Jorge A. Ricardo, Davi Antônio dos Santos, Elisan dos Santos Magalhães
The present work addresses the subsonic aerodynamic coefficients model for bluff ellipsoidal hulls at transitional and turbulent Reynolds number. The drag, lift, and moment aerodynamic coefficients model are based on computational fluid dynamics (CFD) simulations for four bluff ellipsoids with aspect ratio of 1, 2, 3, and 4, in the Reynolds number range of 1 × 103 to 2 × 106 and angle of attack range from 0 to 20 degrees. The Large Eddy Simulation (LES) turbulence model is used with the sub-grid turbulence model Wall-Adapting Local-Eddy Viscosity (WALE) to solve the fluid field. To reduce computational simulation time, at a first instant, the mesh is gradually refined until the point that it does not influence anymore in the final result (mesh independence). For each aerodynamic coefficient a nonlinear equation structure, valid for all the ellipsoids, is proposed as a parametric model with parameters estimated using the least mean square algorithm applied to the results of the computational fluid dynamics simulations. The proposed equations have a superior performance, in terms of precision and number of terms, when compared to polynomial equations fitted to the same data.
{"title":"Aerodynamic Subsonic Model at Transitional/Turbulent Reynolds Number for Bluff-Ellipsoidal Hulls","authors":"Jorge A. Ricardo, Davi Antônio dos Santos, Elisan dos Santos Magalhães","doi":"10.1115/fedsm2020-20340","DOIUrl":"https://doi.org/10.1115/fedsm2020-20340","url":null,"abstract":"\u0000 The present work addresses the subsonic aerodynamic coefficients model for bluff ellipsoidal hulls at transitional and turbulent Reynolds number. The drag, lift, and moment aerodynamic coefficients model are based on computational fluid dynamics (CFD) simulations for four bluff ellipsoids with aspect ratio of 1, 2, 3, and 4, in the Reynolds number range of 1 × 103 to 2 × 106 and angle of attack range from 0 to 20 degrees. The Large Eddy Simulation (LES) turbulence model is used with the sub-grid turbulence model Wall-Adapting Local-Eddy Viscosity (WALE) to solve the fluid field. To reduce computational simulation time, at a first instant, the mesh is gradually refined until the point that it does not influence anymore in the final result (mesh independence). For each aerodynamic coefficient a nonlinear equation structure, valid for all the ellipsoids, is proposed as a parametric model with parameters estimated using the least mean square algorithm applied to the results of the computational fluid dynamics simulations. The proposed equations have a superior performance, in terms of precision and number of terms, when compared to polynomial equations fitted to the same data.","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":"134139127","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}
The application of radially lobed nozzles has seen renewed challenges in the recent past with their roles in combustion chambers and passive flow control. The free jet flow from such nozzles has been studied for different flow conditions and compared to jets from round nozzles, verifying their improved mixing abilities. The precise mixing mechanisms of these nozzles are, however, not entirely understood and yet to be analyzed for typical jet parameters and excitation modes. While past studies have proposed the presence of spanwise Kelvin-Helmholtz instability modes, the roll-up frequencies of the structures indicate more than one primary structure, which is challenging to resolve experimentally. The present study carries out three dimensional CFD simulations of the flow from a tubular lobed nozzle to identify instability mechanisms and vortex dynamics that lead to enhanced mixing. We initially validate the model against existing hotwire and LDV data following which a range of Large Eddy Simulations (LES) are carried out. The free jet flow was at a Reynolds number of around 5 × 104, based on the effective jet diameter. Initial results are compared to that of a round nozzle to demonstrate changes in mixing mechanisms. The lobed nozzle simulations confirmed the presence of K-H-like modes and their evolution. We also track the formation and the transport of coherent structures from the tubular part of the nozzle to the core flow, to reveal the evolution of the large-scale streamwise modes at the crests and corresponding horseshoe-like structures at the troughs.
{"title":"Analysis of the Vortex Dynamics and Instability Mechanisms for a Lobed Nozzle Jet","authors":"Aarthi Sekaran, N. Amini","doi":"10.1115/fedsm2020-20169","DOIUrl":"https://doi.org/10.1115/fedsm2020-20169","url":null,"abstract":"\u0000 The application of radially lobed nozzles has seen renewed challenges in the recent past with their roles in combustion chambers and passive flow control. The free jet flow from such nozzles has been studied for different flow conditions and compared to jets from round nozzles, verifying their improved mixing abilities. The precise mixing mechanisms of these nozzles are, however, not entirely understood and yet to be analyzed for typical jet parameters and excitation modes. While past studies have proposed the presence of spanwise Kelvin-Helmholtz instability modes, the roll-up frequencies of the structures indicate more than one primary structure, which is challenging to resolve experimentally.\u0000 The present study carries out three dimensional CFD simulations of the flow from a tubular lobed nozzle to identify instability mechanisms and vortex dynamics that lead to enhanced mixing. We initially validate the model against existing hotwire and LDV data following which a range of Large Eddy Simulations (LES) are carried out. The free jet flow was at a Reynolds number of around 5 × 104, based on the effective jet diameter. Initial results are compared to that of a round nozzle to demonstrate changes in mixing mechanisms. The lobed nozzle simulations confirmed the presence of K-H-like modes and their evolution. We also track the formation and the transport of coherent structures from the tubular part of the nozzle to the core flow, to reveal the evolution of the large-scale streamwise modes at the crests and corresponding horseshoe-like structures at the troughs.","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":"115507034","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}
Cavitation generates a portion of cavities called a cavitation cloud, which performs a collective unsteady motion of repeating the process of growth and collapse. In particular, it is considered that a high-pressure shock wave propagates associated with the collapse. In order to understand such unsteady behaviors of the cavitation cloud, much effort has been made for the numerical analysis of internal flows of the cavitation cloud. However, it is not clear how such a cavitation cloud can be identified as a physical entity nor how its unsteady collective motion can be elucidated in the context of the multiphase fluid flow. In this study, we make a two-dimensional numerical analysis of the multiphase flow of the submerged bubbly water jet injecting into still water through a nozzle. To model the bubbly water jet, we employ the mixture model of liquids and gases, and we utilize the Smoothed Particle Hydrodynamics method for the numerical analysis of the unsteady flows in Lagrangian description. Finally, in order to clarify the unsteady behaviors of the cloud cavitation, we show how the cavitation cloud can be generated in the context of velocity fields in the multiphase flow and in particular, we clarify how twin vortices induced by the water jet play an essential role in the expansion and shrinkage of the cloud.
{"title":"Numerical Study of Unsteady Behavior of Cloud Cavitation by Smoothed Particle Hydrodynamics","authors":"T. Ushioku, Hiroaki Yoshimura","doi":"10.1115/fedsm2020-20117","DOIUrl":"https://doi.org/10.1115/fedsm2020-20117","url":null,"abstract":"\u0000 Cavitation generates a portion of cavities called a cavitation cloud, which performs a collective unsteady motion of repeating the process of growth and collapse. In particular, it is considered that a high-pressure shock wave propagates associated with the collapse. In order to understand such unsteady behaviors of the cavitation cloud, much effort has been made for the numerical analysis of internal flows of the cavitation cloud. However, it is not clear how such a cavitation cloud can be identified as a physical entity nor how its unsteady collective motion can be elucidated in the context of the multiphase fluid flow. In this study, we make a two-dimensional numerical analysis of the multiphase flow of the submerged bubbly water jet injecting into still water through a nozzle. To model the bubbly water jet, we employ the mixture model of liquids and gases, and we utilize the Smoothed Particle Hydrodynamics method for the numerical analysis of the unsteady flows in Lagrangian description. Finally, in order to clarify the unsteady behaviors of the cloud cavitation, we show how the cavitation cloud can be generated in the context of velocity fields in the multiphase flow and in particular, we clarify how twin vortices induced by the water jet play an essential role in the expansion and shrinkage of the cloud.","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":"117059458","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}
Junshi Wang, Pan Han, Ruixuan Tang, Hong Tang, Y. Kwon, J. Xi, Haibo Dong
Snoring is a common breathing disorder during sleep. It is hypothesized that head posture during sleep could change the bending angle and the cross-sectional area of the airway, which could cause changes in airflow and aerodynamic pressure during sleep. In this work, an experiment-driven computational study was conducted to examine the aerodynamics and pressure behavior in human upper airway during snoring. An anatomically accurate human upper airway model associated with a dynamic uvula was reconstructed from human magnetic resonance image (MRI) and high-speed photography. The airway bending at different head posture and the corresponding change in airway cross-sectional area are modeled based on measurements from literature. An immersed-boundary-method (IBM)-based direct numerical simulation (DNS) flow solver was adopted to simulate the corresponding unsteady flows of the bent airway model in all their complexity. Analyses were performed on vortex dynamics and pressure fluctuations in the pharyngeal airway. It was found that the vortex formation and aerodynamic pressure were significantly affected by the airway bending. A head-neck junction extension posture tends to facilitate the airflow through the upper human airway. Fast Fourier transformation (FFT) analysis of the pressure time history revealed the existence of higher order harmonics of base frequency with significant pressure amplitudes and energy intensities. The results of this study help better understand the pathology of snoring under the influence of head posture from an aerodynamic perspective.
{"title":"Effect of Head Posture on Airflow and Pressure Behavior of Human Upper Airway During Snoring","authors":"Junshi Wang, Pan Han, Ruixuan Tang, Hong Tang, Y. Kwon, J. Xi, Haibo Dong","doi":"10.1115/fedsm2020-20386","DOIUrl":"https://doi.org/10.1115/fedsm2020-20386","url":null,"abstract":"\u0000 Snoring is a common breathing disorder during sleep. It is hypothesized that head posture during sleep could change the bending angle and the cross-sectional area of the airway, which could cause changes in airflow and aerodynamic pressure during sleep. In this work, an experiment-driven computational study was conducted to examine the aerodynamics and pressure behavior in human upper airway during snoring. An anatomically accurate human upper airway model associated with a dynamic uvula was reconstructed from human magnetic resonance image (MRI) and high-speed photography. The airway bending at different head posture and the corresponding change in airway cross-sectional area are modeled based on measurements from literature. An immersed-boundary-method (IBM)-based direct numerical simulation (DNS) flow solver was adopted to simulate the corresponding unsteady flows of the bent airway model in all their complexity. Analyses were performed on vortex dynamics and pressure fluctuations in the pharyngeal airway. It was found that the vortex formation and aerodynamic pressure were significantly affected by the airway bending. A head-neck junction extension posture tends to facilitate the airflow through the upper human airway. Fast Fourier transformation (FFT) analysis of the pressure time history revealed the existence of higher order harmonics of base frequency with significant pressure amplitudes and energy intensities. The results of this study help better understand the pathology of snoring under the influence of head posture from an aerodynamic perspective.","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":"117267065","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}
Nano- and micro-particles dispersion and deposition in a dilute gas-solid turbulent flow in a channel were studied. A pseudo-spectral DNS code was used to solve the Navier-Stokes equations, and to generate the instantaneous turbulent velocity fluctuation field for the gas flow. Under the one-way coupling assumption, the gas flow carries the particles, but the influence of particles on the flow can be neglected. To provide an understanding of the transport behavior of particles of different sizes, 200,000 monodisperse point particles with Stokes numbers of 0.1, 1, 5, 25, and 125 were introduced with a random distribution in the channel. The corresponding Lagrangian particle equation of motion, including the Stokes drag, the gravity, and the lift forces, were solved, and the trajectories of the particles for the duration of 10,000 wall units were evaluated for dilute suspension. The trap boundary condition on the lower and upper walls of the channel was assumed, and the deposition rates of particles with different sizes were evaluated and recorded as a function of time. Ensemble and time averaging of the simulation results were performed, and the corresponding concentration profiles and the deposition velocities of particles were evaluated for various conditions. A series of simulations were performed, and the effects of wall roughness, lift force, and the gravity direction on the deposition rate were carefully examined. It was found that the surface roughness and the direction of gravity in conjunction with the lift force significantly affect the fine particle deposition rate and could improve the agreement of the DNS simulation with the available experimental data.
{"title":"A DNS Study of the Dispersion and Deposition of Nano- and Micro-Particles in a Turbulent Channel Flow","authors":"Amir A. Mofakham, G. Ahmadi, J. McLaughlin","doi":"10.1115/fedsm2020-20110","DOIUrl":"https://doi.org/10.1115/fedsm2020-20110","url":null,"abstract":"\u0000 Nano- and micro-particles dispersion and deposition in a dilute gas-solid turbulent flow in a channel were studied. A pseudo-spectral DNS code was used to solve the Navier-Stokes equations, and to generate the instantaneous turbulent velocity fluctuation field for the gas flow. Under the one-way coupling assumption, the gas flow carries the particles, but the influence of particles on the flow can be neglected. To provide an understanding of the transport behavior of particles of different sizes, 200,000 monodisperse point particles with Stokes numbers of 0.1, 1, 5, 25, and 125 were introduced with a random distribution in the channel. The corresponding Lagrangian particle equation of motion, including the Stokes drag, the gravity, and the lift forces, were solved, and the trajectories of the particles for the duration of 10,000 wall units were evaluated for dilute suspension. The trap boundary condition on the lower and upper walls of the channel was assumed, and the deposition rates of particles with different sizes were evaluated and recorded as a function of time. Ensemble and time averaging of the simulation results were performed, and the corresponding concentration profiles and the deposition velocities of particles were evaluated for various conditions. A series of simulations were performed, and the effects of wall roughness, lift force, and the gravity direction on the deposition rate were carefully examined. It was found that the surface roughness and the direction of gravity in conjunction with the lift force significantly affect the fine particle deposition rate and could improve the agreement of the DNS simulation with the available experimental data.","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":"129396955","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}
This work presents an experimental study of the wake hydrodynamics of a three-blade contra-rotating propeller system (CRP) at advance ratio J = 0.7, 1 and 1.3. The study is carried out in a cavitation tunnel by employing a mixed hardware-software phase-locked acquisition and processing scheme. Flow measurements are thus phase-averaged based on both the forward and aft propeller angular position, so that the effect of their relative position on the flow features is investigated. Average and fluctuating velocity fields along with vorticity are presented and discussed. Strong interactions take place between the forward and aft propellers’ trailing vorticity with regular patterns of vortex reconnection and break-up which depend on the advance coefficient. Flow visualizations, carried out by inducing cavitation in the vortex cores, show that complex though organized patterns of helical coaxial vorticity occur within the wake.
{"title":"Hydrodynamics of the Wake of Contra-Rotating Propellers at Different Loading Conditions","authors":"F. Pereira, A. Capone, F. Felice","doi":"10.1115/fedsm2020-20098","DOIUrl":"https://doi.org/10.1115/fedsm2020-20098","url":null,"abstract":"\u0000 This work presents an experimental study of the wake hydrodynamics of a three-blade contra-rotating propeller system (CRP) at advance ratio J = 0.7, 1 and 1.3. The study is carried out in a cavitation tunnel by employing a mixed hardware-software phase-locked acquisition and processing scheme. Flow measurements are thus phase-averaged based on both the forward and aft propeller angular position, so that the effect of their relative position on the flow features is investigated. Average and fluctuating velocity fields along with vorticity are presented and discussed. Strong interactions take place between the forward and aft propellers’ trailing vorticity with regular patterns of vortex reconnection and break-up which depend on the advance coefficient. Flow visualizations, carried out by inducing cavitation in the vortex cores, show that complex though organized patterns of helical coaxial vorticity occur within the wake.","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":"117010353","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}
F. Rodrigues, Mohammadmahdi Abdollahzadehsangroudi, José C. Páscoa
An experimental investigation was conducted in order to understand the ability of plasma actuators to operate in three different modes: flow control, ice formation detection and ice accumulation prevention. When plasma actuators are operated with voltage levels, above the breakdown voltage, a plasma discharge surface is generated and with that, an ionic wind is produced. By using this phenomena, plasma actuators may be used to manipulate flow fields and control adjacent flows to the surface in which they are applied. However, a big part of the power applied to the device is dissipated as heat. Due to heat dissipation, the actuator surface temperature rises and the adjacent air is heated. Considering this, actuators may operate as ice prevention devices by heating the surface where they are applied and preventing the ice formation and accumulation. On the other hand, plasma actuators present a behavior similar to a capacitor and they may operate as a capacitive sensor. In the presence of water or ice on the top of the surface, the electric field changes and with that, several plasma actuator electrical features change as well. By monitoring that changes, the presence of water or ice on the top of the surface can be detected and the plasma actuator may be used as an ice sensor device. Therefore, in the present study a plasma actuator was experimentally tested operating in these three different operation modes and its feasibility to perform these different tasks is shown.
{"title":"Dielectric Barrier Discharge Plasma Actuators for Active Flow Control, Ice Formation Detection and Ice Accumulation Prevention","authors":"F. Rodrigues, Mohammadmahdi Abdollahzadehsangroudi, José C. Páscoa","doi":"10.1115/fedsm2020-20291","DOIUrl":"https://doi.org/10.1115/fedsm2020-20291","url":null,"abstract":"\u0000 An experimental investigation was conducted in order to understand the ability of plasma actuators to operate in three different modes: flow control, ice formation detection and ice accumulation prevention. When plasma actuators are operated with voltage levels, above the breakdown voltage, a plasma discharge surface is generated and with that, an ionic wind is produced. By using this phenomena, plasma actuators may be used to manipulate flow fields and control adjacent flows to the surface in which they are applied. However, a big part of the power applied to the device is dissipated as heat. Due to heat dissipation, the actuator surface temperature rises and the adjacent air is heated. Considering this, actuators may operate as ice prevention devices by heating the surface where they are applied and preventing the ice formation and accumulation. On the other hand, plasma actuators present a behavior similar to a capacitor and they may operate as a capacitive sensor. In the presence of water or ice on the top of the surface, the electric field changes and with that, several plasma actuator electrical features change as well. By monitoring that changes, the presence of water or ice on the top of the surface can be detected and the plasma actuator may be used as an ice sensor device. Therefore, in the present study a plasma actuator was experimentally tested operating in these three different operation modes and its feasibility to perform these different tasks is shown.","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":"128343527","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}
Small tubes and fins have long been used as methods to increase surface area for convective heat transfer in single-phase flow applications. As demands for high heat transfer effectiveness has increased, implementing evaporative phase-change heat transfer in conjunction with small fins, tubes, and surface structures in advanced heat exchanger and heat sink designs has become increasingly attractive. The complex two-phase flow that results from these configurations is poorly understood, particularly in how the gas phase interacts with the flow structure of the wake created by these bluff bodies. An experimental study of liquid-gas bubbly flow around a cylinder was performed to understand these complex flow physics. A 9.5 mm diameter cylinder was installed horizontally within a vertical water channel facility. A high-speed camera captured the movement of the liquid-gas mixture around the cylinder for a range of bubble sizes. Liquid Reynolds number, calculated based on the cylinder diameter, was varied approximately from 100 to 3000. Time-averaged probability of bubble presence was calculated to characterize the cylinder wake and its effects on the bubble motion. The influence of the liquid Reynolds number, superficial air velocity, and bubble size is discussed in the context of the observed two-phase flow patterns.
{"title":"Two-Phase Wakes in Adiabatic Liquid-Gas Flow Around a Cylinder","authors":"Dohwan Kim, M. Rau","doi":"10.1115/fedsm2020-20279","DOIUrl":"https://doi.org/10.1115/fedsm2020-20279","url":null,"abstract":"\u0000 Small tubes and fins have long been used as methods to increase surface area for convective heat transfer in single-phase flow applications. As demands for high heat transfer effectiveness has increased, implementing evaporative phase-change heat transfer in conjunction with small fins, tubes, and surface structures in advanced heat exchanger and heat sink designs has become increasingly attractive. The complex two-phase flow that results from these configurations is poorly understood, particularly in how the gas phase interacts with the flow structure of the wake created by these bluff bodies. An experimental study of liquid-gas bubbly flow around a cylinder was performed to understand these complex flow physics. A 9.5 mm diameter cylinder was installed horizontally within a vertical water channel facility. A high-speed camera captured the movement of the liquid-gas mixture around the cylinder for a range of bubble sizes. Liquid Reynolds number, calculated based on the cylinder diameter, was varied approximately from 100 to 3000. Time-averaged probability of bubble presence was calculated to characterize the cylinder wake and its effects on the bubble motion. The influence of the liquid Reynolds number, superficial air velocity, and bubble size is discussed in the context of the observed two-phase flow patterns.","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":"121474335","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}
The downhole liquid atomization by supersonic nozzle is an economic and efficient way to alleviate the liquid loading, but the optimal efficiency conditions are still not clear. In this paper, experimental studies were conducted in a 6-m long and 30-mm inner diameter vertical Perspex pipe to evaluate the performance of supersonic nozzle in different conditions. Camera was employed to record the characteristic of fluid flow downstream the nozzle, and the MATLAB was used in combination with DIP-image technology to determine the diameter of droplets. The experimental results show that mist is easy to be captured by the liquid bulk due to the liquid loading downstream the nozzle when the gas-liquid two phase flow pattern downstream nozzle is non-annular flow, thus leading to a failure of this technology. Due to the huge temperature drop in the annular flow condition, small fraction of mist is condensed into droplets and then attaches onto the pipe wall, forming liquid film. The remaining mist can still flow upwards. In this article, when the gas velocities upstream the nozzle range from 2.4m/s to 3.2m/s, the size of droplets range from 50μm to 1000μm correspondingly. Field application indicates that this technology under the effective operating envelops are able to be efficient to remove the liquid-loading, and the gas wells can maintain a long-term stable production.
{"title":"Experimental Study on Effective Operating Envelops of Nozzle to Mitigate Liquid Loading in Gas Wells","authors":"C. Xie, Yonghui Liu, Chengcheng Luo","doi":"10.1115/fedsm2020-20107","DOIUrl":"https://doi.org/10.1115/fedsm2020-20107","url":null,"abstract":"\u0000 The downhole liquid atomization by supersonic nozzle is an economic and efficient way to alleviate the liquid loading, but the optimal efficiency conditions are still not clear. In this paper, experimental studies were conducted in a 6-m long and 30-mm inner diameter vertical Perspex pipe to evaluate the performance of supersonic nozzle in different conditions. Camera was employed to record the characteristic of fluid flow downstream the nozzle, and the MATLAB was used in combination with DIP-image technology to determine the diameter of droplets. The experimental results show that mist is easy to be captured by the liquid bulk due to the liquid loading downstream the nozzle when the gas-liquid two phase flow pattern downstream nozzle is non-annular flow, thus leading to a failure of this technology. Due to the huge temperature drop in the annular flow condition, small fraction of mist is condensed into droplets and then attaches onto the pipe wall, forming liquid film. The remaining mist can still flow upwards. In this article, when the gas velocities upstream the nozzle range from 2.4m/s to 3.2m/s, the size of droplets range from 50μm to 1000μm correspondingly. Field application indicates that this technology under the effective operating envelops are able to be efficient to remove the liquid-loading, and the gas wells can maintain a long-term stable production.","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":"126523541","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}
This study investigates the active flow control on NACA0012 airfoil numerically by introducing dielectric barrier discharge (DBD) plasma actuators. The flow over the airfoil simulations were performed using ANSYS program for free-stream velocity 14.6 m/s with wide range of angle of attacks (from 0 to 20 degrees) on NACA0012 airfoil with applied voltage 16 kV across the electrodes. There are several plasma actuator models, which simulate the effect of the plasma actuator. This paper focuses on two numerical methods: Shyy model and Suzen model. They depend on calculating the induced body force of the plasma and import it in Navier Stokes equation as an external body force. Mesh independence study is performed on the airfoil and validate the results without plasma activation with the experimental results. Two actuators were added at positions 0.1 and 0.3 of the chord length to the airfoil and an investigation is performed on the lift CL and drag Cd coefficients of the airfoil without and with the activation of the plasma. Thereafter, a comparison between the numerical results of two different plasma simulation models that were applied.
{"title":"Simulations of Flow Separation Control Using Different Plasma Actuator Models","authors":"Hatem Abdelraouf, S. Z. Kassab, A. Elmekawy","doi":"10.1115/fedsm2020-20426","DOIUrl":"https://doi.org/10.1115/fedsm2020-20426","url":null,"abstract":"\u0000 This study investigates the active flow control on NACA0012 airfoil numerically by introducing dielectric barrier discharge (DBD) plasma actuators. The flow over the airfoil simulations were performed using ANSYS program for free-stream velocity 14.6 m/s with wide range of angle of attacks (from 0 to 20 degrees) on NACA0012 airfoil with applied voltage 16 kV across the electrodes. There are several plasma actuator models, which simulate the effect of the plasma actuator. This paper focuses on two numerical methods: Shyy model and Suzen model. They depend on calculating the induced body force of the plasma and import it in Navier Stokes equation as an external body force. Mesh independence study is performed on the airfoil and validate the results without plasma activation with the experimental results. Two actuators were added at positions 0.1 and 0.3 of the chord length to the airfoil and an investigation is performed on the lift CL and drag Cd coefficients of the airfoil without and with the activation of the plasma. Thereafter, a comparison between the numerical results of two different plasma simulation models that were applied.","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":"132120623","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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