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A large-eddy simulation/immersed boundary method for particulate flows in an Eulerian framework is utilized to investigate short-term particle re-suspension due to human motion. The simulations involve a human walking through a room, stopping, and then walking in place, causing particles to be re-suspended from a carpet. The carpet layer is modeled as the porous medium and a classical adhesive force model is applied to model the resistance of the carpet-bound material to hydrodynamic forcing. The effects of parameters such as the foot penetration depth and adhesive force coefficient on mass re-suspended during the foot stamping events are examined. Simulations of particulate re-suspension experiments conducted in a room within a U.S. Environmental Protection Agency test house are also described. The simulations vary the type of human motion (stamping in place versus stamping in place with rotation). The results indicate that significant amounts of particulate material are re-suspended from the carpet layer due to the impingement of the feet during the motion event. The net mass re-suspended for human motion with rotation is two times greater than that for the motion without rotation, while the mass of re-suspended small particles is slightly greater than that of large particles. The re-suspension rates are estimated based on several time scales, and the predicted total particle number concentrations at several locations in the room show good agreement with experimental data. The present CFD model can be utilized to predict particle re-suspension rates as induced by human motion, but further work in modeling the fine-scale details of the re-suspension process is needed.

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This study describes how computational fluid dynamics (CFD) has been used to design the directional stability components as well as the identifying the proper placement and orientation of the canard and strut to achieve the desired down force and stability of the American Challenger racecar. Under development by Bill Fredrick, the missile-shaped, rocket-powered car is intended to break the World Land Speed Record, achieving a top speed greater than 800 mph. Designing a transonic car presents many unique challenges that are almost never encountered by land vehicles or aircraft. The CFD++ flow solver has the necessary attributes to handle ground effects at transonic speeds. CFD++ is also used in the selection of a rear strut profile and the positioning of the canard to achieve the desired pitching characteristics and aerodynamic loading. Following completion of these phases, the directional stability was examined at several sideslip angles and through a large range of speeds. While directional stability is easily achieved at low to mid-subsonic speeds, the changes in flow characteristics as the vehicle transitions to transonic speeds can yield drastic changes in surface force distribution. Conversely, design modifications that improve performance in the transonic regime can compromise stability at lower speeds. The current study also focuses on the process of designing and positioning the vertical tail to achieve adequate vehicle stability throughout the drive envelope. The use of CFD++ simulations with both propulsion on and off have helped to ensure that the vehicle will have the desired dynamic characteristics at all phases of the record breaking attempts: acceleration, record phase, and deceleration to full stop.

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