Sinusoidal Flow Research Articles

Numerical study on nitric oxide transport in human nasal airways

Any slight clinical problem in the nasal system may result in inconveniences in our daily lives, being related with respiratory ventilation and nitric oxide (NO) concentration in the respiratory air. It is known that NO is produced and absorbed by the mucosal layer, especially in the nasal system and its concentration is upregulated or downregulated along with nasal inconveniences or nasal deformities. This study numerically investigates the air flows and the transport of gaseous NO in the human nasal system comprising nasal cavity and paranasal sinuses in order to understand the relations among nasal air flow rates, NO concentrations, and nasal structures. Using commercial mesh generation and fluid dynamics simulation codes, we predicted flow fields in the nasal system according to respiration volumes flowing through nasal cavity and entrance diameters of maxillary sinus. Three dimensional simulations with sinusoidal respiratory flow rates show that NO concentrations in frontal sinus are greater than 10000 ppb that are considerably higher than those in other systems, since the former has only one ostium of small diameter while other systems have two gateways of nasal air flowing in and out. Therefore, major mechanism for NO transportation in the former is diffusion, while those in the latter are both convection and diffusion. Concentrations of NO exhaled from nasal cavity are less than 100 ppb and those in maxillary sinus are greater than 2000 ppb, which agree well with experimental observations available in literature.

Irreversible passive energy transfer of an immersed beam subjected to a sinusoidal flow via local nonlinear attachment

Passive vibration control of immersed structures in deep water subjected to the external fluid flow has rarely been studied. With the aim of passively absorbing, vibration of a doubly fixed beam under a sinusoidal flow using a nonlinear attachment is studied in this paper. The beam is modeled using the Euler-Bernoulli beam theory. The essentially nonlinear attachment has purely cubic stiffness and linear damping. Required conditions for occurring relaxation oscillations, Hopf and saddle-node bifurcations in the system response are studied. Analytical and numerical approaches are used to analyze the steady-state responses of the considered model. In addition, the influence of the location, the damping and the stiffness of the nonlinear absorber and external load are investigated on the dynamical behavior of the system. Furthermore, influence of the attachment stiffness on quasi-periodic motion boundaries surveyed. It is shown that in the presence of the nonlinear energy pumping the amplitude of the system response decreases significantly and as the attachment location approaches the beam supports the occurrence of the relaxation oscillations decreases and saddle-node bifurcations take place in the system response. The presented results and the proposed modeling approach can be used to design and enhance the performance of nonlinear vibration absorbers for subsea structures.

Spatial pyramidal cross correlation for particle image velocimetry

A spatial pyramidal cross-correlation based on interrogation area sub-division is introduced to improve the measurement resolution in particle image velocimetry (PIV). The high-resolution velocity can be achieved with a velocity prediction model via coarse cross-correlation. The prediction formula is deduced from the frequency response of the moving average (MA). The performance of this method was assessed using synthetically generated images of sinusoidal shear flow, two-dimensional vortical cellular flow, and homogeneous turbulence. A real PIV experiment of turbulent boundary layer was used to evaluate the new method. The results indicate that the spatial pyramid cross-correlation can robustly increase the spatial resolution.

Origins of Portal Hypertension in Nonalcoholic Fatty Liver Disease.

Nonalcoholic fatty liver disease (NAFLD) advanced to cirrhosis is often complicated by clinically significant portal hypertension, which is primarily caused by increased intrahepatic vascular resistance. Liver fibrosis has been identified as a critical determinant of this process. However, there is evidence that portal venous pressure may begin to rise in the earliest stages of NAFLD when fibrosis is far less advanced or absent. The biological and clinical significance of these early changes in sinusoidal homeostasis remains unclear. Experimental and human observations indicate that sinusoidal space restriction due to hepatocellular lipid accumulation and ballooning may impair sinusoidal flow and generate shear stress, increasingly disrupting sinusoidal microcirculation. Sinusoidal endothelial cells, hepatic stellate cells, and Kupffer cells are key partners of hepatocytes affected by NAFLD in promoting endothelial dysfunction through enhanced contractility, capillarization, adhesion and entrapment of blood cells, extracellular matrix deposition, and neovascularization. These biomechanical and rheological changes are aggravated by a dysfunctional gut-liver axis and splanchnic vasoregulation, culminating in fibrosis and clinically significant portal hypertension. We may speculate that increased portal venous pressure is an essential element of the pathogenesis across the entire spectrum of NAFLD. Improved methods of noninvasive portal venous pressure monitoring will hopefully give new insights into the pathobiology of NAFLD and help efforts to identify patients at increased risk for adverse outcomes. In addition, novel drug candidates targeting reversible components of aberrant sinusoidal circulation may prevent progression in NAFLD.

Numerical investigation for convective heat transfer and friction factor under pulsating flow conditions

For pulsating flow, the behaviours of the convective heat transfer and friction factor for a periodic corrugated channel are investigated numerically. The finite volume method is used in the numerical study. Three different Reynolds Averaged Numerical Simulation based turbulence models, namely the k-ω model, the Shear Stress Transport (SST) model and the transition SST model are used and compared. The results are also compared with the previous experiments for non-pulsating flow. Analyses are conducted for air flow through a corrugated channel which has sharp corrugation peaks with an inclination angle of 30° and a 5mm minimum channel height. Reynolds number is changed in the range 6294 to 7380, while keeping the Prandtl number constant at 0.70. A sinusoidal pulsatile flow condition which is F=400 and uA*=0.5 is used. Variations of the Nusselt number and the friction factor with the Reynolds number are studied. Non-pulsating flow results and pulsating flow results are compared with each other.

空気流速の周期変動に対する伸長円筒状拡散火炎の応答特性（速度変動振幅が火炎応答に及ぼす影響）

An experimental study investigated the frequency characteristics of a stretched cylindrical diffusion flame in response to sinusoidal air flow velocity oscillation. The flame has a convex curvature with respect to the air stream. The fuel was methane diluted with nitrogen, and oxidizer air. The flame was formed in the air stream side from the stagnation surface. The oscillation frequency f ranged from 10 Hz to 250 Hz. In order to clarify the influence of an oscillation amplitude A of the air flow velocity on the flame responses, three kinds of amplitude were chosen. The flame was photographed by the high speed video camera, and flame radius rf, flame thickness δ, and flame luminosity Lf were analyzed. The air flow velocity va at the nozzle outlet was measured by using particle image velocimetry. Though velocity gradient of the air flow ga responds quickly to the changing va regardless of f and A, the gradient of the fuel flow gf delays with increasing f and A. Here, ga correlates to the flame stretch effect, and gf impacts the fuel transportation. Response of rf to varying va also delays with increasing f and A. δ/rf, which relates to the flame curvature effect, responds complicated with the change in f and A. Oscillation amplitudes of Lf have maximum values with respect to f regardless of A. These maximum values are greater than those of a steady flame, over the same air velocity fluctuation ranges. This complex change in the Lf with respect to f is closely related to the phase difference in the respective time variations in δ/rf and gf, and the magnitude of these values.

Effect of shear stress on the migration of hepatic stellate cells.

When the liver is damaged, hepatic stellate cells (HSCs) can change into an activated, highly migratory state. The migration of HSCs may be affected by shear stress due not only to sinusoidal flow but also by the flow in the space of Disse because this space is filled with blood plasma. In this study, we evaluated the effects of shear stress on HSC migration in a scratch-wound assay with a parallel flow chamber. At regions upstream of the wound area, the migration was inhibited by 0.6Pa and promoted by 2.0Pa shear stress, compared to the static condition. The platelet-derived growth factor (PDGF)-BB receptor, PDGFR-β, was expressed in all conditions and the differences were not significant. PDGF increased HSC migration, except at 0.6Pa shear stress, which was still inhibited. These results indicate that another molecular factor, such as PDGFR-α, may act to inhibit the migration under low shear stress. At regions downstream of the wound area, the migration was smaller under shear stress than under the static condition, although the expression of PDGFR-β was significantly higher. In particular, the migration direction was opposite to the wound area under high shear stress; therefore, migration might be influenced by the intercellular environment. Our results indicate that HSC migration was influenced by shear stress intensity and the intercellular environment.

Experimental setup for generation and control of sinusoidal pulsatile channel flow

A scheme of an experimental setup for generation and control of sinusoidal pulsatile channel flow has been presented. A pulsator with the shaped rotating flap ensured a cross section area variation by harmonic law is used. Based on the solution of Bernoulli’s unsteady equation and the numerical solution of the URANS equations, the effect of inertia forces on the law of average velocity variation over the pulsation phase in the test section of the experimental setup has been estimated.

Numerical study on air turbines with enhanced techniques for OWC wave energy conversion

In recent years, the oscillating water column (OWC) wave energy converter, which can capture wave energy from the ocean, has been widely applied all over the world. As the essential part of the OWC system, the impulse and Wells turbines are capable of converting the low pressure pneumatic energy into the mechanical shaft power. As an enhanced technique, the design of endplate or ring attached to the blade tip is investigated numerically in this paper. 3D numerical models based on a CFD-software FLUENT 12.0 are established and validated by the corresponding experimental results from the reports of Setoguchi et al. (2004) and Takao et al. (2001). Then the flow fields and non-dimensional evaluating coefficients are calculated and analyzed under steady conditions. Results show that the efficiency of impulse turbine with ring can reach up to 0.49 when ϕ=1, which is 4% higher than that in the cases for the endplate-type and the original one. And the ring-type Wells turbine with fixed guide vanes shows the best performance with the maximal efficiency of 0.55, which is 22% higher than that of the original one. In addition, the quasi-steady analysis is used to calculate the mean efficiency and output-work of a wave cycle under sinusoidal flow condition. Taking all together, this study provides support for structural optimization of impulse turbine and Wells turbine in the future.

Unsteady RANS Simulations of Wells Turbine Under Transient Flow Conditions

This paper presents our recent numerical simulations of a high-solidity Wells turbine under both steady and unsteady conditions by solving Reynolds-averaged Navier–Stokes (RANS) equations. For steady conditions, the equations are solved in a reference frame with the same angular velocity of the turbine. Good agreement between numerical simulation result and experimental data has been obtained in the operational region and incipient stall conditions. The exact value of stall point has been accurately predicted. Through analyzing the detailed fluid fields, we find that the stall occurs near the tip of the blade while the boundary layer keeps attached near the hub, due to the effect of radial flow. For unsteady conditions, two types of control methods are studied: constant angular velocity and constant damping moment. For the constant angular velocity, the behaviors of the turbine under both high and low sea wave frequency are calculated to compare with those obtained by quasi-steady method. The hysteresis characteristic can be observed and deeply affects the behaviors of the Wells turbine with high wave frequency. For the constant damping moment, the turbine angular velocity is time dependent. Under sinusoidal flow, the incident flow velocity in the operational region can be improved to avoid the stall.

Identification of partial blockages in pipelines using genetic algorithms

A methodology to identify the partial blockages in a simple pipeline using genetic algorithms for non-harmonic flows is presented in this paper. A sinusoidal flow generated by the periodic on-and-off operation of a valve at the outlet is investigated in the time domain and it is observed that pressure variation at the valve is influenced by the opening size of blockage and its location. In this technique, the unsteady (steady oscillatory) pressure time series at only one location is required to identify two blockages. In the proposed methodology, the solution of the governing hyperbolic PDEs of pipe flow is obtained using the method of characteristics. For any piping system similar to the hypothetical pipe system used in the simulations, generalized best amplitude and best frequency of the valve operation are determined, which give maximum deviation in pressure responses for a specific blockage at different locations for a given constant-head reservoir. The generalized best amplitude and best frequency of the valve operation are also obtained for two blockages. Accuracy of the proposed methodology in identifying blockages in a hypothetical simple pipe system with increased noise in the simulated measurements is studied. A non-dimensional variable is proposed to determine whether the proposed methodology is applicable to isolate partial blockages in a piping system. Finally, the proposed methodology is experimentally validated on a laboratory piping system for a single blockage and two blockages.

Stability theory for a two-dimensional channel

A scheme for deriving conditions for the nonlinear stability of an ideal or viscous incompressible steady flow in a two-dimensional channel that is periodic in one direction is described. A lower bound for the main factor ensuring the stability of the Reynolds–Kolmogorov sinusoidal flow with no-slip conditions (short wavelength stability) is improved. A condition for the stability of a vortex strip modeling Richtmyer–Meshkov fluid vortices (long wavelength stability) is presented.

Micro-particle indoor resuspension under periodic airflows: A numerical-analytical study and experimentations

As particles may pose a threat to people during breathing close to surfaces, understanding and identifying the mechanisms by which these particles detach helps in taking preventive measures during cleaning and dusting processes of surfaces, and in the selection and operation of ventilation systems when particles are airborne. This work presents a numerical–analytical coupled model to examine resuspension under the effect of oscillatory flows, taking into account the probabilistic approach of resuspension occurrence due to turbulent bursts for different particle diameters and surface roughness. The results of the model were validated with experiments conducted for flows alternating between constant blowing and suction for different flow velocities and frequencies.A parametric study using the validated model was conducted to study the particle detachment phenomenon of a variety of particle characteristics under sinusoidal flows similar to that of human breathing over different flooring materials. Results showed that micro-particles of relatively high diameters pose a considerable threat over surfaces in indoor environment. The occurrence of resuspension is highly influenced by surface type and roughness. Parquet flooring was found to cause the resuspension of approximately 98% of 80μm lead particles compared to 64.5% of the same particles over marble flooring at certain locations under the effect of normal breathing. Therefore, besides dust removal methods, the choice of flooring material is an essential preventive measure to reduce indoor particle resuspension.

Enhancement of performance of wave turbine during stall using passive flow control: First and second law analysis

Wells turbine is the most common type of self-rectifying air turbine employed by Oscillating Water Column (OWC) wave energy devices due to its technical simplicity, reliability, and design robustness. Because it subjected to early stall, there were many endeavors to improve the energy extraction performance of Wells turbine within the stall regime. Using the multi suction slots as a passive flow control can help obtaining a delayed stall. Two, three and four suction slots were investigated to improve the performance of Wells turbine in the stall regime. In addition the commonly used first law analysis, the present study utilized an entropy generation minimization method to examine the impact of the multi suction slots method on the entropy generation characteristics around the turbine blade. The turbine blade with optimum suction slots number and location was investigated using the oscillating water system based on the real data from the site. To achieve this purpose, two-dimension numerical models for Wells turbine airfoils under sinusoidal wave flow conditions were built and analyze using (ANSYS FLUENT) solver. It is found that the airfoil with three suction slots located at 40%, 55% and 90% from leading edge in chord percentage give the highest torque coefficient by 26.7% before the stall and 51% after the stall.

Research on the effects of in-line oscillatory flow on the vortex-induced motions of a deep draft semi-submersible in currents

A Deep Draft Semi-submersible (DDS) under certain flow conditions could be subjected to Vortex-Induced Motions (VIM), which significantly influences the loads on and life fatigue of the moorings and the risers. To investigate the VIM of a DDS with four rectangular section columns in waves coupled with a uniform current, a numerical study using the computational fluid dynamics (CFD) method was conducted. The issues of the VIM of multi-column floaters can be conveniently converted to the issues of oscillating cylinders in fluid cross flows. This paper looks into the CFD numerical simulation of infinite cylinders having rectangular sections in a two-dimensional sinusoidal timedependent flow field coupled with a uniform current. The resulted hydrodynamic forces and motion responses in different oscillatory flows plus currents both aligned in the same direction for the incidence of 135° of the DDS relative to the flow are compared with the ones in current only cases. The results show that the VIM response of this geometric arrangement of a DDS with four rectangular columns in a current combined with oscillatory flows is more evident than that in the current only case. The oscillatory flows and waves have the significant influence on the VIM response, forces and trajectory, in-plane motions of the DDS.

Effect of sinusoidal Taylor vortex flow on cooling crystallization of L-lysine

An elliptical Couette-Taylor (ECT) crystallizer with a unique sinusoidal Taylor vortex flow was developed to promote the recovery and size distribution of L-lysine crystals in cooling crystallization. When using the ECT crystallizer, the recovery was enhanced to a maximum of 100% with a mean residence time of only 15 min. When comparing the crystallization efficiency, the recovery and size distribution of the L-lysine crystals in the ECT crystallizer were over 33% and 50% higher, respectively, than those in the conventional MSMPR crystallizer and slightly higher than those in the circular Couette-Taylor (CT) crystallizer. This improved crystallization in the ECT crystallizer was explained in terms of the sinusoidal profile of the Taylor vortex intensity. Plus, since the nucleation and growth processes determine the recovery and crystal size distribution, the mean residence time, inner cylinder rotation speed, and feed concentration were all varied to investigate their influence on the crystallization efficiency.

Structure and stability of the equilibrium set in potential-driven flow networks

In this paper we address local bifurcation properties of a family of networked dynamical systems, specifically those defined by a potential-driven flow on a (directed) graph. These network flows include linear consensus dynamics or Kuramoto models of coupled nonlinear oscillators as particular cases. As it is well-known for consensus systems, these networks exhibit a somehow unconventional dynamical feature, namely, the existence of a line of equilibria, following from a well-known property of the graph Laplacian matrix in connected networks with positive weights. Negative weights, which arise in different contexts (e.g. in consensus models in signed graphs or in Kuramoto models with antagonistic actors), may on the one hand lead to higher-dimensional manifolds of equilibria and, on the other, be responsible for bifurcation phenomena. In this direction, we prove a saddle-node bifurcation theorem for a broad family of potential-driven flows, in networks with one or more negative weights. The goal is to state the conditions in structural terms, that is, in terms of the expressions defining the flowrates and the graph-theoretic properties of the network. Not only the eigenvalue requirements but also the nonlinear transversality assumptions supporting the bifurcation motivate an analysis of independent interest concerning the rank degeneracies of nodal matrices arising in the linearized dynamics; this analysis is performed in terms of the contraction–deletion structure of spanning trees and uses several results from matrix analysis. Different examples illustrate the results; some linear problems (including signed graphs) are aimed at illustrating the analysis of nodal matrices, whereas in a nonlinear framework we apply the characterization of saddle-node bifurcations to networks with a sinusoidal (Kuramoto-like) flow.

Resonance-like dynamics in radial cyclic injection flows of immiscible fluids in homogeneous porous media

Interfacial instabilities of immiscible radial displacements in homogeneous porous media are analysed in the case of sinusoidal injection flows. The analysis is carried out through numerical simulations based on the immersed interface and level set methods. Investigations of the effects of the period of the sinusoidal injection flows revealed a novel resonance effect where, for a critical period, the number of fingers as well as their structures are considerably changed. The resonance in the flow development is clearly identified through the abrupt changes in the Fourier spectrum of the interface as well as quantitative characteristics of the flow in the form of the minimum and maximum radii of the interface. For the range of parameters examined in this study that correspond to instabilities dominated by viscous forces, the resonance period was found to correlate with a characteristic time of the flow and the fluids mobility ratio. This new physical phenomenon offers new perspectives for using the flow instability to determine important physical properties such as the viscosity and the surface tension of fluids.

Passive flow control for aerodynamic performance enhancement of airfoil with its application in Wells turbine – Under oscillating flow condition

In this work, the passive flow control method was applied to improve the performance of symmetrical airfoil section in the stall regime. In addition to the commonly used first law analysis, the present study utilized an entropy generation minimization method to examine the impact of the flow control method on the entropy generation characteristics around the turbine blade. This work is performed using a time-dependent CFD model of isolated NACA airfoil, which refers to the turbine blade, under sinusoidal flow boundary conditions, which emulates the actual operating conditions. Wells turbine is one of the most proper applications that can be applied by passive flow control method because it is subjected to early stall. Additionally, it consists of a number of blades that have a symmetrical airfoil section subject to the wave condition. It is deduced that with the use of passive flow control, torque coefficient of blade increases by more than 40% within stall regime and by more than 17% before the stall happens. A significantly delayed stall is also observed.

Frequency characteristics of a vortex flowmeter in various inlet velocity profiles

Although vortex flowmeters are widely used in various industries, the accuracy of vortex flowmeter measurements depends on inlet flow conditions. In this study, flow fields of a vortex flowmeter with various inflow conditions are simulated numerically. In order to model transient turbulent flows, Large Eddy Simulation and vortex shedding frequencies are determined using fast Fourier transform techniques. To determine the frequency characteristics in the area of downstream of the vortex generator, both steady and unsteady velocity profiles are used as inlet conditions, including two different shear flows and various sinusoidal plug flows. For steady inlet conditions, the flow qualities along the pipe are quantified using a proposed definition to express a velocity profile which departs from a fully developed velocity profile. For unsteady inlet conditions, the predominant frequency pattern is successfully predicted and it is linked to the measurement accuracy of the vortex flowmeter.