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M G Mungal - One of the best experts on this subject based on the ideXlab platform.

  • mixing structure and scaling of the jet in crossflow
    Journal of Fluid Mechanics, 1998
    Co-Authors: S H Smith, M G Mungal
    Abstract:

    The mixing of the round jet normal to a uniform crossflow is studied for a range of jet-to-crossflow velocity ratios, r , from 5 to 25. Planar laser-induced fluorescence (PLIF) of acetone vapour seeded into the jet is used to acquire quantitative two-dimensional images of the scalar concentration field. Emphasis is placed on r =10 and r =20 and a few select images are acquired up to r =200. The Reynolds number based on the jet exit diameter, d , and the exit velocity varies from 8400 to 41 500. Images are acquired for conditions in which the product rd is held constant, requiring decreasing d for increasing r . Results from this experimental study concern structural events of the vortex interaction region, and mixing and mean Centreline concentration decay in the near and far fields. The results cover all three regions of the transverse jet, and suggest that the jet scales with three length scales: d , rd and r 2 d . Events within the vortex interaction region display d -scaling, including the crossflow boundary layer separation and roll-up. Over the range of velocity ratios studied, the vortex interaction region shows r -dependent variations in the flow field, including the emergence of jet fluid in the wake structures for r >10 and a slower development of the counter-rotating vortex pair (CVP) in higher- r jets. The trajectory and physical dimension of the jet in both the near and far field display rd -scaling. The near field is characterized by a Centreline concentration decay along the Centreline coordinate s of s −1.3 , different from the decay rate ( s −1 ) of the free jet. When normalized by rd , the decay of each velocity-ratio jet branches away from the s −1.3 decay, approaching a decay of s −2/3 , a rate predicted by modelling efforts. The branch points represent a transition in the flow field from enhanced mixing to reduced mixing compared to the free jet. When normalized by r 2 d , the branch points occur at a uniform jet position, s / r 2 d =0.3, which is viewed to be the division between the near and far fields. Self-similarity is not seen in the near field, but may be present in the far field. The view of the branch points as a place of transition in the flow is supported by the probability density function (p.d.f.) of concentration along the upper edge of the jet. Before the branch points, the p.d.f.s are non-marching in character, and after the branch points, they are tilted in character. Instantaneously, the CVP is asymmetric in shape and concentration. End views reveal extensive motion of the CVP and plan views show this motion can occur in both axisymmetric and sinusoidal motion. Ensemble-averaged images show the jet concentration is asymmetric about the Centreline Plane.

S H Smith - One of the best experts on this subject based on the ideXlab platform.

  • mixing structure and scaling of the jet in crossflow
    Journal of Fluid Mechanics, 1998
    Co-Authors: S H Smith, M G Mungal
    Abstract:

    The mixing of the round jet normal to a uniform crossflow is studied for a range of jet-to-crossflow velocity ratios, r , from 5 to 25. Planar laser-induced fluorescence (PLIF) of acetone vapour seeded into the jet is used to acquire quantitative two-dimensional images of the scalar concentration field. Emphasis is placed on r =10 and r =20 and a few select images are acquired up to r =200. The Reynolds number based on the jet exit diameter, d , and the exit velocity varies from 8400 to 41 500. Images are acquired for conditions in which the product rd is held constant, requiring decreasing d for increasing r . Results from this experimental study concern structural events of the vortex interaction region, and mixing and mean Centreline concentration decay in the near and far fields. The results cover all three regions of the transverse jet, and suggest that the jet scales with three length scales: d , rd and r 2 d . Events within the vortex interaction region display d -scaling, including the crossflow boundary layer separation and roll-up. Over the range of velocity ratios studied, the vortex interaction region shows r -dependent variations in the flow field, including the emergence of jet fluid in the wake structures for r >10 and a slower development of the counter-rotating vortex pair (CVP) in higher- r jets. The trajectory and physical dimension of the jet in both the near and far field display rd -scaling. The near field is characterized by a Centreline concentration decay along the Centreline coordinate s of s −1.3 , different from the decay rate ( s −1 ) of the free jet. When normalized by rd , the decay of each velocity-ratio jet branches away from the s −1.3 decay, approaching a decay of s −2/3 , a rate predicted by modelling efforts. The branch points represent a transition in the flow field from enhanced mixing to reduced mixing compared to the free jet. When normalized by r 2 d , the branch points occur at a uniform jet position, s / r 2 d =0.3, which is viewed to be the division between the near and far fields. Self-similarity is not seen in the near field, but may be present in the far field. The view of the branch points as a place of transition in the flow is supported by the probability density function (p.d.f.) of concentration along the upper edge of the jet. Before the branch points, the p.d.f.s are non-marching in character, and after the branch points, they are tilted in character. Instantaneously, the CVP is asymmetric in shape and concentration. End views reveal extensive motion of the CVP and plan views show this motion can occur in both axisymmetric and sinusoidal motion. Ensemble-averaged images show the jet concentration is asymmetric about the Centreline Plane.

Boob, Sudarshan Shamsundar - One of the best experts on this subject based on the ideXlab platform.

  • Experimental Investigation of the Continual Jet
    2020
    Co-Authors: Boob, Sudarshan Shamsundar
    Abstract:

    This thesis work primarily focusses on the study of the structure and development of the free jet generated though the round air jet nozzle. It also involves the study of the velocity fields generated by round jet at the nozzle exit velocity 5.67 m/s and with corresponding Reynolds number of 3070.The investigation was carried out in 2D (stereo PIV) and 3D (Tomo PIV). The scope of the study was further extended to understand the characteristics of all three velocity components in the developing shear layer and deriving the pressure fields over the space using the available velocity field data. Pulsed laser sheets were aligned such that it illuminates the Centreline Plane of the jet. The set-up was calibrated to translate the resulting pixel displacements into X, Y, and Z velocity components. The measurement was done with varying the laser power and varying the laser pulse time i.e. delay time. For measurement of the Tomo PIV the volume optics were used also volume self-calibration were carried out. The tracer particles used in the experiment were generated from the vegetable oil and compressed air was used for providing the necessary acceleratory movement to the particles. The result helped to study the different structures and development of the free jet along its Centreline axis direction. The velocity range over entire field and pressure variations along the streamline axis are discussed. The maximum particle velocity was found to be 25 m/s in the jet core.This thesis work primarily focusses on the study of the structure and development of the free jet generated though the round air jet nozzle. It also involves the study of the velocity fields generated by round jet at the nozzle exit velocity 5.67 m/s and with corresponding Reynolds number of 3070.The investigation was carried out in 2D (stereo PIV) and 3D (Tomo PIV). The scope of the study was further extended to understand the characteristics of all three velocity components in the developing shear layer and deriving the pressure fields over the space using the available velocity field data. Pulsed laser sheets were aligned such that it illuminates the Centreline Plane of the jet. The set-up was calibrated to translate the resulting pixel displacements into X, Y, and Z velocity components. The measurement was done with varying the laser power and varying the laser pulse time i.e. delay time. For measurement of the Tomo PIV the volume optics were used also volume self-calibration were carried out. The tracer particles used in the experiment were generated from the vegetable oil and compressed air was used for providing the necessary acceleratory movement to the particles. The result helped to study the different structures and development of the free jet along its Centreline axis direction. The velocity range over entire field and pressure variations along the streamline axis are discussed. The maximum particle velocity was found to be 25 m/s in the jet core

Longmire E.k - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of three dimensionality in the near field of a round jet using stereo PIV
    'IOP Publishing', 2002
    Co-Authors: Ganapathisubramani B., Longmire E.k
    Abstract:

    A round air jet at a Reynolds number of 19 000 was studied using stereo PIV techniques in an effort to understand the characteristics of all three velocity components in the developing shear layer and to study the evolution of three dimensionality with increasing axial distance. Pulsed laser sheets were aligned to illuminate the Centreline Plane of the jet. The stereo PIV set-up was suitably calibrated to translate the resulting pixel displacements into axial, radial, and azimuthal velocity components. Details of measurement accuracy are discussed and related to the presence of local velocity gradients. Experimental results show that the RMS of the azimuthal velocity is of the order of 0.1V0 in the shear layer downstream of y/D ? 0.5. This is significantly earlier than reported in previous studies. Various feature extraction schemes based on the velocity gradient tensor were developed to identify the presence of the vortex cores and straining braid regions. Individual fields show that both vortex cores and braids are three dimensional. The braids contain streamwise vortex tubes while the cores can possess significant azimuthal velocity. The initial azimuthal perturbations typically were associated with straining regions immediately upstream of the first vortex ring that formed at the downstream location of y/D ? 0.5. This article was chosen from selected Proceedings of the Second International Symposium on Turbulence and Shear Flow Phenomena (KTH-Stockholm, 27-29 June 2001) ed E Lindborg, A Johansson, J Eaton, J Humphrey, N Kasagi, M Leschziner and M Sommerfeld

Ganapathisubramani B. - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of three dimensionality in the near field of a round jet using stereo PIV
    'IOP Publishing', 2002
    Co-Authors: Ganapathisubramani B., Longmire E.k
    Abstract:

    A round air jet at a Reynolds number of 19 000 was studied using stereo PIV techniques in an effort to understand the characteristics of all three velocity components in the developing shear layer and to study the evolution of three dimensionality with increasing axial distance. Pulsed laser sheets were aligned to illuminate the Centreline Plane of the jet. The stereo PIV set-up was suitably calibrated to translate the resulting pixel displacements into axial, radial, and azimuthal velocity components. Details of measurement accuracy are discussed and related to the presence of local velocity gradients. Experimental results show that the RMS of the azimuthal velocity is of the order of 0.1V0 in the shear layer downstream of y/D ? 0.5. This is significantly earlier than reported in previous studies. Various feature extraction schemes based on the velocity gradient tensor were developed to identify the presence of the vortex cores and straining braid regions. Individual fields show that both vortex cores and braids are three dimensional. The braids contain streamwise vortex tubes while the cores can possess significant azimuthal velocity. The initial azimuthal perturbations typically were associated with straining regions immediately upstream of the first vortex ring that formed at the downstream location of y/D ? 0.5. This article was chosen from selected Proceedings of the Second International Symposium on Turbulence and Shear Flow Phenomena (KTH-Stockholm, 27-29 June 2001) ed E Lindborg, A Johansson, J Eaton, J Humphrey, N Kasagi, M Leschziner and M Sommerfeld