Non-intrusive aerodynamic load estimation is attractive for applications where force balances or pressure instrumentation are impractical, such as the aerodynamic testing of transiting athletes and other full-scale objects.
This thesis investigates whether volumetric particle tracking velocimetry can reconstruct the drag of a freely falling sphere using wake-rake and full control-volume formulations. Spheres of 15 and 25 cm diameter were repeatedly released through a seeded measurement volume of approximately 750 × 750 × 750 mm^3. Tracer-particle motion was recorded by six high-speed cameras and reconstructed using object-aware Shake-The-Box particle tracking.
Measurements from repeated releases were transformed into a sphere-fixed reference frame and ensemble-averaged.
Independent wind-tunnel load-cell measurements provided reference drag coefficients. The reconstructed velocity fields capture the expected bluff-body wake structure, but pressure reconstruction is more demanding.
Two ensemble strategies were compared. In the first, one frame per release was selected at a comparable sphere velocity, producing dynamically similar samples but limited particle support. These velocity-matched datasets required bin sizes of order 0.6D, which is too coarse to resolve the near-wake pressure gradients.
In the second, multiple frames per release were normalised by the instantaneous sphere velocity and combined, increasing particle support and allowing bin sizes of 0.23D–0.24D, close to the sphere-pressure criterion Δb < 0.25D.
This improved the pressure reconstruction but introduced a non-physical downstream decay of the momentum contribution due to velocity-dependent sampling bias.
For the matched-frame 15 cm sphere case, the wake-rake formulation gives the most robust drag reconstruction. Once the downstream integration plane is placed outside the near wake, around y/D ≳ 2, and the lateral integration width is at least approximately ±1.5D, the reconstructed drag coefficient reaches the closest agreement with the wind-tunnel reference. Near-wake planes remain unreliable because pressure and momentum contributions vary rapidly inside and close to the recirculation region.
The full control-volume formulation is highly sensitive to residual mass-flow imbalance. Without mass-conservation correction, small non-cancelling velocity errors over the control-volume faces lead to substantial drag underprediction. The correction reduces this sensitivity and shifts the reconstructed drag towards the reference value but is reliable only for wide control volumes where lateral-face contributions have nearly vanished. In this regime, the full control-volume result effectively reduces to a wake-rake estimate. The study concludes that drag
reconstruction from volumetric PTV measurements of a transiting sphere is feasible using a properly placed wake-rake formulation, but that the full control-volume method does not provide a practical accuracy advantage under
the present experimental conditions. Successful application of the full control-volume method requires a dynamically repeatable experiment with lower mass-flow imbalance, finer spatial resolution, and retained-particle densities
above the lower-bound estimate n_min D^3≈ 2.6×10^3, with additional margin required for outlier rejection, nonuniform seeding and object shadowing. ... Read more

The drone market has been steadily growing over the last decades, resulting in drones becoming more and more common 1. For the majority of the time, the drones provide valuable services, from inspection work and deliveries to applications in emergencies, such as search and rescue, or rapid deliveries of medical supplies. Unfortunately, because drones are available to everyone, misuse cannot be fully prevented. They can cause significant disruptions to aviation, violate privacy, or transport illegal substances, leading to financial losses, or more serious consequences. A notable incident, that caused the delay of close to 1,000 flights affecting approximately 140,000 passengers, took place in 2018 at London Gatwick Airport, where 2 drones caused the airport to shut down for over 24 hours [1]. Additionally, it has been reported by Dubai International Airport, that the estimated costs of halting airport operations due to drones resulted in losses of close to $100,000 per minute of downtime2. To counteract these hazardous situations, current anti-drone methods on the market include drone guns, quadcopters using catching systems, and radio frequency jamming systems. However, all of these methods come with their disadvantages. They either involve human interaction, have high operational costs, or cannot intercept quickly over a large area, leaving a large gap in the market for an efficient anti-drone system. The Air-Guard drone introduced in this report aims to fill this market gap, by providing a quick response time to a threat, while not compromising on neutralizing capabilities. It is a fixed-wing drone capable of autonomous visual tracking and catching unlicensed drones via a shooting net mechanism integrated with a parachute. Compared to multi-rotor drones, the Air-Guard drone concept has a longer range and higher efficiency, allowing it to be readily in the air until an unlicensed drone is detected. This is achieved thanks to its unique design inspired by bird morphology. Birds can actively morph their wings and tail surfaces to actively alter their aspect ratio, wing loading, and stability to achieve the most efficient flight configuration over a wide variety of flight profiles. Similarly, the Air-Guard drone morphs its wing and tail such that the drone can be stable while loitering, to then transition into high-g maneuvers in under a second. This allows the drone to more closely follow unlicensed drones in restricted areas and immobilize these drones in a matter of minutes autonomously. The morphing concept of the drone uses multiple actuators and elastic tendons in combination with specially designed artificial feathers to emulate bird morphology. The design also considers previously neglected areas of bird wing anatomy and incorporates bioinspired aerodynamic surfaces to delay stall and increase the maneuverability of the drone. This report is a follow-up of the midterm report, where the general configuration of the drone was set up. It aims to describe the progress on the Air-Guard project, mostly from a technical point of view, but also economic and operational aspects are covered. The UAV design is multidisciplinary and is influenced by many disciplines related to aerospace engineering. Aerodynamics, performance, structures, stability, control, and electronics considerations were combined to make the design possible. It was an iterative process, requiring careful coordination and communication between all the different departments. The result of this work translates into the design of a dual engine, 3.5 kg drone that is capable of loitering for an hour, with a maximum speed of 48 m/s. The wing span in extended configuration is 1.34 m, with a total length of 1.05 m. To neutralize the threat, the Air-Guard chases the unlicensed drone with the help of its high maneuver ability, then fires a net equipped with a parachute from the nose to capture it. The materials used are balsa wood for the fuselage and fixed-wing, while the morphing surfaces are made of aluminum and 3D-printable Celanese VECTRA A950LCP. A great emphasis was put on the sustainability aspect of the drone, which lead to an electrically powered UAV, having a structure that is 99% recyclable. ... Read more