Complex fluids are characterized by microstructures whose configuration can be driven out of equilibrium by macroscopic flow, and consequently contribute an additional stress that modifies the flow in return. When immiscible complex fluids coexist in a flow system, the fluid-fluid interface introduces an additional length scale into the fluid dynamics, typically intermediate between the microstructures of the bulk fluids and the macroscopic flow. Thus, multicomponent complex fluids often exhibit intriguing features in the interfacial flow, and offer an opportunity to study hydrodynamic coupling across length scales. In this review, we illustrate the novel interfacial dynamics in complex fluids using three examples that involve three types of complex fluids: polymer solutions, liquid crystals and ferrofluids. The focus will be on the dynamics of drops, which coalesce, break up, and self-assemble into regular patterns in these examples. In each case, we present experimental observations of novel interfacial phenomena. Then we explore the underlying fluid-dynamic mechanisms using theoretical models and numerical simulations. Comparing the experimental and computational results, we highlight the roles of the interface in relating complex rheology on the molecular scale to hydrodynamics on the macroscopic scale. Finally we point out outstanding questions and suggest future investigations.
Measurement technique that can be adapted to high temperature and pressure environment in the rocket combustion chamber has been limited to qualitative. Therefore, establishment of a quantitative measurement technique of rocket combustion is demanded. Laser Induced Fluorescence (LIF) method targeting OH radical is the most promising measurement technique on rocket combustion. In the present study, we explored the temperature measurement method by LIF with promising OH(2,0) band measurement for high-pressure environment. The experiment was performed at atmospheric pressure for the verification test. In the present study, Laser Induced Fluorescence Spectroscopy (LIFS) temperature measurement using overlapping excitation line was found to feasible by applying the theory of Planer Laser Induced Fluorescence (PLIF)-2 line method. In addition, the LIFS measurement was found to be advantageous for measurement in high-pressure environment as it allowed discrimination from chemiluminescence.
The effects of cavitation bubble dynamics on material peening and pitting is investigated numerically using a coupled fluid and material dynamics approach. The model is applied here to the study of peening and pitting of metallic materials resulting from non-spherical cavitation bubble collapse near the material. Bubble reentrant jet impact and shock wave emission from the jet impact and from the collapse of the remaining bubble ring can induce permanent micro-deformation, pitting, and residual stresses, which modify the roughness of the material and harden it through pre-stressing. These effects are investigated through a parametric study for different bubble material standoff distances. Quantities such as bubble collapse peak pressure, pit depth, and residual stresses depend strongly on bubble standoff distance, which is an important factor in whether hardening or erosion of the material occurs.
In this work, three-dimensional, time-dependent magnetohydrodynamic (MHD) simulations of a direct-current (dc) plasma spray with an externally applied magnetic field are performed, and also the trajectories and heating histories of in-flight particles in a plasma spray jet are analyzed by Lagrangian method with one-way coupling between particle and plasma jet. The working gas is pure argon (Ar) and the material of in-flight particles is zirconium dioxide (ZrO2). The representative values of operating current and magnetic flux density of externally applied magnetic field in this work are 350 A and 0.8 T, respectively. Numerical results obtained in the MHD simulation demonstrate that the use of externally applied magnetic field yields the rotation of the arc root on the anode. This rotation generates a plasma jet with a swirling component. Furthermore, it is shown from the numerical results that applying the magnetic field increases the operating voltage and thus boosts an amount of input power compared to the one without applying it. The analytical results of in-flight particles suggest that the impact positions of in-flight particles on the substrate in the case with the externally applied magnetic field change temporally due to the swirling component of the plasma jet, even when the injected position of particles is fixed. However, the utilization of externally applied magnetic field enhances heat transfer to particles, which leads to impacting of particles on substrate with well-molten state because of higher enthalpy plasma jet.
There is a growing pressure on industry to reduce carbon dioxide emissions from combustion processes while meeting the growing energy demand, resulting in an increase in the development of carbon capture technology. Current practices available, such as chemical looping combustion (CLC) or cryogenic air separation units, separate oxygen from the atmosphere and feed it into combustor to eliminate any nitrogen in the reactor and produce a rich CO2 exhaust that can be captured and contained for future use. However, by implementing these technologies there is a significant energy penalty. One potential alternative is an oxygen transport membrane reactor that has the potential to provide a large amount of high purity oxygen at minimal energy costs. This work investigates the performance of perovskite-type La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and SrSc0.1Co0.9O3-δ (SSC) membrane reactors for the combustion of methane in various configurations. The ceramic membranes exploited here are oxygen semi-permeable, dense ceramic membranes with mixed oxygen ionic and electronic conductivity at high temperatures. Planar and tubular reactors were fabricated and studied with a methane fuel. The oxygen permeability feasibility of the membrane reactors were studied and confirmed. The CO2 selectivity at various test conditions were also reported with the maximum selectivity achieved 87.0 % selectivity.
The present study is dedicated to understand the combustion characteristics of turbulent premixed swirl flames for ammonia (NH3)/air mixture in gas turbine combustors by a numerical investigation. Although, NH3 has been identified recently as a sustainable fuel because of the carbon-free nature, some physical and chemical characteristics of NH3, such as very low laminar burning velocity, production of large amount of fuel NO during the combustion, hampered the utilization of the NH3 as a commercial fuel. Hence, the large eddy simulation (LES) numerical technique was used to produce a detailed and multi-scale information about the reacting flow field and the chemical species distributions of turbulent premixed NH3/air flames by three dimensional calculations. The study realized that a swirl burner successfully stabilizes the NH3/air premixed flames without any additives. In addition, the study found that even though there is an enormous NO emission than that of the ordinary hydrocarbon fuel at the stoichiometric condition, in the rich flame condition, NO emission is significantly decreased, whereas unburnt NH3 increases with respect to the equivalence ratio. Accordingly, there is an impressive operating condition for NH3/air mixtures, which gives a minimal NO and unburnt NH3 emissions even for turbulent swirl flames. The present study found that, at the initial mixture temperature of 500 K, the equivalence ratio of 1.225 gives the minimal NO and NH3 emissions, and this is the best operating point for the selective catalytic reduction (SCR) process in the downstream of the burner.
An identification method is presented to specify three-dimensional vortical flow topology of a spiral vortex (wing tip vortex) in a wind turbine, from two-dimensional velocity data in planes at different azimuthal angles. This method needs only the two-dimensional velocity field (data) in the parallel planes, and need not change the angle (horizontality) of the planes. The three-dimensional velocity structure is specified by physical properties associated with the velocity gradient tensor, and the formulation of the linear transformation between rotated coordinate systems associated with a spiral vortex derives the unknown components in the three-dimensional velocity gradient tensor. This method specifies the three-dimensional local vortical flow topology in detail including swirl plane, vortical axis and its orthogonality. Swirlity specifies the unidirectionality and intensity of the azimuthal flow, and sourcity does those of the radial flow. It also identifies the vortical flow symmetry that are associated with the important vortical features such as the pressure minimum.
This article summarizes recent results of data evaluation techniques obtained with optical investigations on the combustion behavior of hybrid rocket fuels. Tests are performed in a 2D slab burner configuration with windows on two sides. Liquefying paraffin-based fuels are tested in combination with gaseous oxygen (GOX). High speed videos of combustion tests are recorded in order to investigate the combustion phenomena of this kind of fuels. Hybrid combustion of liquefying fuels is dominated by transient flow dynamics like Kelvin-Helmholtz instability and vortex shedding, also due to the characteristic turbulent diffusion flame. In order to better evaluate these flow phenomena, characteristic frequencies and wavelengths of the main structures of the flow field and of the combustion flame appearing in the video data have to be found. In this work, a spatial and temporal analysis of these structures is carried out by using two different techniques, applied within an automated video evaluation routine. First of all, the Proper Orthogonal Decomposition (POD) technique is used. Its results deliver linearly uncorrelated variables, which are the principal components of the flow field. This method enables to recognize the main structures of the flow field and the combustion flame appearing in the video data. Secondly, the Independent Component Analysis (ICA) technique is applied to the same data. It is able to search for statistically independent, or as independent as possible, structures hidden in the data. It increases the independence to higher statistical orders with respect to POD. The basis functions found with the ICA are expected to describe the essential structure of the data and to resemble some physical processes involved in the combustion. With both methods it is possible to compute spatial and temporal coefficients, which can be later analyzed by applying a Power Spectral Density (PSD) in order to obtain the excited frequencies and wavelengths during the combustion. Finally, the results of the two methods are compared in order to better understand and interpret them. The results collected so far and the comparison of both techniques show that their application is consistent and useful for the automated evaluation of combustion data.
Elucidation of the mechanical interaction between an erythrocyte and an endothelial cell is an important issue that may lead to clarification of mechanisms of cardiovascular diseases and development of new treatments. In order to clarify the interaction, frictional characteristics of erythrocytes moving on various plates have been measured using an inclined centrifuge microscope. The objective of this study was to clarify the mechanical interaction between an erythrocyte moving in medium subject to inclined centrifugal force and endothelial cells on a plate. Three-dimensional (3D) analysis was performed with contact force models between an erythrocyte and glycocalyx on the surface of endothelial cells and two-dimensional (2D) analysis was conducted using a lubrication theory for compressible porous media and a simple erythrocyte model. In the 3D analysis, two contact force models were adopted in which shear stresses acting on the bottom surface of an erythrocyte varied proportional or inversely proportional to the distance to the base plate. As a result, the experimental frictional characteristics for an endothelia-cultured plate were properly reproduced by the inverse proportion model. In the 2D analysis using the lubrication theory, the result without the porous media qualitatively agreed with those of the experiment for the plain and material-coated plates and that of the 3D analysis without contact force models, whereas the result with the porous media was qualitatively different from those of the experiment and the 3D analysis.
The paper is concerned with the generation of sound by the flow through a closed, cylindrical expansion chamber, followed by a long tailpipe. The sound generation is due to self-sustained flow oscillations in the expansion chamber which, in turn, may generate standing acoustic waves in the tailpipe. The main interest is in the interaction between these two sound sources. An analytical, approximate solution of the acoustic part of the problem is obtained via the method of matched asymptotic expansions. The sound-generating flow is represented by a discrete vortex method, which is modified to include the effects of acoustic feedback. It is demonstrated that lock-in of the self-sustained flow oscillations to the resonant acoustic waves in the tailpipe can take place.
The objective of this study is to mimic methane hydrate cores at atmospheric pressure conditions with the same permeability as oceanic methane hydrate cores. This became possible by freezing a solution of water, ethanol, and sodium bicarbonate in Toyoura sand at -10°C. First, partial freeze was measured and theoretically evaluated in a solution of water, NaHCO3 and ethanol. Then, the permeability of the methane hydrate core mimicking samples was evaluated based on the partial freeze evaluation. Finally, the permeability of the methane hydrate core mimicking samples was measured by injecting a solution of water and ethanol at -10°C inside the partially frozen samples. The experimental results suggested that it is possible to control the permeability of the created porous media by changing the volume fraction of ethanol in the solution. Furthermore, the permeability of the methane hydrate core mimicking samples was of the same order as that of real oceanic methane hydrate cores for a weight percent of ethanol in the solution of 8wt%.