摘要:

A numerical study has been conducted to investigate the interaction of two viscous vortex rings along parallel axes. The generation of two vortex rings created by the ejection of a fluid through orifices and their cut-and-connect process were numerically simulated by solving the three-dimensional and time-dependent Navier-Stokes equations. Based on the quantitative velocity and pressure data obtained from the Navier-Stokes simulation, the distribution and the evolution of the vorticity, helicity density and energy dissipation function were analyzed. The helicity density and its relation with the energy dissipation function in three-dimensional flow fields were also examined. It was found that the energy dissipation plays an important role in the cancellation of the vortex circulation during the vortex tubes cutting. This energy dissipation process may be used to explain the cut-and-connect of vortex tubes in the high Reynolds number turbulent flow. The numerical solutions were compared with the experimental observations and measurements under the similar condition. The correspondence between the numerical simulation and the experimental measurement was satisfactory.

ISSN:1061-8562    

DOI:10.1080/10618569408904489

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new predictive control method for operating water regulating gate of dams is presented based on a hydraulic model. To consider the hydrodynamic behavior of surface waves through a reservoir, the shallow water equation is used with the discretization by the finite element method. This method provides the appropriate solution of outflow discharge which prevents the overflow of dam by the operation of water gate assuming that the inflow discharge is known as a function of some moment in the future. To show the applicability of this method, one dimensional channels with single and with multiple dams and Moriyoshizan dam reservoir have been computed as the numerical examples. It is shown that the water surface elevation of a reservoir is sufficiently controlled by the present method.

ISSN:1061-8562    

DOI:10.1080/10618569408904490

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The finite analytic method is used in the present study to calculate the turbulent flow field described with Navier-Stokes equation in body-fitted curvilinear coordinate system The finite analytic method invokes the analytic solution of governing partial differential equation in formulating the algebraic equation that relates a nodal value in an element to its neighbour nodal values according to the direction and the magnitude of convection. It is shown that the finite analytic method has good numerical stability and accuracy. The turbulent flow fields through a single and a tandem cascades of airfoil are numerically simulated by using finite analytic method respectively in this paper. The k − ϵ turbulence model and wall function are employed in. the present study. The agreement of numerical solution with experiment result is quite good.

ISSN:1061-8562    

DOI:10.1080/10618569408904491

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The formulation of artificial dissipation terms for a semi-implicit, pressure based flow solver, similar to SIMPLE type formulations, is presented and is applied to both the Euler and the Navier-Stokes equations. The formulation uses generalized coordinates and a non-staggered grid. This formulation is compared to some SIMPLE and time marching formulations. The relationship between SIMPLE and time marching formulations is discussed briefly. The artificial dissipation inherent in some commonly used semi-implicit formulations, e.g. upwind differencing, powerlaw, QUICK and pressure weighting, is investigated. The scheme used here includes these dissipation terms directly, but retains the ability to mimic previous schemes. The potential for errors introduced by the simultaneous use of artificial dissipation in the continuity equation and central differencing of convective terms, is revealed. The effect of the amount of dissipation on the accuracy of the solution and the convergence rate is quantitatively demonstrated for two-dimensional inviscid flow in a mildly curved duct, three-dimensional laminar flow in a square cross section elbow with strong secondary flows, and two-dimensional turbulent flow through a turbine nozzle. The spurious effects of artificial dissipation, particularly second order dissipation, inherent in some commonly used algorithms, is clearly shown. The effect of artificial dissipation on the convergence rate is also demonstrated. The main conclusion drawn from the results is that the minimum amount of artificial dissipation that gives the required accuracy, but also an adequate convergence rate for a particular case, has to be used. This amount of dissipation is case dependent. The direct inclusion of artificial dissipation terms provides control over the amount of dissipation used.

ISSN:1061-8562    

DOI:10.1080/10618569408904492

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Results are presented to describe the laminar flow patterns around a prolate spheroid at angles of attack of 1, 2, 3, and 30 degrees and complement those obtained previously at 6 degrees. They were obtained by solving the three-dimensional boundary-layer equations with a combination of standard and characteristic box methods and with a stability criterion to ensure numerical accuracy. Emphasis is placed on the nature of separation which is shown to be coincident with a particular skin friction line on the windward side. The results on the leeward side break down prior to separation but suggest that, in agreement with experiment and contrary to some theoretical claims, the separation is open.

ISSN:1061-8562    

DOI:10.1080/10618569408904493

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the present paper, visualization techniques in fluid dynamic experiments such as Schlieren photograph are numerically simulated so that the same output as the experimental flow visualization can be obtained from the computed results for the fair comparison. Numerical methods to simulate optical visualizations, that are Schlieren photograph, shadowgraph and interferogram, are considered. Some examples of pictures obtained by the present methods show the importance of the simulations of visualization techniques for the correct comparisons of the computations and experiments.

ISSN:1061-8562    

DOI:10.1080/10618569408904494

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:1061-8562    

DOI:10.1080/10618569408904495

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor