An approximate solution considering flow inertia between conical surfaces

In this paper, analytical calculation expressions of the pressure distribution, velocity distribution and the rate of the flow between conical surfaces are found by using the method of iterative approximate solution when the inertia terms of the Navier-Stokes equations in conical coordinates are taken into account. Furthermore, we compare the centrifugal flow with the centripetal flow of axisymmetrical passing flow.     

Interaction of viscous wakes with a free surface

The interaction of laminar wakes with.free-surface waves generated by a moving body beneath the surface of an incompressible viscous fluid of infinite depth was investigated analytically. The analysis was based on the steady Oseen equations for disturbed flows.The kinematic and dynamic boundary conditions were linearized for the small-amplitude free-surface waves. The effect of the moving body was mathematically modeled as an Oseenlet.The disturbed flow was regarded as the sum of an unbounded singular Oseen flow which represents the effect of the viscous wake and a bounded regular Oseen flow which represents the influence of the free surface. The exact solution for the free-surface waves was obtained by the method of integral transforms. The asymptotic representation with additive corrections for the free-surface waves was derived by means of Lighthill‘s two-stage scheme. The symmetric solution obtained shows that the amplitudes of the free-surface waves are exponentially damped by the presences of viscosity and submergence depth.     

UNSTEADY DETACHED SEPARATION FROM A CIRCULAR CYLINDER PERFORMING ROTATIONAL OSCILLATIONS IN A UNIFORM VISCOUS INCOMPRESSIBLE FLOW

The origination of detached separation is studied on the basis of a numerical solution of the full Navier–Stokes equations. Fluxes of vorticity with different signs generated with twice the frequency of cylinder oscillation move from the cylinder to the outer surface of a detached liquid layer in the form of concentric rings. Near the critical layer between the attached layer and the main flow these rings are torn and crimped to the regions of separated vortices of the corresponding sign. The form of detached separated vortices is similar to that of vortices originating from a stationary circular cylinder in a uniform flow. Transition of the flow to a non-symmetric form with Karman vortex street generation at a Reynolds number (based on the radius) greater than 17 is revealed. This critical Reynolds number is smaller than that for a stationary circular cylinder in a viscous stream (where Re=20 has been determined to be a critical value) and corresponds to the Reynolds number extrapolated from the critical value for the stationary cylinder by increasing the cylinder radius by the attached layer thickness. The vorticity flux from the cylinder surface immediately into the separation region decreases as the frequency of cylinder oscillation increases. Violation of the flow potentiality in the detached separation region is the main cause of the vorticity generation on the outer surface of the attached liquid layer. © 1997 John Wiley & Sons, Ltd.     

AN IMPROVED MAC METHOD (SIMAC) FOR UNSTEADY HIGH-REYNOLDS FREE SURFACE FLOWS

A modified MAC method (SIMAC; semi-implicit marker and cell) is proposed which accurately treats unsteady high-Reynolds free surface problems. SIMAC solves the Navier–Stokes equations in primitive variables on a non-uniform staggered Cartesian grid by means of a finite difference scheme. The convective term is treated explicitly by employing a second-order upwind scheme in space (HLPA) and the Adams–Bashforth technique in time. The diffusive part is solved by means of the implicit approximate factorization technique. A multigrid technique based on the additive correction strategy is employed to solve the Poisson equation for the pressure. Finally, the free surface treatment is carried out using massless particles which divide the domain of integration into full and empty cells as in a standard MAC method. The algorithm is used for the analysis of large-amplitude water sloshing in rectangular unbaffled and baffled containers. Experimental tests have been carried out in order to validate the algorithm. Numerical results satisfactorily agree with experimental data for the whole range of filing conditions analysed here. © 1997 by John Wiley & Sons, Ltd.     

Simulation of Three-Phase Displacement Mechanisms Using a 2D Lattice-Boltzmann Model

Using a numerical technique, known as the lattice-Boltzmann method, we study immiscible three-phase flow at the pore scale. An important phenomenon at this scale is the spreading of oil onto the gas–water interface. In this paper, we recognize from first principles how injected gas remobilizes initially trapped oil blobs. The two main flow mechanisms which account for this type of remobilization are simulated. These are the double-drainage mechanism and (countercurrent) film flow of oil. The simulations agree qualitatively with experimental findings in the literature. We also simulate steady-state three-phase flow (fixed and equal saturations) in a small segment of a waterwet porous medium under both spreading and nonspreading conditions. The difference between the two conditions with respect to the coefficients in the generalized law of Darcy (which also includes viscous coupling) is investigated.     

Massively separated flows due to transverse sonic jet in laminar hypersonic stream

A numerical simulation of flow interactions due to a transverse sonic jet ejected from a two-dimensional slot into a hypersonic stream is carried out to examine the capability of Navier–Stokes solutions in predicting a massively separated flow upstream of the jet exit. Grid sensitivity has been studied using gradually refined meshes to address the numerical accuracy of the discretised solution of the governing equations. Comparison has been made with published experimental data regarding the separation and reattachment points and the pressure distribution in the separated region. Flow field visualisation provides further insight into the interaction region and reveals a small clockwise vortex immediately ahead of the jet exit, which is found to be responsible for the second peak in the surface pressure distribution. Received 30 June 1998 / Accepted 27 September 1998     

带有摩擦耗能元件的框架结构动力分析

本文提出粘性屈服模型来模拟摩擦耗能元件的力-速度关系,该模型是连续变化的,克服了库仑摩擦模型不连续导致数值计算复杂的缺点,在进行摩擦耗能体系的动力分析中,采用缩减自由度技术,并作适当的变换,则带有摩擦耗能元件体系的动力分析归结为求解微分代数方程,本文采用增量型Rosenbrock二级三阶半隐式Runge-Kutta法求解该方程,以考虑框架和支撑的材料和几何非线性。对带有摩擦耗能元件的钢框架进行了弹塑性动力分析,研究了支撑刚度与结构层刚度的比值、摩擦力的大小以及地震波类型等参数对体系的影响。     

低压蒸汽透平排汽缸内三维粘性流动的数值模拟

采用三维粘性流场求解软件Fine／TURBO[1]对低压蒸汽透平下游排汽缸内的复杂流动进行数值模拟。计算中使用了Jameson的Runge-Kutta中心差分格式[2]和Baldwin-Lomax的代数湍流模型、计算结果同部分实验结果进行了对比,表明数值模拟揭示了排汽缸内复杂的旋涡结构,以及影响排气缸内压力恢复和总压损失的主要因素。     

Geometrical nonlinear waves in finite deformation elastic rods

IntroductionSomenewphenomenaofnonlinearwavesinthesolidmediumsuchasshockwave ,solitarywaveetc.arepaidmoreattentiontoincreasinglybyresearchersbecausetheytakeonalotofimportantproperties.ItistheoreticallyanalyzedinRefs.[1 -6]thattheformationmechanismsofshockwaveandsolitarywaveintheelasticthinrodsaswellastheirpropagationproperties.TheexistenceofsolitarywaveintheelasticmediumsuchasarodandaplatehasbeenverifiedinRef.[7]byexperiments.Shockwaveandsolitarywavearesteadilypropagatingtraveling_wavesgenerat…