Turbulent structure of three-dimensional flow behind a model car: 2. Exposed to crosswind

A full kinematic map of turbulent wake flow behind a model car exposed to crosswind was examined by local measurements of velocity for the approach velocities of 18, 28 and 38 ms^-1 and crosswind speeds of 3.2, 4.9 and 6.7 ms^-1. Results showed that the wake flow becomes highly asymmetric with the crosswind which introduces a rotation to the in-plane velocity field and tilts the system of counter-rotating helical vortices appearing on both sides of the centreline. The current measurements were performed at a single plane and, thus, only part of the full expression for the kinetic energy production could be retrieved from the experimental data. However, they show that the vortex formation plays an important role in the transport and re-distribution of the turbulent kinetic energy produced by the crosswind. And that the turbulent energy is partly regained back to the streamwise mean flow through the vortex centres. As a result, the turbulence produced by the crosswind cannot induce a significant additional drag.