Abstract Developed in this paper is a theoretical description of the fluid flow involved in contactless transport systems that operate using squeeze-film levitation. Regular perturbation methods are employed to solve the appropriate Reynolds equation that governs the viscous, compressible flow of air in the slender film separating the oscillator and the levitated object. The resulting reduced formulation allows efficient computation of the time-averaged levitation force and moment induced by fluid pressure, as well as the accompanying quasistatic thrust force that accounts additionally for shear stresses. Investigated, in particular, is the possibility of combining two distinct methods of thrust generation that have been experimentally demonstrated in previous studies – (i) inclination of the levitated body and (ii) generation of asymmetrical flexural deformations, such as travelling waves, on the oscillator surface – the latter of which is shown to allow a transition from the typically repulsive levitation force to one that is attractive. Computations reveal that systematic control of the inclination angle can provide significant performance benefits for squeeze-film transport systems. In the case of attractive levitation, the amount of improvement that can be obtained appears to correlate closely with the degree of lateral asymmetry exhibited by the flexural oscillations.
{"title":"Benefits of controlled inclination for contactless transport by squeeze-film levitation","authors":"Sankaran Ramanarayanan, A. L. Sánchez","doi":"10.1017/flo.2023.22","DOIUrl":"https://doi.org/10.1017/flo.2023.22","url":null,"abstract":"Abstract Developed in this paper is a theoretical description of the fluid flow involved in contactless transport systems that operate using squeeze-film levitation. Regular perturbation methods are employed to solve the appropriate Reynolds equation that governs the viscous, compressible flow of air in the slender film separating the oscillator and the levitated object. The resulting reduced formulation allows efficient computation of the time-averaged levitation force and moment induced by fluid pressure, as well as the accompanying quasistatic thrust force that accounts additionally for shear stresses. Investigated, in particular, is the possibility of combining two distinct methods of thrust generation that have been experimentally demonstrated in previous studies – (i) inclination of the levitated body and (ii) generation of asymmetrical flexural deformations, such as travelling waves, on the oscillator surface – the latter of which is shown to allow a transition from the typically repulsive levitation force to one that is attractive. Computations reveal that systematic control of the inclination angle can provide significant performance benefits for squeeze-film transport systems. In the case of attractive levitation, the amount of improvement that can be obtained appears to correlate closely with the degree of lateral asymmetry exhibited by the flexural oscillations.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"56600654","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}
Abstract Cohesive particulate flows play an important role in environmental fluid dynamics, as well as in a wide variety of civil and process engineering applications. However, the scaling laws, constitutive equations and continuum field descriptions governing such flows are currently less well understood than for their non-cohesive counterparts. Grain-resolved simulations represent an essential tool for addressing this shortcoming, along with theoretical investigations, laboratory experiments and field studies. Here we provide a tutorial introduction to simulations of fine-grained sediments in viscous fluids, along with an overview of some representative insights that this approach has yielded to date. After a brief review of the key physical concepts governing van der Waals forces as the main cohesive effect for subaqueous sediment suspensions, we discuss their incorporation into particle-resolved simulations based on the immersed boundary method. We subsequently describe simulations of cohesive particles in several model turbulent flows, which demonstrate the emergence of a statistical equilibrium between the growth and break-up of aggregates. As a next step, we review the influence of cohesive forces on the settling behaviour of dense suspensions, before moving on to submerged granular collapses. Throughout the article, we highlight open research questions in the field of cohesive particulate flows whose investigation may benefit from grain-resolved simulations.
{"title":"Investigating cohesive sediment dynamics in open waters via grain-resolved simulations","authors":"B. Vowinckel, K. Zhao, R. Zhu, E. Meiburg","doi":"10.1017/flo.2023.20","DOIUrl":"https://doi.org/10.1017/flo.2023.20","url":null,"abstract":"Abstract Cohesive particulate flows play an important role in environmental fluid dynamics, as well as in a wide variety of civil and process engineering applications. However, the scaling laws, constitutive equations and continuum field descriptions governing such flows are currently less well understood than for their non-cohesive counterparts. Grain-resolved simulations represent an essential tool for addressing this shortcoming, along with theoretical investigations, laboratory experiments and field studies. Here we provide a tutorial introduction to simulations of fine-grained sediments in viscous fluids, along with an overview of some representative insights that this approach has yielded to date. After a brief review of the key physical concepts governing van der Waals forces as the main cohesive effect for subaqueous sediment suspensions, we discuss their incorporation into particle-resolved simulations based on the immersed boundary method. We subsequently describe simulations of cohesive particles in several model turbulent flows, which demonstrate the emergence of a statistical equilibrium between the growth and break-up of aggregates. As a next step, we review the influence of cohesive forces on the settling behaviour of dense suspensions, before moving on to submerged granular collapses. Throughout the article, we highlight open research questions in the field of cohesive particulate flows whose investigation may benefit from grain-resolved simulations.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42423191","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}
Diego A. Huyke, Alexandre S. Avaro, T. Kroll, J. Santiago
Abstract Microfluidic mixers offer new possibilities for the study of fast reaction kinetics down to the microsecond time scale, and methods such as soft X-ray absorption spectroscopy are powerful analysis techniques. These systems impose challenging constraints on mixing time scales, sample volume, detection region size and component materials. The current work presents a novel micromixer and jet device which aims to address these limitations. The system uses a so-called ‘theta’ mixer consisting of two sintered and fused glass capillaries. Sample and carrier fluids are injected separately into the inlets of the adjacent capillaries. At the downstream end, the two streams exit two micron-scale adjoining nozzles and form a single free-standing jet. The flow-rate difference between the two streams results in the rapid acceleration and lamination of the sample stream. This creates a small transverse dimension and induces diffusive mixing of the sample and carrier stream solutions within a time scale of 0.9 microseconds. The reaction occurs at or very near a free surface so that reactants and products are more directly accessible to interrogation using soft X-ray. We use a simple diffusion model and quantitative measurements of fluorescence quenching (of fluorescein with potassium iodide) to characterize the mixing dynamics across flow-rate ratios.
{"title":"Stream lamination and rapid mixing in a microfluidic jet for X-ray spectroscopy studies","authors":"Diego A. Huyke, Alexandre S. Avaro, T. Kroll, J. Santiago","doi":"10.1017/flo.2023.15","DOIUrl":"https://doi.org/10.1017/flo.2023.15","url":null,"abstract":"Abstract Microfluidic mixers offer new possibilities for the study of fast reaction kinetics down to the microsecond time scale, and methods such as soft X-ray absorption spectroscopy are powerful analysis techniques. These systems impose challenging constraints on mixing time scales, sample volume, detection region size and component materials. The current work presents a novel micromixer and jet device which aims to address these limitations. The system uses a so-called ‘theta’ mixer consisting of two sintered and fused glass capillaries. Sample and carrier fluids are injected separately into the inlets of the adjacent capillaries. At the downstream end, the two streams exit two micron-scale adjoining nozzles and form a single free-standing jet. The flow-rate difference between the two streams results in the rapid acceleration and lamination of the sample stream. This creates a small transverse dimension and induces diffusive mixing of the sample and carrier stream solutions within a time scale of 0.9 microseconds. The reaction occurs at or very near a free surface so that reactants and products are more directly accessible to interrogation using soft X-ray. We use a simple diffusion model and quantitative measurements of fluorescence quenching (of fluorescein with potassium iodide) to characterize the mixing dynamics across flow-rate ratios.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46292028","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}
Abstract Ionic fluids subjected to externally applied electric fields experience Joule heating, which increases with the increased electric field and ionic conductivity of the medium. Temperature gradients induced by Joule heating can create buoyancy-driven flows produced by local density changes, as well as electrothermal transport due to the temperature-dependent variations in fluid permittivity and conductivity. This manuscript considers Joule heating-induced transport in microchannels by a pair of electrodes under alternating current electric fields. Resulting buoyancy-driven and alternating current electrothermal (ACET) flows are investigated theoretically, numerically and experimentally. Proper normalizations of the governing equations led to the ratio of the electrothermal and buoyancy velocities, as a new non-dimensional parameter, which enabled the construction of a phase diagram that can predict the dominance of ACET and buoyancy-driven flows as a function of the channel size and electric field. Numerical results were used to verify the phase diagram in various height microchannels for different ionic conductivity fluids and electric fields, while the numerical results were validated using the micro-particle-image velocimetry technique. The results show that ACET flow prevails when the channel dimensions are small, and the electric potentials are high, whereas buoyancy-driven flow becomes dominant for larger channel heights. The present study brings insights into Joule heating-induced transport phenomena in microfluidic devices and provides a pathway for the design and utilization of ACET-based devices by properly considering the co-occurring buoyancy-driven flow.
{"title":"Competing effects of buoyancy-driven and electrothermal flows for Joule heating-induced transport in microchannels","authors":"Mohammad K. D. Manshadi, A. Beskok","doi":"10.1017/flo.2023.19","DOIUrl":"https://doi.org/10.1017/flo.2023.19","url":null,"abstract":"Abstract Ionic fluids subjected to externally applied electric fields experience Joule heating, which increases with the increased electric field and ionic conductivity of the medium. Temperature gradients induced by Joule heating can create buoyancy-driven flows produced by local density changes, as well as electrothermal transport due to the temperature-dependent variations in fluid permittivity and conductivity. This manuscript considers Joule heating-induced transport in microchannels by a pair of electrodes under alternating current electric fields. Resulting buoyancy-driven and alternating current electrothermal (ACET) flows are investigated theoretically, numerically and experimentally. Proper normalizations of the governing equations led to the ratio of the electrothermal and buoyancy velocities, as a new non-dimensional parameter, which enabled the construction of a phase diagram that can predict the dominance of ACET and buoyancy-driven flows as a function of the channel size and electric field. Numerical results were used to verify the phase diagram in various height microchannels for different ionic conductivity fluids and electric fields, while the numerical results were validated using the micro-particle-image velocimetry technique. The results show that ACET flow prevails when the channel dimensions are small, and the electric potentials are high, whereas buoyancy-driven flow becomes dominant for larger channel heights. The present study brings insights into Joule heating-induced transport phenomena in microfluidic devices and provides a pathway for the design and utilization of ACET-based devices by properly considering the co-occurring buoyancy-driven flow.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41397405","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}
Abstract Locomoting organisms often carry loads such as captured prey or young. Load-carrying effects on high-Reynolds-number flight have been studied, but the fluid dynamics of load carrying by low-Reynolds-number microorganisms has not. We studied low-Reynolds-number load carrying using unicellular choanoflagellates, which wave a flagellum to swim and create a water current transporting bacterial prey to a food-capturing collar of microvilli. A regularized Stokeslet framework was used to model the hydrodynamics of a swimming choanoflagellate with bacterial prey on its collar. Both the model and microvideography of choanoflagellates showed that swimming speed decreases as number of prey being carried increases. Flux of water into the capture zone is reduced by bacteria on the collar, which redirect the water flow and occlude parts of the collar. Feeding efficiency (prey captured per work to produce the feeding current) is decreased more by large prey, prey in the plane of flagellar beating and prey near microvillar tips than by prey in other locations. Some choanoflagellates can attach themselves to surfaces. We found that the reduction in flux due to bacterial prey on the collars of these attached thecate cells was similar to the reduction in flux for swimmers.
{"title":"Effects of prey capture on the swimming and feeding performance of choanoflagellates","authors":"H. Nguyen, E. Ross, R. Cortez, L. Fauci, M. Koehl","doi":"10.1017/flo.2023.16","DOIUrl":"https://doi.org/10.1017/flo.2023.16","url":null,"abstract":"Abstract Locomoting organisms often carry loads such as captured prey or young. Load-carrying effects on high-Reynolds-number flight have been studied, but the fluid dynamics of load carrying by low-Reynolds-number microorganisms has not. We studied low-Reynolds-number load carrying using unicellular choanoflagellates, which wave a flagellum to swim and create a water current transporting bacterial prey to a food-capturing collar of microvilli. A regularized Stokeslet framework was used to model the hydrodynamics of a swimming choanoflagellate with bacterial prey on its collar. Both the model and microvideography of choanoflagellates showed that swimming speed decreases as number of prey being carried increases. Flux of water into the capture zone is reduced by bacteria on the collar, which redirect the water flow and occlude parts of the collar. Feeding efficiency (prey captured per work to produce the feeding current) is decreased more by large prey, prey in the plane of flagellar beating and prey near microvillar tips than by prey in other locations. Some choanoflagellates can attach themselves to surfaces. We found that the reduction in flux due to bacterial prey on the collars of these attached thecate cells was similar to the reduction in flux for swimmers.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46592896","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}
Abstract The importance of buoyancy relative to free-stream flow is described using an adapted Froude number $Fr' = U/f_0^{1/3}$, where $U$ is the flow speed and $f_0$ is the exhaust buoyancy flux per unit length. We varied $Fr'$ by changing the free-stream flow rate, the exhaust flow rate and the buoyancy of the exhaust. We have experimentally identified two flow regimes, depending on the value of $Fr'$. For high $Fr'$ (low buoyancy), dispersion is driven by inertial forces in the wake and the amount of a pollutant in the wake is independent of $Fr'$. For moderate $Fr'$, a wall plume develops up the back of the step, directly feeding the pollutant into the shear layer, but without altering the shape of the wake. This wall plume reduces the amount of pollutant trapped behind the step. We developed an analytic model to describe the quantity of pollutant trapped behind the step. The model predicts the transition from buoyancy being negligible to being the dominant transport mechanism within the wake. We have hypothesised and observed some evidence of a third regime at low $Fr'$, when the buoyancy is sufficient to distort the macrostructure of the shear layer and wake.
{"title":"The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step","authors":"Samuel Charlwood, D. Frank, M. D. Davies Wykes","doi":"10.1017/flo.2023.14","DOIUrl":"https://doi.org/10.1017/flo.2023.14","url":null,"abstract":"Abstract The importance of buoyancy relative to free-stream flow is described using an adapted Froude number $Fr' = U/f_0^{1/3}$, where $U$ is the flow speed and $f_0$ is the exhaust buoyancy flux per unit length. We varied $Fr'$ by changing the free-stream flow rate, the exhaust flow rate and the buoyancy of the exhaust. We have experimentally identified two flow regimes, depending on the value of $Fr'$. For high $Fr'$ (low buoyancy), dispersion is driven by inertial forces in the wake and the amount of a pollutant in the wake is independent of $Fr'$. For moderate $Fr'$, a wall plume develops up the back of the step, directly feeding the pollutant into the shear layer, but without altering the shape of the wake. This wall plume reduces the amount of pollutant trapped behind the step. We developed an analytic model to describe the quantity of pollutant trapped behind the step. The model predicts the transition from buoyancy being negligible to being the dominant transport mechanism within the wake. We have hypothesised and observed some evidence of a third regime at low $Fr'$, when the buoyancy is sufficient to distort the macrostructure of the shear layer and wake.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45783376","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}
Adrien Rouviere, L. Pascal, F. Méry, E. Simon, S. Gratton
Abstract Predicting the laminar to turbulent transition is an important aspect of computational fluid dynamics because of its impact on skin friction. Traditional transition prediction methods such as local stability theory or the parabolized stability equation method do not allow for the consideration of strongly non-parallel boundary layer flows, as in the presence of surface defects (bumps, steps, gaps, etc.). A neural network approach, based on an extensive database of two-dimensional incompressible boundary layer stability studies in the presence of gap-like surface defects, is used. These studies consist of linearized Navier–Stokes calculations and provide information on the effect of surface irregularity geometry and aerodynamic conditions on the transition to turbulence. The physical and geometrical parameters characterizing the defect and the flow are then provided to a neural network whose outputs inform about the effect of a given gap on the transition through the ${rm Delta} N$ method (where N represents the amplification of the boundary layer instabilities).
{"title":"Neural prediction model for transition onset of a boundary layer in presence of two-dimensional surface defects","authors":"Adrien Rouviere, L. Pascal, F. Méry, E. Simon, S. Gratton","doi":"10.1017/flo.2023.17","DOIUrl":"https://doi.org/10.1017/flo.2023.17","url":null,"abstract":"Abstract Predicting the laminar to turbulent transition is an important aspect of computational fluid dynamics because of its impact on skin friction. Traditional transition prediction methods such as local stability theory or the parabolized stability equation method do not allow for the consideration of strongly non-parallel boundary layer flows, as in the presence of surface defects (bumps, steps, gaps, etc.). A neural network approach, based on an extensive database of two-dimensional incompressible boundary layer stability studies in the presence of gap-like surface defects, is used. These studies consist of linearized Navier–Stokes calculations and provide information on the effect of surface irregularity geometry and aerodynamic conditions on the transition to turbulence. The physical and geometrical parameters characterizing the defect and the flow are then provided to a neural network whose outputs inform about the effect of a given gap on the transition through the ${rm Delta} N$ method (where N represents the amplification of the boundary layer instabilities).","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41615105","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}
Enwei Zhang, Zhan Wang, Wangxia Wu, Xiaoliang Wang, Qing-quan Liu
Abstract The present paper simplifies the naturally formed dunes (riverbeds) as large-scale three-dimensional staggered wavy walls to investigate the features of the accompanying secondary flows and streamwise vortices via large-eddy simulation. A comparison between the swirling strength and the mean velocities suggests where a secondary flow induces upwash or downwash motions. Moreover, we propose a pseudo-convex wall mechanism to interpret the directionality of the secondary flow. The centrifugal instability criterion is then used to reveal the generation of the streamwise vortices. Based on these analytical results, we found that the streamwise vortices are generated in the separation and reattachment points on both characteristic longitudinal–vertical and horizontal cross-sections, which is related to the curvature effect of the turbulent shear layer. Furthermore, the maximum Görtler number characterized by the ratio of centrifugal to viscous effects suggests that, for fixed ratio of spanwise- to streamwise-wavelength cases, the strongest centrifugal instability occurring on the longitudinal–vertical cross-section gradually dominates with the increases in amplitude. A similar trend for the cases with varied spanwise wavelength can also be found. It is also found that the streamwise vortices are generated more readily via transverse flow around the crest near the separation and reattachment points when the ratio of spanwise- to streamwise-wavelength equals 1.
{"title":"Secondary flow and streamwise vortices in three-dimensional staggered wavy-wall turbulence","authors":"Enwei Zhang, Zhan Wang, Wangxia Wu, Xiaoliang Wang, Qing-quan Liu","doi":"10.1017/flo.2023.13","DOIUrl":"https://doi.org/10.1017/flo.2023.13","url":null,"abstract":"Abstract The present paper simplifies the naturally formed dunes (riverbeds) as large-scale three-dimensional staggered wavy walls to investigate the features of the accompanying secondary flows and streamwise vortices via large-eddy simulation. A comparison between the swirling strength and the mean velocities suggests where a secondary flow induces upwash or downwash motions. Moreover, we propose a pseudo-convex wall mechanism to interpret the directionality of the secondary flow. The centrifugal instability criterion is then used to reveal the generation of the streamwise vortices. Based on these analytical results, we found that the streamwise vortices are generated in the separation and reattachment points on both characteristic longitudinal–vertical and horizontal cross-sections, which is related to the curvature effect of the turbulent shear layer. Furthermore, the maximum Görtler number characterized by the ratio of centrifugal to viscous effects suggests that, for fixed ratio of spanwise- to streamwise-wavelength cases, the strongest centrifugal instability occurring on the longitudinal–vertical cross-section gradually dominates with the increases in amplitude. A similar trend for the cases with varied spanwise wavelength can also be found. It is also found that the streamwise vortices are generated more readily via transverse flow around the crest near the separation and reattachment points when the ratio of spanwise- to streamwise-wavelength equals 1.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41362388","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}
Oussama El Mokkadem, Xintong Chen, Charlene Phan, J. Delva, P. Joseph, A. Dazin, F. Romanò
Abstract The flow dynamics of small-width wall-attached jets generated by a Coand-effect nozzle is investigated by unsteady Reynolds-averaged Navier–Stokes simulations. The data are validated by comparison with hot-wire velocity measurements performed on the same flow configurations. The jets exhibit a complex topology strongly influenced not only by the spanwise vorticity (as usually observed in wall jets) but also by a vorticity component normal to the wall and induced by the shear layer developing on the jet sides. This results in an original U-shaped jet whose characteristics are studied in detail for three different mass flow rates. The robustness of the flow topology on a larger range of injected mass flow rates is finally presented and discussed in terms of the injected momentum near the wall. The resulting flow profiles point out that our injector is expected to be a promising candidate for active flow control in gas-turbine compressors for aeronautical and energy applications.
{"title":"Small-width wall-attached Coandǎ jets for flow control","authors":"Oussama El Mokkadem, Xintong Chen, Charlene Phan, J. Delva, P. Joseph, A. Dazin, F. Romanò","doi":"10.1017/flo.2023.9","DOIUrl":"https://doi.org/10.1017/flo.2023.9","url":null,"abstract":"Abstract The flow dynamics of small-width wall-attached jets generated by a Coand-effect nozzle is investigated by unsteady Reynolds-averaged Navier–Stokes simulations. The data are validated by comparison with hot-wire velocity measurements performed on the same flow configurations. The jets exhibit a complex topology strongly influenced not only by the spanwise vorticity (as usually observed in wall jets) but also by a vorticity component normal to the wall and induced by the shear layer developing on the jet sides. This results in an original U-shaped jet whose characteristics are studied in detail for three different mass flow rates. The robustness of the flow topology on a larger range of injected mass flow rates is finally presented and discussed in terms of the injected momentum near the wall. The resulting flow profiles point out that our injector is expected to be a promising candidate for active flow control in gas-turbine compressors for aeronautical and energy applications.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48719476","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}
Abstract The knuckleball is considered to be one of the hardest pitches to hit in baseball due to its seemingly unpredictable motion. It has gained popularity in cricket in recent times. It is shown that the delivery referred to as knuckleball in cricket, at present, does not exhibit a zigzag motion and is, therefore, a misnomer. We propose a delivery in cricket that is associated with an erratic trajectory similar to the knuckleball pitch in baseball. Force measurement experiments in a wind tunnel on a new cricket ball in various orientations of the seam to the incoming flow and at different Reynolds number are carried out. The results are utilized to estimate the trajectory of knuckleball deliveries. The key parameters are the seam angle, speed and spin rate of the ball at the time of its release. Their effect on the trajectory is studied in detail. The optimal combination of these parameters that result in a knuckleball, which is likely hard for the batter to play, is identified.
{"title":"Is a baseball like knuckleball possible in cricket?","authors":"Kunjal Shah, S. Mittal","doi":"10.1017/flo.2023.12","DOIUrl":"https://doi.org/10.1017/flo.2023.12","url":null,"abstract":"Abstract The knuckleball is considered to be one of the hardest pitches to hit in baseball due to its seemingly unpredictable motion. It has gained popularity in cricket in recent times. It is shown that the delivery referred to as knuckleball in cricket, at present, does not exhibit a zigzag motion and is, therefore, a misnomer. We propose a delivery in cricket that is associated with an erratic trajectory similar to the knuckleball pitch in baseball. Force measurement experiments in a wind tunnel on a new cricket ball in various orientations of the seam to the incoming flow and at different Reynolds number are carried out. The results are utilized to estimate the trajectory of knuckleball deliveries. The key parameters are the seam angle, speed and spin rate of the ball at the time of its release. Their effect on the trajectory is studied in detail. The optimal combination of these parameters that result in a knuckleball, which is likely hard for the batter to play, is identified.","PeriodicalId":93752,"journal":{"name":"Flow (Cambridge, England)","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49021630","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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