Combined Effects Of Curvature Research Articles

Transverse flow under oscillating stimulation in helical square ducts with cochlea-like geometrical curvature and torsion

The cochlea, situated within the inner ear, is a spiral-shaped, liquid-filled organ responsible for hearing. The physiological significance of its shape remains uncertain. Previous research has scarcely addressed the occurrence of transverse flow within the cochlea, particularly in relation to its unique shape. This study aims to investigate the impact of the geometric features of the cochlea on fluid dynamics by characterizing transverse flow induced by harmonically oscillating axial flow in square ducts with curvature and torsion resembling human cochlear anatomy. We examined four geometries to investigate curvature and torsion effects on axial and transverse flow components. Twelve frequencies from 0.125 Hz to 256 Hz were studied, covering infrasound and low-frequency hearing, with mean inlet velocity amplitudes representing levels expected for normal conversation or louder situations. Our simulations show that torsion contributes significantly to transverse flow in unsteady conditions, and that its contribution increases with increasing oscillation frequency. Curvature alone has a small effect on transverse flow strength, which decreases rapidly with increasing frequency. Strikingly, the combined effect of curvature and torsion on transverse flow is greater than expected from a simple superposition of the two effects, especially when the relative contribution of curvature alone becomes negligible. These findings may be relevant to understanding physiological processes in the cochlea, including metabolite transport and wall shear stress. Further studies are needed to investigate possible implications for cochlear mechanics.

Influence of Mach number on the off-design performance of S-shaped compressor transition duct under the combined effect of curvature and pressure gradient

ABSTRACT The compressor transition duct transfers the air from the low-pressure compressor to the high-pressure compressor. An aircraft always experiences off-design conditions except for level flight conditions during aircraft range. So, to throw some light on the performance of transition ducts under off-design conditions, this paper presents its performance assessment numerically for uniform and swirl flow cases under varying Mach numbers (M). This analysis reveals that a higher Mach number provokes an adverse pressure gradient and non-uniformity. In the uniform flow, the non-uniformity attains a maximum value of 0.04366 near the inner wall, which indicates the presence of a highly distorted flow near the inner wall; however, its maximum value is 0.03661 near to the outer wall in the swirl flow. Also, the pressure recovery reduces with an increased Mach number. Notably, as the Mach number increasesfrom the design point, the pressure coefficient along the convex curvature significantly drops to the lowest point of −0.65015 and −0.79324 for uniform and swirl flow, respectively. Consequently, the inner wall experiences a large adverse pressure gradient (−0.90822) compared to the decreasing Mach number from the design point for the uniform flow, whereas it is experienced by the outer wall in the case of swirl flow (−0.94729).

Large Deflection of Clamped Curved Beam Under Finite Clamping and Different Combinations of Bending-Stretching

The paper experimentally and theoretically analyses large deflection behaviour of clamped curved beam subjected to finite clamping and combined bending-stretching loads. The experimental specimen is clamped around central location under vertically concave and convex orientations. For each specimen settings, clamping is done by two different torque values. Application of vertical end loads on the clamped concave and convex systems produces two different combinations of bending and in-plane loadings. Large deflection behaviour of the experimental system is modelled theoretically considering geometric nonlinearities coming from combined bending-stretching, non-uniform curvature and asymmetric geometry. Effect of finite clamping is incorporated in the theoretical model through equivalent additional end loads. Due to the involved geometric nonlinearities, analysis is carried out through variational energy principle based incremental Lagrangian approach in curvilinear system and transformed into global frame. The semi-analytical model is successfully validated by comparing with the experimental results. The combined theoretical-experimental study addresses practical complication associated with local deformation at boundaries. In addition, the physically plausible theoretical model may be of interest for simulation of many real world structures with complicating system parameters. Moreover, observations on combined effects of curvature, loading combinations and finite clamping may provide reference for design optimization of equivalent engineering structures.

Thermally induced postbuckling of higher order shear deformable CNT-reinforced composite flat and cylindrical panels resting on elastic foundations with elastically restrained edges

In spite of considerable importance in engineering practice, especially in aerospace structures, thermal postbuckling behavior of nanocomposite curved panels has received little attention. This article aims to analyze different situations of postbuckling response of carbon nanotube (CNT) reinforced composite flat and cylindrical panels exposed to uniform temperature rise. CNTs are embedded into isotropic matrix through functionally graded distributions. The properties of constitutive materials are assumed to be temperature dependent and effective properties of CNT-reinforced composite are estimated according to an extended rule of mixture. Governing equations of thick panels are established within the framework of higher order shear deformation theory taking into account geometrical nonlinearity, initial imperfection, panel-foundation interaction, and elasticity of tangential constraints of boundary edges. Analytical solutions for simply supported panels are assumed and Galerkin method is adopted to derive nonlinear load-deflection relations from which temperature-deflection equilibrium paths are traced through an iteration algorithm. The study reveals that combined effects of curvature of panel, tangential constraints of edges, and initial geometrical imperfection can lead to the change in type of buckling response. Numerical analyses also indicate different influences on the postbuckling behavior of thermally loaded nanocomposite panels.

Quasi-dimensional, multi-zone combustion modelling of turbulent entrainment and flame stretch for a spark ignition engine fuelled with hydrogen-enriched biogas

A quasi-dimensional, multi-zone combustion model for spark ignition (SI) engines is analytically presented. The model is incorporated into a closed cycle simulation code for the prediction of performance and nitric oxide (NO) emissions of a SI engine operated on biogas, with small amounts of hydrogen added. The burning process is handled based on the combination of turbulent entrainment theory and flame stretch concepts. An expression of the turbulent burning velocity of a flamelet model is adopted for simulating the entrainment speed into the flame zone. A model of flame stretch is also used, in order to assess the flame response on combined effects of curvature, turbulent strain and preferential diffusion. In addition, the burned gas behind the flame is treated using a multi-zone thermodynamic formulation. In this way, the temperature and chemical species concentration gradients of the burned mixture can be captured, which are very important for accurate NO emissions predictions. After calibration of the model, illustrative diagrams are presented concerning the effect of hydrogen addition in biogas on burning rates, characteristic speeds, mass diffusivity of fuel and flame propagation. Furthermore, zone-resolved thermodynamic and geometric characteristics are given for the multiple burned zones. Finally, predictions of NO emissions are compared with the respective measured values.

Extinction and cellular instability of premixed tubular flames

Extinction and cellular instabilities are investigated in premixed tubular flames. A tubular burner has recently been designed and constructed to be capable of operating under a wide range of conditions that allow more accurate and detailed study of tubular premixed and non-premixed flames. Extinction measurements of tubular flames can be carried out through the entire equivalence ratio spectrum for various types of fuels without introducing serious turbulent effects. In this study, the extinction conditions of premixed tubular flames generated by H2/O2 or CH4/O2 mixed with various inert diluents (Ar, CO2, N2) and enriched oxygen are measured. In addition, the onset conditions for flame instability at different cell numbers are reported. Petal shaped cellular flames with symmetric regions of local extinction are observed for lean H2 tubular flames with low Lewis numbers. Wrinkled flames with no local extinction are observed for nearly equidiffusive lean CH4 tubular flames. The combined effects of curvature, diffusive-thermal instability and hydrodynamics are thought to be responsible for the cellular structure. The lack of extinction in the nearly equidiffusive lean CH4 tubular flames indicate that strong diffusive-thermal effects due to non-unity Lewis number are required to produce local extinction in the cellular structure of tubular flames.

Combined effects of curvature, radiation, and stretch on the extinction of premixed tubular flames

The combined effects of flame curvature, radiation, and stretch on the extinction of premixed tubular flames are investigated by using the large-activation-energy asymptotic method with a non-linear radiation model. A general expression for flame speed, flame temperature and extinction limits is obtained and it is used to study the radiation and flame curvature coupling at different Lewis numbers. The results show that the coupling between radiation and flame curvature leads to multiple flame bifurcations and extinction limits. Furthermore, both the stretch and radiation extinction limits are found to be greatly affected by flame curvature.

A general approach to grain growth driven by energy density differences

A general approach to grain growth driven by energy density differences among the grains, associated with curvature and/or extraneous driving forces (e.g. external fields) is developed. A mean field approximation leads to the definition of a threshold energy density, E ∗ , which depends on moments of the current distributions of grain diameters, a, and grain energy densities, E, such that the rate of change, da/ dt, of the diameter of a grain is proportional to ( E ∗–E ). When curvature effects are negligible, the kinetic equations can be solved analytically to obtain the average grain diameter < a> and the diameter distribution as a function of time. A scaling regime is reached for (and only for) power law distributions of E, with a power law kinetics < a>∝ t μ . The combined effects of curvature and extraneous driving forces were studied numerically. The rate of growth and the width of the grain diameter distribution change when compared to pure curvature growth, the sign of the change depending on the initial energy density and diameter distributions.

Effects of anisotropy and spatial curvature on the pre-big-bang scenario

A class of exact, anisotropic cosmological solutions to the vacuum Brans-Dicke theory of gravity is considered within the context of the pre-big-bang scenario. Included in this class are the Bianchi type III, V and ${\mathrm{VI}}_{h}$ models and the spatially isotropic, negatively curved Friedmann-Robertson-Walker universe. The effects of large anisotropy and spatial curvature are determined. In contrast with a negatively curved Friedmann-Robertson-Walker model, there exist regions of the parameter space in which the combined effects of curvature and anisotropy prevent the occurrence of inflation. When inflation is possible, the necessary and sufficient conditions for successful pre-big-bang inflation are more stringent than in the isotropic models. The initial state for these models is established and corresponds in general to a gravitational plane wave.

Influence of Buoyancy on Convective Heat Transfer in Helicoidal Pipes

The combined effects of curvature and buoyancy forces on convective heat transfer in axially vertical and horizontal helicoidal pipes have been explored in this investigation. Distilled water and ethylene glycol were used as working fluids. It has been observed that natural convection causes the peripheral maximum Nusselt number location to shift from the outer coil wall to the bottom of the tube cross section in the vertical coil. In the horizontal coil, the axial temperature distribution becomes periodically wavy with the presence of natural convection. The three following heat transfer regimes have been observed from the local temperature and Nusselt number distributions in the experiment of vertical helicoidal pipes: 1) a regime in which centrifugal force is dominant, 2) a regime in which both the centrifugal and buoyancy forces are effective (mixed regime), and 3) a regime in which the buoyancy force is dominant. Furthermore, it has been found that natural convection enhances heat transfer significantly for high Prandtl number fluids (e.g., ethylene glycol), but its effect is minor on the average Nusselt number for low Prandtl number fluids (e.g., water).

On the curved wall jet influenced by system rotation and self-similar suction or blowing

In this paper we use local nonparallel linear stability theory to study the jet on a concave and convex wall with spanwise system rotation and self-similar suction or blowing. It is found for low negative rotation, i.e. the Coriolis force counteracts the centrifugal force, that the critical Goertler number Go is increased for both the concave and convex wall jet. For the convex wall jet the critical Go is increased up to eight times compared with the nonrotation case. In this region of negative rotation, the principle of exchange of instabilities does not hold for the convex wall jet. For high negative and positive rotation the flow is destabilized on both types of walls. Suction stabilizes the concave wall jet while the convex wall jet is destabilized. For blowing, the concave wall jet is destabilized to a certain limit and then stabilized for increased blowing. The convex wall jet is stabilized for blowing. The combined effects of curvature, system rotation, and self-similar suction or blowing show that the highest critical Go can be increased for the rotating concave wall jet for both suction and blowing. For the rotating convex wall jet the highest critical Go is increased for suction and decreased for blowing.

A theoretical investigation of acoustic enhancement of heat and mass transfer—I. Pure oscillating flow

Effects of an oscillating flow induced by a high intensity acoustic field on heat and mass transfer to and from particles and droplets such as pulverized coal particles and coal-water slurry fuel droplets are investigated. Numerical solutions of two-dimensional, unsteady, laminar conservation equations for mass, momentum and energy transport in the gas phase give the velocity and temperature fields around a particle for different oscillating flows without superposed steady component as a function of time. The local and space-averaged Nusselt numbers depend on the change of imposed oscillating velocity U due to body curvature and flow acceleration. At low frequency (~50 Hz), curvature effects are dominant, resulting in increasing values of Nusselt numbers with increasing U. The Nusselt numbers can be approximated by the quasi-steady analysis. The effects of flow acceleration increase with increasing frequencies (~2000 Hz). The combined effects of curvature and flow acceleration result in the maximum difference of 9% in the space- and time-average Nusselt number for frequencies of 50, 1000 and 2000 Hz for the acoustic Reynolds number varying between 10 and 100. The present results show about 290% increase in the space- and timeaveraged Nusselt number for an acoustic Reynolds number of about 100 compared to that without an acoustic field.

A theoretical study on the acoustically driven oscillating flow around small spherical particles

In order to study the oscillating flow induced by a high intensity acoustic field, a computer code which employs the two-dimensional, unsteady mass and momentum conservation equations for laminar flow in spherical coordinates has been developed. The displacement amplitude of the incident sound wave is large compared to the characteristic length of particles, and the acoustic Reynolds number based on the particle diameter and the velocity amplitude of the oscillating flow is less than about 100. Numerical solutions of these equations give the velocity field, axial pressure gradient, shear stress and flow separation angle around the particle for acoustically oscillating flow as a function of acoustic Reynolds number and Strouhal number. The axial pressure gradient, shear stress and separation angle are proportional to the magnitude of oscillating flow at low frequency (∼50Hz) and can be approximated by the quasi-steady analysis. The effects of flow oscillation increase with increasing frequency (∼2000Hz) due to combined effects of curvature and flow acceleration, giving different values of axial pressure gradient, shear stress and separation angle for different frequencies of 500, 1000 and 2000 Hz.

Entry flow in heated curved pipes

The flow in the entrance region of heated curved pipes is analysed. Two cases of heating—a constant temperature at the wall, and a constant flux of heat at the wall—are considered. Using boundary layer approximations and the method of matched asymptotic expansions, the combined effects of curvature, entrance region and the buoyancy is studied. It is found that buoyancy disturbs the symmetric secondary motion induced by curvature, the deviation depending on the type of thermal input at the wall. It is also found that the oscillatory nature of the Nusselt number in the constant temperature case decreases as the Peclet number is increased.

The Effect of Non-Hydrostatic Stress on Intergranular Water Veins and Lenses in Ice

AbstractPolycrystalline ice at the melting point has been observed in the laboratory to contain veins of water at the places where three grains meet. Under uniaxial compression lenticular water inclusions appeared at grain boundaries perpendicular to the stress, while the nearby vein began to freeze. A similar effect occurred in tension on grain boundaries parallel to the stress. When the stress on the plane of the boundary was a pure shear stress, no effect was observed. The water lenses produced by stress increased in size and decreased in number after the stress was removed. The effect under compression is explained quantitatively by the combined effects of curvature and pressure on the melting point of an ice–water interface. The rate of formation of the lenses and of their coarsening is greatly reduced by the internal pressures set up in the lenses as a result of expansion on freezing and contraction on melting; transient creep to accommodate volume changes is an essential part of the process. The effect in a grain boundary under tension may arise from pressure caused by sliding on other grain boundaries; it was absent in a bicrystal.It is concluded that internal melting and freezing at grain boundaries and veins will occur in temperate glacier ice, with some effect, not discussed here, on its permeability to water. Any pure solid at its melting point which has a dihedral angle for the liquid phase in contact with a grain boundary between 0° and 60° should show similar behaviour, in that non-hydrostatic stress should cause liquid to move away from triple junctions between grains and into grain boundaries. There may be implications for the Frank theory of the upwelling of melt fluid in the Earth’s upper mantle.

The Effect of Non-Hydrostatic Stress on Intergranular Water Veins and Lenses in Ice

AbstractPolycrystalline ice at the melting point has been observed in the laboratory to contain veins of water at the places where three grains meet. Under uniaxial compression lenticular water inclusions appeared at grain boundaries perpendicular to the stress, while the nearby vein began to freeze. A similar effect occurred in tension on grain boundaries parallel to the stress. When the stress on the plane of the boundary was a pure shear stress, no effect was observed. The water lenses produced by stress increased in size and decreased in number after the stress was removed. The effect under compression is explained quantitatively by the combined effects of curvature and pressure on the melting point of an ice–water interface. The rate of formation of the lenses and of their coarsening is greatly reduced by the internal pressures set up in the lenses as a result of expansion on freezing and contraction on melting; transient creep to accommodate volume changes is an essential part of the process. The effect in a grain boundary under tension may arise from pressure caused by sliding on other grain boundaries; it was absent in a bicrystal.It is concluded that internal melting and freezing at grain boundaries and veins will occur in temperate glacier ice, with some effect, not discussed here, on its permeability to water. Any pure solid at its melting point which has a dihedral angle for the liquid phase in contact with a grain boundary between 0° and 60° should show similar behaviour, in that non-hydrostatic stress should cause liquid to move away from triple junctions between grains and into grain boundaries. There may be implications for the Frank theory of the upwelling of melt fluid in the Earth’s upper mantle.