Simulation of unsteady flows

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Simulation of unsteady flows

Islam, Moni

The simulation of unsteady flows is gaining in importance in applications related to vehicle aerodynamics for a number of reasons. First, as other contributions in this publication show, unsteady effects play a role in vehicle dynamics and therefore also passenger response and comfort while driving. Second, unsteady phenomena are tied in closely with other aspects of the flow around a vehicle, most notably aeroacoustics. Third is the simple fact that unsteady flow simulations, in general far more resource-intensive than steady ones, can now be carried out at a reasonable cost thanks to the availability of relatively low-cost high-performance computing power. This, combined with the fundamental realisation that the highly turbulent flows around vehicles are by their very nature inherently unsteady, results in the strong motivation to investigate and understand external aerodynamics through the simulation of unsteady flows. A number of examples of simulations of unsteady flow have been presented here that provide evidence that in order to properly predict both time-averaged and time-resolved flow behaviour, appropriate CFD methods must be employed. For external aerodynamics, in which bluff bodies and the unsteady forces acting on them are of importance, this consists of applying both turbulence models which are inherently capable of capturing unsteady phenomena and solution techniques which resolve the unsteadiness of the flow.