| This research was aimed at determining if unsteady aerodynamic forces exist around an Ahmed body, a model used to represent a road vehicle body. After their detection, the objective was to determine which type of forces were present and if the unsteady forces were due to an instability in the wake or if they were motion induced forces.;To achieve these objectives; tests were performed on a free-to-respond model in the 5 m Vertical Wind Tunnel of the National Research Council Canada (NRC) where the displacement of the model was measured in several degrees of freedom of the oscillation and the aerodynamic damping and stiffness of the model were determined.;In the second phase of the study, a stationary test was performed to measure the steady-state forces and moments applied on the body as well as high frequency surface pressure measurements to quantify the unsteady variations of the aerodynamic force coefficient with time. A high frequency response pressure probe was used to perform measurements of the flow fluctuations in the wake of the model. The tests for this second phase were conducted in the 2 m x 3 m Wind Tunnel at NRC.;Subsequently, a dynamic model of the Ahmed body mounted on springs was developed using the different parameters measured during the two phases of the experimentation. It led to a conclusion on the type of unsteady aerodynamic forces present and a proposed experimental and/or numerical modeling approach.;A small excitation was found in the wake of the Ahmed body reference model, but motion-induced forces were also influencing the dynamics of the model. |
