Thesis abstract: establishing very low speed, disturbance-free flow for anemometry in turbulent boundary layers

摘要

The thesis addresses problems encountered when established the very low air-flow speeds required for experimental investigations of the mechanisms of low-Reynolds-number boundary-layer turbulence. Small-scale mo- tions in the near wall region are important features of turbulent boundary-layer dynam- ics, and, if these features are to be resolved by measurements in air with conventionally- sized hot-wire probes, a well-behaved ca- nonical turbulent boundary layer must be developed at free stream flow speeds no higher than 4 m/s. However, at such low speeds, the turbulent boundary layers de- veloped on the walls of a wind tunnel are very susceptible to perturbation by non- turbulent time-dependent flow structures which are produced in the laminar flow upstream of the test section.