Blood is a suspension of blood cells in a Newtonian fluid of plasma. The red blood cells (RBCs) are most numerous and behave like small deformable capsules containing a Newtonian fluid. How to treat blood flowing through vessels depends on the scale involved. The flow characteristics of blood in the microvessel with a diameter comparable with the RBC size may be determined by the behavior of individual RBCs, for which a multi-phase flow model may provide a good approximation. Some multiphase flow problems of blood flow are studied.
The key to the study of an alluvial process is to elucidate interactions between flow properties, sediment movements and bed or channel configurations. For this reason, any physical model of sediment transport is required to describe reasonably the non-equilibrium state of an alluvial process. From this point of view, the sediment model has been recently reinvestigated on the basis of knowledge accumulated on the mechanism of sediment motion. In this paper. the latest research on development of sediment models is reviewed. Particularly, importance is attached to unified treatment of bed material load, taking into account the transition from bed load motion to suspension both through incipient motion and transport process, and a physical model for description of non-equilibrium situation is proposed by applying a stochastic approach. Further in order to predict the scouring process of river banks, formation of armor coat, incipience of debris flow, etc., the effects of channel boundaries such as side slope, sand mixtures and permeable bed on sediment transport process are discussed.
Stability of liquid film in a counter-current two-phase flow of falling liquid film and upward mist flow, which is generated by spraying the liquid into gas flow, in a vertical pipe have been investigated both experimentally and theoretically. The liquid film flow rate, pressure drop, and interfacial wave velocity were measured for vapor-water and air-water systems. It is shown that, with increasing the spray flow rate under the condition of constant gas-phase velocity, the falling liquid film becomes unstable due to the impact of droplets flowing upward. With the onset of instability, flow reversal of liquid film, entrainment of droplets, and rapid increase of pressure drop occur. This instability occurs even in a stable range of conventional flooding correlation for a counter-current two-phase flow. Based on comparison between experimental results for a vapor-water system at a pressure lower then the atmospheric pressure, and an air-water system at the atmospheric pressure, the droplets' impingement effect on the stability of liquid film is correlated with the ratio of the momentum of the colliding droplets on the liquid film to the interfacial shear stress. A theoretical analysis on the stability of liquid film impinged by droplets is made. Nonlinear stability of a finite-amplitude interfacial wave is treated in the analysis. The theory predicts the existence of a stable finite-amplitude interfacial wave. It also predicts that the flow becomes unstable with increasing the gas velocity and the momentum of impinging droplets. The stability limit predicted by the analysis agrees well with the experimental results.
Measurements of velocity distribution and pressure loss of a turbulent flow of Bingham plastic fluid in rough-walled pipes were made. For the measurements, six rough-walled pipes obtained by gluing geads on the pipe walls with synthetic resin glue and kaolin suspensions of five different densities were used. The relative roughness of pipes and the rheological coefficients of the kaolin suspensions are shown. The experimental results for pressure loss indicate that the friction coefficient value depends on the relative roughness alone and is almost the same as the value of Newtonian fluid flow in the regime and that the coefficient of Bingham plastic fluid in the transition regime is affected by the Reyonlds number, the Hedstrom number and the roughness Hedstrom number. The experimental results for velocity distribution show that the velocity profile of Bingham plastic fluid in the region of transition from hydraulically smooth to rough depends on the roughness Reynolds number, the Hedstrom number and the roughness Hedstrom number, and that the velocity profile in the fully rough region agrees with Eg.(8), which is obtained from the velocity profile of Newtonian fluid flow in the fully rough region by Nikuradse. A mixing length which is suitable for calculating the velocity profile and pressure loss of Newtonian fluid flow in rough-walled pipes is proposed. A guide in assessing the mixing length of Bingham plastic fluid flow in roughwalled pipes is given.
The effect of solid particles on the flow structure of a confined jet was experimentally investigated. Spherical glass particles and light hollow glass particles with almost the same size of 60-80μm were loaded for a constant volume fraction. The confined jet flowed at a jet outlet Reynolds number of 2.2×104 in gravitational direction without a recirculating flow. A laser Doppler velocimeter system capable of particle size discrimination was used to measure both two-component velocities of gas and particles, and their fluctuations. The measured results indicate that the rate of flow development of jet decreased in the two-phase flow and that turbulence intensities of gas phase are reduced by loading particles. Reynolds shear stress and production rate of turbulent energy decreased over the entire cross-sectional area. It was confirmed that heavy particles contributed to the strong reduction of turbulent motion of gas phase.
The paper presents techniques and apparatus for measuring the Lagrangian motion of particles (solid particles, droplets, or bubbles) suspended in a turbulent flow field. The Lagrangian measurement was made by an optical tracking method for illuminated particles, using solid-state image sensors. The experiment was conducted in nearly isotropic turbulent water flow field behind a grid to measure the Lagrangian motion of individual fluid particles (small polystyrene balls without the effect of buoyancy) by two procedures. The measured data and the analysis are found to give useful information on the turbulent particle diffusion and mixing processes.
The one-dimensional transient two phase flow analyzer MINCS has been developed as a computational tool for the development and assessment of constitutive models. In order to assess the numerics of MINCS, it has been applied to the numerical benchmark problems for the two-fluid model proposed by the Workshop on Two-Phase Flow Fundamentals under the auspices of the US Department of Energy and the Electric Power Research Institute. Although the adequacy of constitutive equations has primary importance compared with the accuracy of numerics in two-phase flow simulation, numerical stability is required for computer codes in order to assess the adequacy of constitutive equations. Even with such a stable numerical solution method, difficulties related to the numerics often appear in a complex manner coupled with those of constitutive relations in, for example, safety analyses of light water reactors. Therefore, it is worthwhile to investigate each numerical difficulty by isolating it from physical problems. In this report, the benchmark calculations by MINCS are discussed focusing on the numerical treatment of the missing phase in a single-phase flow and spatial and/or temporal transitions from a single phase to two-phase and vice versa. The selected problems for this purpose are the disappearance of liquid droplets due to evaporation, inception of boiling due to external heating, expulsion of steam by subcooled water and sedimentation. A systematic numerical treatment of missing phase mentioned above and the transition has been developed and assessed through the benchmark calculations.