The Effect of an Upstream Control Object in Low-Speed Rotation upon the Flow past a Long Plate

摘要

In the present study, the authors consider a control of the flow past a semi-infinite plate with a blunt front. The flow is one of the simplest separated-and-reattaching flows, and can be a model such as heat exchangers and flow straighteners commonly seen inside power plants, chemical plants and household appliances. As a control device, a rotating object, which is a small flat plate, is placed in the upstream of the semi-infinite plate. In a wind tunnel, the authors conduct flow-velocity-fluctuation measurements using a hot-wire anemometer for various control-object positions and rotation speeds, showing (1) root-mean-squared values near the leading edge of the semi-infinite plate and (2) dominant frequencies in the downstream. The present test range of the control-object rotation speed is low; specifically, the object's tip velocity is less than the uniform mainstream velocity. Referring to such results, we can classify the controlled flow into four regions. Moreover, in order to clarify the characteristics for each region, the authors carry out (1) flow visualisations with particle-image-velocimetry analyses, and (2) velocity-profile measurements concerning time-mean and turbulence-intensity values.