Applied Mechanics and Materials Vols. 275-277

Abstract: The vortex shedding modes of flow past two circular cylinders in side-by-side arrangement are investigated numerically in this paper. The simulations are carried out using a ghost cell immersed boundary method which imposes the boundary condition through reconstruction of the local velocity field near the immersed boundary. The two-dimensional unsteady incompressible Navier-Stokes equations are solved using an implicit fractional step method based on cell-center, collocated arrangement of the primary variables. Vorticity contours of the flow around the cylinders and force time histories are presented. Anti-phase and in-phase vortex shedding modes were found to exist in the flow simulation. These results of simulations were in agreement with phenomena observed in experiment and numerical results of previous researchers.

Abstract: In order to find the best synthetic jet model for active flow control numerical simulation study, exit velocity model, simply connected domain model and moving boundary model were researched through solving the two dimensional transient Reynolds Average Navier-Stokes(RANS) equations under consistent grid and boundary conditions. Velocity and vortex characteristics of flow field were got. Three models were all able to capture the velocity characteristics compared with experiment data. The moving boundary model can capture the distribution of vortices accurately and was the ideal model for applications, because it considered the spatial distribution and time distribution of diaphragm motion, also because it included the volume change rate of actuator cavity.

Abstract: Over the past two decades, the modeling of flow in a perforated pipe with influx through orifices on the pipe wall has been recognized as an important issue especially in the field of horizontal wells. This article provides a careful analysis of the current models that are all based on laboratory experiments. Results show that the models can be mainly divided into two categories according to the number of openings perforated along the conduit surface . One is developed based on experiments with one single perforation, which includes Asheim model, Yalniz model and Zhou model. This kind of models could not be readily used to calculate the pressure losses of the actual flows such as horizontal wellbore flow without modification and thus has a poor applicability. Another is based on experiments with multiple perforations, which includes Siwon model, Yuan model, Ouyang model, Su model and Wang model. Although these models are appropriate for the pressure losses prediction along the completion, all of them are semi-empirical, which implies the huge complexities of developing accurate ones. In addition, Siwon model and Yuan model are relatively the most comprehensive models which could be used to account for the various factors affecting the flow behaviors in perforated pipes. The equivalent friction factor due to pipe wall perforations of Su model has a more theoretical foundation with more room for improvement. This analysis about the models regarding the pressure drops in perforated pipes indicates that more efforts should be made to acquire a better understanding of the complex flow mechanism and build a unified model which is more theoretical and robust.

Abstract: According to the geological parameters of Shengli Oilfield, sweep efficiency of chemical flooding was analyzed according to injection volume, injection-production parameters of polymer flooding or surfactant-polymer compound flooding. The orthogonal design method was employed to select the important factors influencing on expanding sweep efficiency by chemical flooding. Numerical simulation method was utilized to analyze oil recovery and sweep efficiency of different flooding methods, such as water flooding, polymer flooding and surfactant-polymer compound flooding. Finally, two easy calculation models were established to calculate the expanding degree of sweep efficiency by polymer flooding or SP compound flooding than water flooding. The models were presented as the relationships between geological parameters, such as effective thickness, oil viscosity, porosity and permeability, and fluid parameters, such as polymer-solution viscosity and oil-water interfacial tension. The precision of the two models was high enough to predict sweep efficiency of polymer flooding or SP compound flooding.

Abstract: To analyze hydrodynamic characteristics of small scale body motion near free surface, finite volume method was adopt to compute incompressible Reynolds Averaged N-S (RANS) equations, numerical methods were conducted to simulate changes of drag coefficient and surface shape when moving near free surface. VOF method with Geo-Reconstruct form was used to deal with free surface. Fully developed turbulent flow can be solved by RNG k-ε model, and near wall region by near-wall functions. Quick upwind schemes were used to overcome instability problem when simulating high Reynolds flow. The results showed that VOF method, combined with RNG k-ε model, can be put to use to numerically simulate underwater body moving near free surface, and catch shape change of free surface in high Froude number.

Abstract: Intermittent gas-liquid flow with an unsteady, intermittent and high-pressure drop nature is common in vacuum transport pipelines. The characteristics of intermittent flow in vacuum pipelines were analyzed. A one-dimensional transient hydrodynamic model for two-phase transport of vacuum pipelines, which consists of the film model, the liquid slug model and the mix vortex model was deduced for the first time. The model outlines the relationship between hydrodynamic parameters and presents the calculation method of pressure drop, which would be helpful to uncover the transport mechanism of vacuum pipelines and propose a more seemly system design and simulation method for availability, reliability and energy-saving considerations.

Abstract: Facing the difficulty of flight dynamics modeling about flexible hypersonic flight vehicles, from view on the Lagrange’s equations based on dynamic first principle, this paper firstly developed kinetic energy and flexibility potential energy of the vehicle, then achieved concise flight dynamics equations by quasi-coordinates which could fully include coupling characteristics of flight dynamics, and lastly made necessary analysis about the equations. The result of study illustrates that flight dynamics equations of flexible hypersonic flight vehicles based on quasi-coordinates can satisfy the research of dynamics, stability, control,couplings and so on.

Abstract: The aim of this paper is to prove that compressible Euler equations in two and three space dimensions converge to incompressible Euler equations in the limit as the Mach number tends to zero. No smallness restrictions are imposed on the initial velocity, or the time interval. We assume instead that the incompressible flows exists and is reasonably smooth on a given time interval, and prove that compressible flows converge uniformly on that time interval.

Abstract: A compressible supersonic confluent flow composed of boundary layers and mixing layers are studied by linear stability theory. The flow is confined in a two-dimensional adiabatic channel. A slower flow lying in the center mixes with faster boundary layer flows on both sides and two mixing layers are evolved near the centerline. Different unstable modes were discovered and the first mode was found to be most unstable. Three-dimensional disturbances were investigated and comparison of instability features was made with unconfined boundary layer flows. The investigation of different slow flow widths was also made and a smaller spacing between the boundary layer and mixing layer was found to suppress the growth of disturbance.

Abstract: As one of the important part in aviation industry, nozzles are widely applied on the icing environment experiment. In this paper, we design and validate a novel internal-mixing nozzle for the icing experiment. To begin with, based on the requirements of experiment, the main structure sizes of nozzle are designed and the nozzle is processed for measuring droplet diameter. And then in order to investigate the atomization characteristics of droplet diameter, we model inner flow field of the nozzle and external flow field. Grids are divided to guarantee the simulation accuracy. Finally, the experiment is simulated by FLUENT software, and the simulation results of inner and external flow field are discussed respectively. The experiment shows that the simulation results of the nozzle are in good agreement with the test results.