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Technical Paper

Experimental Study of a Ground Vehicle Body Unsteady Near Wake

1999-03-01
1999-01-0812
The unsteady near wake of a ground vehicle body was investigated using hot wire anemometry and an unsteady pressure measurement system. A three dimensional bluff body model was used to simulate the time dependent, three dimensional near wake flow field generated by trucks, buses, and automobiles. Coherence and coherence phase were effective methods to analyze the unsteady pressure field and to relate different pressure signals. Spectral analysis of the velocity and pressure signals was used to identify periodic wake flow structures. The time averaged near wake contains a ring vortex enclosed by shear layers which start where the model boundary layer separates from the body. At the start of the shear layer, vortex shedding was measured at a dimensionless frequency, StH(shed) = 1.157. As these vortices convected along the shear layer, vortex pairing was observed which approximately halves the characteristic frequency.
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