Giuseppe Rosi, Moira Barnes, Frieder Kaiser, David Rival
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引用次数: 0
Abstract
To better understand how turbulent flow structures develop within shear-thinning suspensions (STSs), we investigate the behavior of a shear layer forming within an STS downstream of a sudden expansion with an expansion ratio of 0.5. Specifically, the shear-layer reattachment behavior downstream of an axisymmetric expansion is characterized through ultrasound imaging velocimetry (UIV) and through pressure measurements, and the observed behavior is used to surmise how the shear layer is modified within the STS. Four fluids are investigated, which include pure water, as well as three 1750 ppm xanthan-gum-in-water solutions mixed with non-reactive mineral microspheres at volume fractions of 0%, 15%, and 30%. Wall-pressure measurements were collected through pressure taps located at 0h to 25.8h downstream of the expansion with subsequent UIV measurements collected from 1h to 9h downstream of the expansion, where h is the step height and equals the difference between the pipe and throat radii. For single-phase cases, pressure-recovery profiles and UIV flow fields indicate a predictably large reattachment length at low Reynolds numbers, which shortens as the Reynolds number increases from \(O(10^2)\) to \({O}(10^4)\) and finally stabilizes at roughly 8h. In contrast, the STSs exhibit pressure-recovery and pipe-wall velocity profiles indicating a reattachment length that is consistently short (8h) and independent of Reynolds number. The results indicate that the suspended phase within the STSs causes the shear layer to diffuse far more rapidly, thereby promoting momentum transfer toward the wall, which results in a consistently short reattachment length.
为了更好地理解剪切变薄悬浮液(STSs)中湍流结构的发展,我们研究了在膨胀比为0.5的突然膨胀下,在STSs下游形成剪切层的行为。具体来说,通过超声成像测速(UIV)和压力测量来表征轴对称膨胀下游的剪切层再附着行为,并使用观察到的行为来推测剪切层如何在STS内被修改。研究了四种流体,包括纯水,以及三种1750 ppm的黄原胶水溶液,其中混合了体积分数为0的非活性矿物微球%, 15%, and 30%. Wall-pressure measurements were collected through pressure taps located at 0h to 25.8h downstream of the expansion with subsequent UIV measurements collected from 1h to 9h downstream of the expansion, where h is the step height and equals the difference between the pipe and throat radii. For single-phase cases, pressure-recovery profiles and UIV flow fields indicate a predictably large reattachment length at low Reynolds numbers, which shortens as the Reynolds number increases from \(O(10^2)\) to \({O}(10^4)\) and finally stabilizes at roughly 8h. In contrast, the STSs exhibit pressure-recovery and pipe-wall velocity profiles indicating a reattachment length that is consistently short (8h) and independent of Reynolds number. The results indicate that the suspended phase within the STSs causes the shear layer to diffuse far more rapidly, thereby promoting momentum transfer toward the wall, which results in a consistently short reattachment length.Graphic abstract
期刊介绍:
Experiments in Fluids examines the advancement, extension, and improvement of new techniques of flow measurement. The journal also publishes contributions that employ existing experimental techniques to gain an understanding of the underlying flow physics in the areas of turbulence, aerodynamics, hydrodynamics, convective heat transfer, combustion, turbomachinery, multi-phase flows, and chemical, biological and geological flows. In addition, readers will find papers that report on investigations combining experimental and analytical/numerical approaches.