Localized Modification of Turbulent Spectra in a Horizontal Mixing Layer by Introducing Microbubbles

Abstract

In order to investigate the modifications of spatial-temporal developing flows by adding microbubbles in O(10 μm) diameter, flow structures appearing in shear flows of a horizontal mixing layer are visualized from velocity distributions obtained by (I) image analysis combining particle tracking velocimetry (PTV) and laser induced fluorescence (LIF), and (II) ultrasound velocity profiling (UVP). As the result of measurement, Reynolds shear stress is increased by introducing microbubbles at the early stage of the mixing-layer. In the developing region, however, Reynolds shear stress is flattened at the center of mixing layer and is reduced in bulk. Energy spectra of the velocity fluctuations show that energy of flow structures, whose length scale is as equivalent to the initial vortex layer thickness, is partially reduced. The size of vortex layer thickness is enlarged due to the local modification of the flow structures appearing in the early stage of mixing-layer.