The Experts below are selected from a list of 2634 Experts worldwide ranked by ideXlab platform

Jiguo Tang - One of the best experts on this subject based on the ideXlab platform.

  • a visualized study of bubble breakup in small rectangular venturi channels
    Experimental and Computational Multiphase Flow, 2019
    Co-Authors: Jiang Huang, Zhengyu Mo, Min Du, Jiguo Tang
    Abstract:

    Venturi channels taken as bubble generators own merits of simplicity in structure, high efficiency, and high reliability. A visualized investigation was carried out on bubble transportation and breakup in two small rectangular Venturi channels with the throat sizes of 1 mm × 1 mm and 1 mm × 2 mm, respectively. Experiments were conducted under ambient conditions with air and water as the working fluids. The experimental results indicate that bubble transportation and breakup in the Venturi channel with the throat size of 1 mm × 1 mm presents some different features compared with the other one: under the same average liquid velocity in the throat, bubbles own higher initial velocity than the average liquid velocity before entering the Diverging Section, and remain this trend till they are split; a binary breakup occurs to the bubbles prior to their final collapse in the recirculation region due to the jet flow in the backward of the bubbles. The bubble transportation and breakup in the Venturi channel with the throat size of 1 mm × 2 mm shows similar characteristics with that in a conventional Venturi channel. Overall, Venturi with smaller size presents a better performance in producing fine bubbles.

  • a visualized study of the motion of individual bubbles in a venturi type bubble generator
    Progress in Nuclear Energy, 2017
    Co-Authors: Liang Zhao, Licheng Sun, Guo Xie, Hongtao Liu, Jiguo Tang
    Abstract:

    Abstract As an equipment for generating millimeter- or micrometer-sized bubbles, venturi-type bubble generator has a great potential application in online poison gas removal for molten salt reactor, water treatment, mineral flotation, flue gas desulphurization, even in drug delivery, etc. While the process of generating bubbles in a venturi tube is quite different from that in a conventional tube. A visualized study was carried out to illustrate the details of the transportation of individual bubbles in a venturi-type bubble generator. Sizes, velocity, acceleration of the bubbles were obtained by Digital Image Analysis (DIA) method. An extremely rapid deceleration and intense breakup process was observed nearby the entrance of the Diverging Section of the bubble generator. Bubbles with average diameter larger than 1.5 mm were usually split before collapse, while the smaller one collapsed directly without split. Within several millimeters, the velocity of the bubbles were almost reduced by half, which is believed to play a key role for triggering their collapse. Once a bubble was decelerated to its minimum velocity, it was collapsed promptly into many tiny bubbles around the position of 8–10 mm from the inlet of the Diverging Section. Increasing the liquid flow rate could intensify the collapse process, while its influence on the position of collapse was weak.

Liang Zhao - One of the best experts on this subject based on the ideXlab platform.

  • A visualized study of interfacial behavior of air–water two-phase flow in a rectangular Venturi channel
    'Elsevier BV', 2018
    Co-Authors: Jiang Huang, Licheng Sun, Liang Zhao
    Abstract:

    A visualized investigation was carried out on the effect of the Diverging angle on the bubble motion and interfacial behavior in a Venturi-type bubble generator. It was found two or three large vortexes formed in the Diverging Section, resulting in strong reentrant jet flow in the front of the bubbles or slugs rushing out of the throat. The jet flow in return bumps into the ongoing bubbles or slugs, leading to strong interaction between the gas and liquid phases. The Diverging angle has significant influence on the reentrant flow process and the performance of the bubble generator as well. Increasing the Diverging angle results in the reentrant flow moving further forward to the upstream and intensifies the interaction between the two phases. As a consequence, the breakup or collapse of bubbles becomes more violent, whereby finer bubbles are generated. As such, the reentrant flow strongly links to the performance of the Venturi channel taken as a bubble generator, and that a moderate increase in the Diverging angle can improve its performance without additional increase in flow resistance like that by increasing liquid flow rate. Keywords: Venturi channel, Reentrant jet flow process, Interfacial behavior, Bubble breakup, Diverging angl

  • a visualized study of the motion of individual bubbles in a venturi type bubble generator
    Progress in Nuclear Energy, 2017
    Co-Authors: Liang Zhao, Licheng Sun, Guo Xie, Hongtao Liu, Jiguo Tang
    Abstract:

    Abstract As an equipment for generating millimeter- or micrometer-sized bubbles, venturi-type bubble generator has a great potential application in online poison gas removal for molten salt reactor, water treatment, mineral flotation, flue gas desulphurization, even in drug delivery, etc. While the process of generating bubbles in a venturi tube is quite different from that in a conventional tube. A visualized study was carried out to illustrate the details of the transportation of individual bubbles in a venturi-type bubble generator. Sizes, velocity, acceleration of the bubbles were obtained by Digital Image Analysis (DIA) method. An extremely rapid deceleration and intense breakup process was observed nearby the entrance of the Diverging Section of the bubble generator. Bubbles with average diameter larger than 1.5 mm were usually split before collapse, while the smaller one collapsed directly without split. Within several millimeters, the velocity of the bubbles were almost reduced by half, which is believed to play a key role for triggering their collapse. Once a bubble was decelerated to its minimum velocity, it was collapsed promptly into many tiny bubbles around the position of 8–10 mm from the inlet of the Diverging Section. Increasing the liquid flow rate could intensify the collapse process, while its influence on the position of collapse was weak.

Van Pelt Timo - One of the best experts on this subject based on the ideXlab platform.

  • Plasma Synthetic Jet Actuator: From characterisation to separation flow control
    2019
    Co-Authors: Van Pelt Timo
    Abstract:

    This project proposes a series of experiments that involve plasma synthetic jet actuators. The first experiment will perform a jet characterisation experiment that will research the effect of orifice geometry on the overall performance of the actuator. The second experiment will built upon the first experiment and will use a plasma synthetic jet array to combat leading edge separation of a NACA 0015 airfoil at Re=1.7⋅105 and U∞=10 m/s and improve the overall performance of this particular airfoil. Special focus will be put in uncovering the underlying mechanics of plasma synthetic jet actuation operating in leading edge separation conditions and how performance is dependent on the actuation frequency. From the jet characterisation experiments a clear performance trend of actuator efficiency with respect to the converging cone angle (θ) is found. The optimal optimal orifice angle is expected to lie between 45º<θ<69º. These geometries experience ∼20% higher jet velocities than the baseline 'straight' orifice, which results in larger mass expulsions and an overall more efficient operation of the actuator. Additionally it is found that adding a small Diverging Section to the orifice improves upon the electro-mechanical efficiency of the plasma synthetic jet actuator. PIV measurements show that this is due to the increased effective orifice area which allows for higher mass flows through the orifice but also the jet velocities remained of similar order as the optimal converging geometries. The flow control experiments show that plasma synthetic jet actuators can indeed improve the performance of a NACA 0015 airfoil at Re=1.7⋅105 and U∞=10 m/s. The force balance measurements show that PSJ actuation suppresses the hysteresis loop present when actuation is absent. Furthermore the angle at which maximum lift is achieved is shifted by ∼7º increasing the maximum achieved lift by ∼23%. Additionally, flow separation can be delayed by about 2º reducing the drag by about ∼40%. Furthermore, the PIV measurements show the mechanisms behind flow separation control. At moderate stall angles flow reattachment is feasible if the actuation frequency is high enough. At higher angles of attack the separation point moves upstream of the actuators and renders the array incapable to suppress flow separation. However, at these conditions the actuators are still able to influence the separation region and higher frequencies, with an optimum of F*=1, are capable to suppress the separation area more. If the above-mentioned experiments translate to aeronautical applications plasma synthetic jets might be a game changer when it comes to demanding flight conditions. Not only is plasma synthetic jet actuation capable of diminishing the hysteresis effect it is also capable of considerably increasing the lift and decreasing the drag forces. These effects can considerably improve the safety of aircraft as the omission of hysteresis can reduce unwanted unsteady loads that advance structural fatigue and the higher lift coefficients reduce the need of high lift devices allowing them to become smaller and less complex in the future. Overall this allows aircraft to fly at more demanding flight conditions than previously feasible.Aerodynamic

  • Plasma Synthetic Jet Actuator: From characterisation to separation flow control
    2019
    Co-Authors: Van Pelt Timo
    Abstract:

    This project proposes a series of experiments that involve plasma synthetic jet actuators. The first experiment will perform a jet characterisation experiment that will research the effect of orifice geometry on the overall performance of the actuator. The second experiment will built upon the first experiment and will use a plasma synthetic jet array to combat leading edge separation of a NACA 0015 airfoil at Re=1.7⋅105 and U∞=10 m/s and improve the overall performance of this particular airfoil. Special focus will be put in uncovering the underlying mechanics of plasma synthetic jet actuation operating in leading edge separation conditions and how performance is dependent on the actuation frequency. From the jet characterisation experiments a clear performance trend of actuator efficiency with respect to the converging cone angle (θ) is found. The optimal optimal orifice angle is expected to lie between 45º<θ<69º. These geometries experience ∼20% higher jet velocities than the baseline 'straight' orifice, which results in larger mass expulsions and an overall more efficient operation of the actuator. Additionally it is found that adding a small Diverging Section to the orifice improves upon the electro-mechanical efficiency of the plasma synthetic jet actuator. PIV measurements show that this is due to the increased effective orifice area which allows for higher mass flows through the orifice but also the jet velocities remained of similar order as the optimal converging geometries. The flow control experiments show that plasma synthetic jet actuators can indeed improve the performance of a NACA 0015 airfoil at Re=1.7⋅105 and U∞=10 m/s. The force balance measurements show that PSJ actuation suppresses the hysteresis loop present when actuation is absent. Furthermore the angle at which maximum lift is achieved is shifted by ∼7º increasing the maximum achieved lift by ∼23%. Additionally, flow separation can be delayed by about 2º reducing the drag by about ∼40%. Furthermore, the PIV measurements show the mechanisms behind flow separation control. At moderate stall angles flow reattachment is feasible if the actuation frequency is high enough. At higher angles of attack the separation point moves upstream of the actuators and renders the array incapable to suppress flow separation. However, at these conditions the actuators are still able to influence the separation region and higher frequencies, with an optimum of F*=1, are capable to suppress the separation area more. If the above-mentioned experiments translate to aeronautical applications plasma synthetic jets might be a game changer when it comes to demanding flight conditions. Not only is plasma synthetic jet actuation capable of diminishing the hysteresis effect it is also capable of considerably increasing the lift and decreasing the drag forces. These effects can considerably improve the safety of aircraft as the omission of hysteresis can reduce unwanted unsteady loads that advance structural fatigue and the higher lift coefficients reduce the need of high lift devices allowing them to become smaller and less complex in the future. Overall this allows aircraft to fly at more demanding flight conditions than previously feasible.Aerospace Engineerin

Licheng Sun - One of the best experts on this subject based on the ideXlab platform.

  • A visualized study of interfacial behavior of air–water two-phase flow in a rectangular Venturi channel
    'Elsevier BV', 2018
    Co-Authors: Jiang Huang, Licheng Sun, Liang Zhao
    Abstract:

    A visualized investigation was carried out on the effect of the Diverging angle on the bubble motion and interfacial behavior in a Venturi-type bubble generator. It was found two or three large vortexes formed in the Diverging Section, resulting in strong reentrant jet flow in the front of the bubbles or slugs rushing out of the throat. The jet flow in return bumps into the ongoing bubbles or slugs, leading to strong interaction between the gas and liquid phases. The Diverging angle has significant influence on the reentrant flow process and the performance of the bubble generator as well. Increasing the Diverging angle results in the reentrant flow moving further forward to the upstream and intensifies the interaction between the two phases. As a consequence, the breakup or collapse of bubbles becomes more violent, whereby finer bubbles are generated. As such, the reentrant flow strongly links to the performance of the Venturi channel taken as a bubble generator, and that a moderate increase in the Diverging angle can improve its performance without additional increase in flow resistance like that by increasing liquid flow rate. Keywords: Venturi channel, Reentrant jet flow process, Interfacial behavior, Bubble breakup, Diverging angl

  • a visualized study of the motion of individual bubbles in a venturi type bubble generator
    Progress in Nuclear Energy, 2017
    Co-Authors: Liang Zhao, Licheng Sun, Guo Xie, Hongtao Liu, Jiguo Tang
    Abstract:

    Abstract As an equipment for generating millimeter- or micrometer-sized bubbles, venturi-type bubble generator has a great potential application in online poison gas removal for molten salt reactor, water treatment, mineral flotation, flue gas desulphurization, even in drug delivery, etc. While the process of generating bubbles in a venturi tube is quite different from that in a conventional tube. A visualized study was carried out to illustrate the details of the transportation of individual bubbles in a venturi-type bubble generator. Sizes, velocity, acceleration of the bubbles were obtained by Digital Image Analysis (DIA) method. An extremely rapid deceleration and intense breakup process was observed nearby the entrance of the Diverging Section of the bubble generator. Bubbles with average diameter larger than 1.5 mm were usually split before collapse, while the smaller one collapsed directly without split. Within several millimeters, the velocity of the bubbles were almost reduced by half, which is believed to play a key role for triggering their collapse. Once a bubble was decelerated to its minimum velocity, it was collapsed promptly into many tiny bubbles around the position of 8–10 mm from the inlet of the Diverging Section. Increasing the liquid flow rate could intensify the collapse process, while its influence on the position of collapse was weak.

Smart Michael - One of the best experts on this subject based on the ideXlab platform.

  • Fundamental scramjet combustion experiments using hydrocarbon fuel
    'American Institute of Aeronautics and Astronautics (AIAA)', 2019
    Co-Authors: Vanyai Tristan, Grieve Sam, Street Oliver, Denman Zachary, Mcintyre Timothy, Wheatley Vincent, Veeraragavan Ananthanarayanan, Smart Michael
    Abstract:

    Combustion of ethylene was examined experimentally via semi-freejet testing of a fundamental, axisymmetric combustor model at conditions representative of Mach 7–8 flight at 100 kPa dynamic pressure. The model consisted of diffuser, constant area isolator, cavity, and Diverging combustor Sections. Pressure data were measured along the wall of the model and were complemented with OH planar laser-induced fluorescence (PLIF) visualization at the exit of the Diverging Section. Robust combustion of ethylene was observed for two stagnation enthalpy cases for fuel-air equivalence ratios of 0.3 or greater. A low-enthalpy, low-equivalence-ratio case showed significant, but structurally different, OH PLIF signals even though there was little combustion-induced pressure rise. Edge-detection techniques were applied to the PLIF images, and the resulting circumferential distributions analyzed. Mean radii and standard deviations are presented for the inner and outer edges of the OH-rich band for four tunnel/fueling conditions. Finally, amplitude spectra of fluctuations in the edge radii are shown, indicating that low-wavenumber oscillations are dominant. These experimental results provide useful data for comparison with numerical simulation in future studies

  • Fundamental scramjet combustion experiments using hydrocarbon fuel
    'American Institute of Aeronautics and Astronautics (AIAA)', 2018
    Co-Authors: Vanyai Tristan, Grieve Sam, Street Oliver, Denman Zachary, Mcintyre Timothy, Veeraragavan Anand, Wheatley Vincent, Smart Michael
    Abstract:

    Combustion of ethylene was examined experimentally via free-jet testing of a fundamental, axisymmetric combustor model at conditions representative of Mach 7-8 flight at 50 kPa dynamic pressure. The model consisted of diffusor, constant area isolator, cavity and Diverging combustor Sections. Pressure data were measured along the wall of the model, and were complemented with OH PLIF visualisation at the exit of the Diverging Section. Robust combustion of ethylene was observed for two stagnation enthalpy cases for equivalence ratios of 0.3 or greater. A low enthalpy, low equivalence ratio case showed significant, but structurally different, OH PLIF signals even though there was little combustion-induced pressure rise. Edge-detection techniques were applied to the PLIF images, and the resulting azimuthal distributions analysed. Mean radii and standard deviations are presented for the inner and outer edges of the OH rich band for four tunnel/fuelling conditions. Finally, amplitude spectra of fluctuations in the edge radii are shown, indicating that low wavenumber oscillations are dominant. These experimental results provide useful data for comparison with numerical simulation in future studies