Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session T24: Control and Instability of Jets |
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Chair: Luiz Hegele, Santa Catarina State University Room: 251 B |
Monday, November 25, 2024 4:45PM - 4:58PM |
T24.00001: Elastic nozzles produce more robust jets Md Emazuddin Alif, Andrew Dickerson Nozzle characteristics modulate the stability of liquid jets, but their role in jet robustness to external disturbances is understudied. Here we produce jets with thin elastic membranes containing a hole of approximately 500 μm in undeformed diameter. Our softest membranes produce the most stable jets in the Rayleigh and first wind-induced breakup regimes. An externally applied upstream pressure pulse lasting approximately 1 ms momentarily reduces the jet breakup distance and morphology. Softer nozzles and higher jet velocities minimize the disruption to the otherwise steady jet. Linear temporal theory for short nozzles, and derived using a dilated nozzle diameter, well predicts breakup length before and after the pressure pulse. We propose a hypothetical flow-rate and associated dilation for which our pressure impulse has no effect on jet stability. Pressure disturbances initiate morphological changes in the jet, introducing novel phenomena like jet thinning and exit coalescence. Our results demonstrate that nozzle compliance can play significant role in damping undesirable disturbances. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T24.00002: Open-Loop Control for Jet Mixing Enhancement Using Acoustic Excitation Luca Franceschelli, Marco Raiola, Stefano Discetti Controlling jet flows is crucial in aviation and industry for enhancing jet mixing and reducing noise, leading to improved performance and efficiency. At Universidad Carlos III de Madrid, we have designed a state-of-the-art jet facility within an anechoic chamber to explore new jet flow control strategies. This facility features two loudspeakers in the stagnation chamber, serving a dual purpose: exciting jet instabilities for control at the nozzle and directly manipulating jet properties. Additionally, six synthetic jets will be installed at the nozzle exit to act radially on the flow, providing greater control over jet dynamics. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T24.00003: Bifurcating flows or helical structures formed in the initial region of a round jet by synthetic jets arranged in a nozzle Akinori Muramatsu, Kohei Tanaka, Yuusuke Kobayashi A round jet is periodically disturbed by synthetic jets at near the exit of a round nozzle. The synthetic jets are formed from holes arranged circumferentially in the round nozzle, because the holes are connected to loudspeakers inputting a sinusoidal wave through vinyl tubes. The number of holes, namely synthetic jets is 3 to 6. When the synthetic jets are driven in the same phase and at the vortex formation frequency of the natural transition of the jet, bifurcating flows can be formed near the nozzle. The number of bifurcating flows is identical to the number of synthetic jets. Consequently, by driving the synthetic jets in symmetric mode, the mixing between the jet and surroundings is enhanced near the nozzle exit. The experimental results can be numerically simulated using OpenFOAM. Numerical simulations are also shown that helical structures can be formed in the potential core by driving the synthetic jets in sequence, that is, by driving the synthetic jets in a rotational manner. In this case, the mixing near the nozzle outlet is suppressed. In addition, when six synthetic jets are used, a double helix structure can be formed by driving them with a phase difference, so that the jet breaks down further downstream. This means that mixing of the jet is further suppressed in this case. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T24.00004: Flow estimation in supersonic turbulent jets Yuhao Zhou, Rutvij Bhagwat, Diego B Audiffred, Igor Maia, Eduardo Martini, André Cavalieri, Peter Jordan, Aaron Towne The turbulent jet of an aircraft can generate intense noise exceeding 140 dB, leading to hearing loss and various health issues, underscoring the importance of reducing jet noise. With flow state estimation as a key enabler, a wavepacket-cancellation noise control approach has emerged as a promising method to reduce jet noise. Our work aims to implement advanced data-driven and resolvent-based estimation for a supersonic jet. The study is structured as follows: first, we generate a supersonic jet database containing flow snapshots and acoustic statistics of an ideally-expanded isothermal jet and an over-expanded overheated jet, generated using the large eddy simulations solver CharLES. Second, we present estimation results obtained using a data-driven implementation of a resolvent-based flow estimation method with and without causality enforcement. Various combinations of sensors and targets are tested and analyzed, including different numbers and types of sensors such as pressure and velocity sensors, as well as different target locations in the flow field and acoustics field. The results reinforce the potential of the wavepacket-cancellation approach for mitigating the noise of supersonic jets. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T24.00005: ABSTRACT WITHDRAWN
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Monday, November 25, 2024 5:50PM - 6:03PM |
T24.00006: Investigation of Characteristic Turbulent Coherent Structures in a Subcritical Carbon Dioxide Jet in a Multiphase Ejector Sreetam Bhaduri, Leonard J Peltier, David Ladd, Eckhard A Groll, Davide Ziviani Ejectors are heavily investigated to improve the performance of refrigeration systems. The efficiency of ejector devices depends on the physics of the entrainment, mixing and diffusing processes under multiphase operations. In this article, high-fidelity Large Eddy Simulation (LES) is employed to investigate a carbon dioxide (CO2) ejector in a multi-evaporator vapor compression cycle. The experimental results utilized for this study are at Reynold’s number (Re) 1.2e5 at the high-pressure inlet (i.e. motive flow) maintaining CO2 in subcritical state. The low-pressure inlet (i.e. suction flow) is maintained at Re 9.8e4 with CO2 in vapor state, providing a pressure lift ratio of 1.2 at the diffuser outlet. A spatial-temporal representation of the flow topology revealed the actual jet morphology. Specifically, finger-like structures are key features to entrain more surrounding warm fluid into the colder dense core fluid at the cost of destabilizing and breaking up the jet by stretching the streamwise vortices and obstructing the increase in pressure-lift ratio. Furthermore, these finger-like turbulent coherent structures have been compared with well-known hairpin / horseshoe vortices structures formed by turbulent boundary layer bursting at the shear layer. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T24.00007: Tri-global resolvent analysis of a supersonic multi-stream rectangular nozzle flow Mitesh Thakor, Datta V Gaitonde, Yiyang Sun We conduct a tri-global resolvent analysis of a supersonic multi-stream rectangular nozzle flow in a three-dimensional (3-D) domain with spanwise periodicity to understand the flow’s global perturbation dynamics. The configuration consists of three primary shear layers: (I) an upper shear layer (USL) forming due to the jet flow and the freestream on the upper side of the nozzle, (II) a splitter plate shear layer (SPSL) from the mixing of a core Mach 1.6 stream and a bypass Mach 1.0 stream, and (III) a lower shear layer (LSL) downstream of the aft-deck plate where jet flow mixes with the freestream flow. The tri-global resolvent analysis uses the 3-D mean flow as the base state. At the resonant frequency (St=3.3), the optimal response mode shows the two-dimensional (2-D) Kelvin-Helmholtz-like roller structures in the SPSL, and at lower frequencies (St<=1) inputs result in the optimal 2-D response in the USL and LSL, indicating the dominance of shear-layer instabilities. However, the sub-optimal modes show 3-D structures in the different shear-layer regions based on input frequency. Moreover, we compare the tri- and bi-global resolvent results to reveal the modeling effect of a spanwise wavenumber on the amplification mechanisms. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T24.00008: Evidence of discrete trapped acoustic waves in high subsonic jets Brandon Chung Yuen Yeung, Peter Jordan, Oliver T Schmidt We offer numerical evidence of the frequency-discrete nature of trapped acoustic waves in subsonic turbulent jets. Acoustic waves trapped within the potential core of high subsonic jets were previously investigated by Towne et al. (J. Fluid Mech. vol. 825, 2017) and Schmidt et al. (J. Fluid Mech. vol. 825, 2017), and found to be capable of resonance in a number of frequency bands. Drawing on mean flow-based global stability analysis, Schmidt et al. further hypothesized that the trapped waves exist at closely-spaced, discrete frequencies within each frequency band. However, classical spectral estimation techniques did not allow these discrete waves to be unambiguously distinguished in data. We analyze data from a large-eddy simulation of the same Mach 0.9 jet that was studied by the aforementioned authors. To extract trapped acoustic modes, we use spectral proper orthogonal decomposition (SPOD) with sine tapers, which achieves high frequency resolution. The SPOD spectrum is substantially elevated over the expected frequency bands. Within each band, the spectrum reveals multiple discrete peaks. Each of these peaks corresponds to a mode with distinct spatial support and structure. The educed structures are consistent with the previously predicted global modes. Experimental evidence is presented. |
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