Flow Structure Near the Bow of a Two-Dimensional Body

1989 ◽  
Vol 33 (04) ◽  
pp. 269-283
Author(s):  
Mark A. Grosenbaugh ◽  
Ronald W. Yeung
Keyword(s):  
Free Surface ◽  
Power Spectra ◽  
Leading Edge ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Bow Wave ◽  
Wave Elevation ◽  
Characteristic Oscillation ◽  
Theoretical Predictions ◽  
Sectional Shape

Flow near a blunt ship's bow is experimentally investigated by studying the flow in front of horizontal, surface-piercing cylinders. A bore-like structure develops at the bow of a cylinder when it is immersed in a uniform stream. Observations indicate that the leading edge of this bow wave coincides with a point at which the main flow separates from the free surface. Experimental measurements of the location of the wavefront and the slope of the free surface at the wavefront are in fair agreement with existing theoretical predictions. Power spectra of the time records of the bow-wave elevation show a characteristic oscillation frequency at Froude numbers above a critical value. The bow-wave oscillation is a function of the cross-sectional shape of the two-dimensional body, the draft, and, to a lesser extent, the flow velocity. The inception of the oscillation depends on the Reynolds number, but the characteristic frequency is governed by inertial and gravitational forces.

Numerical study for the improvement of bead spreading architecture with modified nozzle geometries in additive manufacturing of polymers

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Easir Arafat Papon ◽  
Anwarul Haque ◽  
Muhammad Ali Rob Sharif
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
3D Printing ◽  
Cross Section ◽  
Nozzle Exit ◽  
Cross Sectional ◽  
Content Type ◽  
The Cross ◽  
Viscous Polymer ◽  
Sectional Shape

Purpose This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle geometry. This paper also focuses on the manufacturing feasibility of the nozzles and 3D printing of the molten beads using the developed nozzles. Design/methodology/approach The flow of a highly viscous polymer from a nozzle, the melt expansion in free space and the deposition of the melt on a moving platform are captured using the FLUENT volume of fluid (VOF) method based computational fluid dynamics code. The free surface motion of the material is captured in VOF, which is governed by the hydrodynamics of the two-phase flow. The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian and non-isothermal flow is assumed. Under such assumptions, the spreading characteristic of the polymer is simulated with different nozzle-exit geometries. The governing equations are solved on a regular stationary grid following a transient algorithm, where the boundary between the polymer and the air is tracked by piecewise linear interface construction (PLIC) to reconstruct the free surface. The prototype nozzles were also manufactured, and the deposition of the molten beads on a flatbed was performed using a commercial 3D printer. The deposited bead cross-sections were examined through optical microscopic examination, and the cross-sectional profiles were compared with those obtained in the numerical simulations. Findings The numerical model successfully predicted the spreading characteristics and the cross-sectional shape of the extruded bead. The cross-sectional shape of the bead varied from elliptical (with circular nozzle) to trapezoidal (with square and star nozzles) where the top and bottom surfaces are significantly flattened (which is desirable to reduce the void spaces in the cross-section). The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment. The quantitative comparison of the cross-sectional profiles against experimental observation also indicated a favorable agreement. The significant improvement observed in the bead cross-section with the square and star nozzles is the flattening of the surfaces. Originality/value The developed numerical algorithm attempts to address the fundamental challenge of voids and bonding in the FFF process. It presents a new approach to increase the inter-bead bonding and reduce the inter-bead voids in 3D printing of polymers by modifying the bead cross-sectional shape through the modification of nozzle exit-geometry. The change in bead cross-sectional shape from elliptical (circular) to trapezoidal (square and star) cross-section is supposed to increase the contact surface area and inter-bead bonding while in contact with adjacent beads.

Factors Controlling the Change of Shape of Certain Nemertean and Turbellarian Worms

1958 ◽  
Vol 35 (4) ◽  
pp. 731-748 ◽  
Author(s):  
R. B. CLARK ◽  
J. B. COWEY
Keyword(s):  
Water Conservation ◽  
Ecological Factors ◽  
Longitudinal Axis ◽  
The Body ◽  
Cross Sectional ◽  
Ciliary Action ◽  
Theoretical Predictions ◽  
Observed Behaviour ◽  
Body Wall Musculature ◽  
Sectional Shape

1. Nemerteans and turbellarians have an inextensible fibre system around them in the form of a lattice of left- and right-handed spirals. The effect of this system on the change of shape on these worms has been analysed theoretically and compared with the observed behaviour of nine species of turbellarian and nemertean from widely differing habitats. 2. The following theoretical relationships have been studied: (a) Variation of the angle between the geodesics and the longitudinal axis of the worm during changes in length, and the role of the fibre system in limiting changes in length of the animal. (b) The change in cross-sectional shape during changes in length. (c) The extension of the fibres and the extensibility of the worms, assuming the fibres of the lattice to be elastic. 3. The species investigated conform with the theoretical predictions to varying degrees and have been grouped accordingly: (a) Geonemertes dendyi and Rhynchodemus bilineatus have low extensibilities and fit the prediction well. They are nearly circular in cross-section at all lengths as a result of their low extensibility and this is related to their terrestrial habit and need for water conservation. (b) Amphiporus lactifloreus, Lineus gesserensis and L. longissimus are moderately flattened in the relaxed position and have extensibilities between 6 and 10. They are marine crawling forms using cilia for locomotion and so must present a fairly large ciliated surface to the substratum. The fibre system does not limit contraction; the compression of the epithelial cells causes the observed extensibilities to fall a little short of the theoretical values. (c) Cerebratulus lacteus, Malacobdella grossa, Polycelis nigra and Dendrocoelum lacteum are very flattened forms and have very high theoretical extensibilities, but very low observed ones. The factors causing this are the thickness of the body-wall musculature (Cerebratulus), the limiting effect of longitudinal and circular reticulin fibres in the muscle layers, and the presence of dorso-ventral and diagonal muscles. Their flattened form is correlated with ecological factors (with swimming in Cerebratulus, with its parasitic life in the mantle of bivalves in Melacobdella) or with physical ones in turbellarians where a permanently flattened form is necessary for these worms to move by ciliary action.

Effects of Mesh-Induced Upstream Turbulence on Flip-Flop Flow Inside Diamond-Shaped Cylinder Bundles

Volume 3 ◽  
2004 ◽  
Author(s):  
Shinzaburo Umeda ◽  
Wen-Jei Yang
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Power Spectra ◽  
Dominant Frequency ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Flow Measurements ◽  
Flip Flop ◽  
Flow Cross Section ◽  
Flow Cross

An experimental study is conducted to investigate effects of mesh-induced upstream turbulence on flip-flop flow inside diamond-shaped cylinder bundles. In order to quantitatively treat flip-flop flow induced by the self-excited oscillation of vortices, flow measurements by means of two-dimensional particle image velocimetry (PIV) and two-dimensional laser Doppler velocimetry (LDV) are employed. Flow cross-sectional area and flow rate are varied to change the Reynolds number in the bundles. A turbulence mesh is installed a very short distance upstream from the inlet of the test section. The LDV is employed to measure velocity changes in the flip-flop flow, while power spectra representing its oscillating characteristics are determined from LDV data. The dominant frequency is observed special features are disclosed in the relationship between the Reynolds number and the Strouhal number representing the dimensionless dominant frequency in all power spectra of the flip-flop flow. It is disclosed that both the flow cross section and the upstream turbulence are related to the generation of flip-flop flow in complex manner, and that the effects of the turbulence differ depending upon the flow cross section.

2-D CFD Model for Free Surface River Flow with Tilt Rigid Leave of Submerged Vegetation

2012 ◽  
Vol 212-213 ◽  
pp. 332-335 ◽  
Author(s):  
Yan Hong Li ◽  
Li Quan Xie
Keyword(s):  
Free Surface ◽  
Velocity Profile ◽  
River Flow ◽  
Longitudinal Velocity ◽  
Submerged Vegetation ◽  
Two Dimensional ◽  
Cfd Model ◽  
Cross Sectional ◽  
Vertical Velocity Profile ◽  
Flow Through

Keywords: river flow; two-dimensional CFD model; velocity profile; submerged vegetation leave Abstract. River flow with submerged foliage vegetation in straight and rectangular cross-sectional channel is numerically simulated through a vertical two-dimensional CFD model. Tilt thin strips are assigned in river flow to mimic the configuration of vegetation leave. The free surface line and the vertical profiles of longitudinal velocity are presented. The vertical velocity profile differs from the well acknowledged logarithmic or semi-logarithmic law. The submerged leave canopy resist the flow through it and pilots the flow upward over it, resulting in a decreased velocity within the canopy and an increased velocity above the canopy. The velocity profiles within the leave canopy are impacted by the configurations of the leave.

scholarly journals Fluid Acoustic Properties of Improved Hydraulic Mufflers with Extended Necks

2019 ◽  
Vol 24 (4) ◽  
pp. 638-647
Author(s):  
Fan Yang ◽  
Bin Deng
Keyword(s):  
Plane Wave ◽  
Resonance Frequency ◽  
Insertion Loss ◽  
Acoustic Properties ◽  
Expansion Chamber ◽  
Cross Sectional ◽  
Conical Tube ◽  
Chamber Volume ◽  
Theoretical Predictions ◽  
Sectional Shape

The acoustic properties of three improved hydraulic mufflers with extended necks are investigated theoretically and experimentally. The effect of length and slope of the conical tube, and the perforations on the extended tube is studied on the resonance frequency and the insertion loss. The plane wave approach is used for the constant and the variable area tubes, while Sullivan and Peat's method is applied for the perforation tube unit. Theoretical predictions are compared with experiments for these three different hydraulic noise suppressors, which are fabricated. It is shown that the resonance frequency and the insertion loss characteristics may be controlled by the length and the slope of the conical tube and perforation porosity of the extended tube without changing the expansion chamber volume. Finally, the effect of the cross-sectional shape of the expansion chamber is investigated.

scholarly journals A STUDY ON WATER ENTRY OF TWO-DIMENSIONAL CROSS-SECTIONAL SHAPE USING SNUFOAM

2016 ◽  
Vol 21 (3) ◽  
pp. 55-63
Author(s):  
D.J. Jang ◽  
Y.M. Choi ◽  
H.K. Choi ◽  
S.H. Rhee
Keyword(s):  
Water Entry ◽  
Two Dimensional ◽  
Cross Sectional ◽  
Sectional Shape

Supersonic Flow Past Slender Bodies With Discontinuous Profile Slope

1955 ◽  
Vol 6 (2) ◽  
pp. 114-124 ◽  
Author(s):  
L. E. Fraenkel ◽  
H. Portnoy
Keyword(s):  
Internal Flow ◽  
Leading Edge ◽  
Rate Of Change ◽  
The Body ◽  
Cross Sectional ◽  
Slender Body Theory ◽  
Bodies Of Revolution ◽  
Slender Bodies ◽  
External Forces ◽  
Sectional Shape

SummaryWard’s slender-body theory is extended to derive first approximations to the external forces on slender bodies of general cross section with discontinuous profile slope. Two classes of body are considered: bodies whose profile (typified by the local radius) is continuous between the nose and base, and certain bodies whose profile is discontinuous, such as bodies with annular or side air intakes and wing-bodies on which the wing has an unswept leading edge. (Where air intakes are concerned, it is assumed that they are sharp-edged and that there is no “ spillage ” of the internal flow).The following conclusions apply to the former class of bodies. The variation of drag with Mach number is found to depend only on the discontinuities in the longitudinal rate of change of the cross-sectional area, and is thus independent of cross-sectional shape. The drag itself is unchanged if the direction of the flow is reversed. The expressions for lift and moment assume the same forms as for smooth pointed bodies, the lift depending only on conditions at the base of the body.The general theory is applied to winged bodies of revolution with an unswept wing leading edge: the results bear a marked resemblance to those obtained by Ward. The results for wings alone are seen to be applicable, with one modification, to subsonic as well as to supersonic speeds.

scholarly journals Dispersive shock waves in viscously deformable media

2013 ◽  
Vol 718 ◽  
pp. 524-557 ◽  
Author(s):  
Nicholas K. Lowman ◽  
M. A. Hoefer
Keyword(s):  
Shock Waves ◽  
Volume Fraction ◽  
Initial Conditions ◽  
Leading Edge ◽  
Wave Dispersion ◽  
Cross Sectional ◽  
Theoretical Predictions ◽  
Number Dynamics ◽  
Long Time ◽  
Constitutive Parameters

AbstractThe viscously dominated, low-Reynolds-number dynamics of multi-phase, compacting media can lead to nonlinear, dissipationless/dispersive behaviour when viewed appropriately. In these systems, nonlinear self-steepening competes with wave dispersion, giving rise to dispersive shock waves (DSWs). Example systems considered here include magma migration through the mantle as well as the buoyant ascent of a low-density fluid through a viscously deformable conduit. These flows are modelled by a third-order, degenerate, dispersive, nonlinear wave equation for the porosity (magma volume fraction) or cross-sectional area, respectively. Whitham averaging theory for step initial conditions is used to compute analytical, closed-form predictions for the DSW speeds and the leading edge amplitude in terms of the constitutive parameters and initial jump height. Novel physical behaviours are identified including backflow and DSW implosion for initial jumps sufficient to cause gradient catastrophe in the Whitham modulation equations. Theoretical predictions are shown to be in excellent agreement with long-time numerical simulations for the case of small- to moderate-amplitude DSWs. Verifiable criteria identifying the breakdown of this modulation theory in the large jump regime, applicable to a wide class of DSW problems, are presented.

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