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 L40: Jets: Control |
Hide Abstracts |
Chair: Peter Schmid, Imperial College of London Room: 6b |
Monday, November 25, 2019 1:45PM - 1:58PM |
L40.00001: Determining spray axial velocity from focused-beam X-ray radiography Julie Bothell, Timothy Morgan, Alan Kastengren, Theodore Heindel Coaxial atomizing sprays are used across a variety of industries from gas turbines to food processing. Far-field spray dynamics depend on the primary breakup region, but this region is challenging to study as it contains thick liquid that is opaque to visible light. However, X-rays are capable of penetrating the dense liquid region, providing insight that is unavailable from visible light testing methods. This study modifies a method used in previous studies for determining the mass-average axial velocity from a diesel injector spray, and applies it to investigate the mass-average axial velocity from a coaxial atomizing spray. The original method was developed for a narrow-angle, time-varying spray, but was modified in this study for a wide-angle, steady-state spray. Experiments at the Advanced Photon Source at Argonne National Laboratory provided focused-beam X-ray radiographs along the spray. The mass-average axial velocity along the spray increased linearly with axial distance from the nozzle for varying momentum ratios. The slope of the velocity-distance relation also increased linearly when plotted as a function of gas flow rate. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L40.00002: The azimuthal and wavy deformation of vortex rings and the formation of separated flows in a round jet using synthetic jets Akinori Muramatsu, Kohei Tanaka Vortex rings are periodically formed in the initial region of a round jet and change to a wavy shape in the azimuthal direction. As a result, the vortex rings collapse three-dimensionally. It is suggested that the azimuthal deformation of vortex rings is affected by streamwise vortices. In order to investigate the relation between the azimuthal deformation of the vortex ring and the streamwise vortices, we attempted to artificially deform the vortex ring in the azimuthal direction using synthetic jets. The synthetic jets are formed utilizing a sound wave with a natural frequency for the vortex-ring formation. The vortex rings azimuthally and wavily deform by introducing disturbances through small holes at a nozzle exit, so that the streamwise vortices are generated at certain locations in the round jet. At the same time, the jet branches off slanting upward at the initial region in relation to azimuthal deformation of the vortex ring. The streamwise vortices are formed inside the vortex ring and move to the outside of the vortex ring, when the vortex ring is moving the downstream. At this time, the streamwise vortices are separated from the vortex ring. The branched flows, as similar to side jets, are formed by moving the streamwise vortices. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L40.00003: Adjoint-based analysis of controllability of turbulent jet noise Seung Whan Chung, Jonathan Freund Past efforts have used optimal control theory, based on the numerical solution of the adjoint flow equations, to perturb turbulent jets to reduce radiated sound. These have been successful in that sound is reduced, with concomitant changes to large-scale turbulence structures in the flow. However, control remains challenged by the chaotic dynamics of the turbulence, which degrades smoothness of cost functional in control parameter space, thus limiting control effects to a relatively short time horizon. Wave packets can be a useful and relatively deterministic model for the large-scale noise mechanisms in jets. Using discrete-exact, dual-consistent adjoint gradients in conjunction with high-fidelity simulations, we assess the growth of sensitivity in time and general controllability. The most effective immediate control of a $M = 1.3$ jet is achieved with a control-time horizon of $32.4D/a_{\infty}$; longer or shorter time horizons prove less effective, which thus marks a balance between increasing authority through sensitivity and the disruptive influence of chaotic effect in the turbulence for this objective. After the control period, the rate at which the jet returns to its baseline louder state also presents a potentially important time scale for the flow and chaotic dynamics. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L40.00004: Dynamics of Axisymmetrically Excited Transverse Jets Elijah Harris, David D. W. Ren, Andrea Besnard, Stephen Schein, Robert M'Closkey, Ann Karagozian, Luca Cortelezzi The present experimental study investigates axisymmetric excitation of a gaseous jet issuing into a uniform crossflow as pertains to jet dynamics as well as structural and mixing characteristics. A naturally absolutely unstable (AU) transverse jet, with a jet-to-crossflow momentum flux ratio of J=6, is forced with a variety of different periodic waveforms including sinusoidal, square wave, and multi-pulse square waves. For specific perturbation amplitudes and within specific forcing frequency regimes, the jet locks-in to the forcing frequency, prior to which there is evidence of quasi-periodicity. The critical conditions to achieve lock-in differ amongst the various excitation waveforms, where the sinuous forcing cases have the greatest challenges in achieving lock-in for this AU jet. As one increases the forcing amplitude beyond lock-in, the jet displays complex synchronization dynamics and mode shapes, en route to more chaotic behavior, as quantified through snapshot proper orthogonal decomposition (POD) analysis of the velocity field extracted via stereo particle image velocimetry (PIV), and time delay embedding of velocity fluctuations along the jet shear layer. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L40.00005: Open-loop control of a weakly non-linear swirling jet instability by harmonic forcing Calum Skene, Ubaid Qadri, Peter Schmid Highly swirled flows are often prone to a global instability with an azimuthal wavenumber of $|m|=1$, where the sign is chosen so that the instability precesses against the mean-flow swirl. This instability is linked to the recirculation region typical of a vortex breakdown induced by high swirl, and can affect many types of flow. In particular, in lean premixed combustors swirling flows are often utilised to stabilise a flame onto a burner, as the recirculation region caused by vortex breakdown acts as a natural `flame holder'. We investigate the manipulation of the global instability by harmonic forcing through a weakly non-linear analysis of an incompressible swirling jet. The flow is expanded about the critical Reynolds number where instability first occurs. Linear effects are obtained at first order, including both the unstable mode and the response to harmonic forcing. At second order, harmonics and base-flow modifications caused by non-linear interactions of the mode and forced response are obtained. An equation for the mode amplitude is obtained at third order, allowing for the effect of harmonic forcing to be quantified. In this manner, the effectiveness of control across a variety of forcing frequencies and azimuthal wavenumbers is assessed. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L40.00006: Internal Flow Dynamics and Spray Characteristics in Liquid Swirl Injectors Jacob Gamertsfelder, Prashant Khare The focus of this research effort is to investigate the internal flow dynamics and subsequent spray characteristics in swirling liquid fuel injectors. While significant progress has been made in the past to enhance the understanding of the internal dynamics of the vortex generator and resulting liquid sprays, limited studies exist that capture both the detailed mechanistic processes leading to swirling liquid and the resulting spray formation. This effort will fill this gap in the literature. The theoretical formulation is based on three-dimensional incompressible Navier-Stokes equations with surface tension. A volume of fluid (VOF) method is used for interface capturing. The swirl injector geometry consists of three equally spaced (at 120 degrees) tangential inlets of 1 mm diameter, a 6 mm vortex generator and a 2 mm diameter spray nozzle with a L/D ratio of 12. The operating conditions consists of a Weber number of 1556, corresponding to a flow rate of 25.51 g/s at an injector pressure of 0.579 MPa. The ambient chamber pressure and temperature are 4 MPa and 300 K, respectively. Preliminary results show that the swirl generated in the injector leads to the formation of a hollow cone spray that breaks up to form ligaments and droplets. A systematic analysis will be conducted to quantitatively identify the processes leading to the formation of liquid swirl near the injector walls, air core in the center and subsequent spray formation including droplet size distributions, breakup length and spray angles. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L40.00007: Helical Vortex Characterization in Swirling Jets from Planar Measurements Benjamin Emerson, Tim Lieuwen The fluid mechanics of swirling jets are highly three-dimensional, but most state of the art measurement capabilities are only planar. This work demonstrates an experimental data analysis methodology for swirling jets. The methodology is implemented on planar velocity field data to interpret the dynamical, three-dimensional topology of the velocity field. The methodology blends physical understanding of reacting swirling jets with clues that are present in stereoscopic particle image velocimetry data to infer a helical vortex tube inclination angle. With this inclination angle, the planar measurement data can be revolved to re-construct the three-dimensional velocity field. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700