Unsteady flows are an inherent part of vehicle aerodynamics, affecting the stability, the comfort and the safety of the vehicle. Unsteadiness arises in some regions due to flow separation, in other Instances it is due to changing boundary conditions such as natural wind gusts, static structures such as buildings or road-side obstacles, or when overtaking other vehicles. To study the effect of flow unsteadiness on the overall vehicle aerodynamics, it is necessary to first mathematically describe the flow fluctuations, and the present manuscript introduces the basic statistical quantities used to due this. The equations of fluid motion are first examined and the important length and time scales of velocity fluctuations are identified. Then the statistical description of velocity fluctuations in amplitude and spectral domain is given. Finally, parameters introduced to capture especially the nature of time-dependent boundary conditions and their effect on vehicles are discussed.
Characterisation of unsteady flows
Kennzeichen instationärer Strömungen
2004
26 Seiten, 21 Bilder, 1 Tabelle, 24 Quellen
Aufsatz (Konferenz)
Englisch
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