Aerodynamic resistance is a major factor in track-cycling performance, particularly at the high speeds reached in pursuit and sprint events. Most cyclist-aerodynamics studies consider straight-line motion or a uniform yaw angle, since these conditions can be reproduced relatively easily in a wind tunnel or conventional computational domain. True cornering is more difficult to investigate experimentally because the cyclist follows a curved trajectory while leaning into the bend, causing the local relative velocity to vary over the cyclist bicycle system. A standard wind-tunnel setup cannot reproduce this spatially varying flow exactly with one uniform freestream direction. As a result, the aerodynamic influence of cornering remains less well understood than straight-line and fixed-yaw conditions. This thesis therefore performs CFD simulations to study the aerodynamic wake of a track cyclist under straight-line and yawed-flow conditions, while also developing the numerical framework required to simulate cornering.

The simulations are performed with the finite-volume solver INCA using an implicit large-eddy simulation approach, a Cartesian adaptive mesh and a cut-cell immersed-boundary method. The Generic Cyclist Model is used throughout the study, allowing the straight-line simulations to be compared with available wind-tunnel Particle Image Velocimetry measurements. The numerical sensitivity to mesh resolution, wall treatment and immersed-boundary mixing is first assessed. The numerical approach is then used to investigate two fixed leg positions, a complete cyclist–bicycle configuration, and yaw angles of +6° and −6°. Finally, a constant rotating reference frame in a rectangular domain is introduced to represent cornering motion.

The straight-line simulations reproduce the main large-scale features of the measured wake. The 12 mm mesh with Werner–Wengle wall-function treatment provides the best compromise between wake resolution and computational cost for the cyclist-only cases, while changing the immersed-boundary mixing threshold has little influence on the time-averaged velocity and vorticity fields. The absolute drag forces remain strongly underestimated, showing that the present near-wall and immersed-boundary treatment is not sufficiently accurate for reliable force prediction.

Changing the fixed leg position alters both the lower-body wake and the larger wake structures behind the hips and torso. The results show that the effect of crank position extends several hundred millimetres downstream and that a more symmetric leg position does not necessarily produce a more symmetric wake. The fine full cyclist–bicycle simulation gives a more detailed representation of the lower wake and shows the influence of the bicycle frame, crankset and other components on the flow between and behind the legs. The corresponding surface results confirm that the simulation remains wall modelled, with relatively high local y+ values on exposed and separated regions.

The yawed-flow simulations show that a fixed yaw angle of 6° already causes a clear lateral displacement and reorganisation of the wake. The upper-body, hip and leg-related structures all change with yaw direction, while the asymmetric crank position causes the positive- and negative-yaw cases to respond differently rather than as exact mirror images.

For the cornering case, the required geometrical configuration was established using a rotating reference frame and a partitioned rectangular domain. However, a stable production simulation was not obtained. The treatment of the outer boundary conditions remains the main issue to address before the cornering setup can be used for aerodynamic analysis.
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This thesis project examines the drag crisis trigger mechanism for double layer fabrics on cylindrical cross-flow. The primary goal is to discover why the double layer fabric is able to trigger the drag crisis much sooner than conventional surface roughness.

The methodology employed in this research follows an experimental approach, using balance measurements to determine the aerodynamic drag at varying Reynolds numbers for different configurations. Particle Image Velocimetry (PIV) measurements are performed to examine the boundary layer, flow separation point and other flow phenomena occurring near the cylinder surface.

Over the course of this research, eight different double layer configurations have been the subject of study, as well as six single fabric configurations and two reference configurations consisting of a bare cylinder and a cylinder with zigzag trips. Balance measurements have been performed on all of the configurations to determine which configurations are deemed relevant to be studied with PIV techniques. Thus, PIV measurements have been performed on two double layer configurations with a varying underlayer and the same overlayer, as well as the study of the individual fabrics employed to make up the two-fabric construction. That is to say, the two underlayers and one overlayer used have been studied on their own.

The balance results uncover that the minimum drag coefficient across all double layer configurations is achieved with the smallest rib spacing. Conversely, this minimum drag coefficient is located at the highest critical Reynolds number across all configurations. Additionally, a relationship between the critical Reynolds number and the underlayer rib spacing has been determined for the studied configurations. Furthermore, the PIV measurements provide insight into the normalized velocity fields and reconstructed pressure fields. With these results, the development of the boundary layer on the foreside of the cylinder with double layer fabrics can be studied. Examining the flow near the surface, it can be seen that the presence of the ribs results in a localized flow convergence (upstream of the rib) and divergence (downstream of the rib), these geometric effects accelerate and decelerate the flow locally, causing static pressure oscillations on the foreside of the cylinder. With the appearance of localized adverse pressure gradients on the foreside of the cylinder, flow instabilities are seeded eventually trigger the transition of the boundary layer to a turbulent state, thus allowing the flow to remain attached to the cylinder surface for longer, ultimately delaying separation and reducing pressure drag.

While the study has provided valuable insights regarding the trigger mechanism for the drag crisis on double layer fabrics on cylinders, it has also paved the way for further research regarding this topic and the specific effects of rib height, behavior and performance in unsteady flows and whether the two fabric construction is strictly necessary. These considerations are addressed at the end of the conclusions chapter. ... Read more

This thesis presents the design and development of a new detachable shell component for Paralympic sit skiers. The research is aimed at enhancing the aerodynamics of a sitski without compromising stability, safety, or the user’s ability to control the ski. With user needs as a central focus, the design process began with an in-depth contextual and user experience analysis. This led to an extensive programme of requirements. By utilizing 3D scans of athletes in their ski, a CAD model of the shell was developed and iteratively refined using CFD simulations. 2 designs were created using CFD simulations and validated in a wind tunnel. The final shell component is 3D printed in flexible TPU for a built-in safety mechanism in the event of a crash. To validate reproducibility, the design approach was successfully applied to a second athlete. The finalised CAD models are printed for snow testing. ... Read more

Aerodynamic drag plays a critical role in high-speed sports, including running, where small performance margins can be decisive for victory in elite competitions. Despite its importance, research on running aerodynamics remains underexplored, with most studies relying on stationary mannequins or simulations that do not capture the dynamic behavior of flow around a moving runner. In other words, there is a significant research gap in experimentally visualizing the wake flow and accurately measuring the drag in real-world running scenarios. This study aims to address this research gap.

In recent years, the Ring of Fire measurement technique has emerged as a feasible option to visualise and analyse flow structures of transiting objects based on particle image velocimetry.
The technique has already been proven in sports like cycling and ice skating, but has not yet been applied to running. This study adapts the Ring of Fire measurement method for sprinting athletes, and the raw images are processed by Shake-the-Box (STB) Lagrangian Particle Tracking. This results in a three-dimensional, time-resolved velocity field in the wake of a runner with an uncertainty of less than 5\% of the runner's speed. This velocity field is used for qualitative flow visualisations, as well as for drag estimations, which are computed from a control volume approach by utilising the flow field before and after the passage of the athlete.

The experimental methodology involved nine junior athletes, wearing both standard sprint suits and aerodynamic suits, sprinting at constant speeds through a measurement setup including three high speed cameras, four LED arrays and Helium Filled Soap Bubbles (HFSB).

The results of the investigation include the visualisation of the full wake,
quantification of the velocity deficit, a qualitative vorticity analysis, some lateral velocity findings and the measured values for drag of one of the athletes.

There are multiple interesting findings about the flow around a dynamic runner in this report. One of them is the splitting of the wake into two side-by-side stream tubes in the far wake. The velocity deficit in a relevant region of the dynamic wake has also been quantified, and it is shown to vary with the inverse of the distance behind the runner, which is useful information for trailing runners.
Another interesting observation is that the vorticity field in the near wake generally follows the rules of finite cylinder flow, where the body parts of the athlete are finite cylinders with variable diameter.
The hypothesis that the flow should have a lateral oscillation related to the frequency of the runner's steps has also been confirmed.

This study demonstrates the applicability of the Ring of Fire system to running aerodynamics and offers the full visualisation of the three dimensional flow in the wake of a moving runner, bridging the research gap to pave the way for further advancements in the field. ... Read more

This thesis investigates the aerodynamics of two finite wall-mounted cylinders in tandem, focusing on drag reduction as a function of governing parameters.
For the experimental wind tunnel campaign, two measurement techniques were employed: balance measurements and stereoscopic particle image velocimetry. While balance measurements exhibited good repeatability, drag values obtained with PIV saw high uncertainty and only limited conclusions could be made from it.

Cylinders were mounted to the floor of a closed wind tunnel test section. The trailing cylinder was rigidly attached to the balance underneath, while the leading cylinder could move upstream to the de- sired distance. Stereoscopic PIV images of the wake at various distances upstream and downstream were taken through the transparent sides of the wind tunnel. These images, in combination with the control volume approach, were used to determine the drag of a trailing cylinder.

Coefficients of drag, obtained with a balance for isolated cylinders of various aspect ratios, were in line with similar results from the literature, albeit on the higher side. For cylinders in tandem of the same aspect ratio, AR, as the distance between them increased, the CD of a trailing cylinder converged to that of an isolated cylinder. Comparing tandem configurations with different AR and at the same nondi- mensionalized in-between distance, trailing cylinders with larger AR experienced larger drag reduction.

Introducing cylinder diameter ratio as an additional degree of freedom showed that smaller diameter trailing cylinders experienced greater drag reduction at close distances. However, at a certain distance further downstream, this trend reversed.

The drag reduction values obtained with PIV confirmed the findings from balance measurements. How- ever, due to the limited set of usable data, further work would need to be carried out to gain more confidence in the method. ... Read more

In cycling, the presence of drag reduction from drafting, when multiple cyclists ride in tandem, is a considerable area of performance enhancement for a cycling team and the customisation of this tandem group has the potential of maximising the drag reduction for the entire group or a specific cyclist. The flow interactions between two tandem bluff bodies is complex and incorporates several fluctuating variations in flow phenomena which have considerable effects on the drag forces experienced. An experimental campaign for tandem finite cylinders and cyclists of differing sizes and in different spacing configurations is undertaken, including a drag force measurement and PIV flow visualisation campaign. It is observed that differing magnitudes of drag reduction occur for tandem cylinders and cyclists, which are however, caused by similar variations in flow structures. The size and spacing ratios are found to have notable impact on drag reduction for tandem objects. ... Read more

The design of current skating suits is based on the assumption that the flow across the skater body parts is highly similar to cylinder flow. The latter features drag crisis behaviour, resulting in significant drag reduction at the critical Reynolds number. However, whether the aforementioned assumption is valid and whether a drag crisis along the different body parts occurs, so far remains unknown.

The goal of this study is to investigate Reynolds number effects along the leg of a skater mannequin. To do so, potential drag crisis behaviour is studied via robotic Particle Image Velocimetry and Infrared Thermography for speeds ranging between 5 m/s and 25 m/s. The boundary layer state and the critical velocity distribution along the leg, based on the wake width variation, are evaluated for the bare mannequin and the mannequin wearing a skating suit optimized for ∼ 15 m/s.

Results reveal drag crisis behaviour along the knee, lower and upper leg. Furthermore, the flow topology is not only governed by the leg geometry, but also by streamwise vortices. These streamwise vortices cause an increase of the wake width below the calf and a reduced velocity deficit behind the upper leg. Most significant differences in wake width between the bare and the dressed leg are observed at 17.5 m/s. The latter observation is also supported by the Infrared Thermography results.

It can be concluded that the flow across the leg partly differs from cylinder flow, mainly because of streamwise vortices that locally affect the drag crisis behaviour.
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The AerGo is a recreational ultralight water-aircraft, designed to be transportable by bike and operated without a license. This report outlines its concept, characteristics, and feasibility.

The AerGo features a biwing design with swept wings, closed by vertical plates at the tips. It has a constant wing chord of 0.79 m and a wingspan of 12 m. The aircraft is powered by two six-bladed propellers mounted on the top wing and driven by electric engines. The lower wing is attached to a buoyant hull, stabilized by side floats. A paddle is used for taxiing and docking on water, as the aircraft is designed exclusively for water take-off and landing. The pilot sits inside the hull and controls pitch by shifting weight on a swing. Roll control is achieved through wing warping, and yaw by rudders. The total empty mass is 44.7 kg. A multipurpose trailer system facilitates storage, transport, and deployment. The AerGo is designed for single-person assembly and operation and is safe to fly for over 270 days per year.

A market analysis of ultralight aircraft reveals a European fleet of over 25,000, with 500 in the Netherlands. While most ultralights are custom-built, successful models like the Woopyfly and Lazair have seen large-scale production. The AerGo’s mobility, ease of use, and hydrodynamic capabilities position it competitively. A conservative estimate projects annual sales of 20 units, with 25% for the Dutch market and 75% for Europe. Expansion to North America is a future opportunity.

The design is driven by weight and energy efficiency, with batteries forming a significant part of the empty weight. The primary energy requirement comes from cruise flight, optimized through airfoil selection. The NACA 6415 airfoil, chosen for its high lift coefficient at zero angle of attack, minimizes drag and maximizes cruise efficiency. The hydrodynamic model, based on DSDS data, estimates a take-off speed of 9.9 kg and a 170 m take-off distance. The computed climb rate is 1.43 m/s, reaching a cruise altitude of 150 m in 105 seconds.

The engine and battery design prioritize take-off power while ensuring a minimum flight time of 60 minutes. With a cruise speed of 15 m/s, the AerGo has a range of 40 km. The pilot’s longitudinal position, optimized at 1.6 m, ensures stability. The upper wing has a positive stagger of 0.45 m forward, creating a seesaw effect that smooths weight-shift control. Roll is controlled by wing warping, and yaw by rudders placed at the wing tips. A 15° wing sweep enhances rudder effectiveness, allowing safe operation on a single engine.

The aircraft’s lightweight structure consists of a skin-on-frame design, with a nylon-covered carbon fiber wing weighing 11.3 kg and a dacron-covered carbon fiber hull at 4 kg. Noise reduction is achieved with six-blade propellers, keeping levels below 40 dB at 100 m distance. Approximately 74% of the aircraft is recyclable, with a carbon footprint of 800 kg CO2 per unit.

At an estimated price of €20,000 per unit and annual sales of 20, the break-even point is 9.5 years, with a projected return on investment of €700,000 after 12 years. Further analysis is required on cost budgeting, structural impact resistance, and user assembly instructions to ensure feasibility.

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Aerodynamics investigations in speed sports generally consist of measurements of aerodynamic loads through wind tunnel experiments. Lately, a new technique has emerged, known as the Ring of Fire. It is the only drag measurement technique capable of retrieving flow field data on-site, by using Large-Scale PIV. In this Ring-of-Fire project a Low-Speed PIV system is implemented in an indoor facility and used to test an amateur cyclist in both pedalling and non-pedalling conditions. Twenty cyclist’s passages can be executed in thirty minutes and provide a mean drag area with an uncertainty equal to 2%. Drag differences equal to 6% are measured between two postures. Limitations arise due to the lack of repeatability of seeding density and cyclist’s position. With the contribution of this research, the Ring of Fire becomes a more mature technique to investigate speed sports aerodynamics, with future applications to curvilinear trajectories and multiple athletes.
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Laser diagnostic techniques such as Particle Image Velocimetry and Particle Tracking Velocimetry to measure the flow of a fluid around an object have been in prevalence for a few decades. Typically, the fluid, whose motion is of interest, is seeded with micron scale particles and illuminated with a laser. Due to scattering inefficiencies of these micron scale particles the maximum measurement volumes were about a few litres. Development of the neutrally buoyant sub-millimetre scale Helium-Filled Soap Bubbles allows for much larger scattering cross-sections thus enabling large-scale measurements in air (Caridi et.al. 2015).

Large scale Particle Tracking Velocimetry has been used to study the flow in the wake of a cyclist at typical time-trial speeds. A novel PTV algorithm known as Shake-The-Box (STB) (Schanz et.al. 2013) has been used to obtain the particle tracks from the images acquired in a thin volume in the cyclist’s wake using the wake-scanning method. The Lagrangian particle tracking technique was found to be more accurate than the Time Resolved Tomographic PIV through another experiment. Particularly for large field of views involving scanning at different positions, it produces whole-field results free from the boundary effects that arise between different positions of the scans. This yields accurate velocity components and their gradients that are crucial for pressure reconstruction.

Flow-field results from 4D-PTV show that the wake structure is similar to those found in the literature. Two large regions of momentum deficit are present, one behind the thighs and one near the lower legs and the wheel axis. Furthermore, they reveal the presence of some vortices which were not reported previously. Based on the observed signs of the vortices the points of origination of these vortices are identified based on separation mechanisms. There is a good agreement in the flow-field results with the literature. Pressure fields reconstructed from the velocity flow-field show low pressure pockets in the regions of the vortex cores and separated flow over the lower back.

Wake flow-field is utilised to compute the drag using the control volume approach (van Oudheusden 2007) and compared with the drag forces obtained from an external balance measurement to obtain the accuracy of large scale 4D-PTV. In total, five measurements at different velocities in the range of 13m/s to 15m/s are analysed. The accuracy of the drag estimates from 4D-PTV is obtained within 5%. Out of the three terms of the drag force, the momentum term contributes approximately 95% and the contribution from the pressure term is less than 0.3%. Rest is contributed by the Reynolds stresses in streamwise direction. Almost all the variation in the drag force comes from the momentum term. ... Read more

A novel measurement system, the Ring of Fire, is deployed which enables the aerodynamic drag estimation of transiting cyclists. The system relies upon the use of large-scale stereoscopic PIV and the conservation of momentum within a control volume in a frame of reference moving with the athlete. The rider cycles at a velocity of approximately 8 m/s, corresponding to a torso based Reynolds number of 3.17 × 10^5. The measurements upstream and approximately 1000 × 1700 m^2. The non-dimensional, phase-locked, time-averaged streamwise velocity fields compare well to literature and the time-averaged drag area shows a rather constant value along the wake with an uncertainty of 5%. A comparison with wind tunnel force balance measurements shows significant discrepancies, which may be partly attributed to the bike supports and stationary floor in the wind tunnel measurements. The 25 % drag difference measured between a rider in upright and time-trial position, instead, matches literature well. ... Read more