Spread Of Flow Research Articles

Computational Predictions of Heat Transfer and Film-Cooling for a Turbine Blade With Nonaxisymmetric Endwall Contouring

Three-dimensional contouring of the compressor and turbine endwalls in a gas turbine engine has been shown to be an effective method of reducing aerodynamic losses by mitigating the strength of the complex vortical structures generated at the endwall. Reductions in endwall heat transfer in the turbine have been also previously measured and reported in literature. In this study, computational fluid dynamics simulations of a turbine blade with and without nonaxisymmetric endwall contouring were compared to experimental measurements of the exit flowfield, endwall heat transfer, and endwall film-cooling. Secondary kinetic energy at the cascade exit was closely predicted with a simulation using the SST k-ω turbulence model. Endwall heat transfer was overpredicted in the passage for both the SST k-ω and realizable k-ε turbulence models, but heat transfer augmentation for a nonaxisymmetric contour relative to a flat endwall showed fair agreement to the experiment. Measured and predicted film-cooling results indicated that the nonaxisymmetric contouring limits the spread of film-cooling flow over the endwall depending on the interaction of the film with the contour geometry.

An experimental investigation of film cooling performance of louver scheme

An experimental investigation of the film cooling performance of louver schemes using Thermochromic Liquid Crystal technique is presented in this paper. The louver scheme allows the cooling flow to pass through a bend and encroach with the blade material (impingement effect), then exit to the outer surface of the aerofoil through the film cooling hole. The cooling performance of the louver scheme was analyzed for blowing ratios ranging from 0.5 to 1.5 and for a density ratio of 0.94. The results showed that the louver scheme enhances the local and the average film cooling effectiveness, and the net heat flux reduction better than other published film hole configurations. The louver scheme also provides a wide extensive spread of the secondary flow over the outer surface, thus enhancing the lateral film cooling performance over the downstream surface area. Moreover, the louver scheme produces a lower heat transfer ratio than other film hole geometries at low and high blowing ratios. As a result, the louver scheme is expected to reduce the gas turbine airfoil’s outer surface temperature by provide superior cooling performance than other film cooling schemes hence increasing the airfoil life time.

Modeling of the 2001 lava flow at Etna volcano by a Cellular Automata approach

The 2D Cellular Automata model, MAGFLOW, simulates lava flows and an algorithm based on the Monte Carlo approach solves the anisotropic flow direction problem. The model was applied to reproduce a lava flow formed during the 2001 Etna eruption. This eruption provided the opportunity to verify the ability of MAGFLOW to simulate the path of lava flows which was made possible due to the availability of the necessary data for both modeling and subsequent validation. MAGFLOW reproduced quite accurately the spread of flow. A good agreement was highlighted between the simulated and observed length on steep slopes, whereas the area covered by the lava flow tends to be overestimated. The major inconsistencies found in the comparison between simulated and observed lava flow due to neglecting the effects of ephemeral vent formation.

Numerical simulation of turbulent impinging jet on a rotating disk

AbstractThe calculations of quasi‐three‐dimensional momentum equations were carried out to study the influence of wall rotation on the characteristics of an impinging jet. The pressure coefficient, the mean velocity distributions and the components of Reynolds stress are calculated. The flow is assumed to be steady, incompressible and turbulent. The finite volume scheme is used to solve the continuity equation, momentum equations and k–ε model equations. The flow characteristics were studied by varying rotation speed ω for 0⩽ω⩽167.6 rad/s, the distance from nozzle to disk (H/d) was (3, 5, 8 and 10) and the Reynolds number Re base on VJ and d was 1.45 × 104. The results showed that, the radial velocity and turbulence intensity increase by increasing the rotation speed and decrease in the impingement zone as nozzle to disk spacing increases. When the centrifugal force increases, the radial normal stresses and shear stresses increase. The location of maximum radial velocity decreases as the local velocity ratio (α) increases. The pressure coefficient depends on the centrifugal force and it decreases as the distance from nozzle to plate increases. In impingement zone and radial wall jet, the spread of flow increases as the angular velocity decreases The numerical results give good agreement with the experiment data of Minagawa and Obi (Int. J. of Heat and Fluid Flow 2004; 25:759–766). Copyright © 2006 John Wiley & Sons, Ltd.

Modeling fire-induced smoke spread and carbon monoxide transportation in a long channel: Fire Dynamics Simulator comparisons with measured data

Smoke and toxic gases, such as carbon monoxide, are the most fatal factors in fires. This paper models fire-induced smoke spread and carbon monoxide transportation in an 88 m long channel by Fire Dynamics Simulator (FDS) with large eddy simulation (LES). FDS is now a well-founded fire dynamics computational fluid dynamic (CFD) program, which was developed by National Institute of Standards and Technology (NIST). Two full scale experiments with fire sizes of 0.75 and 1.6 MW were conducted in this channel to validate the program. The spread of the fire-induced smoke flow together with the smoke temperature distribution along the channel, and the carbon monoxide concentration at an assigned position were measured. The FDS simulation results were compared with experimental data with fairly good agreement demonstrated. The validation work is then extended to numerically study the carbon monoxide concentration distribution, both vertically and longitudinally, in this long channel. Results showed that carbon monoxide concentration increase linearly with the height above the floor and decreases exponentially with the distance away from the fire source.

Simulation of Thermal Convection in a Rotating and Strarified Fluids by the Lattice Boltzmann Method

Three-dimensional flow of thermal convection contained in cubic and rectangular vessel placed in a rotating field is simulated by the incompressible Lattice Boltzmann method using two types of particles, that are red and blue ones. The gravitational force and the Coriolis force introduced in the local equilibrium distribution function. In this model, the gravitational force acts on the blue particles only and the Coriolis force acts both the particles. The results proved that the present method simulates the structure of flow and the mechanism how the stratification and the Coriolis force affects on the spread of flow and temperature.

Gap junction remodeling in heart failure

Gap junctions, clusters of transmembrane channels that link adjoining cells, mediate myocyte-to-myocyte electrical coupling and communication. The component proteins of gap junction channels are termed connexins, and gap-junctional channels composed of different connexin types exhibit different biophysical properties. In common with other tissues, the heart expresses multiple connexin isotypes. Spatially defined patterns of expression of 3 connexin isotypes—connexin43, connexin40, and connexin45—form specific cell-to-cell conduction pathways for the spread of current flow that governs the normal cardiac rhythm. Remodeling of gap junction organization and connexin expression is a conspicuous feature of human congestive heart failure and other cardiac conditions in which there is an arrhythmic tendency. This remodeling may take the form of disturbances in the distribution of gap junctions, in which the normal ordered pathways for cell-to-cell conduction are disrupted, or quantitative alterations in connexin expression, notably reduced connexin43 levels, which may contribute to slowing of conduction. Recent evidence from studies in experimental animals strengthens the case that gap junction remodeling is a key determinant of the proarrhythmic substrate in the diseased heart.

Gap junction remodeling and cardiac arrhythmogenesis: cause or coincidence?

Gap junctions, clusters of transmembrane channels that link adjoining cells, mediate myocyte-to-myocyte electrical coupling and communication. The component proteins of gap junction channels are termed connexins and, in in vitro expression systems, gap-junctional channels composed of different connexin types exhibit different biophysical properties. In common with other tissues, the heart expresses multiple connexin isoforms. Spatially defined patterns of expression of three connexin isoforms - connexin43, connexin40 and connexin45 - form the cell-to-cell conduction pathways responsible for the orderly spread of current flow that governs the normal cardiac rhythm. Remodeling of gap junction organization and connexin expression is a common feature of human heart disease conditions in which there is an arrhythmic tendency. This remodeling may take the form of disturbances in the distribution of gap junctions and/or quantitative alterations in connexin expression, notably reduced ventricular connexin43 levels. The idea that such changes may contribute to the development of a pro-arrhythmic substrate in the diseased heart has gained ground over the last decade. Recent studies using transgenic mice models have raised new opportunities to explore the significance of gap junction remodeling in the diseased heart.

Finite element analysis of deformation behaviour in ductile matrix containing hard particles

Three-dimensional finite element analyses were carried out to study the deformation behaviour in ductile matrix-hard particle composite systems. Models with transversely aligned and staggered particle distributions were used. The deformation constraints in the models were investigated and the development of triaxial stress states in the models was studied. It was determined that the strengthening behaviour arises as a result of geometrical hardening in the early stage of composite deformation. Special deformation stages in the overall stress-strain behaviour of the composite microstructures such as initiation of microyielding, expansion of the plastically deformed region, and spread of plastic flow were determined by following the development of plasticity.

Unconfined Expansion of Supercritical Water Flow

The spread of supercritical free-surface flow on a smooth horizontal plane is considered. Experiments with selected approach Froude numbers are presented indicating that the effect of the Froude number may be dropped for hypercritical flow, that is, for values larger than 3. Also, a simple relation between local streamline direction and local flow depth is established. For sufficiently large approach flow depth, the Froude similarity law governs the phenomenon. Assuming that the streamwise velocity component is constant yields a system of equations identical to the one-dimensional simple wave problem. The solutions are compared with observations, and reasonable agreement is noted. Further particularities of hypercritical channel flow are established that are important for the numerical simulation of such currents. The features of expansion flow are documented with selected photographs. Supercritical unconfined expansion flow on a horizontal plane is studied. The governing equations can be shown to simplify considerably for hypercritical flow. A complete description is given based on both computations and experiments.

A FORTRAN 77 program for analyzing broad-scale spatial trends of streamline glacial features

Laurentide ice flow from the Lake Ontario Basin toward the Appalachian Plateau created one of the largest drumlin swarms in North America. A program for analyzing the broad-scale spatial trends of these streamline glacial features is presented. Allowing for variable grid cell dimensions and providing summary information for each quadrangle, the program is appropriate particularly if working with a large number of topographic maps. Orientations of more than 1500 drumlins from an approx. 12,000 km 2 area show a systematic lateral spread of ice flow from the Ontario Lowlands onto the Appalachian Plateau and are suggestive of low boundary shear stresses. The program allows for the ready accumulation of orientation, length, and geographic location of any linear feature from X, Y, coordinate pairs, and establishes a database suitable for plotting or statistical analysis.

Shell-Side Single-Phase Flows and Heat Transfer in Shell-and-Tube Heat Exchangers

Based on the flow visualization study and detailed measurements of local heat transfer coefficient, the Nu-Re correlations are proposed for shell-side heat transfer in segmentally baffled tubular heat exchangers. In the 1st-stage baffle compartment, the Zukauskas correlation for heat transfer from tube bundles works well if local velocity is estimated from the flow model which assumes spread of flow from the inlet through the tube bundle. In the 2nd and subsequent compartments, the flow pattern becomes invariant, and the appropriate correlation is derived.

QCD and the transverse properties of jets in deep inelastic scattering

We study the transverse properties of hadronic jets in deep inelastic scattering, focusing on features which reflect predominantly the underlying QCD structure rather than the process of hadronization. In particular we discuss the QCD induced asymmetries between the transverse size for forward and backward going jets in the virtual boson-nucleon c.m.s. We also analyze the dependence of this transverse spread on the produced hadron energy and indicate how the QCD pattern differs from that expected from hadronization or primordial transverse momentum. We point out, furthermore, the theoretical, and possibly experimental, advantages of studying the average angular spread of the energy flow rather than the transverse momenta of the particle jets.

On the modelling of the spread of the flood flow using Bi-dimensional Tank Model Method

On the modelling of the spread of the flood flow using Bi-dimensional Tank Model Method

Measurements of energy spread of thermal field-emitted electron flow from tungsten

The total energy spread of thermal field-emitted electron flows from an electro-chemically etched tungsten whisker is measured and compared with theoretically expected curves under constant emitted current densities, chosen with practical applications in mind. It is confirmed that the energy spread of thermal field-emitted electron flow is much wider than both cold field and thermal-emitted electron flows, as expected from the theoretical analysis.

Further Examples of Stationary Planetary Flow Patterns in Bounded Basins

Laboratory experiments which supplement those presented by STOMMEL, ARONS and FALLER (1958) are described. Extension of the analysis to include the effects of bottom friction shows that the characteristic spreading of zonal currents, apparent in the original experiments, is due to bottom friction combined with the radial depth variation. The experiments confirm the theoretical prediction of an intense “recirculation” from the western boundary (similar to the “wind-spun vortex” of MUNK, 1950) when a localized interior source or sink is present. Application of the basic concepts of the earlier paper to the geometrically more complicated case with a partial radial barrier gave good agreement between theory and experiment, but the limiting effects of bottom friction were made evident in other examples.
 An eastern boundary current was found to occur in a situation geometrically similar to the intrusion of Mediterranean water into the Atlantic Ocean. Simple transformations illustrate the application of the equations developed in polar coordinates to the flow of a uniform fluid on a sphere, and examples of “recirculation” and the spread of zonal flow are worked out for a barotropic ocean of uniform depth.

Some Examples of Stationary Planetary Flow Patterns in Bounded Basins

Laboratory experiments which supplement those presented by Stommel, Arons and Faller (1958) are described. Extension of the analysis to include the effects of bottom friction shows that the characteristic spreading of zonal currents, apparent in the original experiments, is due to bottom friction combined with the radial depth variation. The experiments confirm the theoretical prediction of an intense “recirculation” from the western boundary (similar to the “wind-spun vortex” of Munk, 1950) when a localized interior source or sink is present. Application of the basic concepts of the earlier paper to the geometrically more complicated case with a partial radial barrier gave good agreement between theory and experiment, but the limiting effects of bottom friction were made evident in other examples. An eastern boundary current was found to occur in a situation geometrically similar to the intrusion of Mediterranean water into the Atlantic Ocean. Simple transformations illustrate the application of the equations developed in polar coordinates to the flow of a uniform fluid on a sphere, and examples of “recirculation” and the spread of zonal flow are worked out for a barotropic ocean of uniform depth. DOI: 10.1111/j.2153-3490.1960.tb01294.x

Experiments on Interaction Between a Traveling Shock Wave and a Turbulent Jet

The interaction of a turbulent jet and a plane shock wave traveling in a shock tube was optically observed. Various arrangements of both subsonic and supersonic jets were used. Some typical shadowgraphs are reproduced and discussed. As a direct result of its passage through the jet, the shock wave developed a bulge. The growth and behavior of this bulge were recorded through a sequence of instantaneous shadowgraphs. The transverse spread and the changing profile of this bulge offer an interesting visual demonstration of the angle of spread and decay of the jet flow. I t is shown that beyond an equivalent distance of about twelve jet diameters the bulge-profile reaches a state of similarity. When the shock and the jet impinged against each other head on, an intense, intermittent, and high frequency acoustic radiation manifested itself in the flow field behind the shock front. Some plausible explanations of this phenomenon are advanced.

A Plastic-Flow Problem Arising in the Theory of Discontinuous Machining

Abstract Plastic flow is analyzed adjacent to the nose of the tool in the initial stages of the formation of a discontinuous-chip segment. It is assumed on the basis of experimental evidence that fracture of the previous chip segment occurred across a plane through the cutting edge of the tool. The present solution applies only while the fracture surface is being deformed, before plastic flow spreads to the initial work surface. The solution demonstrates the influence of the plastic-stress distribution in determining the chip-formation process. It shows that simple shear across a plane between two undeforming regions cannot satisfy stress conditions in typical cases. It is shown that the inclination of the plane of equivalent simple shear is remarkably insensitive to the coefficient of friction at the tool face. The variation to be expected as a result of spread of plastic flow to the initial work surface is discussed briefly. The choice between alternative types of slip-line fields which arise in certain cases is considered.