Water flooding is one of the most important processes in oil production. Water is injected into an oil reservoir to maintain the reservoir's pressure and sweep some of the oil toward the production well. In an actual oil reservoir, in situ water, or connate water, is usually present and significantly impacts the water flooding process. We developed a visualization scheme utilizing a microfocused X-ray CT scanner to three-dimensionally observe the effects of connate water during water flooding at the pore scale. The water phase was injected upward into packed glass beads containing an oil phase both with and without connate water, and the process was scanned every minute until steady state was reached. Three-dimensional images were then constructed from X-ray CT data to clearly show the phenomena. Connate water significantly reduces oil recovery. In the porous medium without connate water, water flooding was able to produce approximately 1.5 times more oil than in the medium with connate water because of steadier interface movement. When injected water came in contact with connate water, the displacement front suddenly expanded into the pores containing connate water, thereby creating a jump-like movement leading to fingering. The pressure gradient between the inlet and outlet forced water to select the shortest route to the outlet. Water reached the outlet earlier when connate water exists. Short-circuiting due to fingering leads to formation of entrapped oil pockets and oil recovery yields.
In the present study, the flow characteristics of a spatially evolving plane jet are investigated, focusing on the dynamics of coherent structure (CS), flow transition, and evolution. Instantaneous and statistical properties obtained by direct numerical simulation (DNS) are discussed noting the influence of the Reynolds number, by analyzing the velocity and scalar fields. It is discovered that the plane jet is clearly dependent on the Reynolds number, especially in the near field. The evolution and scale of CS have a strong dependence on the Reynolds number, which shows significant effects on the transport of the momentum and scalar. The increase of the Reynolds number develops a more contorted interface between the ambient fluid and plane jet, with a smaller scale. A moderate Reynolds number is a good condition for the study of the transition from a laminar jet to a turbulent jet in detail. The results show that, because of a low Reynolds number, the growth of two initial shear layers at the jet boundary is accelerated and the velocity fluctuation is advanced from two-dimensional to three-dimensional. Furthermore, the Reynolds number dependency of the plane jet is more significant on the condition of low Reynolds number.
We developed a technique for the measurement of fluctuating hydraulic-pressure at an arbitrary point in turbulent flow. A pressure-measuring system was composed of a miniature static-pressure probe (SP-probe), a strain-gage-type pressure transducer, and a tube connecting them. A model equation of dynamic response of the pressure-measuring system was introduced, and a calibration technique for determining parameters in the model equation was developed. Effects of the size of the SP-probe, length of the tube, and sensitivity of the pressure sensor were systematically investigated using several SP-probes, tubes, and pressure transducers with different sizes, lengths, and sensitivities, and fluctuating hydraulic-pressure measurement was performed in a wake of a circular cylinder.
Flow-induced acoustic resonance in a piping system containing closed coaxial side-branches was investigated experimentally. Resonance characteristics of the piping system were examined by a microphone. The results revealed that the resonance frequencies of the shear layer instability were locked in corresponding to the natural frequencies of the side-branches. Phase-averaged velocity fields were obtained two-dimensionally in the junction of coaxial side-branches by dynamic particle image velocimetry (PIV), while the acoustic resonance was induced at the first and second hydrodynamic modes. Patterns of jet correspond to two hydrodynamic modes were derived from the phase-averaged velocity fields. The dynamic PIV can acquire time-series velocity fluctuations, then, two-dimensional phase delay maps under resonance and off-resonance conditions in the junction of coaxial side-branches were obtained. Experimental results show that the proposed phase delay map method costs less experiment and computation time and achieves a better accuracy and repetition than the phase-locking technique. In addition, the phase delay map method can obtain phase difference under the different frequency components. This is important when two different acoustic modes were induced in one experimental condition.
We developed a practical method for the computation of liquid-vapor two-phase flows accompanied by phase change at the interface. In this paper, we propose an intrinsic improvement by introducing a boundary condition at the non-equilibrium interface, which was derived by Sone and Onishi (Journal of the Physical Society of Japan, Vol.44, (1978),pp.1981-1994.) on the basis of the kinetic theory of gases. The boundary condition, which gives the relationship between the phase change rate and the jump in physical properties, was appropriately integrated with a numerical simulation based on continuum mechanics. The interface was captured by the volume-of-fluid (VOF) method with the piecewise linear interface construction (PLIC) scheme to improve the conservation property of volume. This method was applied to simulating film condensation around a horizontal cylinder. Our results showed that heat and fluid phenomena, including condensation to a liquid film, were successfully reproduced. The order of the spatially averaged Nusselt number on the cylinder was in good agreement with the theoretical value. We compared the results of our method with those of a method that obtains the phase change rate without considering the boundary condition on a molecular scale. We found that our method was effective at simulating film condensation.
To examine pressure fluctuations in the near acoustic field, the wavenumber-frequency spectrum method was applied to the flow field around a square cylinder placed near a flat plate. Since the pressure fluctuations in the near field contain both acoustic and fluid fluctuations, it is rather difficult to separate those components and estimate the fluctuation level of each component's fluctuation. However, they can be analyzed in the wavenumber domain by the statistical post processing method. That is, the velocity and wavenumber in the sound can be uniquely determined, while many wavenumbers can exist in the turbulent flow. In the present study, the flow structure and the sound field were investigated by applying Computational Fluid Dynamics (CFD) based on the Lattice Boltzmann Method (LBM). The wavenumber-frequency spectrum was calculated by using time series data on the pressure fluctuations from CFD results. The flow structure and the sound field in near field could be clarified from the wavenumber-frequency spectrum. The differences in the convective velocity, the directivity of sound waves and the levels of sound and turbulent flow pressure fluctuations were investigated by changing the distance between the square cylinder and the flat plate. Thus in this paper it is ensured that the wavenumber-frequency spectrum method is useful to analyze the time and spatial averaged flow and sound fields in the near acoustic field.
The present study clarified the smoke generation rate in a tunnel fire, which is essential data for the planning of emergency measures. The smoke generation rate was determined by the least squares method using the results of full-scale tunnel fire experiments and three-dimensional CFD simulation. The following results were obtained. The smoke generation rate per unit area increases gradually with pool fire area, 3.12 to 4.35 g/(s•m2) in the case of 1 m2, 4.18 to 5.85 g/(s•m2) in the case of 4 m2. When pool fire area becomes 9 m2, the smoke generation rate per unit area increases rapidly to 10.1 g/(s•m2). The smoke yield by gasoline reducing rate in the case of a gasoline pan fire with an area of 4 m2 is approximately 4.4 - 6.8 % and reaches around 11 % when the area increases to 9 m2. The heat release rate and smoke generation rate in the case of a large bus fire is nearly equal to a gasoline pan fire of 9 m2.
Magento-rheological Fluid (MRF) and Shear Thickening Fluid (STF) have separately attracted considerable interest due to their fast and reversible response to an external magnetic field or an abrupt shearing loading. In this paper we fabricated a combined phase of Magento-rheological Shear Thickening Fluid (MRSTF) such that it has an MR and a shear thickening effect. To fabricate it, 14 nm primary size fumed silica particles were suspended in ethylene glycol to form a 25% by weight fraction of STF base. Carbonyl iron particles (3-5 μm) were then mixed with the STF base to obtain four MRSTF samples with weight fractions of 5%, 10%, 20%, and 30%. The viscoelastic properties of all four samples, namely their steady state and dynamic behaviour, were investigated with a parallel-plate rheometer. The relevance of the dynamic behaviour to the stress amplitude, frequency, and external magnetic field were investigated and discussed. MRSTFs behave like linear viscoelastic materials for a small range of stress amplitudes, but at large stress amplitudes they are non-linear viscoelastic or viscoplastic, where the storage modulus gradually decreases with the stress amplitude. Within the linear viscoelastic range of shear stress, MRSTFs behave with linear viscoelastic properties as the frequency increases. MRSTFs also exhibit features of both components, but are more prone to MRF with the inception of external field excitations.
In this paper, the simulations of incompressible turbulent flow are presented by applying the seamless immersed boundary method (SIBM) to the large eddy simulation (LES) on the Cartesian grid. The static Smagorinsky model with the wall damping function is adopted as modeling the subgrid-scale (SGS) component in the present approach. In order to validate the SIBM for LES, the turbulent channel flow which is one of the most fundamental wall turbulent flow is considered with Reτ = 180 defined by the friction velocity. In comparison with the reference DNS and LES data, the present result is closer to the DNS data than the LES one. Moreover, the present SIBM results are in good agreement with the results of conventional approach with wall boundary condition. Secondly, the numerical simulations of flow around a sphere which is a basic shape with curvilinear boundary are carried out with the Reynolds number Re = 3700 and 10000 where the flow around a sphere is the turbulent flow. As a result, it is found that the present results are in very good agreement with the reference LES ones with the dynamic SGS model. Then, it is concluded that the present SIBM is very promising for the LES of incompressible turbulent flows.
The circular jet flows generated by a piezoelectric disk were studied experimentally. The velocity distributions were measured using a single hot-wire anemometer, and the effects of the oscillatory flow conditions though a circular orifice were examined. The effects of the dimensionless stroke and Reynolds number of the oscillatory flow on the synthetic jet flows were examined. The stroke was the length of the fluid ejected in an oscillatory cycle and non-dimensionalised by the orifice diameter. The mean velocity distributions were examined for a dimensionless stroke range of 0.60-2.40 with a constant Reynolds number (Re) of 2700. The stroke was found to have a remarkable effect on the streamwise variation in the jet centerline velocity and jet width. As the stroke was increased, the starting point of the jet growth was shifted downstream. This change is discussed by examining the instantaneous velocity signals and attributes in relation to the change in the collapse of vortex rings emitted from the orifice. The momentum of the synthetic jet increased sharply above a critical stroke for the jet formation, and seemed to be saturated for strokes longer than the orifice diameter. The flow field was also examined for a Re range of 1900-3000 with a constant dimensionless stroke of 1.02. In the Re range studied, no significant changes in the jet flows were observed.
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