The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Peter E Hamlington - One of the best experts on this subject based on the ideXlab platform.
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scaling of the puffing Strouhal Number for buoyant jets and plumes
Journal of Fluid Mechanics, 2020Co-Authors: Nicholas T Wimer, Caelan Lapointe, Jason D Christopher, Siddharth P Nigam, Torrey R S Hayden, Aniruddha A Upadhye, Mark Strobel, Gregory B Rieker, Peter E HamlingtonAbstract:Prior research has shown that buoyant jets and plumes ‘puff’ at a frequency that depends on the balance of momentum and buoyancy fluxes at the inlet, as parametrized by the Richardson Number. Experiments have revealed the existence of scaling relations between the Strouhal Number of the puffing and the inlet Richardson Number, but geometry-specific relations are required when the characteristic length is taken to be the diameter (for round inlets) or width (for planar inlets). Similar to earlier studies of rectangular buoyant jets and plumes, in the present study we use the hydraulic radius of the inlet as the characteristic length to obtain a single Strouhal–Richardson scaling relation for a variety of inlet geometries over Richardson Numbers that span three orders of magnitude. In particular, we use adaptive mesh numerical simulations to compute puffing Strouhal Numbers for circular, rectangular (with three different aspect ratios), triangular and annular high-temperature buoyant jets and plumes over a range of Richardson Numbers. We then combine these results with prior experimental data for round, planar and rectangular buoyant jets and plumes to propose a new scaling relation that describes puffing Strouhal Numbers for various inlet shapes and for hydraulic Richardson Numbers spanning over four orders of magnitude. This empirically motivated scaling relation is also shown to be in good agreement with prior results from global linear stability analyses.
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scaling of the puffing Strouhal Number for buoyant jets
arXiv: Fluid Dynamics, 2019Co-Authors: Nicholas T Wimer, Caelan Lapointe, Jason D Christopher, Siddharth P Nigam, Torrey R S Hayden, Aniruddha A Upadhye, Mark Strobel, Gregory B Rieker, Peter E HamlingtonAbstract:Prior research has shown that round and planar buoyant jets "puff" at a frequency that depends on the balance of momentum and buoyancy fluxes at the inlet, as parametrized by the Richardson Number. Experiments have revealed the existence of scaling relations between the Strouhal Number of the puffing and the inlet Richardson Number, but geometry-specific relations are required when the characteristic length is taken to be the diameter (for round inlets) or width (for planar inlets). In the present study, we show that when the hydraulic radius of the inlet is instead used as the characteristic length, a single Strouhal-Richardson scaling relation is obtained for a variety of inlet geometries. In particular, we use adaptive mesh numerical simulations to measure puffing Strouhal Numbers for circular, rectangular (with three different aspect ratios), triangular, and annular high-temperature buoyant jets over a range of Richardson Numbers. We then combine these results with prior experimental data for round and planar buoyant jets to propose a new scaling relation that accurately describes puffing Strouhal Numbers for various inlet shapes and for Richardson Numbers spanning over four orders of magnitude.
Xiwen Dai - One of the best experts on this subject based on the ideXlab platform.
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vortical acoustic resonance in an acoustic resonator Strouhal Number variation destabilization and stabilization
Journal of Fluid Mechanics, 2021Co-Authors: Xiwen DaiAbstract:The impact of acoustic resonance on vortical–acoustic resonance and flow instability is studied by a combined travelling–global mode analysis about a low-speed inviscid parallel shear flow in two-dimensional symmetric duct–cavity configurations. First, in a shallow-cavity case, we show that the difference between incompressible and compressible models in describing the compact feedback loop, consisting of the Kelvin–Helmholtz (KH) instability wave and the Rayleigh–Powell–Rossiter (RPR) feedback, is small and the global mode frequency follows the Strouhal law. Using the compact case as a baseline for comparison, the influence of an acoustic resonator (AR) on the feedback loop is then examined. In this deep-cavity case, phenomena such as frequency deviation from the Strouhal law, global mode switching, global mode destabilization and stabilization, caused by a trapped or a heavily damped acoustic resonant mode, are observed. We show that those phenomena can be explained by the local–global relation of the feedback loop and the dual-feedback view: the coexistence of RPR and AR feedbacks. The Strouhal Number variation is due to the phase difference of the unstable vortical wave between the upstream and downstream cavity edges being changed by the additional AR feedback. It is found that the switching is not a vortical but an acoustic effect. The destabilization and stabilization, near and far from an acoustic resonance, are respectively understood as the result of the total feedback at the upstream edge being strengthened and weakened by the AR feedback.
Kaiivchien Chia - One of the best experts on this subject based on the ideXlab platform.
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on the relationship of effective reynolds Number and Strouhal Number for the laminar vortex shedding of a heated circular cylinder
Physics of Fluids, 2000Co-Authors: Anbang Wang, Zdenek Travnicek, Kaiivchien ChiaAbstract:The laminar vortex shedding of airflow behind a circular cylinder with different heating temperatures was experimentally investigated with emphasis on the relationship of wake frequency and the Reynolds Number. A new method to generate the two-dimensional parallel vortex shedding for the heated cylinder was developed and tested. An “effective Reynolds Number” that employs a kinematic viscosity computed from an “effective temperature” is used to account for the temperature effects on the vortex shedding frequency. The present result shows that the frequency data could be successfully collapsed with the effective temperature computed by Teff=T∞+0.28(TW−T∞) for a wide range of cylinder temperatures, T∞ and TW being the free-stream temperature and cylinder surface temperature, respectively. Moreover, the relationship between Strouhal Number and effective Reynolds Number was found to be “universal.” The physical interpretation of Teff and the applicable region of the St–Reeff curve are discussed.
Y Nakamura - One of the best experts on this subject based on the ideXlab platform.
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vortex shedding from bluff bodies and a universal Strouhal Number
Journal of Fluids and Structures, 1996Co-Authors: Y NakamuraAbstract:Experiments on vortex shedding from bluff bodies were conducted in a wind tunnel, with emphasis on finding the effects of afterbody shape on the vortex-shedding frequency. It is found that the Strouhal Number of a bluff body with afterbody decreases initially with increasing side ratio, with a reduction that is not dependent on the details of afterbody shape but only on the side ratio. This is in sharp contrast to the base suction that is sensitively dependent on afterbody shape. Two normal plates in tandem arrangement are exceptional in that the Strouhal Number increases initially with increasing gap between the two plates. The inapplicability of Roshko's universal Strouhal Number to bluff bodies with afterbodies is mentioned and discussed in some detail.
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stepwise increase in the Strouhal Number for flows around flat plates
International Journal for Numerical Methods in Fluids, 1992Co-Authors: Shigehira Ozono, Y Nakamura, Yuji Ohya, Ryuzo NakayamaAbstract:The unsteady viscous flow around flat plates with square leading and trailing edges is investigated by using a finite difference computation of the incompressible two-dimensional Navier-Stokes equations. The chord-to-thickness ratio of a plate ranges from d/h=3 to 9, with a Reynolds Number based on the plate's thickness equal to 103. The numerical analysis confirms the finding obtained in our previous experiment that vortex shedding from flat plates with square leading and trailing edges is caused by the impinging shear layer instability. The Strouhal Number based on the plate's chord increases stepwise with increasing d/h in accordance with the experiment. The numerical analysis also gives some crucial information on the complicated vortical flow occurring near the trailing edge. Finally, the mechanism of the impinging shear layer instability is discussed in the light of the experimental and numerical findings.
P Nguyen - One of the best experts on this subject based on the ideXlab platform.
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viscous oscillatory flow about a circular cylinder at small to moderate Strouhal Number
Journal of Fluid Mechanics, 1995Co-Authors: H M Badr, S C R Dennis, S Kocabiyik, P NguyenAbstract:The transient flow field caused by an infinitely long circular cylinder placed in an unbounded viscous fluid oscillating in a direction normal to the cylinder axis, which is at rest, is considered. The flow is assumed to be started suddenly from rest and to remain symmetrical about the direction of motion. The method of solution is based on an accurate procedure for integrating the unsteady Navier–Stokes equations numerically. The numerical method has been carried out for large values of time for both moderate and high Reynolds Numbers. The effects of the Reynolds Number and of the Strouhal Number on the laminar symmetric wake evolution are studied and compared with previous numerical and experimental results. The time variation of the drag coefficients is also presented and compared with an inviscid flow solution for the same problem. The comparison between viscous and inviscid flow results shows a better agreement for higher values of Reynolds and a Strouhal Numbers. The mean flow for large times is calculated and is found to be in good agreement with previous predictions based on boundary-layer theory.
