Pub Date : 1900-01-01DOI: 10.1115/ajkfluids2019-4769
Purushotam Kumar, Kai Jin, S. Vanka
In this paper, we have applied a recently-developed numerical technique to study the three-dimensional dynamics of a confined air bubble rising in shear thinning and shear-thickening power-law fluids. The method is a blend of Volume of Fluid and Level Set methods and incorporates a Sharp Surface Force Method (SSF) for surface tension forces by solving a second Pressure Poisson Equation (PPE). The gas-liquid interface is captured by an equation for the liquid volume fraction and advected using the geometry reconstruction method. The interface normal and curvature are computed using level-set and height function methods. The accurate representation of the interface and interfacial forces significantly suppressed the spurious velocities commonly observed with conventional volume of fluid method and the Continuum Surface Force (CSF). The algorithm is implemented in a in-house code called CUFLOW and runs on multiple GPUs platform. We explored the effects of fluid rheology, Bond number, and wall confinement on bubble’s transient shape, rise velocity, rise path, and generated vortex structures. The power-law index is varied from 0.25 to 1.50 covering shear-thinning and shear-thickening regimes. Three Bond numbers (Bo = 2, 10 and 50) and three confinement ratios (Cr = 4, 6 and 8) are considered, and their impacts on bubble’s dynamics are analyzed. For the range of parameters examined here, bubble motion in a shear-thinning fluid is seen to be unsteady with significant shape oscillations. The bubble rises with a secondary motion in the cross-sectional plane along with its primary vertical rise. However, in the Newtonian and shear-thickening fluids, the bubble’s shape is seen to reach a steady-state in a relatively short time and rise with only minor deviations from the vertical path.
{"title":"Numerical Simulation of a Gas Bubble Rising in Power-Law Fluids Using a Sharp Surface Force Implementation","authors":"Purushotam Kumar, Kai Jin, S. Vanka","doi":"10.1115/ajkfluids2019-4769","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4769","url":null,"abstract":"\u0000 In this paper, we have applied a recently-developed numerical technique to study the three-dimensional dynamics of a confined air bubble rising in shear thinning and shear-thickening power-law fluids. The method is a blend of Volume of Fluid and Level Set methods and incorporates a Sharp Surface Force Method (SSF) for surface tension forces by solving a second Pressure Poisson Equation (PPE). The gas-liquid interface is captured by an equation for the liquid volume fraction and advected using the geometry reconstruction method. The interface normal and curvature are computed using level-set and height function methods. The accurate representation of the interface and interfacial forces significantly suppressed the spurious velocities commonly observed with conventional volume of fluid method and the Continuum Surface Force (CSF). The algorithm is implemented in a in-house code called CUFLOW and runs on multiple GPUs platform.\u0000 We explored the effects of fluid rheology, Bond number, and wall confinement on bubble’s transient shape, rise velocity, rise path, and generated vortex structures. The power-law index is varied from 0.25 to 1.50 covering shear-thinning and shear-thickening regimes. Three Bond numbers (Bo = 2, 10 and 50) and three confinement ratios (Cr = 4, 6 and 8) are considered, and their impacts on bubble’s dynamics are analyzed. For the range of parameters examined here, bubble motion in a shear-thinning fluid is seen to be unsteady with significant shape oscillations. The bubble rises with a secondary motion in the cross-sectional plane along with its primary vertical rise. However, in the Newtonian and shear-thickening fluids, the bubble’s shape is seen to reach a steady-state in a relatively short time and rise with only minor deviations from the vertical path.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127898342","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1115/ajkfluids2019-5166
Taisuke Sato, T. Yamashita, K. Ando
In ultrasonic cleaning, violent cavitation bubble dynamics causes material damage to cleaning surfaces, which is called cavitation erosion. The control of the dissolved gas concentration in cleaning liquid is effective to avoid cavitation erosion. The dissolved oxygen (DO) concentration is easily measured by a commercial DO meter, but the dissolved nitrogen (DN) concentration in water where multiple gas species are dissolved cannot be accurately measured with a commercially available DN meter. Therefore, it is important to construct a new method of measurement of DN concentration. In this study, we visualize the diffusion driven dissolution of bubble in air-saturated water and degassed water. The Epstein-Plesset theory considering multiple gas species is derived and compared with the experimental result where the DN concentration is treated as a fitting parameter in order to estimate the unknown DN concentration. Results indicates that the DN concentration can be measured by comparison between the theory and the relatively slow dissolution of bubble.
{"title":"Visualization of Bubble Dissolution As a Means to Measure Dissolved Nitrogen Concentration","authors":"Taisuke Sato, T. Yamashita, K. Ando","doi":"10.1115/ajkfluids2019-5166","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5166","url":null,"abstract":"\u0000 In ultrasonic cleaning, violent cavitation bubble dynamics causes material damage to cleaning surfaces, which is called cavitation erosion. The control of the dissolved gas concentration in cleaning liquid is effective to avoid cavitation erosion. The dissolved oxygen (DO) concentration is easily measured by a commercial DO meter, but the dissolved nitrogen (DN) concentration in water where multiple gas species are dissolved cannot be accurately measured with a commercially available DN meter. Therefore, it is important to construct a new method of measurement of DN concentration. In this study, we visualize the diffusion driven dissolution of bubble in air-saturated water and degassed water. The Epstein-Plesset theory considering multiple gas species is derived and compared with the experimental result where the DN concentration is treated as a fitting parameter in order to estimate the unknown DN concentration. Results indicates that the DN concentration can be measured by comparison between the theory and the relatively slow dissolution of bubble.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127508822","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1115/ajkfluids2019-5322
M. Kawaguchi, T. Fukui, Kenichi Funamoto, Suguru Miyauchi, T. Hayase
Experimental studies were performed to characterize the effects of the microstructure on the rheology of suspension. We focused on the change in the dispersion of the suspended particles under different particle Reynolds number conditions. Suspension flow through a microchannel with a circular cross-section was measured, and the radial dispersion of suspended particles and the velocity profiles were obtained. It was suggested that the particle dispersion could be changed owing to the difference in inertial force acting on the particles.
{"title":"Experimental Study on the Effects of Radial Dispersion of Spherical Particles on the Suspension Rheology","authors":"M. Kawaguchi, T. Fukui, Kenichi Funamoto, Suguru Miyauchi, T. Hayase","doi":"10.1115/ajkfluids2019-5322","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5322","url":null,"abstract":"\u0000 Experimental studies were performed to characterize the effects of the microstructure on the rheology of suspension. We focused on the change in the dispersion of the suspended particles under different particle Reynolds number conditions. Suspension flow through a microchannel with a circular cross-section was measured, and the radial dispersion of suspended particles and the velocity profiles were obtained. It was suggested that the particle dispersion could be changed owing to the difference in inertial force acting on the particles.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"128 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133401671","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.1115/ajkfluids2019-4965
M. Austin, T. Tran-Le, R. Kunz, T. Simpson, R. Ni
Powder Bed Fusion (PBF) cross-flow systems are designed to flow gas across the build plane and entrain metallic powder particles that are ejected during the build, due to the thermal and attendant released kinetic energy of the laser melt process. It is important that these particles be removed from the build chamber so that they do not redeposit on the build surface, as this uncontrolled particle deposition can degrade the part quality. Optimal design of these sub-systems involves tailoring a cross-flow jet such that most of the ejected particles are entrained and removed from the build chamber, while the top layer of particles that are freshly spread on the build plate are not entrained. Accordingly, a combined experimental and CFD study has been executed with the goal of developing engineering design guidance for these cross-flow systems. The closed loop small footprint wind tunnel incorporates a 0.305 m × 0.305 m × 0.915 m test section, a variable height build plate upon which powder can be spread, a variable geometry inlet nozzle, and variable flow rate so that a variety of cross-flow configurations can be tested. Helium bubble particle tracking velocimetry (PTV) was used to characterize the single-phase flow at a number of these operating conditions / configurations. In addition, high speed videography was used to study particle liftoff and entrainment at these same conditions. Using these measurements and attendant CFD models, critical particle liftoff Shield numbers were obtained using CFD predictions of friction velocity. Specifically, close agreement between CFD and measurements were obtained, so that predicted Shields numbers, Sh, could be correlated with particle Reynolds number, Reτ. In this paper we present details of the experimental facility and test program, experimental results including uncertainty/error analysis for the PTV measurements, as well as the videography results for an aluminum alloy powder. The results of the CFD modeling are compared to the single phase measurements. Since very good agreement is observed, predicted wall-shear stress values are used to estimate Sh vs. Reτ at flow rates where incipient particle lift-off is observed experimentally.
粉末床熔融(PBF)横流系统的设计目的是使气体流过构建平面，并夹带金属粉末颗粒，这些粉末颗粒在构建过程中被喷射出来，这是由于激光熔化过程的热和随之而来的释放动能。重要的是要将这些颗粒从构建室中移除，这样它们就不会重新沉积在构建表面上，因为这种不受控制的颗粒沉积会降低零件质量。这些子系统的优化设计包括裁剪一个横流射流，使大多数喷出的颗粒被夹带并从构建室中移除，而新散布在构建板上的顶层颗粒不会被夹带。因此，进行了一项结合实验和CFD的研究，目的是为这些交叉流系统提供工程设计指导。闭环小足迹风洞包括一个0.305 m × 0.305 m × 0.915 m的测试段，一个可变高度的构建板，粉末可以在上面扩散，一个可变几何形状的入口喷嘴，和可变流量，以便于各种交叉流配置可以测试。氦气泡粒子跟踪测速仪(PTV)用于表征这些操作条件/配置下的单相流动。此外，采用高速摄像技术研究了相同条件下的粒子抛射和夹带。利用这些测量数据和相应的CFD模型，通过CFD摩擦速度预测获得了临界颗粒升空屏蔽数。具体来说，CFD和测量结果非常吻合，因此预测的屏蔽数Sh可以与粒子雷诺数Reτ相关联。在本文中，我们详细介绍了实验设备和测试程序，实验结果包括PTV测量的不确定度/误差分析，以及铝合金粉末的摄像结果。将CFD模拟结果与单相测量结果进行了比较。由于观察到非常好的一致性，预测的壁面剪切应力值用于在实验观察到初始颗粒上升的流速下估计Sh与Reτ。
{"title":"Experimental and Computational Studies of Particle Scavenge Flow in Direct Laser Metal Sintering","authors":"M. Austin, T. Tran-Le, R. Kunz, T. Simpson, R. Ni","doi":"10.1115/ajkfluids2019-4965","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4965","url":null,"abstract":"\u0000 Powder Bed Fusion (PBF) cross-flow systems are designed to flow gas across the build plane and entrain metallic powder particles that are ejected during the build, due to the thermal and attendant released kinetic energy of the laser melt process. It is important that these particles be removed from the build chamber so that they do not redeposit on the build surface, as this uncontrolled particle deposition can degrade the part quality. Optimal design of these sub-systems involves tailoring a cross-flow jet such that most of the ejected particles are entrained and removed from the build chamber, while the top layer of particles that are freshly spread on the build plate are not entrained.\u0000 Accordingly, a combined experimental and CFD study has been executed with the goal of developing engineering design guidance for these cross-flow systems. The closed loop small footprint wind tunnel incorporates a 0.305 m × 0.305 m × 0.915 m test section, a variable height build plate upon which powder can be spread, a variable geometry inlet nozzle, and variable flow rate so that a variety of cross-flow configurations can be tested. Helium bubble particle tracking velocimetry (PTV) was used to characterize the single-phase flow at a number of these operating conditions / configurations. In addition, high speed videography was used to study particle liftoff and entrainment at these same conditions. Using these measurements and attendant CFD models, critical particle liftoff Shield numbers were obtained using CFD predictions of friction velocity. Specifically, close agreement between CFD and measurements were obtained, so that predicted Shields numbers, Sh, could be correlated with particle Reynolds number, Reτ.\u0000 In this paper we present details of the experimental facility and test program, experimental results including uncertainty/error analysis for the PTV measurements, as well as the videography results for an aluminum alloy powder. The results of the CFD modeling are compared to the single phase measurements. Since very good agreement is observed, predicted wall-shear stress values are used to estimate Sh vs. Reτ at flow rates where incipient particle lift-off is observed experimentally.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114636485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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