Welke daalhouding is het meest aerodynamisch?

Transcription

1 Welke daalhouding is het meest aerodynamisch? Bert Blocken a,b a Faculteit Bouwkunde, Technische Universiteit Eindhoven, Nederland b Departement Burgerlijke Bouwkunde, KU Leuven, België

2 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

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4 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?

5 Why. this study? Tour de France, Edition 2016, Stage 8, Descent of the Peyresourde

6 Why. this study? Tour de France, Edition 2016, Stage 8, Descent of the Peyresourde

7 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.

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9 Different hill descent positions Different professional cyclists use very different hill descent positions.

10 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.

11 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.

12 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.

13 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.

14 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.

15 Wind tunnel tests 4 models, scale: ¼

16 Wind tunnel tests

17 Wind tunnel tests

18 Wind tunnel tests

19 Wind tunnel tests

20 Wind tunnel tests

21 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%

22 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%

23 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

24 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)

25 Wind tunnel tests Results in CdA (m²):

26 CFD simulations: first: for the four geometries tested in the wind tunnel

27 Boundary conditions Uniform inlet velocity: U = 15 m/s (= 54 km/h) Uniform inlet turbulence intensity: TI = 0.2%

28 Computational grids

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30 20 micrometer cells

31 Computational grids Total cell count: 32 x x10 6 y P = 20 μm (micrometer) y* 1 Prismatic cells near walls Cell size away from surfaces: tetrahedral cells

32 CFD simulations: results

33 CFD simulations: results

34 CFD simulations: results

35 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)

36 Results in terms of drag area

37 CFD simulations: More geometries

38 CFD simulations: More geometries

39 CFD simulations: More geometries

40 CFD simulations: More geometries

41 CFD simulations: More geometries

42 CFD simulations: More geometries

43 CFD simulations: More geometries

44 CFD simulations: Overall ranking regular road race

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56 CFD simulations: Overall ranking individual time trial

57 CFD simulations: Overall ranking individual time trial

58 CFD simulations: Overall ranking individual time trial

59 CFD simulations: Overall ranking individual time trial

60 CFD simulations: time differences For a descent of D = 5 km with an average speed of 72 km/h (= 20 m/s)

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62 Linked In post:

63 Which position is most aerodynamic? A B C D E C

64 Which position is most aerodynamic? A B C D E C

65 D E C

66 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.

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