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