Particle Image Velocimetry Study of Turbulence Characteristics in a Vessel Agitated by a Dual Rushton Impeller

粒子图象 Velocimetry (PIV ) 被用来在搅动的容器充满了到 0.67 m 的液体高度(H = 1.4T ) 的 0.48 m 直径调查骚乱特征。煽动者有 0.19 m 直径(D = 0.4T ) 的双 Rushton impellers。发达流动模式在液体表面下面在容器，在二 impellers 之间的间距，和上面的 impeller 的 submergence 的底上面取决于更低的 impeller 的清理。他们的联合能产生三个基本流动模式，命名、平行、合并并且分叉的流动。速度测量的结果证明在 impeller 喷气流动区域的流动特征几乎不为不同位置变化。平均速度，落后于旋涡并且砍为三个流动模式的紧张率分布被使用 PIV 测量技术。后面的旋涡和它的轨道的特征为那些三个流动模式详细被描述。因为 PIV 的空间决定能仅仅到达亚格子而非 Kolmogorov 规模，大旋涡的 PIV 分析被用来估计狂暴的动能驱散的分发。在合并流动的狂暴的动能和驱散率的分布的比较证明最高狂暴的动能和驱散两个都位于旋涡区域，但是最大值在在片后面的有点不同的地点。大约 37% 全部的精力在双 impeller 喷气流动区域被驱散。获得的分发砍为合并流动的紧张率类似于骚乱驱散，在比在另外的区域高得多的后面的旋涡附近与 shear 紧张评价。

Particle Image Velocimetry （PIV） has been used to investigate turbulence characteristics in a 0.48 m diameter stirred vessel filled to a liquid height （ H = 1.4T ） of 0.67 m. The agitator had dual Rushton impellers of 0.19 m diameter （ D = 0.4T ）. The developed flow patterns depend on the clearance of the lower impeller above the base of the vessel, the spacing between the two impellers, and the submergence of the upper impeller below the liq- uid surface. Their combinations can generate three basic flow patterns, named, parallel, merging and diverging flows. The results of velocity measurement show that the flow characteristics in the impeller jet flow region changes very little for different positions. Average velocity, trailing vortices and shear strain rate distributions for three flow patterns were measured by using PIV technique. The characteristics of trailing vortex and its trajectory were described in detail for those three flow patterns. Since the space-resolution of PIV can only reach the sub-grid rather than the Kolmogorov scale, a large-eddy PIV analysis has been used to estimate the distribution of the turbulent kinetic energy dissipation. Comparison of the distributions of turbulent kinetic energy and dissipation rate in merging flow shows that the highest turbulent kinetic energy and dissipation are both located in the vortex regions, but the maxima are at somewhat different lo- cations behind the blade. About 37% of the total energy is dissipated in dual impeller jet flow regions. The obtained distribution of shear strain rate for merging flow is similar to that of turbulence dissipation, with the shear strain rate around the trailing vortices much higher than in other areas.