No abstract

Infrared thermography, force measurements, and oil flow visualizations are used to investigate the flow patterns around a cambered NACA16-409 airfoil at low Mach number. This cambered profile is widely used for propellers despite the lack of knowledge concerning its flow characteristics. The post-processing of thermograms relies on the analysis of the surface temperature gradient and identification of inflexion points in the temperature distribution. The observations made on the thermograms, based on the distribution of the temperature and Stanton number, are substantiated by the oil flow visualizations. RANS simulations with a transitional SST k-ω & γ turbulence model corroborate the analysis and deliver detailed insight in the flow around the airfoil. Depending on the angle of attack, three distinct flow patterns have been identified: laminar flow with early separation, laminar separation bubble with trailing edge separation, and turbulent flow with trailing edge separation. The shift between the last two regimes occurs sharply. The prediction capability of the transitional RANS simulations and XFOIL in terms of separation as well as reattachment location are compared with the experimental results. The force-coefficients dependency on the angle-of-attack, obtained by experiments, XFOIL, and RANS simulations, bear the traces from these flow patterns.

Human-walking-induced particle resuspension in indoor environments is believed to be an important source of particulate matter. Aerodynamic disturbance generated by the human foot during a gait cycle are the main driver for particle detachment and dispersion in the room. In this work, the hot-wire anemometry technique was employed to investigate the airflow generated by one phase of the human gait cycle: the foot tapping. This phase was simulated by a mechanical simulator that consists of a wooden rectangular 25 × 8 × 1.2 cm plate, and a servomotor that allows downward and upward rotations of the plate with a constant velocity. A correction procedure based on the hot-wire velocity measurements and the analytical solution of Falkner–Skan has been derived to correct the hot-wire readings in the near-wall region. Results show a sharp increase of airflow velocity in front of the simulator after the simulator rotation. Transverse hot-wire measurements downstream of the simulator show that the profile of the maximal velocities reaches a peak at a distance y = 8 × 10−3 m from the wall. The expulsed air from the volume under the simulator propagates downstream from the foot to reach near zero velocity values at 0.15 m away from the top of the simulator.