Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B15: Turbulence: Jets |
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Chair: Azur Hodzic, DTU Mekanik Institut for Mekanisk Teknologi Room: 310 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B15.00001: Particle image velocimetry inside emanating jets to study jet shape and evolution Cees Van Rijn, Daniel Bonn, Bodjie Van Brummen, Jerry Westerweel Jets resulting from drop impact on a fluid are a fascinating and remarkably robust phenomenon. However, their beautiful shapes remain incompletely understood. We perform PIV experiments to probe dynamic fluid motion inside an emanating jet to relate the fluid flow to the jet evolution and shape. Several theories exist relating jet shape and internal fluid motion, but none so far can describe all the different features of the jet. We find that for some experimental parameters that the jet acquires a large upward velocity in a small upward acceleration region located near the jet base due to collapse of a cavity formed during impact of the falling drop. The PIV allows to distinguish three jet regions: a small acceleration region, a long ballistic region where fluid moves with a nearly constant momentum, and a jet tip region where drop formation happens. In most views on jet shape and formation the role of surface tension is neglected; our experiments however demonstrate that both the ballistic and tip region of the jet are strongly decelerated by surface tension forces, that also affect the jet shape. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B15.00002: A Tensor Formulation of the Lumley Decomposition Applied to the Jet Far-field Azur Hodzic, Knud Erik Meyer, William K. George, Clara M. Velte A tensor formulation of the Lumley Decomposition (LD) is applied to the jet far-field which is analyzed in curvilinear coordinates. Fourier-based eigenfunctions along the streamwise direction are deduced directly from the LD, but only if a specific weighted inner-product space is chosen for the decomposition. A Galerkin projection of the turbulence kinetic energy (TKE) production term is then analyzed in order to quantify the TKE production capabilities of the eigenfunctions. It is shown that a wide range of mode- and wavenumbers exhibit similar rates of energy extraction directly from the mean flow, as hypothesized by [Wänström 2009]. Data obtained from PIV measurements of the jet far-field then suggest that the energy transport between eigenfunctions is not strictly governed by the classical Richardson cascade model, but that a wide range of modes are – at least partially - able to circumvent this cascade. \\ \\ \noindent [W{\"a}nstr{\"o}m 2009] Spatial decompositions of a fully-developed turbulent round jet sampled with particle image velocimetry. Ph.d. thesis, Chalmers University of Technology. [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B15.00003: The dynamics of streamwise vortices in high Re jets Jahnavi Kantharaju, Benjamin Leclaire, Laurent Jacquin Streamwise vortices play an important role in the mixing and entrainment in the near field of jets. They are dynamically active structures that lead to additional flow features such as side jets and streaks. Their coexistence with and wrapping around the vortex rings suggest their possible influence on the rings as has been remarked in several studies. We present results supporting one such possible interaction between streamwise vortices and the axisymmetric ($m=0$) mode in round jets (Davoust et. al JFM 2012) at $Re$ in the range of $9.2 \times 10^4$ to $3.5 \times 10^5$. High speed particle image velocimetry was performed at one and two diameters downstream of the nozzle. We varied the strengths of the axisymmetric mode relative to streamwise vortices through acoustic excitation. It is shown that as the axisymmetric mode is strengthened, there is a shift in the organization of streamwise vortices from radial (in unforced case) to an azimuthal configuration that has been classically observed at low Re. Using conditional averaging, this organization was distinguished in the ring and braid region. For the excited jets, it agreed well with the literature. A theoretical model is being sought to represent this interaction and predict its effect on the near field entrainment. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B15.00004: Three-dimensional Lagrangian statistics of a turbulent free-shear jet Bianca Viggiano, Thomas Basset, Romain Volk, Laurent Chevillard, Micka\"el Bourgoin, Ra\'ul Bayo\'an Cal A fundamental study of a free-shear jet is performed to investigate the highly anisotropic and inhomogeneous flow field through Lagrangian statistics. Experiments were conducted within a Lagrangian Exploration Module, an icosahedron apparatus, to facilitate optical access of three high speed cameras. This enables the generation of 3D particle trajectories by implementing stereoscopic particle tracking velocimetry and results in three component tracks of position, velocity and acceleration of the tracer particles within the vertically-oriented jet. The total measurement volume is 80 x 80 x 200 mm$^3$, which includes over 50 nozzle diameters downstream, where the jet becomes self-similar. Lagrangian statistical analysis is performed to identify intermittent behavior at the centerline of the jet and at the turbulent/non-turbulent interface. Further, the applicability of Taylor's frozen flow hypothesis is investigated. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B15.00005: Non-equilibrium Turbulent/non Turbulent Interface velocity scaling in turbulent planar jets Gioacchino Cafiero, John Christos Vassilicos We investigate the turbulent/non-turbulent interface (TNTI) of a turbulent planar jet using stereo-PIV and HWA. Following Zhou \& Vassilicos (JFM 2017) we derive an expression for the entrainment velocity $\frac{d}{dx} \langle \int_{{A}_{T}}udydz\rangle =$$\mathcal{L}$ $v_{n} $, where $x$ is the streamwise coordinate, $u$ is the streamwise velocity, $\mathcal{A}_{T}$ is the area of the turbulent region in a plane orthogonal to the mean flow, and $\mathcal{L}$ is the length of the TNTI in this plane. $\mathcal{L}$ can be expressed as $\mathcal{L}$$\sim\delta(\eta_I/\delta)^{1-D}$, where $\delta(x)$ is the jet width at $x$, $\eta_I\sim\nu/v_n$ (Corrsin 1955) is a characteristic interface thickness and $D$ is the line interface's fractal dimension. Non-equilibrium dissipation self-similar jet theory (Cafiero \& Vassilicos PRSA 2019) predicts that $v_n/v_{\eta}$ (where $v_{\eta}$ is the Kolmogorov velocity) is a decreasing function of $x$, which is at odds with the classical Corrsin scaling $v_n \sim v_{\eta}$. Our experimental results confirm Corrsin's $\eta_I\sim \nu/v_n$ but also show that $v_n/v_{\eta}$ is indeed a decreasing function of $x$. Our measurements support the scaling $v_n \sim v_{\lambda}$ (=\nu/\lambda$, being $\lambda$ the Taylor scale) predicted by our theory. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B15.00006: Round and Plane, Turbulent, Twin Jets TAYE MELAKU TADDESSE, Joseph Mathew Multiple jets are found in several applications such as fuel injection, smoke stacks, jets engines of aerospace vehicles, etc. Even a pair of round jets can have a distinctive development because, after the inevitable merging, there can be axis witching. While plane jet pairs may be expected to behave like a single plane jet after merger, significant differences have been observed in experiments. LES of parallel, twin jets, round and plane, reveal the structure and mechanisms of these two types. The LES is by an explicit filtering method. The twin round jets are at a Reynolds number Re of $2.3 \times 10^5$, based on diameter and mean velocity at exit. Distance between jet centers was 5 diameters. Close quantitative agreement with experiment was found on the development of mean profiles and spreading. Velocity fluctuations between the jets are weaker than those on the outer boundaries. Axis switching was observed. Twin plane jets were at $Re = 8.75\times10^3$ based on jet width, spaced 12 jet widths apart were also simulated. The enhanced growth rate of twin jets has been captured in the simulations. [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B15.00007: Mixing of temperature and helium in turbulent co-axial jets Alais Hewes, Laurent Mydlarski There are relatively few studies of turbulent multi-scalar mixing, despite the occurrence of this phenomenon in common processes (e.g. chemically reacting flows, oceanic mixing). In the present work, we study the mixing of two passive scalars (temperature and helium concentration) in turbulent co-axial jets using a novel, 3-wire, thermal-anemometry-based probe designed to simultaneously measure velocity, temperature, and concentration. We emphasize that unlike most previous investigations of multi-scalar mixing, the instantaneous velocity field is measured in addition to the scalar fields, as it is required to fully describe turbulent scalar mixing. Our experiments are performed in vertically oriented co-axial jets consisting of a central jet of helium and air and an annular flow of (unheated) pure air, emanating into a slow co-flow of (pure) heated air (similar to the experimental set-up of Cai et al. (J. Fluid Mech., 2011)). We present measurements made in the near field of the jets, including variances and scalar fluxes, and focus on the evolution of the joint velocity-scalar PDFs, joint scalar PDFs, and the conditional Laplacians of the scalars, which provide valuable data for the testing and development of mixing models. [Preview Abstract] |
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