Numerical Solution Of Navier-Stokes Equations Research Articles

Patrones de flujo según diferentes marcos de referencia

En una evaluación de diagnóstico sobre mecánica de fluidos, en la que se pide a los estudiantes graficar diagramas de flujo de un caso de geometría simple, se observa una notable confusión asociada a cambios de marcos de referencia. Como herramienta didáctica, se propone un análisis comparativo de diagramas de flujo en diferentes condiciones de movimiento relativo de un mismo sistema, consistente en un tubo cilíndrico que contiene líquido y un objeto esférico pequeño. Tales diagramas son mapas de velocidad y líneas de corriente obtenidos por resolución numérica de la ecuación de Navier-Stokes.

1301 三次元性地形効果により励起される有限振幅内部重力波の振舞(OS-7 密度成層・自由境界)

Finite-amplitude internal waves resonantly excited by three-dimensional topography in the flow of a weakly and nearly uniformly stratified fluid are studied. This flow is mainly governed by a stratification profile and the Froude number. The numerical solutions of Navier-Stokes equations show various wave patterns, such as the Mach reflection and upstream propagation of solitary waves, depending on the values of these parameters. A comparison with solutions of fully nonlinear model equation is also made.

A nonlinear operator-based speech feature analysis method with application to vocal fold pathology assessment.

Traditional speech processing methods for laryngeal pathology assessment assume linear speech production with measures derived from an estimated glottal flow waveform. They normally require the speaker to achieve complete glottal closure, which for many vocal fold pathologies cannot be accomplished. To address this issue, a nonlinear signal processing approach is proposed which does not require direct glottal flow waveform estimation. This technique is motivated by earlier studies of airflow characterization for human speech production. The proposed nonlinear approach employs a differential Teager energy operator and the energy separation algorithm to obtain formant AM and FM modulations from filtered speech recordings. A new speech measure is proposed based on parameterization of the autocorrelation envelope of the AM response. This approach is shown to achieve impressive detection performance for a set of muscular tension dysphonias. Unlike flow characterization using numerical solutions of Navier-Stokes equations, this method is extremely computationally attractive, requiring only a small time window of speech samples. The new noninvasive method shows that a fast, effective digital speech processing technique can be developed for vocal fold pathology assessment without the need for direct glottal flow estimation or complete glottal closure by the speaker. The proposed method also confirms that alternative nonlinear methods can begin to address the limitations of previous linear approaches for speech pathology assessment.

Hypersonic flow in an MHD-acceleration facility and under full-scale conditions

A formulation of the problem, a method of solution, and calculated results are considered for flow past the windward side of a sphere under conditions of an aerodynamic facility (a wind tunnel) with magnetohydrodynamic (MHD) acceleration of the air flow and the corresponding full-scale flight conditions in the Earth's atmosphere. Calculations were performed on the basis of numerical solution of Navier-Stokes equations taking into account thermochemical nonequilibrium of air and catalytic properties of the body surface. Results of the mathematical simulation of flow around a sphere in an MHD-acceleration wind tunnel are compared with experimental data obtained at the Central Aerohydrodynamic Institute (TsAGI). The problem of recalculation of experimental data for full-scale conditions is analyzed.

Interaction of vortices with a progressive surface wave

Interaction of submerged vortices with a progressive surface wave is investigated by the finite-difference numerical solution of Navier-Stokes equations. The progressive wave is the surface gravity water wave in a finite depth. The initial vortex model is Oseen vortex. The numerical computations show that a special pattern of the wave surface may be observed by the interaction from the submerged vortices. The influences of Froude number, the initial geometric configuration of vortices, and the amplitude, initial phase of surface wave on the wave pattern are discussed.

Numerical solution of navier-stokes equations for an incompressible liquid in channels with a porous insert

Numerical solution of navier-stokes equations for an incompressible liquid in channels with a porous insert

A Study of Flow Field around Full Ship Forms in Maneuvering Motion

In the previous report dealing with oblique towing condition, the flow field around tow full ships with different aft hull-forms were investigated by numerical computation and experiments. Thereafter, additional studies of comparison between numerical computation and experiments were carried out for the same ships in steady turning condition. As in the previous investigation, detailed measurement of hydrodynamic pressure on the whole hull surface was executed, and then the longitudinal distribution of sectional lateral force was obtained by integrating the measured pressure along a contour of transverse section of ship's hull at various square stations. The measured pressure on the hull and longitudinal distribution of sectional lateral force were compared with numerical solutions of Navier-Stokes equation. The results are fully described in the present paper. The comparison denotes that agreement between numerical computation and experiments is fairly good. In particular, it should be noted that the difference in hydrodynamic lateral force and turning moment between two ships with different hull-forms can be successfully predicted by numerical computation, and the difference in maneuverability of two ships can be definitely correlated to the difference in lateral force distribution caused by the difference in hull-form by means of numerical computation and experiments as well.

A high accuracy defect-correction multigrid method for the steady incompressible Navier-Stokes equations

The solution of large sets of equations is required when discrete methods are used to solve fluid flow and heat transfer problems. Although the cost of the solution is often a drawback when the number of equations in the set becomes large, higher order numerical methods can be employed in the discretization of differential equations to decrease the number of equations without losing accuracy. For example, using a fourth-order difference scheme instead of a second-order one would reduce the number of equations by approximately half while preserving the same accuracy. In a recent paper, Gupta has developed a fourth-order compact method for the numerical solution of Navier-Stokes equations. In this paper we propose a defect-correction form of the high order approximations using multigrid techniques. We also derive a fourth-order approximation to the boundary conditions to be consistent with the fourth-order discretization of the underlying differential equations. The convergence analysis will be discussed for the parameterized form of a general second-order correction difference scheme which includes a fourth-order scheme as a special case.

Effect of swirl on jet atomization

Introduction B ECAUSE of its practical significance, the subject of jet atomization has been given considerable attention in the literature.' However, the number of published investigations on the problem of the effect of swirl on the atomization of a liquid jet has been very limited. The most comprehensive theoretical treatment of the problem is that of Ponstein. More recently, Kang and Lin studied the spatial instability of a swirling liquid jet, including the effect of nonaxisymmetric disturbances in their analysis. Lian and Lin investigated the convective instability of a viscous liquid jet emanating into a swirling in viscid gas. All of the previous studies of the effect of swirl on liquid jet atomization were conducted via the linear theory of hydrodynamic stability. The problem with the linear stability analysis is the assumption that the perturbations are infinitesimally small, since, after a finite interval of time, unstable perturbations will have grown to finite quantities. Because of the limitations of the linear stability theory, alternative methods of analysis have been sought. These include the method of strained coordinates. Direct numerical solution of Navier-Stokes equations in their axisymmetric form was attempted by Shokoohi and Elrod. Bogy used the Cosserat theory developed by Green. A weakly nonlinear instability analysis was advanced by Ibrahim and Lin. Though mathematically or computationally elegant, all of the aforementioned methods suffer inherent complexity. Lee developed a one-dimensional nonlinear direct-simulation technique that proved to be a simple and practical approach to investigate the nonlinear instability of a liquid jet. Lee's direct-simulation approach formed the basis of a comprehensive treatment of the jet instability and atomization presented by Chuech et al. In the present work we shall extend the direct-simulation analysis of Chuech et al. to include the effect of swirl on jet atomization.

Acoustic boundary layers in solid propellant rocket motors using Navier-Stokes equations

The numerical solution of laminar, two-dimensional, compressible, and unsteady Navier-Stokes equations is aimed at a complete description of acoustic boundary layers that develop above a burning pro pell ant. Such acoustic boundary layers can be responsible for the so-called flow turning losses. They can govern the local unsteady flow conditions that are seen by the burning propellant to which it finally responds. In those respects, a complete understanding of such acoustic boundary layers is essential to improve existing solid rocket stability prediction codes. The full numerical solution of the Navier-Stokes equations incorporates into the analysis all the features of two-dimension al rocket chamber mean flowfield in a natural manner. After a standing wave pattern is established through forcing at a given frequency, a special Fourier treatment is used to transform the numerical results in a form directly comparable to available linear acoustic data. The presented results indicate that the acoustic boundary layer is substantially thinner than predicted by simplified models. Moreover, its acoustic admittance is found to vary significantly along the chamber, a result that is of major importance to stability predictions. Finally, the acoustic field is found to be rotational over a significant volume of the chamber.

Numerical solution of navier-stokes equations for viscous gas by the semimarching method

Numerical solution of navier-stokes equations for viscous gas by the semimarching method

Numerical solution of Navier-Stokes equations for two-dimensional viscous compressible flows

A nodal-point, finite-volume space discretization of viscous fluxes in compressible Navier-Stokes equations is presented. To advance the solution in time, an explicit five-stage Runge-Kutta scheme has been used. To accelerate the rate of convergence to steady state, local time stepping, residual averaging, and enthalpy damping have been employed. The scheme has been evaluated by solving laminar flow over a semi-infinite flat plate and an NACA 0012 air foil using thin-layer approximation. It has been observed here that fourth-order artificial dissipation is sufficient for numerical stability. The results have been compared with available theoretical and numerical solutions.

Free surface flow and heat transfer in conduction mode laser welding

Temperature profiles and fluid flow fields in a weld pool are simulated through numerical solutions of Navier-Stokes equation and the equation of conservation of energy for low power laser welding in conduction mode. Experimentally determined weld pool surface topography, peak temperature, and the secondary dendrite arm spacings are found to be in fair agreement with the corresponding theoretically calculated values.

Flow of coaxial impingement of opposing laminar jets.

The mixing process of opposing jets by coaxial impingement in the mixing chamber of a reaction injection molding has not been clarified. This paper presents the results obtained from numerical experiments for the coaxial impingement of opposing laminar jets. The numerical solution of Navier-Stokes equations is obtained by a finite-difference approximation which is extended from the exisiting solution for a laminar jet. The effects of the jet Reynolds number, the velocity profile at the nozzle exit and the distance from the nozzle to the impingement surface on the flow after the impingement are shown, and their effects on the flow mixing of the two jets are discussed.

Circulation flow at the front surface of a sphere in a supersonic wake

Several theoretical and experimental studies of supersonic flow past a blunt body located in the wake behind another body have been made [1–7]. It has been shown that a reverse-circulation flow can occur in the shock layer at the front surface. The possibility of such a flow forming depends on the nonuniformity of the freestream flow and the Reynolds number. This paper presents new results of the theoretical study of the structure of the shock wave at the front surface of such a sphere, obtained on the basis of numerical solution of Navier-Stokes equations. It is shown that for a fixed nonuniformity of the freestream flow, an increase in the Reynolds number and cooling of the surface of the body lead to the formation of a secondary vortex in the region where the contour of the body intersects the axis of symmetry. A study is made of the variations of the drag and heat transfer parameters over the front surface of a cooled and thermally insulated sphere. The possibility of numerical simulation of the flow on the basis of the Euler equations is discussed.

Numerical solution of Navier-stokes equations for laminar fluid flow in rows of plates in staggered arrangement

Laminar fluid flow in rows of plate elements with staggered arrangement has been investigated by solving the complete Navier-Stokes equations using numerical methods. The results have been compared with those obtained on the basis of boundary-layer simplifications. The theoretical pressure-drop values compare well with available numerical and experimental data

Numerical solution of Navier-Stokes equations for an arbitrary two-dimensional body

Numerical solution of Navier-Stokes equations for an arbitrary two-dimensional body