Experimental Investigation on the Motion of Particle Cloud in Viscous Fluids

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Amir H. Azimi
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Viscous Fluids ◽  
Air Bubbles ◽  
Aspect Ratios ◽  
Particle Clouds ◽  
Flow Through ◽  
Using Data ◽  
The Stability ◽  
Individual Particles

Laboratory experiments were conducted to study the dynamics of particle clouds in viscous fluids. Different shapes of frontal head and trailing stems were observed, and particle clouds were classified using data mining methodology. The stability of the frontal head of particle clouds was found to be correlated with the nozzle diameter and mass of sand particles in the form of an initial aspect ratio. The formation of particle clusters into a torus and the split of the frontal head into two or three clusters were investigated in detail. The cluster of particles flow through viscous fluid experienced partial separation due to the release of air bubbles from the rear of frontal head. It was observed that the time and location of major particle separation increase linearly with the aspect ratio. The oscillatory motion of the frontal head, caused by an uneven release of air bubbles from the rear of the frontal head, was found to be correlated with the initial aspect ratio. Both amplitude and wavelength exhibited a linear relationship with nondimensional time. The average drag coefficient of particle clouds Cd in viscous fluids was calculated for different aspect ratios, and the results were compared with the drag coefficient of individual particles. It was found that the averaged drag coefficients of particle clouds were smaller than the drag coefficient of individual particles, and Cd slightly increases with the increasing initial aspect ratio.

The Effect of Aspect Ratio on the Drag of Bare Cylinders

2019 ◽  
Author(s):  
Douglas A. Potts ◽  
Jonathan R. Binns ◽  
Andrew E. Potts ◽  
Hayden Marcollo
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Critical Evaluation ◽  
Data Sets ◽  
Infinite Length ◽  
Linear Effect ◽  
Aspect Ratios ◽  
Offshore Industry ◽  
Insignificant Correlation ◽  
Design Guidance

Abstract The drag coefficient for long-slender structures that is typically provided in design guidance has been determined from test specimens of sufficient length that they are unaffected by the aspect ratio (L/D), whereby they are considered to be of “infinite” length. However, it is apparent from the literature that aspect ratio does have a significant non-linear effect at short L/D ratios. DNV provides guidance on the aspect ratio effect on the drag coefficient of a cylinder, for which no experimental source data has been cited. The DNV design guidance has wide usage in the offshore industry and merits critical evaluation. This paper critically reviews the literature and presents the results of a series of tow tank experiments performed by the authors. A series of tow tank tests of a surface-piercing cylinder has been undertaken using a range of aspect ratios as well as testing the effect of various end conditions, where the effects of VIV and ventilation has been deemed insignificant. Correlation of the various data sets of the literature and the experimental test programme provides the basis for developing an alternate design guidance curve for the effect of aspect ratio on the drag coefficient of cylinders.

FIV Characteristics of U-Tubes Due to Relocation of the Tube Support Plate

2005 ◽  
Author(s):  
Ki-Wahn Ryu ◽  
Hyung-Jin Kim ◽  
Chi-Yong Park
Keyword(s):  
Aspect Ratio ◽  
Steam Generator ◽  
Mode Shapes ◽  
Design Stage ◽  
Parameter Study ◽  
Stability Ratio ◽  
Integrity Assessment ◽  
Support Plate ◽  
Aspect Ratios ◽  
The Stability

Fluid-elastic instability and turbulence excitation for an under developing steam generator are investigated numerically. The stability ratio and the amplitude of turbulence excitation are obtained by using the PIAT (Program for Integrity Assessment of Steam Generator Tube) code from the information on the thermal-hydraulic data of the steam generator. The aspect ratio, the ratio between the height of U-tube from the upper most tube support plate (h) and the width of two vertical portion of U-tube (w), is defined for geometric parameter study. Several aspect ratios with relocation of tube support plates are adopted to study the effects on the mode shapes and characteristics of flow-induced vibration. When the aspect ratio exceeds value of 1, most of the mode shapes at low frequency are generated at the top of U-tube. It makes very high value of the stability ratio and the amplitude of turbulent excitation as well. We can consider that the local mode shape at the upper side of U-tube will develop the wear phenomena between the tube and the anti-vibration bars such as vertical, horizontal, and diagonal strips. It turns out that the aspect ratio reveals very important parameter for the design stage of the steam generator. The appropriate value of the aspect ratio should be specified and applied.

The Effect of a Transversely Injected Stream on the Flow through Turbine Cascades—Part III: Influence of Aspect Ratio

1979 ◽  
Vol 101 (1) ◽  
pp. 61-67
Author(s):  
B. A. Aburwin ◽  
N. R. L. Maccallum
Keyword(s):  
Aspect Ratio ◽  
Stagnation Pressure ◽  
Dimensional Theory ◽  
One Dimensional ◽  
Flow Capacity ◽  
Aspect Ratios ◽  
New Instrumentation ◽  
Flow Through ◽  
Turbine Cascades ◽  
End Wall

An experimental investigation has been made of the effect of a transversely injected stream on the flow through turbine cascades similar to those in which previous studies [1, 2] had been made, but having aspect ratios of 1.5 and 1.0 compared to the previous value of 3.0. New instrumentation includes a five-hole probe. The average losses in stagnation pressure and the changes in flow capacity remain in agreement with one-dimensional theory. The exit vortex is moved towards the end-wall as aspect ratio is reduced. The strength of the vortex is diminished when the aspect ratio is reduced from 3.0 to 1.5, but there is little change for the further reduction of aspect ratio.

Stokes flow through periodic orifices in a channel

1994 ◽  
Vol 263 ◽  
pp. 207-226 ◽  
Author(s):  
Y. Zeng ◽  
S. Weinbaum
Keyword(s):  
Aspect Ratio ◽  
Stokes Flow ◽  
Three Dimensional ◽  
Plane Wall ◽  
Channel Height ◽  
Infinite Plane ◽  
Electron Microscopic ◽  
Dimensional Solution ◽  
Aspect Ratios ◽  
Flow Through

This paper develops a three-dimensional infinite series solution for the Stokes flow through a parallel walled channel which is obstructed by a thin planar barrier with periodically spaced rectangular orifices of arbitrary aspect ratio B’/d’ and spacing D’. Here B’ is the half-height of the channel and d’ is the half-width of the orifice. The problem is motivated by recent electron microscopic studies of the intercellular channel between vascular endothelial cells which show a thin junction strand barrier with discontinuities or breaks whose spacing and width vary with the tissue. The solution for this flow is constructed as a superposition of Hasimoto's (1958) general solution for the two-dimensional flow through a periodic slit array in an infinite plane wall and a new three-dimensional solution which corrects for the top and bottom boundaries. In contrast to the well-known solutions of Sampson (1891) and Hasimoto (1958) for the flow through zero-thickness orifices of circular or elliptic cross-section or periodic slits in an infinite plane wall, which exhibit characteristic viscous velocity profiles, the present bounded solutions undergo a fascinating change in behaviour as the aspect ratio B’/d’ of the orifice opening is increased. For B’/d’ [Lt ] 1 and (D’ –- d’)/B’ of O(1) or greater, which represents a narrow channel, the velocity has a minimum at the orifice centreline, rises sharply near the orifice edges and then experiences a boundary-layer-like correction over a thickness of O(B’) to satisfy no-slip conditions. For B’/d’ of O(1) the profiles are similar to those in a rectangular duct with a maximum on the centreline, whereas for B’/d’ [Gt ] 1, which describes widely separated channel walls, the solution approaches Hasimoto's solution for the periodic infinite-slit array. In the limit (D’ –- d’)/B’ [Lt ] 1, where the width of the intervening barriers is small compared with the channel height, the solutions exhibit the same behaviour as Lee & Fung's (1969) solution for the flow past a single cylinder. The drag on the zero-thickness barriers in this case is nearly the same as for the cylinder for all aspect ratios.

The Plate Buckling Coefficient

1967 ◽  
Vol 71 (673) ◽  
pp. 37-40 ◽  
Author(s):  
P. S. Bulson
Keyword(s):  
Aspect Ratio ◽  
Close Approximation ◽  
Families Of Curves ◽  
Aspect Ratios ◽  
Plate Buckling ◽  
Plate Aspect Ratio ◽  
Exact Shape ◽  
Buckling Coefficient ◽  
Thin Walled ◽  
The Stability

SummaryThe stability of a compressed plate is examined, using the energy method, with transverse deflections defined by a function giving the exact shape, but never specified. By this means it is possible to make observations about the form of the plate buckling coefficient. This form is examined tor two cases of loading, and it is demonstrated that a close approximation to the complete curve linking the buckling coefficient with plate aspect ratio can be deduced. The method is applicable to single plates or thin walled members consisting of an assembly of plates, and enables families of curves connecting buckling coefficients with aspect ratios to be summarised in a single relationship.

scholarly journals The wave-induced flow of internal gravity wavepackets with arbitrary aspect ratio

2017 ◽  
Vol 834 ◽  
pp. 385-408 ◽  
Author(s):  
T. S. van den Bremer ◽  
B. R. Sutherland
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Mean Flow ◽  
One Dimensional ◽  
Unidirectional Flow ◽  
Aspect Ratios ◽  
Non Local ◽  
Flow Through ◽  
Induced Flow ◽  
Wave Induced

We examine the wave-induced flow of small-amplitude, quasi-monochromatic, three-dimensional, Boussinesq internal gravity wavepackets in a uniformly stratified ambient. It has been known since Bretherton (J. Fluid Mech., vol. 36 (4), 1969, pp. 785–803) that one-, two- and three-dimensional wavepackets induce qualitatively different flows. Whereas the wave-induced mean flow for compact three-dimensional wavepackets consists of a purely horizontal localized circulation that translates with and around the wavepacket, known as the Bretherton flow, such a flow is prohibited for a two-dimensional wavepacket of infinite spanwise extent, which instead induces a non-local internal wave response that is long compared with the streamwise extent of the wavepacket. One-dimensional (horizontally periodic) wavepackets induce a horizontal, non-divergent unidirectional flow. Through perturbation theory for quasi-monochromatic wavepackets of arbitrary aspect ratio, we predict for which aspect ratios which type of induced mean flow dominates. We compose a regime diagram that delineates whether the induced flow is comparable to that of one-, two- or compact three-dimensional wavepackets. The predictions agree well with the results of fully nonlinear three-dimensional numerical simulations.

An Experimental Investigation of Aspect Ratio and Incidence Angle Effects for the Flow Around Surface-Mounted Finite-Height Square Prisms

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
J. F. McClean ◽  
D. Sumner
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Incidence Angle ◽  
Lift Coefficient ◽  
Ground Plane ◽  
Aspect Ratios ◽  
Square Prism ◽  
The Mean

The flow around a surface-mounted finite-height square prism was investigated using a low-speed wind tunnel. The experiments were conducted at a Reynolds number of Re = 7.3 × 104 for prism aspect ratios of AR = 3, 5, 7, 9, and 11 and incidence angles from α = 0 deg to 45 deg. The thickness of the boundary layer on the ground plane relative to the side length was δ/D = 1.5. Measurements of the vortex shedding frequency were made with a single-component hot-wire probe, and measurements of the mean drag and lift forces were obtained with a force balance. For all aspect ratios and incidence angles, the mean drag coefficient and Strouhal number were lower than those of an infinite prism, while the mean lift coefficient was of nearly similar magnitude. As the aspect ratio was increased from AR = 3 to 11, the force coefficients and Strouhal number slowly approached the infinite-square-prism data. The mean drag coefficient and Strouhal number for the finite prism were less sensitive to changes in incidence angle compared to the infinite square prism. The critical incidence angle, corresponding to minimum mean drag coefficient, minimum (most negative) mean lift coefficient, and maximum Strouhal number, shifted to a higher incidence angle compared to the infinite square prism, with values ranging from αcritical = 15 deg to 18 deg; this shift was greatest for the prisms of higher aspect ratio. The behavior of the force coefficients and Strouhal number for the prism of AR = 3 was distinct from the other prisms (with lower values of mean drag coefficient and mean lift coefficient magnitude, and a different Strouhal number trend), suggesting the critical aspect ratio was between AR = 5 and AR = 3 in these experiments. In the wall-normal direction, the power spectra for AR = 11 and 9 tended to have weaker and/or more broad-banded vortex shedding peaks near the ground plane and near the free end at α = 0 deg and 15 deg. For AR = 7 to 3, well-defined vortex shedding peaks were detected along the entire height of the prisms. For AR = 11 and 9, at α = 30 deg and 45 deg, vortex shedding peaks were absent in the power spectra in the upper part of the wake.

Aerodynamic Forces and Vortex Shedding for Surface-Mounted Finite Square Prisms and the Effects of Aspect Ratio and Incidence Angle

2012 ◽  
Author(s):  
John F. McClean ◽  
David Sumner
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Incidence Angle ◽  
Lift Coefficient ◽  
Ground Plane ◽  
Aspect Ratios ◽  
Square Prism ◽  
The Mean

The flow around a surface-mounted square prism of finite height was investigated experimentally using a low-speed wind tunnel. Of interest were the effects of aspect ratio and incidence angle on the mean aerodynamic forces and vortex shedding. Compared to the case of the “infinite” (or two-dimensional) square prism, the flow around the finite square prism has not been extensively studied. The experiments were conducted at a Reynolds number of Re = 7.2 × 104 for aspect ratios of AR = 3, 5, 7, 9, and 11 and incidence angles of α = 0°, 15°, 30° and 45°. The thickness of the boundary layer on the ground plane relative to the side length was δ/D = 1.5. Measurements of the vortex shedding frequency were made with a single-component hot-wire probe in the wake, and measurements of the mean drag and lift forces were obtained with a force balance. For all aspect ratios and incidence angles, the Strouhal number and the mean drag coefficient were lower than those of an infinite prism, while the mean lift coefficient was of nearly similar magnitude. As the aspect ratio was increased from AR = 3 to 11, the force coefficients and Strouhal number slowly approached the infinite-square-prism data. The behaviours of the mean drag coefficient and Strouhal number with incidence angle were less sensitive compared to the case of the infinite square prism, although a minimum mean drag coefficient, minimum (most negative) mean lift coefficient, and maximum Strouhal number were found at α = 15°. The reduced sensitivity to incidence angle is attributed to the complex three-dimensional flow over the free end of the prism and the downwash flow that enters the near wake. The behaviour of the force coefficients and Strouhal number for the prism of AR = 3 was distinct from the other prisms (with lower values of drag coefficient and lift coefficient magnitude, and a different Strouhal number trend), suggesting the critical aspect ratio was between AR = 5 and AR = 3 in these experiments. In the wall-normal direction, the power spectra for AR = 11 and 9 tended to have weaker and/or more broad-banded vortex shedding peaks near the ground plane and near the free end at α = 0° and 15°. For AR = 7 to 3, well-defined vortex shedding peaks were detected along the entire height of the prisms. For AR = 11 and 9, at α = 30° and 45°, vortex shedding peaks were absent in the power spectra in the upper part of the wake.

The role of advance ratio and aspect ratio in determining leading-edge vortex stability for flapping flight

2014 ◽  
Vol 751 ◽  
pp. 71-105 ◽  
Author(s):  
R. R. Harbig ◽  
J. Sheridan ◽  
M. C. Thompson
Keyword(s):  
Aspect Ratio ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Leading Edge Vortex ◽  
Aspect Ratios ◽  
Edge Vortex ◽  
Advance Ratio ◽  
Vorticity Production ◽  
The Stability

AbstractThe effects of advance ratio and the wing’s aspect ratio on the structure of the leading-edge vortex (LEV) that forms on flapping and rotating wings under insect-like flight conditions are not well understood. However, recent studies have indicated that they could play a role in determining the stable attachment of the LEV. In this study, a numerical model of a flapping wing at insect Reynolds numbers is used to explore the effects of these parameters on the characteristics and stability of the LEV. The word ‘stability’ is used here to describe whether the LEV was attached throughout the stroke or if it was shed. It is demonstrated that increasing the advance ratio enhances vorticity production at the leading edge during the downstroke, and this results in more rapid growth of the LEV for non-zero advance ratios. Increasing the wing aspect ratio was found to have the effect of shortening the wing’s chord length relative to the LEV’s size. These two effects combined determine the stability of the LEV. For high advance ratios and large aspect ratios, the LEV was observed to quickly grow to envelop the entire wing during the early stages of the downstroke. Continued rotation of the wing resulted in the LEV being eventually shed as part of a vortex loop that peels away from the wing’s tip. The shedding of the LEV for high-aspect-ratio wings at non-zero advance ratios leads to reduced aerodynamic performance of these wings, which helps to explain why a number of insect species have evolved to have low-aspect-ratio wings.

The Stability of Simply Supported Rectangular Surfaces in Uniform Subsonic Flow

1973 ◽  
Vol 40 (1) ◽  
pp. 68-72 ◽  
Author(s):  
C. H. Ellen
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Stability Result ◽  
Fluid Flows ◽  
Inviscid Fluid ◽  
Low Frequencies ◽  
Critical Flow Velocity ◽  
Simply Supported ◽  
Aspect Ratios ◽  
The Stability

A study is made of the stability of a simply supported flat plate set in an infinite rigid baffle when an inviscid fluid flows uniformly at subsonic speed past one side of the surface. The generalized pressures are derived for low frequencies with two and three-dimensional flows. The three-dimensional generalized pressures are expanded asymptotically for high and low aspect ratios, and analytic forms derived for the critical flow velocity at instability. The asymptotic expansions enable the effect of aspect ratio on stability to be determined. It is shown that the incompressible limit, for two-dimensional flows, is singular but the stability criterion is associated with first-mode divergence and is identical with the three-dimensional high aspect ratio stability result, although there are certain detailed differences in the nature of the instability.

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