The importance of aerodynamic efficiency in the cycling sport is well known. Simple calculations demonstrate the considerable impact of just a few percentages in drag savings on the outcome of a competition where the margins can be incredibly small. Achieving a drag reduction can, however, be challenging as the flow topology of a cyclist is extremely complex. Nonetheless, the manipulation of flow structures in other research areas is proven to be an effective method for reducing aerodynamic resistance. Hence, the potential of achieving a drag reduction for a cyclist in a time trial position through the manipulation of the 3D flow topology is investigated.

Two devices are introduced named the Hip Vortex Control (HVC) and wingsuit aiming to reduce the streamwise vorticity at the hips and upper arms respectively. A reduction of a crosswind-dependent weighted drag area of -1.35% for the HVC and -5.45% for the wingsuit is measured experimentally. Computational Fluid Dynamics (CFD) simulations and robotic volumetric Particle Tracking Velocimetry (PTV) provide the trends in the drag-reducing mechanisms. The HVC promotes separation on the lower back of the cyclist, reducing the presence of the hip vortices leading to an increase of the pressure on the lower back. The wingsuit limits the formation of the streamwise vortices around the upper arms, slightly increasing the wake and increasing the pressure on the upper arms resulting in the drag reduction.

The numerical and experimental results largely agree on the variations in the flow topology for each configuration. The results indicate that a reduction in streamwise vorticity in the wake of a bluff body can reduce the drag considerably. Both devices lead to an expansion of the wake which should be kept to a minimum to effectively reduce the drag. The results motivate the continuation of the research into the reduction of streamwise vortices in the development of cycling equipment and in other high-velocity sports.

Major delivery companies such as DHL, UPS or Amazon have been developing small drones to deliver packages. This alternative to truck delivery is expected to start operating in the near future. The advantages of it are its speed, price, safety and sustainability: parcels would not be subjected to traffic and they would be delivered within an hour, it is 10% less expensive and it means a 73% reduction in CO2 emissions when compared to truck delivery, as well as a relieve in the road traffic network. The only drawback is that the noise produced by current drones is deemed by humans as more annoying than car noise due to its high frequency. The mission of the Silent Delivery Drone project is to provide a drone delivery system that is faster, less expensive and has lower emissions than truck delivery while complying with Dutch noise regulations. The presented innovative configuration is a combination of a quadcopter, suitable for Vertically Taking-Off and Landing (VTOL) in densely populated regions, and a flying wing, optimized for the cruise phase. It consists of a horizontal propeller used during cruise and four vertical propellers for VTOL. The drone can carry a payload of up to 2.5 kg, which corresponds to 89% of the packages delivered yearly worldwide. Four packages can be delivered while flying the maximum range of 30 km. Thanks to the low required revolutions per minute, the absolute maximum noise caused by the drone is 58 dBA at take-off from 7.5 m and 25 dBA during cruise from a distance of 120 m. This meets the Dutch night noise regulations which stablish a peak noise level of 65 dBA and average noise level of 40 dBA. We believe that a fleet of Silentium drones would revolutionize the way we perceive package delivery and it would mark the next step towards a greener, smarter and more connected future.