Flow-Acoustic Interactions in T-Junctions

2002 ◽  
Author(s):  
A. Scott ◽  
S. Ziada
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Acoustic Pressure ◽  
Separation Bubble ◽  
Test Cases ◽  
Number Range ◽  
Acoustic Coupling ◽  
Acoustic Modes ◽  
Numerical Studies ◽  
Reynolds Number Range

The flow-acoustic nature of sharp-edged T-junctions is investigated experimentally. Tests are performed for a Reynolds number range of 54,000 < ReD < 470,000. Four test cases are studied corresponding to: (a) T-junction with flow from the two branches; (b) T-junction with flow from one branch; (c) T-junction with flow into the two branches and (d) T-junction with flow into one branch. It is found that the separation bubble formed when the flow goes around the T-junction corner provides a source of turbulence excitation. For cases (c) and (d) the dimensionless pressure amplitudes of the acoustic modes reach a maximum at a Strouhal number which is in agreement with the broadband peak measured in the separation bubble. Cases (a) and (b) exhibit a different type of flow-acoustic coupling. In both cases, the maximum acoustic pressure is stronger than in Cases (c) and (d) and occurs at a Strouhal number which is different from that observed in the separation bubble. The results are compared to experimental and numerical studies from the literature.

On vortex shedding from a circular cylinder in the critical Reynolds number régime

1969 ◽  
Vol 37 (3) ◽  
pp. 577-585 ◽  
Author(s):  
P. W. Bearman
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Critical Reynolds Number ◽  
Narrow Band ◽  
Critical Regime ◽  
Number Range ◽  
Velocity Fluctuations ◽  
Reynolds Number Range

The flow around a circular cylinder has been examined over the Reynolds number range 105 to 7·5 × 105, Reynolds number being based on cylinder diameter. Narrow-band vortex shedding has been observed up to a Reynolds number of 5·5 × 105, i.e. well into the critical régime. At this Reynolds number the Strouhal number reached the unusually high value of 0·46. Spectra of the velocity fluctuations measured in the wake are presented for several values of Reynolds number.

Vortex shedding behind a square cylinder in transonic flows

1987 ◽  
Vol 178 ◽  
pp. 303-323 ◽  
Author(s):  
Takeo Nakagawa
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Shock Waves ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Acoustic Waves ◽  
Strong Shock ◽  
Square Cylinder ◽  
Number Range ◽  
Reynolds Number Range

This paper is primarily concerned with Mach-number effects on the vortex shedding behind a square cylinder (side length D = 20 mm) in a Reynolds-number range of 0.696 × 105 < Re < 4.137 × 105, and a Mach-number range of 0.1522 < M < 0.9049.Regular periodic vortex shedding is present, irrespective of the appearance of shock waves around a square cylinder. The shape of the vortices is, however, deformed by the shock waves, and each vortex centre becomes non-uniform while the vortex passes through the gap between the upper and lower shock waves. Weak shock waves around the square cylinder do not alter the Strouhal number, but strong shock waves weaken the vortex shedding and increase the Strouhal number suddenly. Acoustic waves have been recorded by the Mach-Zehnder interferometer when the Mach number is close to the critical value. The acoustic waves are generated most strongly at the instant when each vortex hits the foot of the shock waves formed above and below the vortex formation region.From the present work and that of Okajima (1982), it is suggested that the Strouhal number of alternating vortices shed from a square cylinder can be estimated to be about 0.13 in the Reynolds-number range between 102 and 3.4 × 105.

Vortex shedding from a circular cylinder in moderate-Reynolds-number shear flow

1980 ◽  
Vol 101 (4) ◽  
pp. 721-735 ◽  
Author(s):  
Masaru Kiya ◽  
Hisataka Tamura ◽  
Mikio Arie
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Transverse Velocity ◽  
Number Range ◽  
Uniform Shear ◽  
Reynolds Number Range ◽  
Moderate Reynolds Number ◽  
Shear Parameter

The frequency of vortex shedding from a circular cylinder in a uniform shear flow and the flow patterns around it were experimentally investigated. The Reynolds number Re, which was defined in terms of the cylinder diameter and the approaching velocity at its centre, ranged from 35 to 1500. The shear parameter, which is the transverse velocity gradient of the shear flow non-dimensionalized by the above two quantities, was varied from 0 to 0·25. The critical Reynolds number beyond which vortex shedding from the cylinder occurred was found to be higher than that for a uniform stream and increased approximately linearly with increasing shear parameter when it was larger than about 0·06. In the Reynolds-number range 43 < Re < 220, the vortex shedding disappeared for sufficiently large shear parameters. Moreover, in the Reynolds-number range 100 < Re < 1000, the Strouhal number increased as the shear parameter increased beyond about 0·1.

scholarly journals Asymmetrical Split-and-Recombine Micromixer with Baffles

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 844 ◽  
Author(s):  
Wasim Raza ◽  
Kwang-Yong Kim
Keyword(s):  
Reynolds Number ◽  
Geometrical Parameters ◽  
Mixed Species ◽  
Mixing Index ◽  
Number Range ◽  
Mixing Performance ◽  
Curved Channels ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
Reynolds Number Range

The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number range of 0.1–80. The variance of the concentration of the mixed species was considered to quantify the mixing index. The micromixer showed far better mixing performance over whole Reynolds number range than an earlier split-and-recombine micromixer. The mixer achieved mixing indices greater than 90% at Re ≥ 20 and a mixing index of 99.8% at Re = 80. The response of the mixing quality to the change of three geometrical parameters was also studied. A mixing index over 80% was achieved within 63% of the full length at Re = 20.

Computational Fluid Dynamics Study of a Flexible Flapping Hydrofoil Propulsor

2016 ◽  
Author(s):  
Harikrishnan Vijayakumaran ◽  
Parameswaran Krishnankutty
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Number ◽  
Strouhal Number ◽  
Thrust Coefficient ◽  
Number Range ◽  
Wake Field ◽  
Propulsive Performance ◽  
Velocity Magnitude ◽  
Maximum Angle ◽  
Motion Parameters

A CFD study to understand the hydrodynamics and fluid flow around a chordwise flexible hydrofoil with combined sway and yaw motion which imitates the caudal fin flapping in thunniforms, is presented. The dependency of motion parameters of the flexible flapping hydrofoil to its propulsive performance is studied by carrying out the analyses over a Strouhal number range of 0.1 to 0.4 in steps of 0.025 at three maximum angle of attacks viz. 10°,15°,20°. Qualitative observations of the wake field and trailing jet is presented using velocity magnitude contours and vorticity contours. The analyses carried out at 40,000 Reynolds number and sway amplitude of 0.75 chordlength, revealed that the average thrust coefficient increases with increase in Strouhal number and maximum angle of attacks. The highest efficiency is achieved when the maximum angle of attack is 15° and Strouhal number is 0.225.

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