Title: Experimental study of velocity statistics in wall-bounded turbulent emulsions Show Chinese title

Title: 壁面受限湍流乳液的速度统计实验研究

Abstract: Turbulent emulsions are ubiquitous in chemical engineering, food processing, pharmaceuticals, and other fields. However, our experimental understanding of this area remains limited due to the multi-scale nature of turbulent flow and the presence of extensive interfaces, which pose significant challenges to optical measurements. In this study, we address these challenges by precisely matching the refractive indices of the continuous and dispersed phases, enabling us to measure local velocity information at high volume fractions. The emulsion is generated in a turbulent Taylor-Couette flow, with velocity measured at two radial locations: near the inner cylinder (boundary layer) and in the middle gap (bulk region). Near the inner cylinder, the presence of droplets suppresses the emission of angular velocity plumes, which reduces the mean azimuthal velocity and its root mean squared fluctuation. The former effect leads to a higher angular velocity gradient in the boundary layer, resulting in greater global drag on the system. In the bulk region, although droplets suppress turbulence fluctuations, they enhance the cross-correlation between azimuthal and radial velocities, leaving the angular velocity flux contributed by the turbulent flow nearly unchanged. In both locations, droplets suppress turbulence at scales larger than the average droplet diameter and increase the intermittency of velocity increments. However, the effects of the droplets are more pronounced near the inner cylinder than in the bulk, likely because droplets fragment in the boundary layer but are less prone to breakup in the bulk. Our study provides experimental insights into how dispersed droplets modulate global drag, coherent structures, and the multi-scale characteristics of turbulent flow. Show Chinese abstract

Abstract: 湍流乳液在化学工程、食品加工、制药和其他领域中普遍存在。 然而，由于湍流的多尺度特性以及大量界面的存在，我们对这一领域的实验理解仍然有限，这给光学测量带来了重大挑战。 在本研究中，我们通过精确匹配连续相和分散相的折射率，解决了这些挑战，使我们能够在高体积分数下测量局部速度信息。 乳液是在湍流泰勒-库埃特流动中生成的，速度在两个径向位置进行测量：靠近内圆柱体（边界层）和中间间隙（主体区域）。 在靠近内圆柱体的地方，液滴的存在抑制了角速度射流的发射，这降低了平均切向速度及其均方根波动。 前一种效应导致边界层中的角速度梯度更高，从而增加了系统的整体阻力。 在主体区域，尽管液滴抑制了湍流脉动，但它们增强了切向和径向速度之间的交叉相关性，使得由湍流产生的角速度通量几乎保持不变。 在两个位置，液滴在大于平均液滴直径的尺度上抑制了湍流，并增加了速度增量的间歇性。 然而，液滴的影响在靠近内圆柱体的地方更为显著，这可能是因为液滴在边界层中发生破碎，而在主体区域则不太容易破碎。 我们的研究为分散液滴如何调节整体阻力、相干结构以及湍流的多尺度特性提供了实验见解。