Air resistance

PhD candidate Luuk Hendriksen imaged the airflow around a cyclist using an advanced form of Particle Image Velocimetry (PIV). Further development of this technique is one of the ongoing activities of the Large Scale 3D PIV research group led by Professor Fulvio Scarano (Faculty of Aerospace Engineering). A mist of helium bubbles was injected into an airflow of 8 metres per second from the wind tunnel. The helium bubbles, measuring no more than 0.5 millimetres in diameter, are exactly as heavy as air and thus follow the airflow. Unlike air, however, the bubbles light up under short flashes of LED light. Seven cameras filmed the airflow around the cyclist from all sides. They were calibrated relative to each other so that the exact 3D position of each bubble could be reconstructed. The cyclist is a 3D-printed scale model (1:7) that fits the dimensions of the wind tunnel well. The measurement takes 1.6 seconds, during which period five thousand time steps are recorded. Fifteen thousand bubbles are tracked in each time step. A day’s worth of calculation was needed to reconstitute the course of each individual bubble.