2,000 research outputs found
Inertial particle segregation and deposition in large-eddy simulation of turbulent wall-bounded flows
No full textCurrent capabilities of Large-Eddy Simulation (LES) in Eulerian-Lagrangian studies of dispersed flows are limited by the modeling of the Sub-Grid Scale (SGS) turbulence effects on particle dynamics. In this paper, the possibility is examined to account explicitly for SGS effects by incorporating ad-hoc closure models in the Lagrangian equations of particle motion. Specifically, a candidate model based on approximate deconvolution is considered and applied to particle-laden turbulent channel flow. Results show that, even if the fraction of SGS turbulent kinetic energy for the fluid velocity field (not resolved in LES) is recovered, quantitative prediction of local segregation and, in turn, of near-wall accumulation may still be inaccurate. This failure indicates that reconstructing the correct amount of fluid and particle velocity fluctuations is not enough to reproduce the effect of SGS turbulence on particles and that further information on the flow structure at the sub-grid scales must be incorporated
When Does Eddy Viscosity Damp Subfilter Scales Sufficiently?
No full textLarge eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. The very essence is that the LES-solution contains only scales of size ≥Δ, where Δ denotes some user-chosen length scale. This property enables us to perform a LES when it is not feasible to compute the full, turbulent solution of the Navier-Stokes equations. Therefore, in case the large eddy simulation is based on an eddy viscosity model we determine the eddy viscosity such that any scales of size <Δ are dynamically insignificant. In this paper, we address the following two questions: how much eddy diffusion is needed to (a) balance the production of scales of size smaller than Δ; and (b) damp any disturbances having a scale of size smaller than Δ initially. From this we deduce that the eddy viscosity νe has to depend on the invariants q = ½tr(S^2) and r =−⅓tr(S^3) of the (filtered) strain rate tensor S. The simplest model is then given by νe = 3/2(Δ/π)^2|r|/q. This model is successfully tested for a turbulent channel flow (Reτ = 590).
Numerical Simulations of Transitional Axisymmetric Coaxial Jets
No full textDirect numerical simulations of spatially evolving axisymmetric coaxial jets are carried out using nonreflecting radiative boundary conditions at the outflow. The sensitivity of the numerical solution to the domain size is investigated, pointing out the feedback effect of the boundary conditions on the pressure at the inlet. The effects of the Reynolds number on the characteristics of the flow are studied. In the initial phase following an impulse, the evolution of the startup vortex is found to be independent of the Reynolds number, whereas the circulation per unit length at the vortex center increases with the Reynolds number. The Reynolds number is also found to affect the further development of the shear-layers' instabilities. Finally, the effects of the inlet conditions on the dynamics of vortical structures are investigated. Two simulations are carried out, in which the inlet velocity profile is unperturbed and perturbed randomly, and the results are compared with flow visualizations from experiments. In the unperturbed case the rollup of the external shear layer occurs at a much larger distance from the jets exit than in experiments, whereas in the perturbed case a good agreement with the experiments is obtained
Statistical properties of an ideal subgrid-scale correction for Lagrangian particle tracking in turbulent channel flow
No full textOne issue associated with the use of Large-Eddy Simulation (LES) to investigate the dispersion of small inertial particles in turbulent flows is the accuracy with which particle statistics and concentration can be reproduced. The motion of particles in LES fields may differ significantly from that observed in experiments or direct numerical simulation (DNS) because the force acting on the particles is not accurately estimated, due to the availability of the only filtered fluid velocity, and because errors accumulate in time leading to a progressive divergence of the trajectories. This may lead to different degrees of inaccuracy in the prediction of statistics and concentration. We identify herein an ideal subgrid correction of the a-priori LES fluid velocity seen by the particles in turbulent channel flow. This correction is computed by imposing that the trajectories of individual particles moving in filtered DNS fields exactly coincide with the particle trajectories in a DNS. In this way the errors introduced by filtering into the particle motion equations can be singled out and analyzed separately from those due to the progressive divergence of the trajectories. The subgrid correction term, and therefore the filtering error, is characterized in the present paper in terms of statistical moments. The effects of the particle inertia and of the filter type and width on the properties of the correction term are investigated
The effects of diuretic and beta-blocker tretment on cardiac and vascular structural changes in untreated essential hypertensive patients
No full textState-homomorphisms on -algebras
No full textsummary:Riečan [12] and Chovanec [1] investigated states in -algebras. Earlier, Riečan [11] had dealt with analogous ideas in -posets. In the monograph of Riečan and Neubrunn [13] (Chapter 9) the notion of state is applied in the theory of probability on -algebras. We remark that a different definition of a state in an -algebra has been applied by Mundici [9], [10] (namely, the condition (iii) from Definition 1.1 above was not included in his definition of a state; in other words, only finite additivity was assumed). Below we work with the definition from [13]; but, in order to avoid terminological problems we use the term “state-homomorphism” (instead of “state”). The author is indebted to the referee for his suggestion concerning terminology. Let be an -algebra which is defined on a set with . In the present paper we show that there exists a one-to-one correspondence between the system of all state-homomorphisms on and the system of all -closed maximal ideals of . For -algebras we apply the notation and the definitions as in Gluschankof [3]. The relations between -algebras and abelian lattice ordered groups (cf. Mundici [8]) are substantially used in the present paper
A 60 mV Input Voltage, Process Tolerant Start-Up System for Thermoelectric Energy Harvesting
No full textThis paper presents a 60 mV input voltage start-up system for thermoelectric energy harvesting. A new process tolerant inverter cell is proposed, which is functional at supply voltages as low as 60 mV. Using the proposed unit cell, a ring oscillator has been implemented. The ring oscillator is followed by 40 charge-pump stages, an ultra-low-power level detector, and a boost converter. The energy harvesting system can generate an output voltage of 1 V and delivers a maximum power of 4.5 μW from a 60 mV supply. This system has been implemented in a standard 0.18 μm CMOS technology, uses neither zerothreshold voltage (normally-on) negative-channel metal-oxide semiconductor nor microelectromechanical systems switches and occupies 3.3 mm2.Accepted author manuscriptBio-Electronic
On some properties of quasi-MV algebras and √′ quasi-MV algebras. Part II
No full textThe present paper is a sequel to Paoli F, Ledda A, Giuntini R, Freytes H (On some properties of QMV algebras and √′ QMV algebras, submitted). We provide two representation results for quasi-MV algebras in terms of MV algebras enriched with additional structure; we investigate the lattices of subvarieties and subquasivarieties of quasi-MV algebras; we show that quasi-MV algebras, as well as cartesian and flat √′ quasi-MV algebras, have the amalgamation property. © Springer-Verlag 2007.We gratefully acknowledge the precious information and insights we gathered from conversations or e-mail exchanges with Roberto Giuntini and Danica Jakubikova-Studenovska. We are especially indebted to Matthew Spinks for his extensive and detailed comments on a preliminary draft of the paper. The first author is partially supported by Grants MTM2004-03101 and TIN2004-07933-C03-02 from the Spanish Ministerio de Educación y Ciencia and Grant 2001SGR-00017 from the Generalitat de CatalunyaPeer Reviewe
Measles virus causes immunogenic cell death in human melanoma
No full textNoOncolytic viruses (OV) are promising treatments for cancer, with several currently undergoing testing in randomised clinical trials. Measles virus (MV) has not yet been tested in models of human melanoma. This study demonstrates the efficacy of MV against human melanoma. It is increasingly recognised that an essential component of therapy with OV is the recruitment of host antitumour immune responses, both innate and adaptive. MV-mediated melanoma cell death is an inflammatory process, causing the release of inflammatory cytokines including type-1 interferons and the potent danger signal HMGB1. Here, using human in vitro models, we demonstrate that MV enhances innate antitumour activity, and that MV-mediated melanoma cell death is capable of stimulating a melanoma-specific adaptive immune response
A 10-mV-Startup-Voltage Thermoelectric Energy Harvesting System With a Piezoelectric Starter
No full textAn ultra-low-startup-voltage thermoelectric energy harvesting system assisted by a piezoelectric generator (PEG) is presented in this paper. When the energy harvesting system is implemented in a place where there is mechanical vibration, the associated PEG can generate a stable clock signal and drive the boost converter to start from the cold state even at extremely low thermoelectric generator (TEG) voltage. The proposed system is designed and simulated in a 180-nm BCD process. The simulations show that the proposed system can start the TEG system from the cold state from as low as 10 mV of TEG voltage while keeping a 63.9% efficiency. The peak power conversion efficiency is achieved at 74.9% when the TEG voltage is 50 mV.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Instrumentatio
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