Article
Mechanics
L. R. Gareev, J. S. Zayko, A. D. Chicherina, V. V. Trifonov, A. Reshmin, V. V. Vedeneev
Summary: This paper studies the development of perturbations in a submerged air jet with a round cross-section and a long laminar region. The results of experiments are in good agreement with theoretical calculations, demonstrating that small perturbations closely follow the predictions of inviscid linear stability theory.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
O. O. Ivanov, D. A. Ashurov, L. R. Gareev, V. V. Vedeneev
Summary: This study identifies the non-modal "lift-up" growth mechanism through experiments and confirms that the development of disturbances qualitatively corresponds to the theoretically calculated optimal perturbations. The features of the transition to turbulence caused by non-modal growth are discussed.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Michael N. Stavropoulos, Matteo Mancinelli, Peter Jordan, Vincent Jaunet, Joel Weightman, Daniel M. Edgington-Mitchell, Petronio A. S. Nogueira
Summary: Spatial linear stability analysis is used to study the axisymmetric screech tones generated by twin converging round nozzles. Different waves supported by the flow at different conditions are identified using vortex-sheet and finite-thickness models. The frequency-wavenumber regions at which the upstream-propagating guided jet modes are neutrally stable vary with solution symmetry, jet separation, S, and the velocity profile. Screech-frequency predictions from both models agree well with experimental data, but the predictions from the finite-thickness model match the measured screech tones better than the vortex sheet. The present results suggest that the feedback loop generating these screech tones is similar to that observed for single-jet resonance.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Shahram Karami, Julio Soria
Summary: This study uses large-eddy simulations to investigate the influence of nozzle external geometry on upstream-travelling waves in under-expanded supersonic jets. It is found that the external geometry significantly affects the first-order statistics and leads to multiple peaks in the energy spectra at distinct frequencies. Different forms of upstream-travelling wavepackets contribute to the receptivity process with their contributions and strength altered by the change of the external geometry of the nozzle.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Multidisciplinary Sciences
Jie Tang, Jun A. Zhang, Pakwai Chan, Kaikwong Hon, Xiaotu Lei, Yuan Wang
Summary: The study analyzes aircraft-collected data during Typhoon Kalmaegi (1415) and Typhoon Nida (1604) to confirm the existence of sub-kilometer-scale rolls in the atmospheric boundary layer of tropical cyclones. The presence of these rolls in the outer-core region is determined to significantly modulate turbulent transfer. Flight legs with rolls were found to have an averaged momentum flux 2.5 times higher than legs without rolls, suggesting a significant impact on turbulent fluxes in the tropical cyclone boundary layer.
SCIENTIFIC REPORTS
(2021)
Article
Mechanics
Masato Hayashi, Tomoaki Watanabe, Koji Nagata
Summary: This study uses direct numerical simulations to investigate the characteristics of small-scale shear layers, detecting shear layers through shearing motion tensor analysis and confirming intense shear layer structures through flow visualization in a biaxial strain field.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Aerospace
Yu Zeng, Hongbo Wang, Wen Ao, Huifeng Chen
Summary: In this study, a sinusoidal lobed mixer was used to enhance mixing between subsonic and supersonic flows, with parameter experiments and large eddy simulations conducted to investigate mixing performance. The results show good similarity between numerical and experimental conclusions, indicating that the performance of lobed mixer is influenced by its amplitude and wavelength.
AEROSPACE SCIENCE AND TECHNOLOGY
(2022)
Article
Thermodynamics
B. W. Skews, B. Ndebele
Summary: Experiments and numerical simulations were conducted to examine the flow field surrounding a flat-faced body impacting on a flat surface, revealing high pressure generated during impact and supersonic jet velocities. Computational fluid dynamic simulations provided detailed evaluation of flow characteristics in different regions of the flow field.
JOURNAL OF APPLIED FLUID MECHANICS
(2021)
Letter
Mechanics
Shahrzad Norouzi, Arnaud Le Floc'h, Giuseppe Di Labbio, Lyes Kadem
Summary: By optimizing experimental AAA flow models, this study proposes a method to assess AAA severity based on underlying flow, with simplified models capturing relevant pathological flow features for a more comprehensive clinical evaluation.
Article
Chemistry, Multidisciplinary
Patrick Fillingham, Arjun Viswanathan, Igor Novosselov
Summary: This study investigates the wall stress resulting from inclined under-expanded planar jets using computational fluid dynamics and establishes an empirical relationship between wall shear stress and jet parameters. The findings can be applied to design and assess the performance of practical systems.
APPLIED SCIENCES-BASEL
(2022)
Article
Mechanics
Milad Samie, Vlad Aparece-Scutariu, Philippe Lavoie, Dong-hyuk Shin, Andrew Pollard
Summary: This study uses direct numerical simulation to investigate three-dimensional vortical and very-large-scale coherent structures in a turbulent round jet at a Reynolds number of 7300. The results show the importance of horseshoe vortices in the jet and the existence of symmetric and asymmetric horseshoe vortices that affect the high and low momentum regions in the flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Gioacchino Cafiero, Giusy Castrillo, Tommaso Astarita
Summary: High-resolution particle image velocimetry experiments were performed to characterize the flow field of fractal grids in a turbulent round jet exit section. Results were compared with square grids, a regular grid, and a jet without turbulator, revealing differences in turbulence properties. Correction is needed to properly scale turbulence intensity profiles with a length scale based on grid parameters. The interaction of small eddies shed by central grid items produces the typical turbulence intensity profile in fractal grid jets.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Zeeshan Saeed, Elizabeth Weidner, Blair A. Johnson, Tracy L. Mandel
Summary: Through theoretical analysis, it is demonstrated how buoyancy shapes flow behavior by enhancing mean shear and increasing the conversion of mean kinetic energy into turbulent kinetic energy. This study also highlights the primary role of buoyancy in strengthening the eddy vorticity in plumes through enhancing mean flow and mean shear.
Article
Mathematics, Applied
Aleksandar Badza, Trent W. Mattner, Sanjeeva Balasuriya
Summary: Lagrangian coherent structures (LCSs) are time-varying entities that capture the most influential transport features of a flow. This article systematically investigates whether LCS methods are self-consistent in their conclusions under the uncertainty of realistic Eulerian velocity data. The methods detecting full-dimensional coherent flow regions are found to be significantly more robust than those detecting lower-dimensional flow barriers.
PHYSICA D-NONLINEAR PHENOMENA
(2023)
Article
Physics, Multidisciplinary
Aaron Hui, Brian Skinner
Summary: A resistor at finite temperature produces white noise fluctuations of the current called Johnson-Nyquist noise, which can be used to measure the electron temperature. While the Johnson-Nyquist theorem has been generalized for Ohmic devices, a similar generalization is needed for hydrodynamic electron systems. In a rectangular geometry, low-frequency Johnson noise in the hydrodynamic setting is found to be geometry dependent due to nonlocal viscous gradients, but ignoring the geometric correction only leads to a maximum error of 40% compared to the Ohmic result.
PHYSICAL REVIEW LETTERS
(2023)