Due to gravity, solids in slurries will settle if density differences between the solids and liquid are positive (i.e., particle has a negative buoyant force) unless rheological properties and flow conditions are adequate to overcome the gravitational effects. The rate of settling depends on the force balance of the particle, which includes the surface forces associated with fluid rheology. Given the same fluid and solid properties, the larger and more dense particles tend to settle faster. When pumping slurry into a vessel at concentrations precluding hindered settling with insufficient mixing, particle and density distributions can result in preferential settling, creating stratification in the solids concentration within the vessel. For vessels with transfer line inlets located in the lower portion of the tank, the stratified solids concentration may be detrimental to the transfer system performance. Elevated concentrations of solids in the slurry entrained at the inlet to the transfer line can result in the effective viscosity or slurry bulk density exceeding the design limits of the pump. These conditions could result in plugging of the transfer line or onset of cavitation of the pumps because of excessive pressure drop. These conditions can be exacerbated with periodic inlet conditions existing at the transfer line inlet. Periodic conditions can result when vessel mixing is intermittent such as with pulsed jet mixers (PJM). The transfer line inlet conditions are impacted by the periodic nature of the PJM operations with respect to suspension of solids and their transport to the inlet of the transfer line. A scaling approach is presented, and corresponding test requirements are developed for assessing the prevention of plugging the pipeline. Line plugging mechanisms are addressed that exclude plugging due to steady-state high-density slurry entering the transfer line and reducing the net positive suction head available (NPSHA) at the pump inlet to below that required for pump operation. Items considered include the transition to reduced relative flow velocities, such that the critical pipe velocity for solids deposition, Ucd, is not maintained, and segregation of heavy solids during the transport. The recommended requirements to prevent plugging include: • Limits for viscosity and density for entrained slurry to prevent the pressure drop in the pipeline from exceeding pump capacity. • Limits for viscosity and density for entrained slurry to prevent the net positive suction head available (NPSHA) from falling below the net positive suction head required (NPSHR) for operating the pump. • Transfer line velocity and flow rate requirements to maintain solids in suspension, while avoiding line plugging that results from deposition of solids within the transfer line. This paper describes the development of the scaling and testing requirements to verify that proposed approaches for transfer and pump out are appropriately developed for operat
{"title":"Evaluating Transfer and Pumping of Slurries From Pulsed Jet Mixed Vessels","authors":"C. Enderlin, J. Bamberger, M. Minette","doi":"10.1115/fedsm2020-20390","DOIUrl":"https://doi.org/10.1115/fedsm2020-20390","url":null,"abstract":"\u0000 Due to gravity, solids in slurries will settle if density differences between the solids and liquid are positive (i.e., particle has a negative buoyant force) unless rheological properties and flow conditions are adequate to overcome the gravitational effects. The rate of settling depends on the force balance of the particle, which includes the surface forces associated with fluid rheology. Given the same fluid and solid properties, the larger and more dense particles tend to settle faster. When pumping slurry into a vessel at concentrations precluding hindered settling with insufficient mixing, particle and density distributions can result in preferential settling, creating stratification in the solids concentration within the vessel.\u0000 For vessels with transfer line inlets located in the lower portion of the tank, the stratified solids concentration may be detrimental to the transfer system performance. Elevated concentrations of solids in the slurry entrained at the inlet to the transfer line can result in the effective viscosity or slurry bulk density exceeding the design limits of the pump. These conditions could result in plugging of the transfer line or onset of cavitation of the pumps because of excessive pressure drop.\u0000 These conditions can be exacerbated with periodic inlet conditions existing at the transfer line inlet. Periodic conditions can result when vessel mixing is intermittent such as with pulsed jet mixers (PJM). The transfer line inlet conditions are impacted by the periodic nature of the PJM operations with respect to suspension of solids and their transport to the inlet of the transfer line. A scaling approach is presented, and corresponding test requirements are developed for assessing the prevention of plugging the pipeline. Line plugging mechanisms are addressed that exclude plugging due to steady-state high-density slurry entering the transfer line and reducing the net positive suction head available (NPSHA) at the pump inlet to below that required for pump operation. Items considered include the transition to reduced relative flow velocities, such that the critical pipe velocity for solids deposition, Ucd, is not maintained, and segregation of heavy solids during the transport. The recommended requirements to prevent plugging include:\u0000 • Limits for viscosity and density for entrained slurry to prevent the pressure drop in the pipeline from exceeding pump capacity.\u0000 • Limits for viscosity and density for entrained slurry to prevent the net positive suction head available (NPSHA) from falling below the net positive suction head required (NPSHR) for operating the pump.\u0000 • Transfer line velocity and flow rate requirements to maintain solids in suspension, while avoiding line plugging that results from deposition of solids within the transfer line.\u0000 This paper describes the development of the scaling and testing requirements to verify that proposed approaches for transfer and pump out are appropriately developed for operat","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131340948","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}
Luis F. Rodriguez, Vinod Kumar, Arturo Rodríguez, V. Kotteda, V. Gudimetla, J. Munoz
We have simulated atmospheric turbulence at several instances of possible laser propagation paths and turbulent flow regime regions within the area of interest. At a control volume that is in between two Hawaii mountains. We have applied statistical correlations between Large-Eddy Simulations results using CFD modeling and parametrizing optical variables of interest, such as refractive index structure function. By comparing our Large-Eddy Simulations with specified parameters against other Large-Eddy Simulations with almost all same parameters except for one allows us to perform a sensitivity study. To study the changes on how a parameter can affect other scenarios of Large-Eddy Simulations parametric studies. With the end goal of validating the capacity of a sensitivity analysis study using Large-Eddy Simulations versus other Large-Eddy Simulations by a way of simulating and parametrizing turbulent flow studies found in the field of CFD modeling. Allowing us to achieve our stochastic analysis by applying sensitivity studies to see how our distributions change as a function of different parameters, but one at a time. After a comparison between CFD modelling simulations we have found that after a complete parametric study, a correlation was formed between turbulent flow parameters and optical parameters of interest.
{"title":"Parameter Sensitivity and Statistical Correlation Found in Atmospheric Turbulence Studies","authors":"Luis F. Rodriguez, Vinod Kumar, Arturo Rodríguez, V. Kotteda, V. Gudimetla, J. Munoz","doi":"10.1115/fedsm2020-20254","DOIUrl":"https://doi.org/10.1115/fedsm2020-20254","url":null,"abstract":"\u0000 We have simulated atmospheric turbulence at several instances of possible laser propagation paths and turbulent flow regime regions within the area of interest. At a control volume that is in between two Hawaii mountains. We have applied statistical correlations between Large-Eddy Simulations results using CFD modeling and parametrizing optical variables of interest, such as refractive index structure function. By comparing our Large-Eddy Simulations with specified parameters against other Large-Eddy Simulations with almost all same parameters except for one allows us to perform a sensitivity study. To study the changes on how a parameter can affect other scenarios of Large-Eddy Simulations parametric studies. With the end goal of validating the capacity of a sensitivity analysis study using Large-Eddy Simulations versus other Large-Eddy Simulations by a way of simulating and parametrizing turbulent flow studies found in the field of CFD modeling. Allowing us to achieve our stochastic analysis by applying sensitivity studies to see how our distributions change as a function of different parameters, but one at a time. After a comparison between CFD modelling simulations we have found that after a complete parametric study, a correlation was formed between turbulent flow parameters and optical parameters of interest.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126191857","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}
Free jets have been studied in detail over much of the last century, but the theory for offset and attached jets remains incomplete. Attached jets differ from free jets in that they lose momentum to nearby surfaces, attenuating their velocities. The velocity profiles of free circular jets are nearly Gaussian, with quantitative mathematical descriptions derived from first principles by Goertler and Tollmien (Rajaratnam, 1976). In contrast, mathematical descriptions of three-dimensional attached jets from circular nozzles remain much less mature. Agelin-Chaab and Tachie (2011) used particle imaging velocimetry of a three-dimensional attached jet to show that the scaled velocity decays with scaled distance from the nozzle with a power law exponent between −1.15 and −1.20, which is larger in magnitude than that of a free jet. However, quantitative analytical expressions for the velocity profiles of attached jets similar to those of free jets remain elusive. This paper addresses this critical gap. Here we evaluate the velocity profiles of three-dimensional offset jets emerging from circular nozzles that become attached jets. These jets lose momentum due to interactions with nearby surfaces and are important to evaluating flows in mixing vessels and to suspending solids and trapped gases in radioactive waste tanks. Despite the importance of attached jets, prior insight has been purely experimental, limited to overly simplistic analytical models, or restricted to computationally expensive computational fluid dynamics case studies. We compare the expression of Verhoff (1963) to experimental results to find reasonable quantitative agreement. As stated by Agelin-Chaab and Tachie (2011), “detailed velocity measurements of 3D offset jets are rare.” Such remains the case. This study adds to the literature by providing information at two additional Reynolds numbers (1.43 · 106 and 1.87 · 106) and evaluating simple but accurate expressions for velocity profiles. These Reynolds numbers and corresponding velocities are higher, typically orders of magnitude higher, than other reports. The semi-empirical stream wise velocity profile perpendicular to the surface proposed by Verhoff (1963) is in approximate agreement with these velocity profiles, which is surprising because these attached jets are three-dimensional instead of two-dimensional as evaluated by Verhoff. However, additional work is necessary to fully describe these profiles quantitatively.
{"title":"Attached Jet Velocity Profiles in Mixing Tanks","authors":"L. Pease, J. Bamberger","doi":"10.1115/fedsm2020-20220","DOIUrl":"https://doi.org/10.1115/fedsm2020-20220","url":null,"abstract":"\u0000 Free jets have been studied in detail over much of the last century, but the theory for offset and attached jets remains incomplete. Attached jets differ from free jets in that they lose momentum to nearby surfaces, attenuating their velocities. The velocity profiles of free circular jets are nearly Gaussian, with quantitative mathematical descriptions derived from first principles by Goertler and Tollmien (Rajaratnam, 1976). In contrast, mathematical descriptions of three-dimensional attached jets from circular nozzles remain much less mature. Agelin-Chaab and Tachie (2011) used particle imaging velocimetry of a three-dimensional attached jet to show that the scaled velocity decays with scaled distance from the nozzle with a power law exponent between −1.15 and −1.20, which is larger in magnitude than that of a free jet. However, quantitative analytical expressions for the velocity profiles of attached jets similar to those of free jets remain elusive. This paper addresses this critical gap.\u0000 Here we evaluate the velocity profiles of three-dimensional offset jets emerging from circular nozzles that become attached jets. These jets lose momentum due to interactions with nearby surfaces and are important to evaluating flows in mixing vessels and to suspending solids and trapped gases in radioactive waste tanks. Despite the importance of attached jets, prior insight has been purely experimental, limited to overly simplistic analytical models, or restricted to computationally expensive computational fluid dynamics case studies. We compare the expression of Verhoff (1963) to experimental results to find reasonable quantitative agreement.\u0000 As stated by Agelin-Chaab and Tachie (2011), “detailed velocity measurements of 3D offset jets are rare.” Such remains the case. This study adds to the literature by providing information at two additional Reynolds numbers (1.43 · 106 and 1.87 · 106) and evaluating simple but accurate expressions for velocity profiles. These Reynolds numbers and corresponding velocities are higher, typically orders of magnitude higher, than other reports. The semi-empirical stream wise velocity profile perpendicular to the surface proposed by Verhoff (1963) is in approximate agreement with these velocity profiles, which is surprising because these attached jets are three-dimensional instead of two-dimensional as evaluated by Verhoff. However, additional work is necessary to fully describe these profiles quantitatively.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131963787","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}
Turbulent particle-laden flows are of high interest due to their presence in many industrial applications. High Reynolds number flows containing solid particles, create complex flows and erosive environments. The effect that the particles have on the turbulence of the surrounding fluid is referred to in the literature as turbulence modulation. This is an area of research in which there is still much to learn to enable a deeper understanding of the physics behind these complex flows. Data that would be of particular usefulness are at higher Reynolds numbers (Re ≥ 100,000), and dense loadings (ΦV ≥ 1%). In this work, turbulent particle-laden flow through a simplified industrial geometry was studied at an upper Reynolds number of 115,000 and particle loadings up to 5% by weight/volume (specific gravity = 1) to address these needs. The flow within a tee junction with the 90-degree branch closed-off downstream was studied. This is analogous to a duct flow but with an exposed region of fluid at the location of the closed-off branch. Super absorbent particles were used as the solid phase, which became index-matched and neutrally buoyant upon saturation with water. Data were acquired using 2-D planar particle image velocimetry (PIV) along the center span of the tunnel. Mean and root-mean-square (rms) velocities were calculated for the fluid phase. Particle loadings studied were 0%, 1%, 3%, and 5 at flow Reynolds numbers of 11,500 and 115,000. Velocity contour plots are presented to provide a macro description of the flow. Three horizontal positions within the shear layer region were selected for profile comparison (x* = −0.45, 0, 0.45). Prior literature suggested that the particles would attenuate the turbulence, however, the result showed no single trend in the current data. The mean velocities were nominally unaffected by loading for a respective Reynolds number case. Turbulence modulation of the flow was found to be sensitive to the Reynolds number, as at x* = −0.45 weakening of the rms was observed in the low Reynolds number case and strengthening in the high Reynolds number case for the same particle loading in the same region of the geometry.
{"title":"Effect of Neutrally Buoyant Particles on Horizontal Turbulent Flow Through a Tee-Junction","authors":"Andrew M. Bluestein, D. Bohl","doi":"10.1115/fedsm2020-20364","DOIUrl":"https://doi.org/10.1115/fedsm2020-20364","url":null,"abstract":"\u0000 Turbulent particle-laden flows are of high interest due to their presence in many industrial applications. High Reynolds number flows containing solid particles, create complex flows and erosive environments. The effect that the particles have on the turbulence of the surrounding fluid is referred to in the literature as turbulence modulation. This is an area of research in which there is still much to learn to enable a deeper understanding of the physics behind these complex flows. Data that would be of particular usefulness are at higher Reynolds numbers (Re ≥ 100,000), and dense loadings (ΦV ≥ 1%). In this work, turbulent particle-laden flow through a simplified industrial geometry was studied at an upper Reynolds number of 115,000 and particle loadings up to 5% by weight/volume (specific gravity = 1) to address these needs. The flow within a tee junction with the 90-degree branch closed-off downstream was studied. This is analogous to a duct flow but with an exposed region of fluid at the location of the closed-off branch. Super absorbent particles were used as the solid phase, which became index-matched and neutrally buoyant upon saturation with water. Data were acquired using 2-D planar particle image velocimetry (PIV) along the center span of the tunnel. Mean and root-mean-square (rms) velocities were calculated for the fluid phase. Particle loadings studied were 0%, 1%, 3%, and 5 at flow Reynolds numbers of 11,500 and 115,000. Velocity contour plots are presented to provide a macro description of the flow. Three horizontal positions within the shear layer region were selected for profile comparison (x* = −0.45, 0, 0.45). Prior literature suggested that the particles would attenuate the turbulence, however, the result showed no single trend in the current data. The mean velocities were nominally unaffected by loading for a respective Reynolds number case. Turbulence modulation of the flow was found to be sensitive to the Reynolds number, as at x* = −0.45 weakening of the rms was observed in the low Reynolds number case and strengthening in the high Reynolds number case for the same particle loading in the same region of the geometry.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134435616","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}
Elongated particles, such as asbestos and mineral fibers, are considered severe inhalation hazards due to their ability to penetrate into the deep lung. Frequently the dynamic behavior of the fibrous particles is attributed to their unique needle-like geometry. Therefore, understanding the interactions of the inhaled elongated particles with the airflow environment is of great significance. In this study, the transport and deposition of elongated micro-fibers in a realistic human nasal cavity is investigated numerically. The motion of the micro-fiber is resolved by solving the system of equations governing its coupled translational and rotational motions. The governing equations included the drag, the hydrodynamic torques that were evaluated using the Jeffrey model. The influence of the shear lift force was also included in these simulations. The no-slip wall boundary condition for airflow in the airways was used. Since the surface of airways is covered with mucus, when a fiber touches the surface, it was assumed to be deposited with no rebound. The study allows a close look at the non-spherical particle-flow dynamics with respect to the translation, rotation, coupling, and how the rotation affects the particle’s macroscopic transport and deposition properties. A series of simulations for different microfiber diameters and aspect ratios were performed. The simulation results are compared with the existing experimental data, and earlier computational model predictions and good agreements were obtained. The present study also seeks to provide additional insight into the transport processes of microfibers in the upper respiratory tract.
{"title":"Computational Analysis of Fiber Dynamics in Human Nasal Cavity","authors":"Jiawei Ma, J. Tu, L. Tian, G. Ahmadi","doi":"10.1115/fedsm2020-20035","DOIUrl":"https://doi.org/10.1115/fedsm2020-20035","url":null,"abstract":"\u0000 Elongated particles, such as asbestos and mineral fibers, are considered severe inhalation hazards due to their ability to penetrate into the deep lung. Frequently the dynamic behavior of the fibrous particles is attributed to their unique needle-like geometry. Therefore, understanding the interactions of the inhaled elongated particles with the airflow environment is of great significance. In this study, the transport and deposition of elongated micro-fibers in a realistic human nasal cavity is investigated numerically. The motion of the micro-fiber is resolved by solving the system of equations governing its coupled translational and rotational motions. The governing equations included the drag, the hydrodynamic torques that were evaluated using the Jeffrey model. The influence of the shear lift force was also included in these simulations. The no-slip wall boundary condition for airflow in the airways was used. Since the surface of airways is covered with mucus, when a fiber touches the surface, it was assumed to be deposited with no rebound. The study allows a close look at the non-spherical particle-flow dynamics with respect to the translation, rotation, coupling, and how the rotation affects the particle’s macroscopic transport and deposition properties. A series of simulations for different microfiber diameters and aspect ratios were performed. The simulation results are compared with the existing experimental data, and earlier computational model predictions and good agreements were obtained. The present study also seeks to provide additional insight into the transport processes of microfibers in the upper respiratory tract.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131765112","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}
M. Allaf, Zahra Habibi, Z. Samadi, C. DeGroot, L. Rehmann, J. R. Bruyn, H. Peerhossaini
Design of photobioreactors (PBRs) for microalgae and cyanobacteria cultivation involves the interplay between fluid flow, microbe biokinetics, and radiative transport phenomena, in which the physical and rheological properties of the active fluid play a crucial role. In this study, we focus on the variation of physical and rheological properties of dilute suspensions of Synechocystis sp. CPCC534 with the shear stress applied to the fluid. Experiments were carried out at three different stirring rates in well-controlled conditions and the results were compared with stationary conditions where only molecular diffusion and cell motility govern the transport phenomena, and cell growth. Our results show that the growth and biomass production of Synechocystis sp. under various shear conditions were improved significantly, and the yield was nearly doubled by adding agitation to the system. The viscosity of Synechocystis suspensions, subjected to different shear stress levels, was measured with two different methods. The viscosity data showed shear stress independent Newtonian behavior. However, the viscosity of Synechocystis suspensions increased moderately with cell volume fraction up to 10%, beyond which it increased more rapidly. The shear stress history of the cell suspensions did not show any effect on the fluid viscosity.
{"title":"Physical and Rheological Properties of Active Fluids Under Shear Stress: Suspensions of Synechocystis","authors":"M. Allaf, Zahra Habibi, Z. Samadi, C. DeGroot, L. Rehmann, J. R. Bruyn, H. Peerhossaini","doi":"10.1115/fedsm2020-20104","DOIUrl":"https://doi.org/10.1115/fedsm2020-20104","url":null,"abstract":"\u0000 Design of photobioreactors (PBRs) for microalgae and cyanobacteria cultivation involves the interplay between fluid flow, microbe biokinetics, and radiative transport phenomena, in which the physical and rheological properties of the active fluid play a crucial role. In this study, we focus on the variation of physical and rheological properties of dilute suspensions of Synechocystis sp. CPCC534 with the shear stress applied to the fluid.\u0000 Experiments were carried out at three different stirring rates in well-controlled conditions and the results were compared with stationary conditions where only molecular diffusion and cell motility govern the transport phenomena, and cell growth. Our results show that the growth and biomass production of Synechocystis sp. under various shear conditions were improved significantly, and the yield was nearly doubled by adding agitation to the system.\u0000 The viscosity of Synechocystis suspensions, subjected to different shear stress levels, was measured with two different methods. The viscosity data showed shear stress independent Newtonian behavior. However, the viscosity of Synechocystis suspensions increased moderately with cell volume fraction up to 10%, beyond which it increased more rapidly. The shear stress history of the cell suspensions did not show any effect on the fluid viscosity.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128526647","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}
Separating and reattaching turbulent flows induced by a forward-facing step submerged in thick oncoming turbulent boundary layers developed over smooth and rough walls were investigated using time-resolved particle image velocimetry. Both smooth and fully rough upstream bottom wall conditions were examined and the resultant oncoming boundary layer thickness were 4.3 and 6.7 times the step height, respectively. The Reynolds number based on the step height and free-stream velocity was 7800. The mean velocities, Reynolds stresses analyzed in both Cartesian and curvilinear coordinate systems, eddy viscosity, correlation coefficient and third order moments are discussed. The results indicate that, due to the enhanced turbulence intensity and shear rate in the fully rough case, distinct elevated regions of vertical and shear Reynolds stresses are consistent upstream of the leading edge of the step while the magnitude of the Reynolds stresses are consistently higher than observed in the smooth case. The correlation coefficient, eddy viscosity and third order moments also show distinct elevated regions upstream of the leading edge of the step in the fully rough case. Above the step, distinct elevated regions of the Reynolds stresses, eddy viscosity and correlation coefficient are observed in both cases with the peak values at a vertical location corresponding to the maximum elevation of the mean separating streamline.
{"title":"The Effects of Upstream Wall Roughness on Separated and Reattached Flows Over a Forward-Facing Step","authors":"S. Kumahor, Xingjun Fang, W. Ediger, M. Tachie","doi":"10.1115/fedsm2020-20257","DOIUrl":"https://doi.org/10.1115/fedsm2020-20257","url":null,"abstract":"\u0000 Separating and reattaching turbulent flows induced by a forward-facing step submerged in thick oncoming turbulent boundary layers developed over smooth and rough walls were investigated using time-resolved particle image velocimetry. Both smooth and fully rough upstream bottom wall conditions were examined and the resultant oncoming boundary layer thickness were 4.3 and 6.7 times the step height, respectively. The Reynolds number based on the step height and free-stream velocity was 7800. The mean velocities, Reynolds stresses analyzed in both Cartesian and curvilinear coordinate systems, eddy viscosity, correlation coefficient and third order moments are discussed. The results indicate that, due to the enhanced turbulence intensity and shear rate in the fully rough case, distinct elevated regions of vertical and shear Reynolds stresses are consistent upstream of the leading edge of the step while the magnitude of the Reynolds stresses are consistently higher than observed in the smooth case. The correlation coefficient, eddy viscosity and third order moments also show distinct elevated regions upstream of the leading edge of the step in the fully rough case. Above the step, distinct elevated regions of the Reynolds stresses, eddy viscosity and correlation coefficient are observed in both cases with the peak values at a vertical location corresponding to the maximum elevation of the mean separating streamline.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121068613","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}
Particle size and settling speed determine the rate of particulate mass transfer from the ocean surface to the sea bed. Turbulent shear in the ocean can act on large, faster-settling flocculated particles to break them into slower-settling primary particles or sub-aggregates. However, it is difficult to understand the disruption behavior of aggregates and their response to varying shear forces due to the complex ocean environment. A study was conducted to simulate the disruption behavior of marine aggregates in the mixed layer of the ocean. The breakup process was investigated by aggregating and disrupting flocs of bentonite clay particles in a rotating and oscillating cylindrical tank 10 cm in diameter filled with salt water. This laboratory tank, which operated based on an extension of Stokes’ second problem inside a cylinder, created laminar oscillating flow superimposed on a constant rotation. This motion allowed the bentonite particles to aggregate near the center of the tank but also exposed large aggregates to high shear forces near the wall. A high-speed camera system was used, along with particle tracking measurements and image processing techniques, to capture the breakup of the large particle aggregates and locate their radial position. The breakup response of large aggregates and the sizes of their daughter particles after breakup were quantified using the facility. The disruption strength of the aggregated particles is presented and discussed relative to their exposure to varying amounts of laminar shear.
{"title":"Disruption Behavior of Aggregates in a Rotating/Oscillating Cylindrical Tank and Implications for Particle Transport in the Ocean","authors":"Yixuan Song, M. Rau","doi":"10.1115/fedsm2020-20237","DOIUrl":"https://doi.org/10.1115/fedsm2020-20237","url":null,"abstract":"\u0000 Particle size and settling speed determine the rate of particulate mass transfer from the ocean surface to the sea bed. Turbulent shear in the ocean can act on large, faster-settling flocculated particles to break them into slower-settling primary particles or sub-aggregates. However, it is difficult to understand the disruption behavior of aggregates and their response to varying shear forces due to the complex ocean environment. A study was conducted to simulate the disruption behavior of marine aggregates in the mixed layer of the ocean. The breakup process was investigated by aggregating and disrupting flocs of bentonite clay particles in a rotating and oscillating cylindrical tank 10 cm in diameter filled with salt water. This laboratory tank, which operated based on an extension of Stokes’ second problem inside a cylinder, created laminar oscillating flow superimposed on a constant rotation. This motion allowed the bentonite particles to aggregate near the center of the tank but also exposed large aggregates to high shear forces near the wall. A high-speed camera system was used, along with particle tracking measurements and image processing techniques, to capture the breakup of the large particle aggregates and locate their radial position. The breakup response of large aggregates and the sizes of their daughter particles after breakup were quantified using the facility. The disruption strength of the aggregated particles is presented and discussed relative to their exposure to varying amounts of laminar shear.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127540181","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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