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, windtunnel 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, windtunnel 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, windtunnel 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%
Wind tunnel tests 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): F D = Drag force (N) A = Frontal area (m²) C D = Drag coefficient (-) = Air density (kg/m³) U = Relative air speed (m/s)
Wind tunnel tests Results in CdA (m²):
CFD simulations: first: for the four geometries tested in the wind tunnel
Boundary conditions Uniform inlet velocity: U = 15 m/s (= 54 km/h) Uniform inlet turbulence intensity: TI = 0.2%
Computational grids
20 micrometer cells
Computational grids Total cell count: 32 x10 6-38 x10 6 y P = 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 F D = Drag force (N) A = Frontal area (m²) C D = 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.