Lars Morten Bardal

Aerodynamical Resistance in Cycling on a Single Rider and on Two Drafting Riders: CFD Simulations, Validation and Comparison with Wind Tunnel Tests

The present work intends to validate computational fluid dynamics (CFD) simulations to subsonic wind tunnel experiments. The models tested in the wind tunnel at NTNU (a mannequin and real cyclist in static position) were scanned using a 3D scanner consisting 48 single-lens reflex cameras surrounding the object in three heights (low/ground-midi-above). The simulations were obtained using the Unsteady Reynolds Averaged Navier-Stokes solver STARCCM+ from CD-Adapco. A hybrid meshing technique was used in order to discretize both surface and volume. Polyhedral cells were used on the model surface and in the near volume while a structured grid was used in the rest of the domain. An unsteady RANS approach was used and the turbulence was modeled using the Menter implementation of the k-ω model. The boundary layer was fully resolved and no wall functions were used and. The first part of the paper aims to validate the numerical model. In the second part CFD simulations were used to analyse the aerodynamic properties of two drafting cyclists varying the distance between them from 1 to 4 m with 1 m increments. A good overall agreement between the simulations and the experiments was found proving the value of CFD as a complementary tool to conventional wind tunnel testing.

Aerodynamical Resistance in Cycling - CFD Simulations and Comparison with Experiments

The present work shows a comparison between computational fluid dynamics (CFD) simulations obtained using the Unsteady Reynolds Averaged Navier-Stokes solver STARCCM+ from CD-Adapco and experiments carried out in the subsonic wind tunnel at NTNU. The models tested in the wind tunnel (a mannequin and real cyclist in static position) were 3D scanned using a 3D scanner, consisting 48 single-lens reflex cameras surrounding the object in three heights (low/ground-midi-above). A hybrid meshing technique was used in order to discretize the surface and the volume. Polyhedral cells were used on the model surface and in the near volume while a structured grid was used in the rest of the domain. An unsdeady RANS approach was used and the turbulence was modelled using the Menter implementation of the k-ω model. No wall functions were used and the boundary layer was fully resolved. The first part of the paper focuses on the mannequin while in the second part the comparison between the experimental results and simulation on the real cyclist are presented. An overall good agreement between the simulations and the experiments was found proving that CFD could be a complementary tool to wind tunnel testing.

Low Aerodynamic Drag Suit for Cycling - Design and Testing

The focus on garment aerodynamics is increasing in high velocity sports where aerodynamics is crucial such as cycling, speed skating and alpine skiing. Recently published research show that a low drag suit manipulating the flow around the body can considerably enhance an athlete’s performance. This project seeks to improve the Norwegian sportswear manufacturer Trimtex Sport AS’ pro cycling kit using the best currently available textiles. Changes from the original design are made with the intention of optimizing fabric zones and seam placement. Drag measurements on cylinder models, cyclists and full-scale mannequins of the upper and lower body were conducted in the wind tunnel. The reduction in aerodynamic drag was significant on cylinders, and final power savings of 8 watts due to drag reductions was obtained on the jersey and 5 watts on the bib shorts for a cyclist racing at 50 km/h.

Individual Performance Optimization of Elite Cyclists

The present work focuses on individual posture optimization with the aim to individually reduce the drag and increase the power output on six elite cylists. In order to be able to quantify the changes in drag, power output and VO2max, wind tunnel tests combined with power output and oxygen intake measurements were carried out on each of the athletes tested. Drag measurements were performed in the large scale wind tunnel at NTNU at a constant wind speed of 14.2m/s using a AMTI high frequency force plate. Simultaneously with the drag measurements, the volume of oxygen intake and the power output generated by the athletes during the test in different positions were acquired respectively with a Metamax II portable analyzer from Cortex Biophysic and a Tacx Bushido cycling rig. The main results show that lowering the handlebar while raising the seat in order to obtain a smaller frontal area and a straighter back, lowers the aerodynamic drag but will possibly affect the volume of oxygen intake. The handlebar repositioning leaded to similar results and it might then be questionable whether it is worth reducing the air resistance if the athlete does not sit as comfortably. In most cases a lower handlebar positioning and a narrower set up of the handlebar resulted in a considerable drag reduction without compromising the volume of oxygen intake. Being the present work a preliminary test, no statistical results are presented but as an overall conclusion, it can be pointed out the need to couple drag force measurements with oxygen intake and power production measurements in order to have a clearer picture of the effectiveness of the wind tunnel testing.