NUMERICAL STUDIES OF THE COLD FLOW FIELD IN MODEL COMBUSTION CHAMBERS

Numerical analyses of the cold turbulent flow in model combustion chambers were made by using κ-Ε turbulent model. The hybrid difference scheme and SNIP method were employed. Numerical solutions for retouchment length and velocity distributions were obtained in the recirculating zone of the combustion chambers. The calculation results were in fairly good agreement with the reported experimental data. The work presented in this paper was a basic part of the calculation model of sudden-enlarged combustion chambers.

Hot Compressive Flow Stress of TA5 Alloy

The compressive true stress-true strain curves of TA5 alloy in α phase region have been measured and mathematically analyzed at Ε=10-1&middots-1 and 800-900°C. It is concluded that the curves are characteristic of dynamic recovery. A mathematical model of flow stress has been proposed on the basis of mathematical analysis.

SIMILARITY SOLUTIONS OF ROUND JETS AND PLUMES

The turbulent flow of vertical round plume with temperature variation and round jet without temperature variation were studied. The k-Ε model with the effect of buoyancy on turbulent kinetic energy and its dissipation rate was adopted. There were similarity solutions in the uniform environment for the system of equations including the equation of continuity, the equations of vertical momentum and heat flux, and the equations of k, Ε. The finite analytic method was applied to obtain the similarity solution. The calculated data of velocity and temperature distribution for round plumes were in good agreement with the experimental data at Prt=0.4. It shows that the present model is good, i.e., the effect of buoyancy on turbulent kinetic energy and its dissipation rate and the conservation of momentum and heat flux should be taken into account, while in previous works these factors were neglected.

CONTAMINANT CONTRACTION IN TWO-DIMENSIONAL OSCILLATORY FLOWS

If the vertically-mixing time is comparable with the period of oscillatory current, the contaminant contraction may occur, then the coefficient of shear dispersion will be negative (singularity). According to the two-dimensional delay-diffusion equation derived by Liu in another paper, The equations for X(t), Y(t), central displacement as well as dispersion tensor were derived. Generally speaking, δDij/δτ is positive when τ is small; but when τ is large, the memory functions may be negative. The analytical expressions for Dij and X,Y were also given.

Oxygen Incorporation in Czochralski Growth of Silicon under a Horizontal Magnetic Field

A mechanism of oxygen transportation in Czochralski growth of silicon crystals under a horizontal magnetic field (HMCZ) is proposed. Oxygen depleted surface melt, driven to the growth interface by the thermal Marangoni flow, determines oxygen concentration in the grown crystals. Systematic study was carried out to investigate effects of growth parameters on oxygen incorporation into crystals.

EVOLUTION OF SLOWLY MODULATED WAVE TRAIN ON POROUS SEA BED

In this paper, the problem of evolution of slowly modulated wave train on porous sea bed is investigated with the method of multiple scales. For the sea water in the upper region, the classical potential theory is used while the fluid motion in the porous sea bed is described by Darcy's law. The equations of the first and second order modulations of wave amplitude are derived by using matching conditions on the sea bed. The corresponding solutions are found and seepage pressures are also given at the same time.

INVESTIGATION OF THE TURBULENT MODEL FOR PRESSURE FLUCTUATIONS WITH SPECTRAL THEORY

The pressure fluctuations in turbulent shear flows were investigated with the theory of spectral analysis. An expression for pressure spectra was analytically derived in terms of velocity spectra based on a formal solution of Navier-Stokes equation and on quasi-normal assumption to express the third and fourth order velocity correlations in terms of double velocity correlation. Then, a turbulent model for computing the pressure fluctuation intensity with Reynolds stress and mean flow velocity gradients was established. The turbulent constants in the model were calculated from the assumptions about the general behaviour of velocity spectra in high Reynolds number flows. Comparison with direct simulation of turbulent boundary layer was made. It was found that the turbulent-turbulent, cross correlation, and turbulent-shear source terms for mean square value of pressure fluctuation are of the same magnitude.

TWO DIMENSIONAL DISTRIBUTION OF SEDIMENT CONCENTRATION NEAR THE BOTTOM OF STANDING WAVES IN SHALLOW WATER

In this paper, the formula of turbulent viscous coefficient of standing waves in shallow water is obtained with Karman theory. Then, the two dimensional solution of sediment concentration near the bottom of standing waves in shallow water is deduced, which is in good agreement with Hattori's semi-empirical result (1969, 1971).

NUMERICAL SIMULATION OF TURBULENT FLOW THROUGH THROAT-TYPE ENERGY-DISSIPATORS

The flow through the throat-type energy-dissipators is calculated by using an axis-symmetrical K-Ε turbulence model. The velocity field, the pressure field and the distributions of turbulent energy and its dissipation rate are acquired. The energy dissipation through the throat-type energy-dissipators can be seen in detail. The calculated pressure distribution is compared with the measured and is in good agreement. The results are useful to understand deeply the flow characteristics of the throat-type energy-dissipators.

NUMERICAL SIMULATION OF 3-D FLOW FIELD IN ARCIFORM PLUNGE POOL

The 3-D complex turbulent flow fields in a plunge pool with arciform bottom are simulated by using the k-Ε model in body-fitted coordinates. The calculated results reveal the flow characteristics in the arciform plunge pool under the different flood discharge conditions, which can not be easily obtained in the physical model test because the measurement of the complex velocity is very difficult. The calculated flow fields are helpful to understand the hydraulic characteristics of plunge pool deeply. The calculated and the measured pressure distributions on the pool bottom are compared and in good agreement.

GRID GENERATION AND NUMERICAL SIMULATION OF 2-D RIVER FLOW

This paper presents new weighting functions in grid generation and new discretizing scheme of momentum equations in numerical simulation of river flow. By using the new weighting functions, the curvilinear grid could be concentrated as desired near the assigned points or lines in physical plane. By using the new discretizing scheme, the difficulties caused by movable boundary and dry riverbed can be overcome. As an application, the flow in the Wuhan Section of Yangtze River is simulated. The computational results are in good agreement with the measured results. The new method is applicable to the numerical simulation of 2-D river flow with irregular region and moveable boundary.

EXPERIMENTAL INVESTIGATION OF INCEPTION CAVITATION IN LIQUIDSOLID TWO PHASE TURBULENT FLOW

The experimental investigation of inception cavitation of liquid-solid two phase turbulent flow has been carried out in a two dimensional hydraulic tunnel. The experimental result shows that the cavitation existing in the sediment laden flow is different from that in the clear water. We also found that the inception cavitation of sediment laden flow only has a weak relation with the shape of the experimental model in which the cavitation originated, yet it has direct relation with the density of sediment concentration in the flow and the diameter of the sediment particles and the distribution of particle sizes. The results given in the paper could be used for engineering designing and hydraulic machine making.

RESEARCH ON MOTION CHARACTERISTICS OF GAS-SOLID JET FLOW

Evolution of vortex structures in round jet was simulated with a three-dimensional discrete vortex filament method. The motion of the particles was described by a Lagrangian equation and the counteraction of particles on the flow was taken into account by using a modified velocity model. It is indicated that in two-phase jet flow the introduced particles restrain the crosswise dispersion of jet shear layer and mergence of vortex structures. With the increase of St number, the influence of flow on particles motion is decreased, but the counteraction of particles on the flow is increased. The difference of flow field obtained with two models, one-way coupling model and two-way coupling model, is greater than that of particles trajectories.

PREDICTION OF TURBULENT FLOW CHARACTERISTICS IN THE CURVED DUCT WITH A BAFFLE

The changes of developing turbulent flow characteristics in curved duct after adding a baffle were studied numerically at a body-fitted coordinate. A k-Ε model was used to represent the turbulent characteristics. A curved duct with a rectangular cross-section was computed firstly. Two kinds of square ducts were studied: One was normal curved duct, the other was a duct with a baffle. The computational results show that the secondary flow in duct with a baffle is characterized by four vortices structure, compared with the duct without a baffle,the intensity of the secondary flows is reduced. This has much more significant meaning in engineering.

COMPUTER-AIDED ANALYSIS OF UNSTEADY PARTIALLY FILLED FLOWS IN DRAINAGE SYSTEMS

Partially filled pipeflows were encountered in drainage systems belonging to a family of unsteady flow problems. Basic equations were developed and numerically solved also by the characteristic different methods with time-line interpolation scheme. The boundary conditions for the inflow, outflow, moving hydraulic jump and junctions were developed experimentally and numerically. Full scale model experiments were carried out. It is consequently clarified that numerical model is capable of predicting flow characteristics in realistic drainage networks.

DISPERSION IN COUPLE STRESS FLUIDS-EFFECTS OF CHEMICAL REACTION

In this paper, the dispersion of a soluble matter in couple stress fluids flowing through pipes and channels is investigated by taking into account the effects of homogeneous chemical reaction. The analytical expressions of the relative concentration distribution Cˉ and the effective diffusion coefficient D* are derived under Taylor's simplified assumptions, and the numerical computation is carried out. The effects of couple stress parameters αˉ, ηˉ and chemical reaction rate constant λ on those quantities above are discussed.

FINITE ELEMENT ANALYSIS OF COMPLEX INCOMPRESSIBLE FLOWS

The complex flow has been simulated with finite element method for Navier-Stokes equations. Both two and three dimensional, laminar and turbulent problems were included. The velocity-pressure decoupling method was adopted and related algorithm was discussed. Effects of turbulence were accounted by large eddy simulation.

NECESSARY PRINCIPLES FOR ESTABLISHING FUNDAMENTAL EQUATIONS OF MULTIPHASE FLOW

The fundamental equations of multiphase flow that have been established so far fall into two main groups, the multifluid model and the mixture model [1] [2]. Because of the different forms of the equations derived from these two models, many disputes arose [1] [3] [4]. This paper deals mainly with the basic principles for establishing the fundamental equations of multiphase flow, namely the principles of consistency, invariance of material coordinates and material indifference. The results lead to the consistent description of the two models.

GENERALIZED STRONGLY NONLINEAR QUASI-COMPLEMENTARITY PROBLEMS IN HILBERT SPACES

In this paper, we introduce a new kind of generalized strongly nonlinear quasi-complementarity problems in Hilbert space and discuss the existence of solutions for this kind of problems and the convergence of sequences generated by algorithms. The results presented in this paper improve and extend a number of known results.

NUMERICAL SOLUTION OF INCOMPRESSIBLE VISCOUS FLOW OVER AEROFOIL WITH H-TYPE GRID

In the computational fluid dynamics there are three types of body-fitting grid generation method for incompressible viscous flow over an aerofoil, i.e. O-type, C-type and H-type. The numerical solution of H-type grid and a special difference scheme were obtained. In order to prevent the oscillation of pressure, u was defined at the nodes of the mesh, but v and p were defined as staggered grid. Upwind scheme in the convective terms was used and the iteration with success lower relaxation of implicit difference equations were unconditional stability. The method of mass flux correction was introduced with the success in order to accelerate convergence in iteration of velocity and pressure calculation. Numerical results indicate that H-type grid generation is successful to solve problem of external flow and artificial compressity method with correction technique of total mass flux can improve convergence rate.