/h
Streamline comparisonG
ER
ITA
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
Speed 140 km/h
drag lift
H=50 mm 142.9 320.4
H=70 mm 137.7 303.7
H=70 mm 133.8 167.7
h=50 mm
h=70 mm
Comparison of performances
…but we know we can do better!
h=70 mm
Aerodynamic profile of shell
Rounded boumpers
Flat bottom
Better shape
Shape of wings
Chute
… other design modifications implemented
Rounded boumpers
… and final result!
Still to be tested • in lab to confirm
results of CFD simulations
• in the field … to win next bob championship