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Farrukh S. Alvi - One of the best experts on this subject based on the ideXlab platform.

  • Velocity field measurements on high-frequency, supersonic microactuators
    Experiments in Fluids, 2016
    Co-Authors: Phillip A. Kreth, Erik J. Fernandez, Farrukh S. Alvi
    Abstract:

    The resonance-enhanced microjet actuator which was developed at the Advanced Aero-Propulsion Laboratory at Florida State University is a fluidic-based device that produces pulsed, supersonic Microjets by utilizing a number of microscale, flow-acoustic resonance phenomena. The microactuator used in this study consists of an underexpanded source jet that flows into a cylindrical cavity with a single, 1-mm-diameter exhaust orifice through which an unsteady, supersonic jet issues at a resonant frequency of 7 kHz. The flowfields of a 1-mm underexpanded free jet and the microactuator are studied in detail using high-magnification, phase-locked flow visualizations (microschlieren) and two-component particle image velocimetry. These are the first direct measurements of the velocity fields produced by such actuators. Comparisons are made between the flow visualizations and the velocity field measurements. The results clearly show that the microactuator produces pulsed, supersonic jets with velocities exceeding 400 m/s for roughly 60 % of their cycles. With high unsteady momentum output, this type of microactuator has potential in a range of ow control applications.

  • Active-Adaptive Control of Inlet Separation Using Supersonic Microjets
    2013
    Co-Authors: Farrukh S. Alvi
    Abstract:

    Flow separation in internal and external flows generally results in a significant degradation in aircraft performance. For internal flows, such as inlets and transmission ducts in aircraft propulsion systems, separation is undesirable as it reduces the overall system performance. The aim of this research has been to understand the nature of separation and more importantly, to explore techniques to actively control it. In this research, we extended our investigation of active separation control (under a previous NASA grant) where we explored the use of Microjets for the control of boundary layer separation. The geometry used for the initial study was a simple diverging Stratford ramp, equipped with arrays of Microjets. These early results clearly show that the activation of Microjets eliminated flow separation. Furthermore, the velocity-field measurements, using PIV, also demonstrate that the gain in momentum due to the elimination of separation is at least an order of magnitude larger (two orders of magnitude larger in most cases) than the momentum injected by the Microjets and is accomplished with very little mass flow through the Microjets. Based on our initial promising results this research was continued under the present grant, using a more flexible model. This model allows for the magnitude and extent of separation as well as the microjet parameters to be independently varied. The results, using this model were even more encouraging and demonstrated that microjet control completely eliminated significant regions of flow separation over a wide range of conditions with almost negligible mass flow. Detailed studies of the flowfield and its response to Microjets were further examined using 3-component PIV and unsteady pressure measurements, among others. As the results presented this report will show, Microjets were successfully used to control the separation of a much larger extent and magnitude than demonstrated in our earlier experiments. In fact, using the appropriate combination of control parameters (microjet, location, angle and pressure) separation was completely eliminated for the largest separated flowfield we could generate with the present model. Separation control also resulted in a significant reduction in the unsteady pressures in the flow where the unsteady pressure field was found to be directly responsive to the state of the flow above the surface. Hence, our study indicates that the unsteady pressure signature is a strong candidate for a flow state sensor , which can be used to estimate the location, magnitude and other properties of the separated flowfield. Once better understood and properly utilized, this behavior can be of significant practical importance for developing and implementing online control.

  • Experiments on Resonance Enhanced Pulsed Microjet Actuators in Supersonic Cross flow
    6th AIAA Flow Control Conference, 2012
    Co-Authors: Magdalena Topolski, Nishul Arora, John T. Solomon, Farrukh S. Alvi, Florida A
    Abstract:

    An array of high-bandwidth, high-momentum pulsed supersonic Microjets, called Resonance Enhanced Microjets (REM), were implemented to study the effect of pulsed actuation in a M=1.5 supersonic cross flow over a flat plate. Cross correlated, phase locked flow imaging and unsteady pressure measurements were used to characterize the shock wave-boundary layer interactions resulting from the pulsed actuation. Pulsed microjet actuators in supersonic cross flow have generated oblique shocks whose strength and shock angle are observed to have an invariable correlation with the pulsing phase of the Microjets. Unsteady pressure measured downstream also shows a strong correlation to the pulsing phase of the actuator and the resulting oblique shock properties. These experiments clearly point to the potential capabilities of the resonance enhanced microjet actuator to manipulate the unsteady properties of the boundary layer of a supersonic flow.

  • generation and control of oblique shocks using Microjets
    AIAA Journal, 2011
    Co-Authors: Rajan Kumar, Farrukh S. Alvi, L Venkatakrishnan
    Abstract:

    Jets in a supersonic crossflow are known to produce a three-dimensional bow-shock structure due to the blockage of the flow. In the present study, streamwise linear arrays of high-momentum Microjets are used to generate either single or multiple oblique shocks in a supersonic crossflow. The shocks generated using Microjets can be tailored in terms of their strength and be made either parallel or coalescing, depending on the application. Flow visualization using shadowgraph and density field measurements using background-oriented schlieren (BOS) technique were carried out for a range of microjet operating conditions. The results obtained using the two methods are consistent and complementary and show a linear variation of oblique shock angles with a microjet pressure ratio over the range of conditions tested. The density field obtained using BOS clearly shows the oblique shocks generated using these microjet arrays, the jump in density across the shock, the extent of the high-density field, the expansion fan, and the associated decrease in density. The results suggest that microjet arrays can be successfully used to develop techniques for sonic boom mitigation and high-performance supersonic inlets.

  • Piezoelectric Controlled Pulsed Microjet Actuation
    Volume 2: Multifunctional Materials; Enabling Technologies and Integrated System Design; Structural Health Monitoring NDE; Bio-Inspired Smart Material, 2009
    Co-Authors: Josh Hogue, John T. Solomon, William S. Oates, Farrukh S. Alvi
    Abstract:

    A piezohydraulic actuator has been designed and tested for broadband flow control of a microjet actuator. This actuator is under development to understand fundamental flow characteristics near a pulsed flow microjet for active flow control on a number of aircraft structures including impinging jets, cavities, and jet inlets. Recent research has shown substantial reductions in flow separation and noise reduction using steady blowing Microjets. This approach often leads to inefficiencies due to excessive mass flux that is typically bled off of an aircraft compressor. Reductions in mass flux without performance losses are desired by actively pulsing the microjet. A piezohydraulic actuator design is presented to investigate this concept. The actuator includes a piezoelectric stack actuator and hydraulic circuit to achieve sufficient displacement amplification to throttle a 400 μm diameter microjet. This system is shown to provide broadband pulsed flow actuation up to 900 Hz. Key parameters contributing to dynamic actuation are shown to include hydraulic fluid behavior, biased microjet air pressure, and voltage inputs to the stack actuator.Copyright © 2009 by ASME

V. M. Aniskin - One of the best experts on this subject based on the ideXlab platform.

  • structure of subsonic plane Microjets
    Microfluidics and Nanofluidics, 2019
    Co-Authors: V. M. Aniskin, A. A. Maslov, K A Mukhin
    Abstract:

    Results of experiments aimed at studying subsonic Microjets escaping from a plane nozzle are reported. The Reynolds numbers based on the nozzle height and mean flow velocity at the nozzle exit are varied from 27 to 139, whereas the nozzle size is fixed at 83.3 × 3823 µm. The test gas is air at room temperature. The distributions of velocity and velocity fluctuations along the jet axis and in the lateral and transverse directions are determined. The fact of the laminar–turbulent transition in the jet is detected. The data obtained are compared with theoretical predictions for laminar plane jets. The experimental and theoretical data are found to be in good agreement at the laminar segment of the microjet.

  • Gas-Dynamic Structure and Stability of Gas Microjets
    Micro- and Nanoflows, 2018
    Co-Authors: Valery Ya. Rudyak, V. M. Aniskin, Anatoly A. Maslov, Andrey V. Minakov, S. G. Mironov
    Abstract:

    Microjets are widely used for the mixing of gases and the protection of surfaces from chemically aggressive and high-temperature media. The basic technological characteristics of jets in this case are their penetration capability and the intensity of mixing processes. The goal of the present chapter is to study the structure and stability of Microjets. The overview of the works on the study of the gas dynamics of subsonic and supersonic mini- and Microjets is given in Sect. 2.1. As tools used in experimental investigations are also very important, they are described in much detail. Diagnostic methods and the results of studying subsonic plane jet stability are described in Sect. 2.2. Experiments aimed at studying the structure and stability of supersonic axisymmetric Microjets and the results obtained therein are discussed in Sect. 2.3. Much attention is paid to the techniques used to obtain experimental data. Finally, the problem of microjet modeling with the use of commonly used similarity parameters is discussed in Sect. 2.4.

  • Supersonic axisymmetric Microjets: structure and laminar–turbulent transition
    Microfluidics and Nanofluidics, 2015
    Co-Authors: V. M. Aniskin, A. A. Maslov, S. G. Mironov, I. S. Tsyryulnikov
    Abstract:

    The supersonic core length of Microjets and the influence of the laminar–turbulent transition on the core length are considered. Axisymmetric mini- and micronozzles with diameters from 341 to 10.4 μm are used. The microjet is studied with the use of a Pitot microtube, shadow flow visualization and hot-wire anemometry. It is demonstrated that the laminar–turbulent transition in the jet mixing layer exerts a dominating effect on the supersonic core length. The increasing of the supersonic core length is associated with the laminar flow in microjet. Decreasing of the supersonic core length is connected with the laminar–turbulent transition in microjet. Based on experimental results, a chart of microjet regimes is constructed. The influence of the Pitot tube diameter on the accuracy of supersonic core length determining is considered. The effect of the nozzle edge roughness on the supersonic core length is examined.

  • supersonic axisymmetric Microjets structure and laminar turbulent transition
    Microfluidics and Nanofluidics, 2015
    Co-Authors: A. A. Maslov, S. G. Mironov, V. M. Aniskin, I. S. Tsyryulnikov
    Abstract:

    The supersonic core length of Microjets and the influence of the laminar–turbulent transition on the core length are considered. Axisymmetric mini- and micronozzles with diameters from 341 to 10.4 μm are used. The microjet is studied with the use of a Pitot microtube, shadow flow visualization and hot-wire anemometry. It is demonstrated that the laminar–turbulent transition in the jet mixing layer exerts a dominating effect on the supersonic core length. The increasing of the supersonic core length is associated with the laminar flow in microjet. Decreasing of the supersonic core length is connected with the laminar–turbulent transition in microjet. Based on experimental results, a chart of microjet regimes is constructed. The influence of the Pitot tube diameter on the accuracy of supersonic core length determining is considered. The effect of the nozzle edge roughness on the supersonic core length is examined.

  • The structure of supersonic underexpanded nitrogen Microjets
    2011
    Co-Authors: V. M. Aniskin, A. A. Maslov, S. G. Mironov, Rd Micro
    Abstract:

    This article contains the results of investigating the gas-dynamic structure of supersonic underexpanded axisymmetric Microjets of nitrogen flowing from sound nozzles with a diameter of 10 ÷ 340 μm. The length of the supersonic part of the jet significantly increases together with a decrease in nozzle diameter starting from the size 23 μm. Measurement results are compared with known data obtained for macroand Microjets.

Oliver G Schmidt - One of the best experts on this subject based on the ideXlab platform.

  • modeling of unidirectional overloaded transition in catalytic tubular Microjets
    Journal of Physical Chemistry C, 2017
    Co-Authors: Anke Klingner, Veronika Magdanz, Oliver G Schmidt, Islam S M Khalil, V M Fomin, Sarthak Misra
    Abstract:

    A numerical time-resolved model is presented for predicting the transition between unidirectional and overloaded motion of catalytic tubular Microjets (Ti/Fe/Pt rolled-up microtubes) in an aqueous solution of hydrogen peroxide. Unidirectional movement is achieved by periodic ejection of gas bubbles from one end, whereas formation of multiple bubbles hinders microjet movement in overloaded regime. The influence of nucleation positions of bubbles, hydrogen peroxide concentration, liquid-platinum contact angle, microjet length, and cone angle on the bubble ejection frequency and microjet speed are investigated. We find agreement between the theoretical speeds of the microjet for a range of bubble nucleation positions (0.4L ≤ x0 ≤ 0.6L) and our measurements (108 ± 35 μm/s) for unidirectional motion. In addition, we observe experimentally that transition to overloaded motion occurs for hydrogen peroxide concentration of 5%, whereas our model predicts this transition for concentrations above 2.5%.

  • stimuli responsive Microjets with reconfigurable shape
    Angewandte Chemie, 2014
    Co-Authors: Veronika Magdanz, Oliver G Schmidt, Samuel Sanchez, Georgi Stoychev, Leonid Ionov
    Abstract:

    Flexible thermoresponsive polymeric Microjets are formed by the self-folding of polymeric layers containing a thin Pt film used as catalyst for self-propulsion in solutions containing hydrogen peroxide. The flexible Microjets can reversibly fold and unfold in an accurate manner by applying changes in temperature to the solution in which they are immersed. This effect allows Microjets to rapidly start and stop multiple times by controlling the radius of curvature of the microjet. This work opens many possibilities in the field of artificial nanodevices, for fundamental studies on self-propulsion at the microscale, and also for biorelated applications.

  • wireless magnetic based closed loop control of self propelled Microjets
    PLOS ONE, 2014
    Co-Authors: Islam S M Khalil, Veronika Magdanz, Oliver G Schmidt, Samuel Sanchez, Sarthak Misra
    Abstract:

    In this study, we demonstrate closed-loop motion control of self-propelled Microjets under the influence of external magnetic fields. We control the orientation of the Microjets using external magnetic torque, whereas the linear motion towards a reference position is accomplished by the thrust and pulling magnetic forces generated by the ejecting oxygen bubbles and field gradients, respectively. The magnetic dipole moment of the Microjets is characterized using the U-turn technique, and its average is calculated to be 1.3|10210 A.m2 at magnetic field and linear velocity of 2 mT and 100 mm/s, respectively. The characterized magnetic dipole moment is used in the realization of the magnetic force-current map of the Microjets. This map in turn is used for the design of a closed-loop control system that does not depend on the exact dynamical model of the Microjets and the accurate knowledge of the parameters of the magnetic system. The motion control characteristics in the transient- and steady-states depend on the concentration of the surrounding fluid (hydrogen peroxide solution) and the strength of the applied magnetic field. Our control system allows us to position Microjets at an average velocity of 115 mm/s, and within an average region-of-convergence of 365 mm.

  • Magnetic control of self-propelled Microjets under ultrasound image guidance
    2014
    Co-Authors: Alonso Sanchez, Veronika Magdanz, Oliver G Schmidt, Sarthak Misra
    Abstract:

    This paper demonstrates closed-loop control of self-propelled Microjets using feedback extracted from B-mode ultrasound images. Previous work on control of self-propelled microrobots has mainly employed video cameras equipped with microscopic lenses in order to obtain the required feedback. Nonetheless, in medical applications such as targeted drug delivery, the use of video cameras might be unsuitable for localizing microrobots that navigate within the human body. This issue is a major obstacle for transferring medical microrobotic technologies into the clinic. On that account, the first reported methods and results on control of self-propelled Microjets using ultrasound equipment are provided herein. In order to exploit the Microjets' self-propulsion mechanism, their motion is directed towards a predefined target by exerting magnetic torques to steer them. Binary image analysis techniques are used to estimate the microjet's position from the ultrasound images. Two air-cored coils are used to generate the steering torques within a plane. Coil currents are calculated using the estimated position error. Results show that our system employing ultrasound images allows control of Microjets at an average velocity of 156±35.1 μm/s and with an average tracking error of 250.7±164.7 μm. As a reference, when microscopic image feedback is used in the setup, an average velocity and tracking error of 207±25.9 μm/s and 183.2±84.31 μm, respectively, are observed.

  • The Control of Self-Propelled Microjets Inside a Microchannel With Time-Varying Flow Rates
    IEEE Transactions on Robotics, 2014
    Co-Authors: Islam S M Khalil, Veronika Magdanz, Oliver G Schmidt, Samuel Sanchez, Sarthak Misra
    Abstract:

    We demonstrate the closed-loop motion control of self-propelled Microjets inside a fluidic microchannel. The motion control of the Microjets is achieved in hydrogen peroxide solution with time-varying flow rates, under the influence of the controlled magnetic fields and the self-propulsion force. Magnetic dipole moment of the Microjets is characterized using the U-turn and the rotating field techniques. The characterized magnetic dipole moment has an average of 1.4×10-13 A.m2 at magnetic field, linear velocity, and boundary frequency of 2 mT, 100 μm/s, and 25 rad/s, respectively. We implement a closed-loop control system that is based on the characterized magnetic dipole moment of the Microjets. This closed-loop control system positions the Microjets by directing the magnetic field lines toward the reference position. Experiments are done using a magnetic system and a fluidic microchannel with a width of 500 μm. In the absence of a fluid flow, our control system positions the Microjets at an average velocity and within an average region-of-convergence (ROC) of 119 μm/s and 390 μm, respectively. As a representative case, we observe that our control system positions the Microjets at an average velocity and within an average ROC of 90 μm/s and 600 μm and 120 μm/s and 600 μm when a flow rate of 2.5 μl/min is applied against and along the direction of the Microjets, respectively. Furthermore, the average velocity and ROC are determined throughout the flow range (0 to 7.5 μl/min) to characterize the motion of the Microjets inside the microchannel.

Sarthak Misra - One of the best experts on this subject based on the ideXlab platform.

  • modeling of unidirectional overloaded transition in catalytic tubular Microjets
    Journal of Physical Chemistry C, 2017
    Co-Authors: Anke Klingner, Veronika Magdanz, Oliver G Schmidt, Islam S M Khalil, V M Fomin, Sarthak Misra
    Abstract:

    A numerical time-resolved model is presented for predicting the transition between unidirectional and overloaded motion of catalytic tubular Microjets (Ti/Fe/Pt rolled-up microtubes) in an aqueous solution of hydrogen peroxide. Unidirectional movement is achieved by periodic ejection of gas bubbles from one end, whereas formation of multiple bubbles hinders microjet movement in overloaded regime. The influence of nucleation positions of bubbles, hydrogen peroxide concentration, liquid-platinum contact angle, microjet length, and cone angle on the bubble ejection frequency and microjet speed are investigated. We find agreement between the theoretical speeds of the microjet for a range of bubble nucleation positions (0.4L ≤ x0 ≤ 0.6L) and our measurements (108 ± 35 μm/s) for unidirectional motion. In addition, we observe experimentally that transition to overloaded motion occurs for hydrogen peroxide concentration of 5%, whereas our model predicts this transition for concentrations above 2.5%.

  • wireless magnetic based closed loop control of self propelled Microjets
    PLOS ONE, 2014
    Co-Authors: Islam S M Khalil, Veronika Magdanz, Oliver G Schmidt, Samuel Sanchez, Sarthak Misra
    Abstract:

    In this study, we demonstrate closed-loop motion control of self-propelled Microjets under the influence of external magnetic fields. We control the orientation of the Microjets using external magnetic torque, whereas the linear motion towards a reference position is accomplished by the thrust and pulling magnetic forces generated by the ejecting oxygen bubbles and field gradients, respectively. The magnetic dipole moment of the Microjets is characterized using the U-turn technique, and its average is calculated to be 1.3|10210 A.m2 at magnetic field and linear velocity of 2 mT and 100 mm/s, respectively. The characterized magnetic dipole moment is used in the realization of the magnetic force-current map of the Microjets. This map in turn is used for the design of a closed-loop control system that does not depend on the exact dynamical model of the Microjets and the accurate knowledge of the parameters of the magnetic system. The motion control characteristics in the transient- and steady-states depend on the concentration of the surrounding fluid (hydrogen peroxide solution) and the strength of the applied magnetic field. Our control system allows us to position Microjets at an average velocity of 115 mm/s, and within an average region-of-convergence of 365 mm.

  • Magnetic control of self-propelled Microjets under ultrasound image guidance
    2014
    Co-Authors: Alonso Sanchez, Veronika Magdanz, Oliver G Schmidt, Sarthak Misra
    Abstract:

    This paper demonstrates closed-loop control of self-propelled Microjets using feedback extracted from B-mode ultrasound images. Previous work on control of self-propelled microrobots has mainly employed video cameras equipped with microscopic lenses in order to obtain the required feedback. Nonetheless, in medical applications such as targeted drug delivery, the use of video cameras might be unsuitable for localizing microrobots that navigate within the human body. This issue is a major obstacle for transferring medical microrobotic technologies into the clinic. On that account, the first reported methods and results on control of self-propelled Microjets using ultrasound equipment are provided herein. In order to exploit the Microjets' self-propulsion mechanism, their motion is directed towards a predefined target by exerting magnetic torques to steer them. Binary image analysis techniques are used to estimate the microjet's position from the ultrasound images. Two air-cored coils are used to generate the steering torques within a plane. Coil currents are calculated using the estimated position error. Results show that our system employing ultrasound images allows control of Microjets at an average velocity of 156±35.1 μm/s and with an average tracking error of 250.7±164.7 μm. As a reference, when microscopic image feedback is used in the setup, an average velocity and tracking error of 207±25.9 μm/s and 183.2±84.31 μm, respectively, are observed.

  • The Control of Self-Propelled Microjets Inside a Microchannel With Time-Varying Flow Rates
    IEEE Transactions on Robotics, 2014
    Co-Authors: Islam S M Khalil, Veronika Magdanz, Oliver G Schmidt, Samuel Sanchez, Sarthak Misra
    Abstract:

    We demonstrate the closed-loop motion control of self-propelled Microjets inside a fluidic microchannel. The motion control of the Microjets is achieved in hydrogen peroxide solution with time-varying flow rates, under the influence of the controlled magnetic fields and the self-propulsion force. Magnetic dipole moment of the Microjets is characterized using the U-turn and the rotating field techniques. The characterized magnetic dipole moment has an average of 1.4×10-13 A.m2 at magnetic field, linear velocity, and boundary frequency of 2 mT, 100 μm/s, and 25 rad/s, respectively. We implement a closed-loop control system that is based on the characterized magnetic dipole moment of the Microjets. This closed-loop control system positions the Microjets by directing the magnetic field lines toward the reference position. Experiments are done using a magnetic system and a fluidic microchannel with a width of 500 μm. In the absence of a fluid flow, our control system positions the Microjets at an average velocity and within an average region-of-convergence (ROC) of 119 μm/s and 390 μm, respectively. As a representative case, we observe that our control system positions the Microjets at an average velocity and within an average ROC of 90 μm/s and 600 μm and 120 μm/s and 600 μm when a flow rate of 2.5 μl/min is applied against and along the direction of the Microjets, respectively. Furthermore, the average velocity and ROC are determined throughout the flow range (0 to 7.5 μl/min) to characterize the motion of the Microjets inside the microchannel.

  • IROS - Magnetotactic bacteria and Microjets: A comparative study
    2013 IEEE RSJ International Conference on Intelligent Robots and Systems, 2013
    Co-Authors: Islam S M Khalil, Veronika Magdanz, Oliver G Schmidt, Samuel Sanchez, Sarthak Misra
    Abstract:

    We provide a comparative study between two self-propelled microrobots, i.e., magnetotactic bacteria and Microjets. This study includes characterization of their fluidic properties (linear and rotational drag coefficients) based on their morphologies and characterization of their magnetic properties using the rotating-field technique. Further, the control characteristics of our microrobots are evaluated in the transient- and steady-states. The average boundary frequencies of our magnetotactic bacteria and Microjets are 2.2 rad/s and 25.1 rad/s, respectively. The characterized fluidic properties and boundary frequencies are used in the characterization of the magnetic properties of our microrobots. The average magnetic dipole moments of our magnetotactic bacteria and Microjets are 1.4×10-17 A.m2 and 1.5×10-13 A.m2 at magnetic field of 2 mT and linear velocities of 32 μm/s (approximately 6 body lengths per second) and 119 μm/s (approximately 2 body lengths per second), respectively. These characterized magnetic dipole moments are utilized in the realization of closed-loop control systems for the magnetotactic bacteria and Microjets. Our closed-loop control system positions the magnetotactic bacteria and the Microjets within the vicinity of reference positions with average diameters of 23 μm (approximately 4 body lengths) and 417 μm (approximately 8 body lengths), respectively.

I. S. Tsyryulnikov - One of the best experts on this subject based on the ideXlab platform.

  • Supersonic axisymmetric Microjets: structure and laminar–turbulent transition
    Microfluidics and Nanofluidics, 2015
    Co-Authors: V. M. Aniskin, A. A. Maslov, S. G. Mironov, I. S. Tsyryulnikov
    Abstract:

    The supersonic core length of Microjets and the influence of the laminar–turbulent transition on the core length are considered. Axisymmetric mini- and micronozzles with diameters from 341 to 10.4 μm are used. The microjet is studied with the use of a Pitot microtube, shadow flow visualization and hot-wire anemometry. It is demonstrated that the laminar–turbulent transition in the jet mixing layer exerts a dominating effect on the supersonic core length. The increasing of the supersonic core length is associated with the laminar flow in microjet. Decreasing of the supersonic core length is connected with the laminar–turbulent transition in microjet. Based on experimental results, a chart of microjet regimes is constructed. The influence of the Pitot tube diameter on the accuracy of supersonic core length determining is considered. The effect of the nozzle edge roughness on the supersonic core length is examined.

  • supersonic axisymmetric Microjets structure and laminar turbulent transition
    Microfluidics and Nanofluidics, 2015
    Co-Authors: A. A. Maslov, S. G. Mironov, V. M. Aniskin, I. S. Tsyryulnikov
    Abstract:

    The supersonic core length of Microjets and the influence of the laminar–turbulent transition on the core length are considered. Axisymmetric mini- and micronozzles with diameters from 341 to 10.4 μm are used. The microjet is studied with the use of a Pitot microtube, shadow flow visualization and hot-wire anemometry. It is demonstrated that the laminar–turbulent transition in the jet mixing layer exerts a dominating effect on the supersonic core length. The increasing of the supersonic core length is associated with the laminar flow in microjet. Decreasing of the supersonic core length is connected with the laminar–turbulent transition in microjet. Based on experimental results, a chart of microjet regimes is constructed. The influence of the Pitot tube diameter on the accuracy of supersonic core length determining is considered. The effect of the nozzle edge roughness on the supersonic core length is examined.