突扩圆管内液-固两相流固体颗粒运动特性的DPM数值模拟

采用考虑颗粒碰撞的欧拉一拉格朗日数值模拟方法(DPM),对水平突扩圆管中液固两相流固体颗粒的碰撞过程进行了数值计算.在模型中,对液相采用欧拉法建立控制方程,对离散颗粒采用拉格朗日方法模拟.采用硬球模型描述颗粒间的碰撞作用.计算结果表明,该模型可以真实地模拟液固两相流中固体颗粒运动的动态变化过程以及颗粒的非均匀分布特征,从单颗粒层次上提供颗粒的运动信息,这有助于深入研究液固两相流中固体颗粒的运动规律.     

Effect of boundary layer thickness before the flow separation on aerodynamic characteristics and heat transfer behind an abrupt expansion in a round tube

Results of numerical investigation of the boundary layer thickness on turbulent separation and heat transfer in a tube with an abrupt expansion are shown. The Menter turbulence model of shear stress transfer implemented in Fluent package was used for calculations. The range of Reynolds numbers was from 5·10³ to 105. The air was used as the working fluid. A degree of tube expansion was (D ₂/D ₁)² = 1.78. A significant effect of thickness of the separated boundary layer both on dynamic and thermal characteristics of the flow is shown. In particular, it was found that with an increase in the boundary layer thickness the recirculation zone increases, and the maximum heat transfer coefficient decreases. The work was financially supported by the Russian Foundation for Basic Research (project codes 07-08-00025 and 06-08-00300).     

Density of indium antimonide at high temperatures

The density of solid and liquid indium antimonide was studied by irradiating the samples with a narrow beam of monochromatic gamma-radiation in the temperature range of 293–1950 K, including the range of melting — crystallization. The measurement errors for the density and thermal expansion coefficients were ±(0.25–0.40) % and ± 4 %, correspondingly. The approximating equations and tables of reference data were obtained for the temperature dependence of thermal properties. Measurement results were compared with the known published data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 06-08-00040).     

Zonal-iterative calculation method for radiation heat transfer in cavity systems

The zonal-iterative calculation method for radiation heat transfer is developed for arbitrary number of zones (opaque diffusely-radiating and reflecting surfaces). This method is based on transformation of the initial integral equations to equivalent system of integral equations with smaller kernel norm. The method provides high accuracy at a small number of the zones. The method was used for analysis of effective radiation in an isothermal tube cavity with a longitudinal pyrometric slit. In this case one zone was enough and one of the particular solutions can be obtained analytically. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 06-08-01561).     

Thermal radiation of axisymmetric semitransparent systems

The properties of thermal radiation of the axisymmetric systems formed by an absorbing medium are analysed. Analysis of absorption and propagation abilities of the systems with an impermeable boundary on the basis of integral radiation equations is suggested together with absorption, transmission, and reflection abilities of the systems with a boundary permeable for radiation. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 08-08-00587-a).     

Experimental and numerical study of heat transfer enhancement in a turbulent bubbly flow in a sudden pipe expansion

Results of an experimental and numerical simulation of heat transfer in an upward bubbly flowin a sudden pipe expansion are presented. The experimental study of the heat transfer has been performed using infrared thermography. The measurements of the bubble size before the pipe expansion area were carried out by the shadow photographymethod. The numerical simulation of the bubbly flow structure in the sudden pipe expansion has been performed using the Eulerian approach in the presence of heat transfer between the two-phase flow and the wall surface. The model uses the system of Reynolds-averaged Navier–Stokes equations in an axisymmetric approximation, written with consideration of the back effect of bubbles on the averaged and pulsation characteristics of the flow. It has been experimentally and numerically shown that addition of air bubbles causes a significant (up to 3-fold) increase in the heat transfer intensity, these effects growing with bubble concentration. The largest rise in the heat transfer has been revealed in the region of flow relaxation downstream of the flow attachment point.     

Experimental study and mathematical modelling of heat transfer processes in heat accumulating media

Experimental results on reversing non-stationary heat transfer are presented for filtration of an air flow through an immobile heat accumulating medium consisting of lead (D = 2.0, 3.5, and 4.5 mm) and glass (D = 3.2 mm) balls. The studied device imitated the cyclic modes of heat regeneration in the ventilation system for domestic and office rooms. Dependency between the time of flow switching and Re number was measured. The mathematical model describing heat transfer between a gas flow and an immobile layer of balls was developed. Good correspondence between the experimental data and calculation results is observed for high Reynolds numbers. For low Re numbers the effect of heat losses is considerable, and experimental time of flow switching is shorter than the calculation one. The work was financially supported by the President of the Russian Federation (Grant No. NSh 6526.2006.3), Russian Foundation for Basic Research (Grant No. 06-08-00982), Foundation “Global energy” and Program “Energy saving of SB RAS”.     

Non-stationary radiative-conductive heat transfer in a layer with partially absorbing boundaries

Here we consider one-dimensional heating of a layer of gray semitransparent medium by an outer source of radiation and convection. The sample boundaries reflect, absorb (radiate), and transmit radiation. It is shown that heating dynamics and character of temperature fields depend significantly on optic parameters of the boundaries. The work was financially supported by the President of the Russian Federation (MK-601.2008.8) and Russian Foundation for Basic Research (Grant No. 08-08-00527-a).     

Thermal conductivity and thermal diffusivity of tantalum in the temperature range from 293 to 1800 K

Thermal diffusivity of polycrystalline tantalum at the temperature range from 293 to 1800 K has been measured by the laser flash method with the error of 2–4 %. Thermal conductivity has been calculated with the use of reference data on density and heat capacity. Approximating equations and tables of reference data for the temperature dependence of heat transfer coefficients have been obtained; comparison with the published data has been carried out. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-08-00071).     

Analysis of the properties of heat radiation of the axisymmetric semitransparent systems with permeable boundaries

Numerical analysis of hemispherical values of absorptive, transmitting, and reflective abilities of a flat layer and absorptivity of a sphere is presented in this paper depending on the optic thickness and refractive index. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 08-08-00587) and the grant of the President of the Russian Federation for young scientists (Grant MK-601.2008-8).     

Numerical analysis of the influence of angle of attack on turbulent flow around a thick goettingen airfoil with vortex cells

On the basis of the solution by multi-block computational technologies of Reynolds equations closed with the aid of the equations of the model of Menter’s shear stresses transfer, an analysis of the flow around a thick airfoil of classical geometry with vortex cells is given at an arrangement of suction from the surface of central bodies placed inside them. The suction velocities, angles of attack, and location of vortex cells on the contour are determined, under which the flow around an airfoil of 35,2% thickness is ensured close to a separation-free flow, for high Reynolds numbers (Re = 10⁵). The integral force characteristics of the Goettingen and EKIP profiles are compared for the distributed and concentrated suction in vortex cells. The work was financially supported by the Russian Foundation for Basic Research (Grants Nos. 06-08-81002 and 05-01-00162) and by the European Union, the program Framework-6 (Project VortexCell2050).     

Modelling of condensation at spherical expansion of water vapor into vacuum

The mathematical model of water vapor condensation was developed for the direct simulation Monte Carlo method. This model describes a chain of reactions providing formation and decay of water clusters with consideration of accompanying energy transfer processes. One-dimensional expansion of water vapor into vacuum from an evaporating spherical surface was studied numerically within the range of parameters, corresponding to the flows transitional by the Knudsen number. The influence of condensation on the gas-dynamic pattern of the flow, including the parameters of the Knudsen layer, is discussed. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-01-00354-a).     

Heat transfer in a turbulent separation region with superimposed stream pulsations

Experimental data on heat transfer in turbulent separation region behind obstacle in a broad frequency range of superimposed free-stream pulsations are reported. The heat-transfer coefficient was determined by solving an inverse non-stationary heat conduction problem based on experimentally measured wall transient temperature. Substantial heat-transfer intensification in the separation region of the pulsating flow was identified. This work was supported by the President of the Russian Federation (Grant NSh-8574.2006.8) and by the Russian Foundation for Basic Research (Grants Nos. 05-02-16263, 06-08-00521, and 07-08-00330).     

Surface instability of the liquid turbulent flows in the open inclined channels

The flow of a viscous liquid layer in an open inclined channel under the turbulent mode is considered in this paper. To describe turbulent viscosity, the Van Driest model is used. The spectrum of characteristic values of the problem on linear stability of a plane-parallel flow is studied numerically. Parameters of the maximal growth waves are found out, the surface tension effect is studied, and theoretical results are compared with experimental data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 05-08-33585a).     

Peculiarities of high-temperature two-phase flow of combustion products in channels with an intentionally structured system of shock-waves

Theoretical and simulation study was carried out for eliciting conditions when an intentionally formed system of oblique shocks can be used for control of parameters of condensed phase in supersonic flow. The key features of flow were analysed for two versions of duct, which are different in geometry of nozzle and acceleration headpiece. The results confirmed the feasibility of intentional impact on the structure of developing set of shock waves through changes in the duct profile: this would change the particle trajectories. This research was financially supported by the Russian Foundation for Basic Research (Grant No. 05-08-01414-a).     

Influence of the intensity of chemical heat-release source on the heat exchange at a flow of pseudo-plastic liquid in the initial interval of coaxial duct

The critical regimes of heat exchange at a laminar steady flow of a pseudo-plastic liquid in the initial interval of a coaxial duct are investigated with regard for both dissipative and chemical sources in the Arrhenius representation [5] under the conditions of an insignificant variation of the concentrations of reacting substances. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 05-08-50043), FANI (State Contract No. 02.434.11.5009), and the Presidium of RAS (Program P-09).     

Resonance effect of the bottom topography on the surface of an inclined layer of a viscous liquid

The reaction of the film interface to low-amplitude waviness of the wall was studied. A linearized version of the problem described by the Orr — Sommerfeld equation was considered; the solution was sought by asymptotic expansion in small parameter 1/Re, and usual spectral problem concerning stability to perturbations of exp[iα(x-ct)] type was solved. According to calculations, for some specially chosen wave numbers α the drift and dispersion effects balance each other, providing zero resulting velocity c _R = 0. If we assume that a rigid wall is corrugated with the same α, we can say that stationary waves caused by the wavy wall are in resonance with intrinsic perturbations of the second kind. The work was financially supported by the Russian Foundation for Basic Research (Grants Nos. 05-08-33585a and 06-08-96637-r-yug-a.)     

Spatial structure of the flow at round jet outflow into a narrow channel

Results on visual studies of the flow structure in case of the round submerged jet in a narrow channel are presented. These studies were carried out for the laminar and turbulent flows. The typical large-scale structures and zones of intensive turbulent mixing were identified in the flow. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 08-08-00417-a).