welke daalhouding is het meest aerodynamisch? - kivi · 2017-10-10 · welke daalhouding is het...
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Welke daalhouding is het meest aerodynamisch? Bert Blocken a,b
a Faculteit Bouwkunde, Technische Universiteit Eindhoven, Nederland b Departement Burgerlijke Bouwkunde, KU Leuven, België
Welke daalhouding is het meest aerodynamisch?
Bert Blocken a,b, Thijs van Druenen a, Yasin Toparlar a, Thomas Andrianne c, Thierry Marchal d
a Department of the Built Environment, Eindhoven University of Technology, The Netherlands b Department of Civil Engineering, KU Leuven, Belgium
c Department of Aerospace and Mechanical Engineering, University of Liège, Belgium d ANSYS International
Different professional cyclists use very different hill descent positions
indicating there is no consensus on which is best. Which hill descent
position is most aerodynamic?
. Why this study?
• Tour de France, Edition 2016, Stage 8, Descent of the Peyresourde
. Why this study?
• Tour de France, Edition 2016, Stage 8, Descent of the Peyresourde
. Why this study?
• Tour de France, Edition 2016, Stage 8, Descent of the Peyresourde
• Top cyclist Chris Froome (team Sky) assumed a very particular position, won the
race, and took the prestigious yellow jersey.
Different hill descent positions
• Different professional cyclists use very different hill descent positions.
Different hill descent positions
• Different professional cyclists use very different hill descent positions.
• There is at present (2017) no consensus in the peloton on which position is really
superior.
Different hill descent positions
• Different professional cyclists use very different hill descent positions.
• There is at present (2017) no consensus in the peloton on which position is really
superior.
• Most cyclists did not test many different positions, for example in wind tunnels, to find
which position would give them the largest advantage.
Different hill descent positions
• Different professional cyclists use very different hill descent positions.
• There is at present (2017) no consensus in the peloton on which position is really
superior.
• Most cyclists did not test many different positions, for example in wind tunnels, to find
which position would give them the largest advantage.
• This project: two different and independently applied research methods, wind-
tunnel testing and CFD simulations, to investigate which cyclist hill descent position is
aerodynamically superior.
Different hill descent positions
• Different professional cyclists use very different hill descent positions.
• There is at present (2017) no consensus in the peloton on which position is really
superior.
• Most cyclists did not test many different positions, for example in wind tunnels, to find
which position would give them the largest advantage.
• This project: two different and independently applied research methods, wind-
tunnel testing and CFD simulations, to investigate which cyclist hill descent position is
aerodynamically superior.
• Comments on safety and power generation.
Different hill descent positions
• Different professional cyclists use very different hill descent positions.
• There is at present (2017) no consensus in the peloton on which position is really
superior.
• Most cyclists did not test many different positions, for example in wind tunnels, to find
which position would give them the largest advantage.
• This project: two different and independently applied research methods, wind-
tunnel testing and CFD simulations, to investigate which cyclist hill descent position is
aerodynamically superior.
• Comments on safety and power generation.
• Some of the results are counter-intuitive.
Wind tunnel tests
• 4 models, scale: ¼
Wind tunnel tests
Wind tunnel tests
Wind tunnel tests
Wind tunnel tests
Wind tunnel tests
Wind tunnel tests
• 4 models, scale: ¼ • Cyclist model on force balance • Wind speed U = 54 km/h x 4 = 216 km/h, turbulence intensity TI = 0.2%
Wind tunnel tests
• 4 models, scale: ¼ • Cyclist model on force balance • Wind speed U = 54 km/h x 4 = 216 km/h, turbulence intensity TI = 0.2%
• Dimensions in mm • Elevated platform to reduce boundary layer height • Cyclist full-scale height and weight: 189 cm & 84 kg • Blockage ratio < 3 % but corrections needed • Wheels fixed • Boundary-layer height (model-scale): 6 cm
Wind tunnel tests
• Results in CdA (m²):
Wind tunnel tests
FD = Drag force (N)
A = Frontal area (m²)
CD = Drag coefficient (-)
= Air density (kg/m³)
U = Relative air speed (m/s)
• Results in CdA (m²):
Wind tunnel tests
CFD simulations: first: for the four geometries tested in the wind tunnel
• Uniform inlet velocity: U = 15 m/s (= 54 km/h) • Uniform inlet turbulence intensity: TI = 0.2%
Boundary conditions
Computational grids
20 micrometer cells
Computational grids
• Total cell count: 32 x106 - 38 x106 • yP = 20 μm (micrometer)
y* 1 • Prismatic cells near walls • Cell size away from surfaces: tetrahedral cells
CFD simulations: results
CFD simulations: results
CFD simulations: results
Results in terms of drag area
FD = Drag force (N)
A = Frontal area (m²)
CD = Drag coefficient (-)
= Air density (kg/m³)
U = Relative air speed (m/s)
Results in terms of drag area
CFD simulations: More geometries
CFD simulations: More geometries
CFD simulations: More geometries
CFD simulations: More geometries
CFD simulations: More geometries
CFD simulations: More geometries
CFD simulations: More geometries
CFD simulations: Overall ranking – regular road race
CFD simulations: Overall ranking – individual time trial
CFD simulations: Overall ranking – individual time trial
CFD simulations: Overall ranking – individual time trial
CFD simulations: Overall ranking – individual time trial
CFD simulations: time differences
For a descent of D = 5 km with an average speed of 72 km/h (= 20 m/s)
Linked In post:
Which position is most aerodynamic?
A B C
D E C
Which position is most aerodynamic?
A B C
D E C
D E C
• Aerodynamic drag can be analyzed with wind-tunnel tests and CFD simulations
• Large differences in aerodynamic drag between different positions.
• Infamous “Froome position” of the Tour 2016 is not faster, not safer and does not allow more power generation than other positions.