Jeffery-Hamel flow of non-Newtonian fluid with nonlinear viscosity and wall friction

A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary conditions based on similarity relationships. Unlike the usual power law model, this paper develops nonlinear viscosity based only on a tangential coordinate function due to the radial geometry shape. Two kinds of solutions are developed, i.e., analytical and semi-analytical （numerical） solutions with suitable assumptions. As a result of the parametric examination, it has been found that the Newtonian normalized velocity gradually decreases with the tangential direction progress. Also, an increase in the friction coefficient leads to a decrease in the normalized Newtonian velocity profile values. However, an increase in the Reynolds number causes an increase in the normalized velocity function values. Additionally, for the small values of wedge semi-angle, the present solutions are in good agreement with the previous results in the literature.

A preliminary study of variations of the Changjiang Diluted Water between August of 1999 and 2006

A large area hypoxia has been already reported respectively by two interdisciplinary surveys off the Changjiang Estuary since summer of 1999 and 2006. The bypoxic zone shows distinct year-to-year variations. Observed oceanographic data are first analysized and reveal a big difference for the Changjiang Diluted Water （CDW） between these two periods. These great changes are related to the tremendous reduction of the freshwater discharge and variations of wind fields between these two years. It is also found that the monthly mean intrusion of Kuroshio and its branches has increased in the northern East China Sea （ECS）, but decreased in the southern ECS in August of 2006 as compared with 1999 on the base of general circulation models. Then, the Regional Ocean Modelling Systems is applied to the East China Sea to evaluate the contributions and relative importance of impacts from the river discharge, wind forcing and open boundary data. Our simulations reproduce the phenomena that more fresh water extends northeastward in 2006 and forms a negative SSS anomaly to the northeast of the river mouth as compared with 1999, which is consistent with observations. The five group numerical tests suggest that the wind forcing dominates the CDW variations followed by the Kuroshio and its branches. The study implies important roles played by hydrodynamic processes on the variability of hypoxic zone in the study areas.

Weak Nonlinearity of Ablative Rayleigh-Taylor Instability

单个模式的弱非线性的政体夺格的 Rayleigh-Taylor 不稳定性被学习，与考虑预热效果和脱离前面的宽度。Rayleigh-Taylor 线性生长率与直接数字的模拟同意很好。为密度不安，而那些分别地第二和第三泛音有二和三山峰价值，基本模式的振幅分发有一山峰价值。泛音产生对波浪数字也被给，它接近直接数字的模拟的结果。

Non-linear characteristics of Rayleigh-Taylor instable perturbations

The direct numerical simulation method is adopted to study the non-linear characteristics of Rayleigh-Taylor instable perturbations at the ablation front of a 200 μm planar CH ablation target. In the simulation, the classical electrical thermal conductivity is included, and NND difference scheme is used. The linear growth rates obtained from the simulation agree with the Takabe formula. The ampli- tude distribution of the density perturbation at the ablation front is obtained for the linear growth case. The non-linear characteristics of Rayleigh-Taylor instable perturbations are analyzed and the numerical results show that the amplitude distributions of the compulsive harmonics are very different from that of the fundamental perturbation. The characteristics of the amplitude distributions of the harmonics and their fast growth explain why spikes occur at the ablation front. The numerical results also show that non-linear effects have relations with the phase differences of double mode initial perturbations, and different phase differences lead to varied spikes.

Unified gas-kinetic simulation of slider air bearing

The unified gas-kinetic scheme （UGKS） is presented and used in this letter to study the slider air bearing problem. The UGKS solutions are first val- idated by comparison with direct simulation Monte Carlo results. After valida- tion, the UGKS is used to study the air-bearing problem under different non- equilibrium conditions. On the surface of the slider, the dependency of the gas pressure and normal force on the Mach and Knudsen numbers are fully evaluated. The non-equilibrium effect on the force loading in the whole transition regime up to the free molecular limit is also studied.

Biogeochemistry of Plane Trees as a Tool to Detect Atmospheric Pollution

The plane tree, which is a valuable tool to detect atmospheric pollution, is one of the most common trees in European cities. Soil and leaf samplings were carried out in Barcelona and its environs (NE Spain) to establish the soil-plant relationship. Dry and ashed leaves and soils were analyzed by Instrumental Neutron Activation Analysis and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP/OES) at the ACTLABS laboratories in Ontario, Canada. Given that diesel is the main fuel used in vehicles in Europe, we sought to establish the role of diesel in atmospheric pollution. Diesel samples were obtained from service stations and analyzed after preconcentration using ICP/MS at the geochemistry laboratories of the University of Barcelona. The average content of diesel oil shows high values of Pb, Cu, Cr, Ag, Cd and Mn. High values of Pb, Cu, Au, Hg and Sb in leaves and soils were detected downtown and along main roads outside the city, whereas low levels of these elements were observed in rural areas.

Ferrofluid moving thin films for active flow control

Ferrofluid moving thin films and their possible significance with regard to active flow control for lift and attack angle enhancement are discussed.In this strategy,a very thin film of ferrofluid is strongly attached at the wall of the wing by a normal magnetic field from below and pumped tangentially along the wing.Utilizing a simplified physical model and from the available experimental data on moving walls,the expected lift enhancement and effect on the attack angle were assessed.Additional research and design is required in order to explore the possibilities in the use of ferrofluid moving thin films.

Three-dimensional human thermoregulation model based on pulsatile blood flow and heating mechanism

A three-dimensional thermoregulation mathematical model of temperature fluctuations for the human body is developed based on predecessors＇ thermal models. The following improvements are necessary in real situations： ellipsoids and elliptical cylinders are used to adequately approximate body geometry, divided into 18 segments and five layers; the core layer consists of the organs; the pulsation of the heart cycle, the pulsatile laminar flow, the peripheral resistance, and the thermal effect of food are considered. The model is calculated by adopting computational fluid dynamics（CFD） technology, and the results of the model match with the experimental data. This paper can give a reasonable explanation for the temperature fluctuations.

The extractable hydrokinetic power from an oscillating membrane-based harvester

The extractable hydrokinetic power from an oscillating membrane in standing motion and induced by a water flow and its possible significance with regard energy harvesting is discussed.The main attractiveness of such an energy harvester lies in the possibility of an inexpensive technology able to be used in those water flows which either because limitation of space(narrow channels) or a limited differential pressure drop with the surrounding but yet with a non negligible velocity are not well suited to be turbined. Utilizing a simplified geometrical model, an estimate of the extractable output density power per area of membrane was derived. Preliminary experiments were performed using a rectangular thin rubber membrane and for a typical domestic water intake as source. The experimental data quantitatively agree very well with the theoretical prediction where it was found that for water flows around 2 m/s the output power density from the membrane may be around 30 mW/cm^2 of membrane. Additional research and development is required in order to arrive at a reliable practical and commercial design.

Numerical simulation of the dual-core structure of the Bohai Sea cold bottom water in summer

Regional Ocean Modeling Systems (ROMS 3.0) and the κ-ε turbulence closure scheme has been applied to investigating the seasonal evolution of the thermsocline in the Bohai Sea. The simulation reproduces the stratifications lasting from early April to early September and reveals the existence of marked Asymmetric Dual-Core Cold Bottom Water (ADCCBW) in the south and north depression basin respectively under the thermocline. The bottom temperature in the north depression is about 1―4℃ lower than that in the south depression basin which is in good agreement with observations. Model results suggest that the local bathymetry characteristics and inhomogeneous net heat flux due to the latitude difference are the major cause for the early formation of the ADCCBW. Numerical Lagrangian drifter experiments support the finding that the ADCCBW is maintained throughout the stratification periods by the inflow of cold bottom water from the northern Yellow Sea and deep channel in the western side of Liaodong Peninsula. The inflow cold water contributes to the north depression basin distinctively larger than to the south one. Tidal mixing enhances the bottom temperature asymmetry between the two basins.

Experimental Study of Rotor Flow Separation Control using a New Type of Dielectric Barrier Discharge Plasma Actuator

Flow separation occurring on rotor blades is an important limiting factor for helicopter performance. This paper presents a new type of dielectric barrier discharge(DBD) plasma actuator for rotor blade flow separation control called bipolar DBD plasma actuator. The bipolar DBD plasma actuator's connection mode differs from traditional plasma actuators and eliminates reverse discharge between electrodes. The experiments in this work were carried out by smoke-wire flow visualization and PIV technology in the open test section of a low speed wind tunnel, and solved the problem of high voltage electricity supplied to the plasma actuator while the rotor rotated. In this experiment, the rotor, camera, and laser were synchronized to obtain results. Smoke-wire results and PIV results illustrated that the flow separation weakened with increasing rotor speed; the separated flow area was large at a rotating speed of 300 r/min and gradually became smaller at the rotating speed of 600 r/min, the flow separation disappeared at the rotating speed of 1200 r/min. When the plasma was active, both smoke-wire results and PIV results showed the flow separation area was greatly reduced at the rotating speed of 300 r/min and disappeared at the rotating speeds of 600 r/min and 1200 r/min, the rotor flow separation at high angles of attack could be effectively controlled by the new DBD plasma actuator.

Square cavity flow driven by two mutually facing sliding walls

We investigate the flow inside a 2D square cavity driven by the motion of two mutually facing walls independently sliding at different speeds.The exploration,which employs the lattice Boltzmann method(LBM),extends on previous studies that had the two lids moving with the exact same speed in opposite directions.Unlike there,here the flow is governed by two Reynolds numbers(Re_(T),Re_(B))associated to the velocities of the two moving walls.For convenience,we define a bulk Reynolds number Re and quantify the driving velocity asymmetry by a parameterα.Parameterαhas been defined in the rangeα∈[-π4,0]and a systematic sweep in Reynolds numbers has been undertaken to unfold the transitional dynamics path of the two-sided wall-driven cavity flow.In particular,the critical Reynolds numbers for Hopf and NeimarkSacker bifurcations have been determined as a function ofα.The eventual advent of chaotic dynamics and the symmetry properties of the intervening solutions are also analyzed and discussed.The study unfolds for the first time the full bifurcation scenario as a function of the two Reynolds numbers,and reveals the different flow topologies found along the transitional path.

Transonic flows in narrow channels

This article is the written version of a lecture given at the Festkolloquium on the occasion of Prof. Dr.-Ing.Dr.techn. E.h. Jiirgen Zierep's 80th birthday held at the Universitat Karlsruhe, 21 January 2009. It deals withlaminar viscous inviscid interactions in transonic narrow channel flows. Special emphasis is placed on the internalstructure of pseudo-shocks and properties of nozzle flows. Also, it is shown that the theory, first formulated forperfect gases, can easily be extended to the case of general single phase fluids.

Are Runners More Prone to Become Infected with COVID-19?An Approach from the Raindrop Collisional Model

It is known that COVID-19 spread mainly from person-to-person through respiratory droplets produced when an infected person coughs or sneezes,and as a result certain ideas about contagious of COVID-19 have been spread.One of them is the widespread belief that close runners,owing to the stronger exhalation,can be more prone to be infected with COVID-19 because the collision with the suspended respiratory droplets should the runner in front be infected.However,because of the low Stokes number this idea cannot be generalized without carefully thought and in fact can be put into question.Utilizing the raindrop collisional model and with the help of computational fluid dynamics (CFD),it is shown that the probability of collision with respiratory droplets is not always increasing with the approaching velocity of the runner but rather there is a maximum velocity threshold at which the efficiency of collision drops.