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.

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.

On Oscillation of a Confined Jet With a Downstream Obstacle

2003 ◽  
Author(s):  
Katsuya Hirata ◽  
Jiro Funaki ◽  
Katsuya Yamada ◽  
Hirohisa Wakisaka
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Distance Effect ◽  
Geometrical Parameters ◽  
Two Dimensional ◽  
Number Range ◽  
Reynolds Number Effect ◽  
Square Prism ◽  
Optimal Configurations ◽  
Oscillatory Phenomenon

In the present study, the authors investigate an oscillatory phenomenon of a two-dimensional confined jet with a square prism, by experiments and computations. In experiments in an air duct, jet’s frequencies were measured near the target by a hot-wire anemometer, in the Reynolds-number range of 300–5000. In computations, the numerical method adopted here is a finite difference method formulated in terms of vorticity and stream function. As a result, we can see the Reynolds-number effect, the target-distance effect and the target-size effect upon Strouhal number. Regarding the Reynolds-number effect, it was found that there is less influence, which guarantees widerange workability as a flowmeter or a mixer. Regarding geometrical parameters, the results show information for optimal configurations. The results can be surnmarised in an empirical formula describing the relation between Strouhal number and geometrical parameters, with a specified unstable range. Computed jet’s frequencies were confirrned to be in good agreement with experimental ones, which indicates that the phenomenon is intrinsically two-dimensional. Numerical results reveal details of flow field and possibility for applications.

Aerodynamic Subsonic Model at Transitional/Turbulent Reynolds Number for Bluff-Ellipsoidal Hulls

2020 ◽  
Author(s):  
Jorge A. Ricardo ◽  
Davi Antônio dos Santos ◽  
Elisan dos Santos Magalhães
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Turbulence Model ◽  
Computational Simulation ◽  
Superior Performance ◽  
Grid Turbulence ◽  
Aerodynamic Coefficients ◽  
Number Range ◽  
Turbulent Reynolds Number

Abstract The present work addresses the subsonic aerodynamic coefficients model for bluff ellipsoidal hulls at transitional and turbulent Reynolds number. The drag, lift, and moment aerodynamic coefficients model are based on computational fluid dynamics (CFD) simulations for four bluff ellipsoids with aspect ratio of 1, 2, 3, and 4, in the Reynolds number range of 1 × 103 to 2 × 106 and angle of attack range from 0 to 20 degrees. The Large Eddy Simulation (LES) turbulence model is used with the sub-grid turbulence model Wall-Adapting Local-Eddy Viscosity (WALE) to solve the fluid field. To reduce computational simulation time, at a first instant, the mesh is gradually refined until the point that it does not influence anymore in the final result (mesh independence). For each aerodynamic coefficient a nonlinear equation structure, valid for all the ellipsoids, is proposed as a parametric model with parameters estimated using the least mean square algorithm applied to the results of the computational fluid dynamics simulations. The proposed equations have a superior performance, in terms of precision and number of terms, when compared to polynomial equations fitted to the same data.

Fluid Dynamics Measurements and Flow Visualizations of a Free Slot Jet of Air

2003 ◽  
Author(s):  
F. Gori ◽  
E. Nino
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Number ◽  
Jet Flow ◽  
Hydraulic Diameter ◽  
Hot Wire ◽  
Number Range ◽  
Reynolds Number Range ◽  
Experimental Apparatus ◽  
Hot Wire Anemometry ◽  
Flow Visualizations

The paper reports flow visualizations of a free slot jet of air, obtained with the shadowgraph technique, in the Reynolds number range allowed by the experimental apparatus, i.e. from Re=1,682 to Re=22,107. The Reynolds number is based on the hydraulic diameter of the slot. The shadowgraphs have confirmed the presence of the undisturbed region of flow, which is the zone of the jet flow where velocity and turbulence are about the same as those measured on the slot exit. The undisturbed region of flow is dependent on the Reynolds number. It is higher than three times the slot height, for Re=1,682, and equal to the slot height, for Re=22,107. To confirm the findings of the visualizations, fluid dynamics measurements have been carried out with the hot wire anemometry. The fluid dynamics measurements have confirmed these values with a little over-prediction.

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.

A CFD Simulation of Strouhal Number for U-Shaped Section Aqueducts

2012 ◽  
Vol 204-208 ◽  
pp. 4738-4741
Author(s):  
Yu Chun Li ◽  
Xiao Jie Zhang ◽  
Shi Wen Jia
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Cfd Simulation ◽  
Reynolds Numbers ◽  
Vortex Induced Vibration ◽  
Computational Fluid Dynamics Cfd ◽  
Shaped Section

The method of computational fluid dynamics (CFD, Fluent code) was applied to simulate the Strouhal numbers of the empty and fulfilled U-shaped sections. Based on the N-S equation and k-ε turbulence model, the effects of Reynolds numbers and height/width ratios of the sections on the Strouhal numbers were investigated. The results of this study show that the Reynolds number has little influence on the Strouhal numbers, which decrease with the increase of height/width ratios of the sections. The conclusion of present study provides a foundation for the further study of vortex-induced vibration of U-shaped aqueduct bridges.

Fluctuating Lift Forces of the Karman Vortex Streets on Single Circular Cylinders and in Tube Bundles: Part 1—The Vortex Street Geometry of the Single Circular Cylinder

1972 ◽  
Vol 94 (2) ◽  
pp. 603-610 ◽  
Author(s):  
Y. N. Chen
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Vortex Street ◽  
Circular Cylinders ◽  
Number Range ◽  
Pressure Drag ◽  
Minimum Drag ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Better Than

The geometry of the vortex street for single circular cylinders will be calculated from the measured values given by numerous investigators about the steady pressure drag coefficient and the Strouhal number, whereby the Kronauer minimum drag criterion comes into use. The calculated results will be compared with the experimentally determined ones. A good agreement can be achieved between both. The Bearman-Strouhal number SB = fh/Us will also be computed as a function of the Reynolds number. Furthermore a new wake number C = fh2/Γ will be introduced. It will be shown that this new number is universally much better than the Bearman one. It remains constant at 0.165 for an ideal flow over the whole Reynolds number range up to the highest value of 107 ever measured hitherto.

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 &lt; ReD &lt; 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.

scholarly journals Oscillations in cylinder wakes at Mach 4

2015 ◽  
Vol 785 ◽  
Author(s):  
B. E. Schmidt ◽  
J. E. Shepherd
Keyword(s):  
Reynolds Number ◽  
Supersonic Flow ◽  
Strouhal Number ◽  
Subsonic Flow ◽  
Reynolds Numbers ◽  
Acoustic Signals ◽  
Cylinder Surface ◽  
Periodic Oscillations ◽  
Number Range ◽  
Subsonic Region

The wake behind a circular cylinder in Mach 4 flow is examined experimentally in the Reynolds number range $2\times 10^{4}$ to $5\times 10^{5}$. Periodic oscillations of the sliplines in the wake are observed. The Strouhal number of the oscillations based on the diameter of the cylinder is found to increase monotonically from 0.30 to 0.50 with increasing Reynolds number. If the Strouhal number is formed using the length of the sliplines, however, it has a constant value of approximately 0.48 for all Reynolds numbers studied. This scaling indicates that the oscillations in supersonic flow are likely driven by acoustic signals propagating back and forth through the subsonic region between the separation points on the cylinder and the neck where the sliplines converge, unlike in subsonic flow where oscillations are caused by vortices shed from the cylinder surface.

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