Abstract:
The results of an experimental investigation of the bootdeck flow structure of a
36 per cent scale model notchback car are presented together with a general
review of advanced laser diagnostic techniques suitable for large-scale wind
tunnel flow measurement. The tests were used to characterize the flow behaviour
over the Reynolds number range 0.74 x 10(6)-4.93 x 10(6) in the Cranfield
University 2.4 m x 1.8 m wind tunnel. The experiments involved flow
visualization, rear bootdeck and backlight three-dimensional stereoscopic
particle image velocimetry (PIV) measurements, and mean static and unsteady
static pressure measurements. Initial results from the flow visualization
suggested flow asymmetries originating in the backlight region that were
sensitive to the Reynolds number. The PIV data and static pressure data,
however, showed little or no sensitivity of flow to Reynolds number with
consistent flow structure and levels of unsteadiness from the backlight to the
rear bootdeck region. At this stage no definitive reasons can be given for the
discrepancies between the flow visualization and the other data, although the
flow visualization data were particularly difficult to interpret near the
backlight, and the near-wake structure may be bi-stable in this Reynolds number
range. More detailed three-dimensional stereoscopic, time-resolved PIV flow data
are now planned to quantify conclusively the correct flow structure and its
sensitivities.
