Streamline Shape Research Articles

Finite-element modelling of simple shear flow in Newtonian and non-Newtonian fluids around a circular rigid particle

The flow perturbation around a circular rigid particle during simple shear deformation has been investigated for both Newtonian and non-Newtonian (power-law) fluids by finite-element modelling. If the particle is rotating under the applied shear couple and no-slip occurs at the particle–fluid interface, a ‘bow-tie-shaped’ streamline pattern results for both Newtonian and power-law fluids and the shape of streamlines does not change noticeably if the stress exponent ( n) is changed. In contrast, if the fluid is allowed to separate from the particle, a ‘double-bulge-shaped’ flow develops in the case of Newtonian fluids, and the type of streamline pattern is influenced by n. We suggest that both stair-stepping and non-stair-stepping geometries of porphyroclast tails may be produced in mylonites, depending on the degree of coherence between the porphyroclasts and the embedding matrix. A different behaviour of the fluid–particle interface may occur as the result of changing fluid rheology, owing to the contrasting stress fields developed for Newtonian and non-Newtonian fluids.

The Effects of Vibrational Relaxation on Hypersonic Flow Past Blunt Bodies

SummaryThe analysis of Freeman is extended to the hypersonic flow of an inviscid, vibrationally relaxing gas past a bluff body. Expressions for the shock shape, streamline shapes and stand-off distance are derived; these expressions have been evaluated for a sphere for various values of an appropriate non-equilibrium parameter Λ.

Inviscid Batchelor-model flow past an airfoil with a vortex trapped in a cavity

An efficient method of constructing inviscid Batchelor-model flows is developed. The method is based on an analytic continuation of the potential part of the flow into the closed-streamline vortex region. Numerical solutions are presented for Batchelor-model flows past airfoils with cavities. With the airfoil and dividing streamline shape, the eddy vorticity, and the jump in the Bernoulli constant across the eddy boundary given, the program calculates the corresponding cavity shape and the entire flow.

Radiation-driven Magnetohydrodynamic Wind Solutions for Hot Luminous Stars

view Abstract Citations (1) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiation-driven Magnetohydrodynamic Wind Solutions for Hot Luminous Stars Rotstein, Nestor ; Gimenez de Castro, Carlos Guillermo Abstract Solutions for the stellar winds of hot luminous stars are obtained by solving the magnetohydrodynamic (MHD) equations combined with the radiatively driven outflow formalism given by Castor, Abbott, & Klein. We consider the interaction of radiation pressure and collimated magnetic fields for a nonrotating star. The streamline shape has been prescribed from a phenomenological point of view. In order to decouple the MHD equations, we assume all the lines contributing to the radiation pressure are optically thick. Spherically and nonspherically symmetric mass distributions are considered. In both cases, the dependence of the terminal velocity on the star luminosity and magnetic strength is discussed. It is found that the terminal flow speed is strongly affected by slight variations of both the luminosity and the mass distribution asymmetry but shows a weak correlation with the magnetic field intensity. The present formalism can be thought of as a wide generalization of the MHD solutions introduced by Low & Tsinganos. Highly collimated magnetic structures, as well as rotation, are considered in another paper. Publication: The Astrophysical Journal Pub Date: June 1996 DOI: 10.1086/177373 Bibcode: 1996ApJ...464..859R Keywords: MAGNETOHYDRODYNAMICS: MHD; STARS: MAGNETIC FIELDS; STARS: MASS LOSS full text sources ADS |

Interaction of helical vortices

A characteristic feature of atmospheric vortices of a convective nature is the powerful radial motions of the medium at their base. In order to take these motions into account in analytical and numerical modeling, it is necessary to use point or distributed vortex sinks (vortex sources), which we will call helical vortices (from the shape of the streamlines of the flows produced) [1]. It seems likely that the interaction of point helical vortices was first considered in the until recently little-known study [2] which was included in the collection [3] and partially overlaps with the more recent studies [4, 5].

中国トルファンの乾燥地における２列の防風林による微気象，堆砂，作物への影響

Effects of double line windbreaks on climatic elements, sand accumulation and crop are evaluated at arid or dry land of Turfan, Northwest China. Main results are as follows:(1) The effects on wind speed, temperatures and humidity are accumulated by the increase of windbreak line.(2) The increase and decrease of surface soil temperature are small by shade of sunshine in the daytime and by small radiation cooling in the nighttime based on windbreak, respectively.(3) Relative humidity increased from 10 to 15% based on effects of transpiration from tree leaves and of evaporation from soil, particularly at weak wind night in summer. The effect is accumulated by increases of windbreak line and width.(4) Variations of air temperature and humidity seem to be generally symmetrical patterns in particular, their characteristics and frequency are significant and high under the dry condition. The increasing and decreasing effects on air temperature by windbreak are based on decreasing wind and use of latent heat of transpiration, respectively, therefore, the effects are canceled each other and patterns are not changed in appearance.(5) The climatic improvement by windbreak is very important at dry land. As windbreak trees seem to be streamline shape in relation to strong wind, dryness, sand accumulation, etc., the recover of wind is fast and the effective region is relatively small. The construction of ideal-shape windbreak needs earnest effort under the severe climatic condition.(6) The fine-dense leaves and branches of tamarisk are effective on sand accumulation, and preventions of wind erosion and drifting sand. As the elongation of tamarisk is large, the tree can grow even if it is covered by sand. Tamarisk is suitable for windbreaks at dry land.(7) Though the maximum effect on crop height is found from 2 to 5 H (maltiple distance of windbreak height) and the effect destroys relatively fast under the severe dry condition, windbreaks are indispensable to crop cultivation in dry land.

Size, shape, and surface area of beaver, Castor canadensis, a semiaquatic mammal

The beaver, Castor canadensis, is a large, herbivorous, semiaquatic rodent. Beaver forage on land as well as in water; thus functional compromise between competing activities should result in a less streamlined body shape than expected for a similarly sized marine mammal. Standard morphometrics and surface areas of 70 Wisconsin beaver ranging in size from 5 to 35 kg were measured. Geometric similarity of surface area was maintained during growth (i.e., area was proportional to body mass raised to the 2/3 power). Scaly-tail area was positively allometric with body mass; hind foot web area was weakly negatively allometric. The surface area of the unfurred extremities (hind feet and scaly tail) comprised 30% of the total surface area of adults and over 50% for younger beaver. The average surface area of 21 adult beaver (mean body mass = 20 kg) was 0.52 m2. This value was significantly lower (P < 0.001) than predicted from the Meeh equation for terrestrial mammals, but similar to that expected for a marine mammal of equivalent mass. Body shape was described by the fineness ratio (a hydrodynamic index of streamlining). The fineness ratio for beaver was 4.8, a value similar to that for phocid seals. Therefore, in spite of expected constraints on body shape imposed by herbivory and the competing demands of terrestrial and aquatic foraging, beaver do not differ significantly in overall shape from other, more aquatic, species. However, shape alone is not a reliable indicator of either hydrodynamic or energetic efficiency. Future comparative studies should incorporate both phylogeny and biomechanical data into evaluations of mammalian morphology.

Heat transfer from aerofoils in cross-flow

Heat transfer and pressure drop measurements from an aerofoil in cross-flow, arranged in single, six-row aligned and staggered positions, have been reported in the Reynolds number range of 50,000 to 135,000. Comparison of the measured values of Stanton number and pressure loss factors with the available data on circular and some stream-lined shapes, show a good promise for the use of aerofoil elements in cross-flow exchangers.

Wake effects on the prediction of transonic viscous flows around airfoils

A semi-inverse viscous/inviscid coupling technique for the calculations of compressible airfoil flows is presented. The Euler equations in integral form are solved in the inviscid part and the integral compressible boundary-layer equations in inverse form are solved in the viscous part. Both displacement and curvature effects have been included in the wake computation. Interaction is realized using the equivalent sources method. This technique has been applied to the calculation of the aerodynamic characteristics of airfoils both in subsonic and transonic regimes. It has been shown that the contributions of body displacement, wake displacement, and wake curvature effects are particularly important in the evaluation of the aerodynamic coefficients, especially drag. Different ways of computing the equivalent sources fluxes in the wake and the influence of the fixed-wake dividing streamline shape have been investigated and are discussed.

Reversible Epithelial Adhesion Closes the Mouth of Beroe, a Carnivorous Marine Jelly.

We investigated how the ctenophore Beroe, a carnivore of the marine zooplankton, keeps its mouth shut to maintain a streamlined body shape during forward swimming in search of prey. In big-mouthed, thin-walled beroids we found that mouth closure requires neither muscular nor nervous activity. Instead, mouth adhesion is due to paired strips of adhesive epithelial cells on opposing stomodaeal walls. The two joined epithelial layers make numerous close appositions interrupted by vacuolar intercellular spaces. At regions of apposition, the plasma membranes are highly folded and interdigitated with each other, and are separated by a uniform distance of about 15 nm. A dense cytoplasmic coat underlies the membranes at such appositions. Synapses of neurites are found on the basal ends of the adhesive cells. We found two orthogonally different orientations of the stomodaeal adhesive strips in B. sp. vs. B. forskali, correlated with different distributions of feeding macrocilia inside the stomodaeum. Mouth opening in response to food requires muscular contractions of the lips. However, the stomodaeal adhesive strips are not pulled apart all at once, but are peeled apart starting from a site of vigorous muscular tension. The mouth re-seals after feeding, or after being experimentally pulled open, showing that tissue adhesion is functionally reversible. Epithelial adhesion in Beroe appears to be a useful method for closing the mouth and streamlining the body of a gelatinous predator that spends most of its time swimming mouth-forward in search of prey. Opening of the mouth appears to be an efficient process as well, because peeling apart of the adhesive strips requires a smaller applied force than does separating them all at once. Tissue adhesion in Beroe shares many structural and functional properties with transient adhesions formed between moving cells in embryos and in culture, and may be a useful experimental system for studying the mechanisms and regulation of dynamic cell adhesions. "Loose lips Sink ships." --U. S. Navy slogan, WW II.

Separating inviscid flows

The separating flow of an inviscid fluid is not only a limit solution of the steady separating, laminar fluid flow at high values of the Reynolds number but it is also part of its structure (Smith [1], [2]). This work aims at reexamining the separating flow of inviscid fluid past a bluff body which is fixed in an otherwise uniform stream of fluid. For the purpose of this paper we will assume that the bluff body is a circular cylinder but the theory is applicable to bodies of any shape. It is further assumed that the fluid is in steady two-dimensional motion and is inviscid and of constant density. The flow structure is assumed to consist of a separated flow region, caviting flows in which there exists a free surface on which the pressure is constant, and a wake. A twin spiral vortex model is used in order to determine the shape of the free streamline. Based on the free streamline theory the problem reduces to solving a mixed boundary value problem and a Hilbert solution for the inverse problem in the auxiliary plane is obtained. When we consider the flow in the physical plane the problem is transformed into a direct problem in which the geometry of the solid body is given in advance. We assume that the separation is smooth and thus the curvature of the free streamline at the point of free detachment be equal to that of the body surface. A numerical method for solving the two-dimensional potential flows past arbitrarily shaped curved bluff bodies is developed. When the cavitation number is zero the angle of separation is approximately 55° and the computed results predict that the position of the separation point will move backward as the cavition number increases. The relationships between the drag coefficient, and the width and length of the cavity is determined and is found to be in very good agreement with the predictions of Smith [1].

Melt transformation coextrusion. II: Flow analysis

AbstractMelt Transformation Coextrusion for power law fluids was analyzed with particular attention being paid to the influence of the die's geometrical shape on flow patterns, and to skin layer effect on the velocity profile and shear stress at the interface between layers in a three‐layered system. Volumetric flow rate expressions were also generated for the aforementioned system, and stream and potential functions were derived for a free boundary converging film geometry. Newtonian as well as non‐Newtonian fluids were considered for this analysis in which the streamline shape changes their convergence downstream into the land section. Also, a finite element solution technique was utilized to reveal shear stress profiles that arise from the flow of high density polyethylene at 200°C in a converging fixed boundary geometry.

A Method for Aerodynamic Design of Blades in Quasi-Three-Dimensional Calculation of Turbomachines

A special inverse problem is formulated in which the shape of the mean streamline and the circumferential thickness distribution of the profile are given. On the basis of the series expansion method on a selected streamline, in quasi-three-dimensional aerodynamic design, the blade profile thickness is automatically fulfilled by computer. Six radial sections of a turbine blade are designed by this method.

The effects of capillarity on the contraction coefficient of a jet emanating from a slot

This study is concerned with the effects of surface tension on the steady potential flow of a liquid issuing from a two-dimensional slot with inclined walls. The mathematical problem, which is characterized by a nonlinear boundary condition along the free streamline, is solved using a novel numerical technique based on the fast direct Poisson solver. Numerical solutions were obtained for various Weber numbers and slot angles, and the results are compared with the free streamline shapes and contraction coefficients of the corresponding classical potential solutions without surface tension, and with some available theoretical results. When the numerical grid size is reduced or when the Weber number is sufficiently small, undesirable standing waves appear on the free surface that violate a causality condition. The cause of these waves was examined. A criterion was found for the occurrence of the waves.

Ｓｈｏｃｋ‐ｉｎ‐Ｒｏｔｏｒ型超音速軸流圧縮機翼列の一設計

A design method of the cascade for a shock-in-rotor supersonic axial-flow compressor is presented. The inlet flow is uniform and satisfies simplified radial equilibrium. The flow just before the normal shock is uniform and satisfies simplified radial equilibrium. The supersonic portion between the inlet and the normal shock is designed by using the method of weak wave. In the subsonic portion the flow is quasi-axisymmetric. The shape of mean streamline is assumed to be circular arc. The passage walls are composed of circular arcs. A two-dimensional supersonic cascade which is designed by the method in this report includes the three-dimensional effect by taking into account radial equilibrium conditions.

直角分岐管のキャビテーション流れの研究

A theory was developedf or cavitation flow in a two-dimensional right-angled branch duct. In analysis, the wake model was used. As a numerical example, the shape of the cavity streamline originating from the branch corner, the length of the cavity and the cavity height (thickness) were obtained for the values of 0.5, 1.0 and 2.0, which was the width ratio of the main duct to the lateral duct. The length and thickness of the resulting cavity were determined as a function of the cavitation parameter and the velocity of the lateral stream to the mainstream. That is, the length and thickness of the cavity increased as the cavitation parameter and the velocity ratio decreased, and as a result, the flow width of the lateral duct decreased. The cavitation parameters on the condition of the supercavitation were increased as the velocity ratio decreased a, nd these parameters agreed well with experimental results of the author's previous paper.

Falling water films on a vertical cylinder with a downward step

This study concerns falling water films on a vertical cylinder of 45 mm diameter with a downward step in the region where the film flow is not developed and has very weak waves. Varying the step height H from 1.5 to 5.0 mm and the film Reynolds number Re from 50 to 2000, film flows were observed and film thicknesses were measured by the needle contact method near the step. The effects of the steps on water films were compared with each other and discussed. The streamline shapes of free water films formed under the step were theoretically obtained when the ring-shaped air layer was observed. The results agree well with the experimental curves obtained from the photographs.

Falling water films on a vertical cylinder with a downward step.

Abstract This study concerns falling water films on a vertical cylinder of 45 mm diameter with a downward step in the region where the film flow is not developed and has very weak waves. Varying the step height H from 1.5 to 5.0 mm and the film Reynolds number Re from 50 to 2000, film flows were observed and film thicknesses were measured by the needle contact method near the step. The effects of the steps on water films were compared with each other and discussed. The streamline shapes of free water films formed under the step were theoretically obtained when the ring-shaped air layer was observed. The results agree well with the experimental curves obtained from the photographs.

An exact partial solution to the compressible flow problems of jet formation and penetration in plane, steady flow

The particle solution of the problem of the symmetric impact of two compressible fluid stream is derived. The plane two-dimensional flow is assumed to be steady, and the inviscid compressible fluid is of the Chaplygin (tangent gas) type. The equations governing this flow are transformed to the hodograph plane where an exact, closed-form solution for the stream function is obtained. The distribution of fluid properties along the plane of symmetry and the shape of free surface streamlines are determined by transformation back to the physical plane. The problem of a compressible fluid jet penetrating an infinite target of similar material is also solved by considering a limiting case of this solution. Differences between compressible and incompressible flows of the type considered are illustrated.

Potential Flow From a Tapering Nozzle Impinging on a Flat Plate

A perfect flow from a two-dimensional nozzle is considered discharging against a normally placed flat plate. Particular attention is given to the effect of the angle of the nozzle, and results for angles of 15, 30, 45, and 60 deg are compared with those for a parallel-sided orifice. This model can be regarded as a two-dimensional representation of a plate valve or flapper valve in which the flow does not reattach to the land of the nozzle. The variations of the back pressure and the contraction coefficient with valve aperture have been plotted, and the shape of the free streamlines and the pressure distribution on the plate have been found. By considering the effect of fluctuations far upstream, the flow in a tapering orifice is shown to be inherently more unstable than that in a parallel-sided orifice. It is also shown that the control of the valve aperture over the back pressure is better in parallel-sided orifices than in angled ones.