Abstract
The complex mechanisms by which turbulence is generated in the wake of non-connecting perpendicular cylinders and bars immersed in a uniform airflow have been investigated by undertaking a wind tunnel study. The effects, upon both the flow around each member in the configuration and the fluid motion in the near wake, of changes in the member spacing were assessed, and in this respect a critical separation distance has been identified. It was found that the overall flow field created by the perpendicular geometry can be divided into an inner region of highly disturbed conditions and an outer region of quasi two dimensional flow. The characteristics of the turbulent inner region were ascertained from comprehensive measurements of surface pressures, mean velocities, flow vorticity, and turbulence parameters including intensities, length scales, spectral energies and kinetic energies. The results revealed that, with regard to both section types, two fundamental regimes are possible, and that these are separated by a critical member spacing of three diameters/section depths. When the spacing is below this critical value the mechanism of turbulence generation is dominated by a pair of horseshoe vortices which develop around the centre of the downstream span. At the critical spacing, these horseshoe vortices are replaced by weaker longitudinal trailing vortices which persist over the range of spacings examined up to ten diameters/ section depths. Although the general characteristics of these mechanisms are similar in the case of both the perpendicular cylinders and perpendicular bars, the precise nature of each regime was found to be dependent upon section type. In addition, during the course of this research it was necessary to design and construct electronic equipment incorporating a dual channel analogue to digital conversion process. This enabled the simultaneous acquisition of data from two hot-wire anemometers for the purpose of obtaining spatial correlation coefficients.