The General Ocean Turbulence Model (GOTM) is applied to the diagnostic turbulence field of the mixing layer (ML) over the equatorial region of the Atlantic Ocean. Two situations were investigated: rainy and dry seasons, defined, respectively, by the presence of the intertropical convergence zone and by its northward displacement. Simulations were carried out using data from a PIRATA buoy located on the equator at 23º W to compute surface turbulent fluxes and from the NASA/GEWEX Surface Radiation Budget Project to close the surface radiation balance. A data assimilation scheme was used as a surrogate for the physical effects not present in the one-dimensional model. In the rainy season, results show that the ML is shallower due to the weaker surface stress and stronger stable stratification; the maximum ML depth reached during this season is around 15 m, with an averaged diurnal variation of 7 m depth. In the dry season, the stronger surface stress and the enhanced surface heat balance components enable higher mechanical production of turbulent kinetic energy and, at night, the buoyancy acts also enhancing turbulence in the first meters of depth, characterizing a deeper ML, reaching around 60 m and presenting an average diurnal variation of 30 m.; O modelo General Ocean Turbulence Model (GOTM) é aplicado para diagnosticar o campo de turbulência da camada de mistura oceânica (CM) na região equatorial do Oceano Atlântico. Foram investigadas as estações chuvosa e seca...

We study compressible magnetohydrodynamic turbulence, which holds the key to many astrophysical processes, including star formation and cosmic-ray propagation. To account for the variations of the magnetic field in the strongly turbulent fluid, we use wavelet decomposition of the turbulent velocity field into Alfven, slow, and fast modes, which presents an extension of the Cho & Lazarian decomposition approach based on Fourier transforms. The wavelets allow us to follow the variations of the local direction of the magnetic field and therefore improve the quality of the decomposition compared to the Fourier transforms, which are done in the mean field reference frame. For each resulting component, we calculate the spectra and two-point statistics such as longitudinal and transverse structure functions as well as higher order intermittency statistics. In addition, we perform a Helmholtz-Hodge decomposition of the velocity field into incompressible and compressible parts and analyze these components. We find that the turbulence intermittency is different for different components, and we show that the intermittency statistics depend on whether the phenomenon was studied in the global reference frame related to the mean magnetic field or in the frame defined by the local magnetic field. The dependencies of the measures we obtained are different for different components of the velocity; for instance...

We study a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian and Vishniac (1999) using three-dimensional direct numerical simulations. The model has been already successfully tested in Kowal et al. (2009) confirming the dependencies of the reconnection speed V-rec on the turbulence injection power P-inj and the injection scale l(inj) expressed by a constraint V-rec similar to P(inj)(1/2)l(inj)(3/4)and no observed dependency on Ohmic resistivity. In Kowal et al. (2009), in order to drive turbulence, we injected velocity fluctuations in Fourier space with frequencies concentrated around k(inj) = 1/l(inj), as described in Alvelius (1999). In this paper, we extend our previous studies by comparing fast magnetic reconnection under different mechanisms of turbulence injection by introducing a new way of turbulence driving. The new method injects velocity or magnetic eddies with a specified amplitude and scale in random locations directly in real space. We provide exact relations between the eddy parameters and turbulent power and injection scale. We performed simulations with new forcing in order to study turbulent power and injection scale dependencies. The results show no discrepancy between models with two different methods of turbulence driving exposing the same scalings in both cases. This is in agreement with the Lazarian and Vishniac (1999) predictions. In addition...

Turbulence is one of the key problems of classical physics, and it has been the object of intense research in the last decades in a large spectrum of problems involving fluids, plasmas, and waves. In order to review some advances in theoretical and experimental investigations on turbulence a mini-symposium on this subject was organized in the Dynamics Days South America 2010 Conference. The main goal of this mini-symposium was to present recent developments in both fundamental aspects and dynamical analysis of turbulence in nonlinear waves and fusion plasmas. In this paper we present a summary of the works presented at this mini-symposium. Among the questions to be addressed were the onset and control of turbulence and spatio-temporal chaos. (C) 2011 Elsevier B. V. All rights reserved.; FAPESP; FAPESP; CNPq; CNPq; CAPES; CAPES; Fundacao Araucarias; Fundacao Araucarias; RNF-CNEN (Brazilian Fusion Network); RNFCNEN (Brazilian Fusion Network)

Turbulence in a superfluid in the zero-temperature limit consists of a dynamic tangle of quantized vortex filaments. Different types of turbulence are possible depending on the level of correlations in the orientation of vortex lines. We provide an overview of turbulence in superfluid 4He with a particular focus on recent experiments probing the decay of turbulence in the zero-temperature regime below 0.5 K. We describe extensive measurements of the vortex line density during the free decay of different types of turbulence: ultraquantum and quasiclassical turbulence in both stationary and rotating containers. The observed decays and the effective dissipation as a function of temperature are compared with theoretical models and numerical simulations.

We discuss several improvements in the detection of atmospheric turbulence using SLOpe Detection And Ranging (SLODAR). Frequently, SLODAR observations have shown strong ground-layer turbulence, which is beneficial to adaptive optics. We show that current methods which neglect atmospheric propagation effects can underestimate the strength of high altitude turbulence by up to ~ 30%. We show that mirror and dome seeing turbulence can be a significant fraction of measured ground-layer turbulence, some cases up to ~ 50%. We also demonstrate a novel technique to improve the nominal height resolution, by a factor of 3, called Generalized SLODAR. This can be applied when sampling high-altitude turbulence, where the nominal height resolution is the poorest, or for resolving details in the important ground-layer.

Atmospheric turbulence is a random and chaotic process brought about by energy transport mechanisms in the atmosphere. Of particular focus in this research program is the energy transport occurring in the atmospheric surface layer between ground heated air parcels and the air directly above. This dynamic process is impacted by so many apparently random initial conditions and boundary states that a precise analytical description of the process is beyond current computation. The process of turbulence can, however, be statistically analysed and characterised empirically. Observable phenomena such as scintillation have been found to have a range dependence and even the micro-meteorological structure of the turbulent eddies (chiefly responsible for the convective energy transport) have had their spatial distribution, scale size and power spectra examined in detail. As complex as the field is, one is left in no doubt, when viewing a scene through strong turbulence, that this dynamic and random process disrupts and perturbs the passage of visible radiation and is seen to severely degrade the quality of imagery. So the question raised is: “How can the strength of atmospheric turbulence be determined from either physical measurements of meteorological data or from sequences of perturbed imagery?" In order for imagery to be corrected for turbulence-induced degradation...

For the resistive pressure-gradient-driven turbulence model, the transition from laminar regime to fully developed turbulence is not simple and goes through several phases. For low values of the plasma parameter β, a single quasicoherent structure forms. As β increases, several of these structures may emerge and in turn take the dominant role. Finally, at high β, fully developed turbulence with a broad spectrum is established. A suitable characterization of this transition can be given in terms of topological properties of the flow. Here, we analyze these properties that provide an understanding of the turbulence-induced transport and give a measure of the breaking of the homogeneity of the turbulence. To this end, an approach is developed that allows discriminating between topological properties of plasma turbulence flows that are relevant to the transport dynamics and the ones that are not. This is done using computational homology tools and leads to a faster convergence of numerical results for a fixed level of resolution than previously presented in Phys. Rev. E 78, 066402 (2008).; Part of this research was sponsored by the Dirección General de Investigación of Spain under Project No. ENE2006-15244-C03-01. One of us (BAC) is grateful for the "Cátedra de Excelencia" from Universidad Carlos III and Banco Santander. The authors thankfully acknowledge the computer resources...

The presence of turbulence in multiple areas of our society--food, fuel, and finances-being but three critical areas presently being impacted means that long-held assumptions are no longer true, that the past is not prologue, and that the future is not clear. And enter into this unstable present the discipline of evaluation-a discipline formed and shaped in the past fifty years of stability, little turbulence, and strong assumptions that everything will go according to plan. If things do not go well, it is because of either a poor theory of change on how to bring about positive outcomes, or weak efforts at implementation. It is not because of the stormy present upsetting our quiet past. As it is, conventional evaluation behavior and beliefs are ill suited for these times. The transformational nature of the 'Arab Spring' is just one arena in which it is clear that a business as usual approach to evaluation is entirely inappropriate. The papers in this volume are from the 2011 Global Assembly of the International Development Evaluation Association (IDEAS). Nearly 350 development evaluators from eighty-five countries came together in Amman, Jordan to discuss and analyze the consequences of turbulence on evaluation. The intent of these papers is to systematically assess what changes have come during this time of turbulence and how these changes are impacting the craft of development evaluation. To be clear: this book is not about how to assess the impacts of crises on development and on people's lives. It is about the meaning of a changed world and changed assumptions on the concepts and methods used in evaluation.

This course presents the phenomena, theory, and modeling of turbulence in the Earth's oceans and atmosphere. The scope ranges from the fine structure to planetary scale motions. The regimes of turbulence include homogeneous flows in two and three dimensions, geostrophic motions, shear flows, convection, boundary layers, stably stratified flows, and internal waves.

13 pages, 6 figures, 3 tables.-- Printed version published Oct 2007.-- Full-text version available Open Access at: http://www.icm.csic.es/bio/projects/icmicrobis/pdf/2007BerdaletJPY.pdf; Turbulence has been shown to alter different aspects of the physiology of some dinoflagellates. The response appears to be species-specific and dependent on the experimental design and setup used to generate small-scale turbulence. We examined the variability of the response of three dinoflagellate species to the turbulence, following the same experimental design used by Berdalet (1992) on Akashiwo sanguinea (Hirasaka) Ge. Hansen et Moestrup (=Gymnodinium nelsonii G. W. Martin). In all experiments, turbulence was generated by an orbital shaker at 100 rpm, which corresponded on bulk average, to dissipation rates (ε, quantified using an acoustic Doppler velocimeter) of ≈2 cm2·s−3. Turbulence did not appreciably affect Gymnodinium sp., a small dinoflagellate. However, Alexandrium minutum Halim and Prorocentrum triestinum J. Schiller exhibited a reduced net growth rate (33% and 28%, respectively) when shaken during the exponential growth phase. Compared to the still cultures, the shaken treatments of A. minutum and P. triestinum increased the mean cell volume (up to 1.4- and 2.5-fold...

15 pages, 7 figures, 5 tables, 1 appendix.-- Printed version published Jul 2006.-- Issue title: "Workshop on Future Directions in Modelling Physical-Biological Interactions (WKFDPBI)".; Full-text version available Open Access at: http://www.icm.csic.es/bio/projects/icmicrobis/pdf/Peters%20et%20al%202006.pdf; The effect of turbulence on the nutrient flux towards osmotrophic cells is predicted to be size dependent. This should translate into growth. We experimentally followed and modelled the growth of two marine diatoms of different size (Thalassiosira pseudonana, 6 μm in diameter and Coscinodiscus sp., ca. 109 μm in diameter) under still water and turbulent conditions, using a shaker table. Experiments were done with phosphorus-limited cultures and lasted for ca. 5 days. Turbulence enhanced the growth of Coscinodiscus sp. in agreement with theory but not the growth of T. pseudonana, which was actually slightly lower under turbulence. At the end of the experiments there were about 1.7 times as many Coscinodiscus sp. cells in the turbulent treatment than in the still treatment, while for T. pseudonana almost the same cell concentration was found in both conditions. In addition, the Coscinodiscus sp. cells growing under still conditions presented a higher specific alkaline phosphatase activity than those growing in turbulence which indicates a higher need for phosphorus in the still cultures. A simple dynamic model...

13 pages, 6 figures, 1 table.-- PACS nrs.: 92.10.Lq; 67.40.Vs; 47.27.E-; 47.53.+n.-- Available online Dec 31, 2008.-- Issue title: "Special issue on marine turbulence"; It has been often argued that oceanic turbulence is similar to 2D turbulence; they share many properties and more particularly they seem to be driven by the dynamics of coherent vortices over large scales. For this reason, the application of techniques based on the extraction of coherent vortices as the Coherent Vortex Extraction (CVE) seems a natural choice for the description of ocean data. In this paper we will discuss on the properties of oceanic turbulence under the perspective of the Microcanonical Multifractal Formalism (MMF), and specifically for the description of altimetry data. We will see that MMF gives a good description of the geometry and statistical properties of altimetry data. We will show that a direct application of CVE on altimetry data has a rather low performance in comparison to other systems, which we justify as a consequence of the inhomogeneous character of ocean turbulence. We also show that a MMF-based separation criterion improves the standard CVE and allows to mitigate these problems. The results are discussed in the perspective of a cascade-based description of ocean turbulence.; A. Turiel is supported by a Ramón y Cajal contract from the Spanish Ministry of Education and Science. This is a contribution to CSIC OCEANTECH project (PIF2006)...

[EN] Turbulence at different scales, from generation to dissipation, influences planktonic communities. Many experimental studies have recently been done to determine the effects of small-scale turbulence on plankton, but it is difficult to state the relevance of the findings since there is little unbiased information on turbulence variability in the sea. In this study, we use wind velocity data series from several meteorological stations located along the Catalan coast to estimate the spatial and temporal variability of small-scale turbulence in the upper ocean. Using a peaks-over-threshold approach, we develop a statistical model to assess the frequency of wind events as a function of their persistence and intensity. Finally, the wind speed data series are converted into turbulent energy dissipation rate estimates at 1 m depth to determine the general distribution of turbulence on the Catalan coast. Geographical variability is larger than seasonal variability in frequency and persistence of wind events, owing to differences in local relief. These statistical models developed for wind events combined with empirical relationships between wind and turbulence, are tools for estimating the occurrence and persistence of turbulent events at a given location and season. They serve to put into context the past...

Renewed interest in open rotor aeroengines, due to their fuel efficiency, has driven renewed interest in all aspects of the noise they generate. Noise due to the ingestion of distorted atmospheric turbulence, known as Unsteady Distortion Noise (UDN), is likely to be higher for open rotors than for conventional turbofan engines since the rotors are fully exposed to oncoming turbulence and lack ducting to attenuate the radiated sound. However, UDN has received less attention to date, particularly in wind-tunnel and flight testing programmes. In this thesis a new prediction scheme for UDN is described, which allows inclusion of many key features of real open rotors which have not previously been investigated theoretically. Detailed features of the mean flow induced by the rotor, the form of atmospheric turbulence, asymmetries due to installation features, and the effect of rotor incidence are all considered. Parameter studies are conducted in each of these cases to investigate their effect upon UDN in typical static testing and flight conditions. A thorough review of the technological issues of most relevance and previous theoretical work on all types of turbulence-blade interaction noise is first undertaken. The prediction scheme is then developed for the case in which the mean flow into the rotor is axisymmetric. This shows excellent qualitative agreement with previous findings...

This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.compfluid.2015.12.007; Turbulence is substantially laminarised, when the mean flow experiences streamwise acceleration above a certain critical acceleration parameter. Recently, to essentially reveal aero engine intake acceleration scenarios, Direct Numerical Simulations (DNS) have been performed for turbulent flow through a rapidly contracting channel. On average, the streamwise acceleration parameter K_s is of the magnitude of 1?10^?5. Converged statistics show that it is the streamwise acceleration that causes the first term of the production rate for u?u? to be negative. This initiates the degeneration towards laminar flow and also closes the usual wall turbulence self-sustaining mechanism. Further downstream, the progressive turbulence recovery is largely streamwise dominant. Importantly, the laminarisation effects are lagging to the rate of contraction. To assess the corresponding turbulence model performance and for better modelling, for the same flow configurations, Reynolds-averaged Navier-Stokes (RANS) predictions are compared, using some available Reynolds-stress (RSM) and eddy-viscosity models. These are the second-order closure with the strain-? formulation...

Pharmaceutical inhalation aerosol technology has become an important therapy for the treatment of both respiratory and non-respiratory illness. Targeting therapeutic aerosols to the small airways of the lung can effectively treat many of these diseases. Delivery of the therapeutic agent directly to the site of action, for cases involving respiratory diseases, ensures an adequate therapeutic level of the drug is reached, without leading to side effects due to high systemic concentrations. For non-respiratory diseases, the periphery of the lung offers enormous surface area (approximately 100m2) for rapid absorption into circulation. In either case, the appropriate spray characteristics (0.5 um

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Kukulka, Tobias; Extreme winds and complex wave field, which vary in space and time, drive upper ocean turbulence in tropical cyclone conditions. Motivated by Lagrangian float observations of mixed layer averaged (i.e. bulk) vertical kinetic energy (VKE) under Hurricane Gustav, upper ocean turbulence is investigated based on large eddy simulation (LES) of the wave-averaged Navier-Stokes equations. The wave-driven residual current (Stokes drift) interacts with the sheared Eulerian currents to create Langmuir circulations, whose wide range of temporal and spatial scales characterizes them as a type of turbulence. To realistically capture wind and wave-driven Langmuir turbulence (LT), the LES model imposes the Stokes drift vector from spectral wave simulations; both, the LES and the wave model are forced by the NOAA HRD surface wind analysis product (H*WIND). Results strongly suggest that without LT effects, simulated VKE underestimates the observed VKE. LT increases the VKE indicating that it plays a significant role in upper ocean turbulence dynamics. Consistent with observations, the LES predicts a suppression of VKE near the hurricane eye due to wind-wave misalignment. However, this decrease is weaker and of shorter duration than that observed...

The sensitivity of a bidimensional cloud model with an upgraded turbulence parameterization is tested. This model, denoted as University of Buenos Aires model (UBA) has the ability to simulate a credible convective scenario in a real data case characterized by observed strong outflows. The main improvements have been made over the turbulence parameterization for the mixed phase microphysics using a first order turbulence closure. Four experiments were performed to accomplish this objective. Results show that the new turbulence parameterization affects the simulation of convection. The emphasis is in the representation of one of the significant features of the convective event used in this sensitivity test. Maximum surface wind speed corresponding to the strongest downdraft is better approached by the representation of a variable Km. In order to find out whether the sensitivity of the UBA model to the turbulence parameterization is a peculiar characteristic of this model, the Advanced Regional Prediction System (ARPS) was also implemented to check results from the UBA model. ARPS model also shows sensitivity to the turbulence parameterization with a stronger impact. Compared with all 2-D experiments, the inclusion of the third dimension enhances the vertical motions but reduces the divergent outflows at the surface. The UBA model performance proves to be higher than the ARPS 2-D version in terms of convective outflow strength near the surface in this simulated case...