aerodynamic analysis of a two-man bobsleigh centro interdipartimentale di fluidodinamica e idraulica...
TRANSCRIPT
![Page 1: Aerodynamic analysis of a two-man bobsleigh Centro Interdipartimentale di Fluidodinamica e Idraulica Università di Udine Sport Aerodynamics- CISM course](https://reader038.vdocument.in/reader038/viewer/2022103015/5519a85b550346ce608b478d/html5/thumbnails/1.jpg)
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 mDifference in height : 114 mBends: 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
Pilot Brakeman
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 d’Ampezzo, 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 GERMANY RUSSIA
AirfoilBobsleight International rules:
h ≤ 100 mm
Observation 1: bobsleights have variable distances from bottom wall
Low “h” (50 mm)
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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!
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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
USAGERMANYITALIA
Rounded nose
Triangular 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 shape Bumpers and wings Shell 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 comparisonG
ER
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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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
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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