Characteristics of the turbulent motion in a cylinder wake have been measured during passage through a distorting section of a wind tunnel, the overall effect of the distortion being considerable lateral extension and compression without a considerable change of flow velocity. However, the sectional area is not constant and rates of longitudinal extension are comparable with the rates of lateral straining. Hot-wire anemometers, mostly in X-configurations, are used to measure mean velocities, turbulent intensities, Reynolds stresses, intermittency factors and spectra, and velocity correlations have been calculated from digital recordings of the outputs from arrays of eight single-wire anemometers. In contrast to previous investigations, the direction of compression is parallel to the axis of the cylinder, and the original entrainment eddies of the plane wake are suppressed rather than amplified.

The results show that substantial changes in stress-intensity ratios, entrainment rates, dissipation rates and turbulence length-scales occur in response to the three-dimensional distortion. In particular, the ratio of Reynolds stress to total intensity increases during the initial acceleration of the flow before decreasing as the flow is strained laterally, and correlations show that length-scales do not change in proportion to the lateral extension and become relatively small compared to the flow width.