Generator geometry effect on wave dispersion of a gas in a liquid

The influence of the channel diameter and length of the hydrodynamic oscillation generator on gas bubble dimensions in the case of wave dispersion of a gas in a liquid is experimentally investigated. The technique of measuring the bubble diameters based upon the computer analysis of the gas-liquid jet photos is presented. It is shown that on the gas flow rate range from 0.5 to 32 dm³/min the mean diameter of the gas bubbles produced by wave dispersers in water is estimated by an interval from 0.45 to 0.75 mm in optimum performance regimes.     

Wave dispersion of a gas in a liquid

A novel method of dispersing a gas in a liquid by pressure pulses generated by waves propagating from a hydrodynamic oscillation generator is proposed. Devices that realize this method, wave dispersers, are created and investigated experimentally. The amplitude-frequency characteristics of the wave processes in the dispersers and the size distribution density functions of the gas bubbles are obtained. It is shown that there are optimal pressure values at the disperser inlet at which a minimum bubble size is achieved. The average diameter of the gas bubbles produced by water wave dispersers in the optimal operation regimes varied on the range from 0.3 to 0.6 mm, depending on the gas flow-rate.     

Investigation of breakup of gas bubbles and its effect on the structure of moderate-intensity solitary pressure waves in a liquid with gas bubbles

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 45–49, January–February, 1991.     

Experimental study of the interaction of pressure waves of moderate intensity in a liquid with gas bubbles

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 83–87, September–October, 1991.     

Reflection of pressure waves of moderate intensity at a solid wall in a liquid with bubbles of a readily soluble gas

The present paper is concerned with an experimental study of the process of gas dissolution behind a shock wave in a liquid with bubbles of a readily soluble gas, the influence of gas dissolution on the wave evolution, and strengthening of the shock wave after reflection from a solid wall. Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 5, pp. 19–24, September–October, 1998.     

The added mass coefficient of a dispersion of spherical gas bubbles in liquid

Models published in the two-phase flow literature for the added mass coefficient of a dilute bubbly dispersion are discussed and compared. It is shown that the differences between the models are mainly due to the different ways in which the added mass is defined. Also, approximate expressions for the added mass coefficient of non-dilute bubbly dispersions are given. Finally, the use of the models in an equation for the average motion of the bubbles is briefly discussed.     

Viscosity of the liquid phase in a dispersion

The motion of a dispersion (continuous medium and particles) may be described [1] via the equations ot conservation of matter and momentum for the two phases separately. Here it is necessary to know how the viscosity, pressure in the solid, and other quantities vary with the parameters of the motion. This difficulty occurs even for the very simple model where the internal stresses in the dispersed phase are taken as zero, as there is then an uncertainty as to the viscosity of the medium, which is not a material constant and is dependent on the concentration. There is also uncertainty as to the forces of interaction between the phases. There are numerous empirical relationships for these forces, and also a theoretical one [2]. Here an analogous method is applied to derive an expression for the viscosity of the liquid. This viscosity applies to a liquid filtering through a porous medium in the particular case where the concentration is such as to produce close packing of the solid particles. The result corresponds to standard formulas in the case of low concentrations.     

Methods of calculating the roots of the dispersion equation for free oscillations of a gas bubble in a liquid

The problem of free radial oscillations of gas bubbles in a liquid is considered. The structure of the roots of the dispersion equation in the presence of heat transfer between the phases is studied in detail. It is shown that this equation has two complex-conjugate roots and an infinite number of real roots; all of the roots lie in the left complex half-plane, providing damping of radial oscillations. Approximate expressions for these roots are obtained.     

Special characteristics of the breakup of liquid drops with a high gas pressure

In a majority of power plants, the conversion of a liquid fuel into combustion products takes place at high pressure and with a high velocity of the motion of the gas. It is natural that in the choice of the working scheme of the process account must be taken of the effect of possible changes in the characteristics of the atomization process of a liquid fuel, connected with a change in the density of the gas. Of particular importance is the effect of perturbations of the pressure and the velocity on the behavior of liquid drops in a high-density gas flow. The number of communications in which such questions are discussed is very limited, since an overwhelming number of experiments were made at atmospheric pressure [1–7]. Only articles [8, 9] give qualitative concepts with respect to the effect of perturbations of the pressure on the breakup of drops with a gas pressure up to 30 atm. From the information given in [8, 9] it is difficult to form a judgment with respect to the change in the critical conditions and the time parameters of the process of the breakup of drops with a rise in the initial pressure (density) of the gas.     

粒子法中压力振荡问题的研究

传统移动粒子半隐式法MPS(Moving Particle Semi-implicit Method)中一直存在压力振荡问题,针对此问题对MPS方法进行改进。改进的MPS方法,采用一种新型抑制压力振荡的压力泊松方程离散格式;在核函数的选择方面,采用能够增加计算稳定性的二次样条核函数;并且针对MPS方法中粒子插值不完整问题,对粒子插值不完整性进行了修正。应用改进的MPS方法对溃坝问题进行数值模拟验证。结果表明,应用改进的MPS方法能够得到更为光滑的压力场空间分布。对模拟过程中的检测点压力进行采集,并且与实验值进行对比分析,发现改进的MPS方法能够有效地抑制模拟过程中的压力振荡,而且与实验值接近。同时应用改进的MPS方法对静水问题进行验证模拟,发现改进的MPS方法能够有效地抑制模拟过程中的压力振荡,而且监测点的压力与理论解接近。改进的MPS方法对今后应用MPS方法模拟实际工程问题,并且获得准确稳定的压力值有着重要的意义。     

Roughness and turbulence intensity effects on the induced flow oscillation of a single cylinder

The effects of the surface roughness and the turbulence intensity on the dynamic characteristics of the flow induced oscillations of an elastically supported single circular cylinder in a cross flow in the vortex shedding and fluid elastic regions were experimentally investigated. The results of these experiments indicate that, for the vortex shedding region, increasing the surface roughness results in a reduction of the amplitude of oscillation, while in the fluid elastic region, increasing the surface roughness tends to enhance the oscillations. A similar trend for the dynamic response of the cylinder in the vortex shedding region was also observed when the free stream turbulence intensity was varied, while in the fluid elastic region variations in the free stream turbulence intensity were observed to have no drastic effect on the dynamic response of the cylinder.     

Roughness and turbulence intensity effects on the induced flow oscillation of a single cylinder

The effects of the surface roughness and the turbulence intensity on the dynamic characteristics of the flow induced oscillations of an elastically supported single circular cylinder in a cross flow in the vortex shedding and fluid elastic regions were experimentally investigated. The results of these experiments indicate that, for the vortex shedding region, increasing the surface roughness results in a reduction of the amplitude of oscillation, while in the fluid elastic region, increasing the surface roughness tends to enhance the oscillations. A similar trend for the dynamic response of the cylinder in the vortex shedding region was also observed when the free stream turbulence intensity was varied, while in the fluid elastic region variations in the free stream turbulence intensity were observed to have no drastic effect on the dynamic response of the cylinder.     

Investigation of the effect of pressure angle on gear performance in asymmetric gears

Meccanica - In this study, asymmetric gear mechanisms having the same working conditions, material and dimensions as symmetric gears but with different pressure angles were designed and compared...