Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E30: Jets: General |
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Chair: Jun Sakakibara, Meiji University Room: Georgia World Congress Center B402 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E30.00001: The Stability of a Charged Viscous Dielectric Jet William J Doak, Paul R Chiarot Atomization of a dielectric micro-jet is achieved using an electrohydrodynamic charge injection process. The atomizer is comprised of a grounded nozzle housing and a high voltage internal probe that is concentric with the emitting orifice. The internal probe is held at electric potentials up to 20 kV. A pressurized reservoir drives dielectric fluid through the orifice with a diameter ranging from 100 µm to 500 µm. Fluid fills the cavity between the probe and housing, impeding the transport of electrons as it passes through the atomizer. This process imparts charge into the flowing fluid. Before it is charged, the jet breaks up via the Rayleigh-Plateau (axisymmetric) instability. Once it is charged, the jet assumes a bending (non-axisymmetric) instability. Both instabilities grow with increasing jet electric charge; i.e. the intact jet length shortens and bending amplitude increases as the charge is increased. We utilized high speed microscopy and Fast Fourier Transform analysis of the bending mode to measure the dominate unstable wavelengths. Our results show good agreement with the predicted fastest growing unstable wavelength (Saville, J. Fluid Mech., 48:815, 1971). |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E30.00002: 3D-PTV measurements of jet flow between parallel flat plates Hiroki Kubo, Jun Sakakibara Jet flow in between parallel flat plates was studied experimentally. The plates were rectangular, and separated by a gap H (=10mm). The nozzle having a square cross-section with a side length of B (=H) was installed at an edge of the parallel plates and air was issued into the gap. We used the three-dimensional particle tracking velocimetry (3D-PTV) to measure the velocity field. We used four cameras to measure three dimensional and three components of velocity vectors. Velocity profile at central plane between the plates has self-similarity along the streamwise direction and agrees well with Goertler’s solution and Tolmien’s solution of the planar free jet. Centerline velocity UCL decays more rapidly than that of the planar free jet due to the secondary flow has occurred in the near field and the wall friction. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E30.00003: Tank draining through an orifice: wetting effects Lucile Favreau, Jérémy Ferrand, Sylvain Joubaud, Eric Freyssingeas We performed an experimental study of wetting effects on tank draining. Water flows from a tank through an orifice set at the tank bottom under its own weight. The hole's size is on the order of magnitude of the capillary length. As expected, flows follow Torricelli-like behavior, however, important wetting effects are highlighted. Wetting effects are manifested in two main aspects. First of all, the speed of drainage exhibits a non-monotonous variation with the static wetting angle of the fluid on the bottom plate of the tank. The fluid flow rate goes through a minimum as the outside surface of the tank bottom plate changes from hydrophilic to hydrophobic. The second striking aspect of the effect of wetting on fluid flows through an orifice is the existence of a jet shape disturbance right at the hole outlet. To our knowledge such a disturbance of the jets has never been described before. We believe that the origin of both phenomena lies in the meniscus formed by the fluid at hole's outlet. I will present experimental results showing the effects of surface wettability, as well as a model we developed, which could explain wetting effects on the drainage speed. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E30.00004: Jet ejection of inelastic and elastic non-Newtonian fluids by laser-induced shockwave Andres Franco-Gomez, Yuichiro Nagatsu, Yoshiyuki Tagawa Controlled ejection of fluids with relatively high viscosity or non-Newtonian properties is of great recent interest for printing-electronics, 3D-manufacturing or bioprinting applications. However, traditional nozzle printing methods are limited to low viscous fluids, otherwise problems of clogging or jamming may occur. In this contribution we investigate jet ejection of two non-Newtonian polymeric solutions with similar shear-thinning behaviour, but different inelastic (xanthan-gum 0.35 wt%) and elastic (sodium polyacrylate 0.4 wt%) properties by using a nozzle-free method based in a shockwave laser-induced technique (Tagawa et al. 2012, Delrot et al. 2016). Results of jet speed versus shockwave cavitation bubble energy, and jet speed against time of the non-Newtonian solutions are compared with similar results using a glycerin/water mixture of 100 cSt. We demonstrate that jets generated with the inelastic solution (XG) evolve into drop formation comparable to glycerin/water jets, whereas for the elastic solution (SPA) jets experience a retraction after ejection. These observations indicate a strong dependence on the different extensional flow properties of the non-Newtonian fluids under consideration. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E30.00005: Improving the accuracy of entrainment coefficients in one-dimensional volcanic plume models James S McNeal, Graham Freedland, Larry Mastin, Raúl Bayoán Cal, Stephen Solovitz Ash-cloud transport models can be used to help to mitigate the downstream impact of volcanic ash. The accuracy of these models relies on using correct values for input parameters for plume height H and mass eruption rate MER. One-dimensional plume models can be used to infer MER from H, but the accuracy of the inversion is limited by uncertainties in the air entrainment rate, especially in the bending region. The radial entrainment coefficient α is better constrained than the crossflow entrainment coefficient β. Wind tunnel experiments used stereo particle image velocimetry SPIV to measure the centerline trajectory of a jet orthogonally injected at speed U into crossflow at speed W under varying ratios U/W. Regression methods compared the experimental data to trajectories predicted by a one-dimensional plume model. Values of a and b were incremented in the model, and best-fit a-β combinations were found for each ratio U/W. The overall best-fit coefficient values (α = 0.07, β = 0.46) were applied to model estimates of historical eruptions to gauge model improvement. The results constrain the effects of data uncertainties on the accuracy of 1-D plume models, which are used to provide input to ash cloud models. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E30.00006: Flow development of buoyant round jets in cross-flow Graham Freedland, Larry Mastin, Stephen Solovitz, Raul Bayoan Cal The physics of wind-bent plumes has been studied for many applications, including volcanic ash transport models used to predict hazards. Simple laboratory experiments of air jets in crossflow provide a deeper understanding of the interaction and mixing with cross-flow. Because volcanos are more complicated than these experiments, jets of air, helium, and argon (Re $\approx 10^5$) are injected orthogonally into a closed-loop wind tunnel with several cross-flow velocities to compare varying densities. Mean flow statistics are collected using particle image velocimetry (PIV) to characterize the interactions between the cross-flow and jet. These are used to identify the leading edge and lee-side shear layer where the inertial and Reynolds stress terms of the momentum and energy equation are evaluated. By varying the density of the jet and changing the inflow conditions, relationships for the rate of entrainment through the bending region can be evaluated for negative, neutral and positively buoyant plumes. |
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