On POD analysis of PIV measurements applied to mixing in a stirred vessel with a shear thinning fluid

P.O.D. technique is applied to 2D P.I.V. data in the field of hydrodynamics in a mixing tank with a Rushton turbine and a shear thinning fluid. Classical eigen-value spectrum is presented and phase portrait of P.O.D. coefficients are plotted and analyzed in terms of trailing vortices. A spectrum of dissipation rate of kinetic energy is introduced and discussed. Length scales associated to each P.O.D. modes are proposed

Large-scale transdisciplinary collaboration for adaptation research: Challenges and insights

An increasing number of research programs seek to support adaptation to climate change through the engagement of large-scale transdisciplinary networks that span countries and continents. While transdisciplinary research processes have been a topic of reflection, practice, and refinement for some time, these trends now mean that the global change research community needs to reflect and learn how to pursue collaborative research on a large scale. This paper shares insights from a seven-year climate change adaptation research program that supports collaboration between more than 450 researchers and practitioners across four consortia and 17 countries. The experience confirms the importance of attention to careful design for transdisciplinary collaboration, but also highlights that this alone is not enough. The success of well-designed transdisciplinary research processes is also strongly influenced by relational and systemic features of collaborative relationships. Relational features include interpersonal trust, mutual respect, and leadership styles, while systemic features include legal partnership agreements, power asymmetries between partners, and institutional values and cultures. In the new arena of large-scale collaborative science efforts, enablers of transdisciplinary collaboration include dedicated project coordinators, leaders at multiple levels, and the availability of small amounts of flexible funds to enable nimble responses to opportunities and unexpected collaborations

Transformation, adaptation and development: relating concepts to practice

In recent years there has been a growing number of academic reviews discussing the theme of transformation and its association with adaptation to climate change. On the one hand this has stimulated exchange of ideas and perspectives on the parameters of transformation, but it has also given rise to confusion in terms of identifying what constitutes a non-incremental form of adaptation on the ground. What this article aims to do instead is help researchers and practitioners relate different interpretations of transformation to practice by proposing a typological framework for categorising forms of change that focuses on mechanisms and objectives. It then discusses how these categorisations link to the broader conceptions and critiques noted above, with the idea that this will enable those who seek to analyse or plan adaptation to better analyse what types of action are potentially constitutive of transformation. In doing so, it should equally assist in the identification and specification of critical questions that need to be asked of such activity in relation to issues of sustainability and equity. As the term transformation gains ground in discussions of climate change adaptation, it is necessary to take a step back, review quite what commentators mean when they use the word, and consider the implications on people, especially the most vulnerable and marginalised, of “doing” or promoting transformation in its different forms

Flood vulnerability and resilience in peri-urbanizing Vietnam : a case study from Ninh Binh province

Peri-urban areas in Vietnam are caught between development and conservation needs, between economic development and environmental protection, between cultural preservation and sustainable development. This chapter/article examines vulnerabilities and challenges from flooding in peri-urban communities of the city of Ninh Binh, focusing on: (a) local socioeconomic development policy and the establishment of the Khanh Phu Industrial Zone; (b) impacts caused by flooding and lack of regulations, unplanned built environments, and underdeveloped water infrastructure; and (c) the varying adaptations of different social groups of households. It also explores how institutional adaptation programmes together with household responses collectively determine the resilience of the system

Reconstruction of the 3D hydrodynamics in a baffled stirred tank using Proper Orthogonal Decomposition

International audienceIn this work, the unsteady turbulent flow in a four-baffled stirred tank equipped with a Rushton turbine is computed with ANSYS FLUENT (R) using the sliding mesh technique. The POD algorithm is applied first to each mesh zone (fixed and rotating) and, in a novel and original way, to the full 3D CFD data without distinguishing between the stationary and rotating zones. The resulting modes cannot be regarded as spatial modes revealing the underlying flow structure. The POD results showed that 99.9% of the system variance is recovered with the first three modes. The reconstruction of the velocity field from these modes reveals the trailing vortices plus the mean flow. The accuracy of the POD reconstructed flow fields is quantified. The present work is the first evidence of a POD reconstruction of the unsteady turbulent flow performed over the entire 3D domain in a baffled stirred tank

Evaluation of local kinetic energy dissipation rate in the impeller stream of a Rushton turbine by time-resolved PIV

International audienceThe present paper is dedicated to the direct measurement of the dissipation rate of kinetic energy, ¯ε, by means of time-resolved 2D-PIV, in the impeller region of a stirred vessel. Experimental estimation of ¯ε is carried out without simplifications, since all spatial gradients of the fluctuating velocity components are directly measured. At each point, measurements have thus been realized in three orthogonal planes. The present results have been compared with previous ones and discussed according to experimental techniques. A special attention is focused on the contribution of measurements in each plane and some newideas have been suggested for the assessment of ¯ε. In addition, in each measurement plane, the time-variation of the instantaneous fluctuating velocity gradients have been also presented, exhibiting periodicity, with large values of instantaneous dissipation rate, linked to the trailing vortex induced by the blade rotation

LES and URANS simulations of hydrodynamics in mixing tank: Comparison to PIV experiments

Dissipation rate of turbulent kinetic energy is a key parameter in a number of chemical and biochemical processes. In stirred tank, its overall value is readily estimated; however its distribution is far from homogeneous. The experimental determination of dissipation rate is difficult and often limited to small regions of a reactor. Therefore, CFD appears to be a useful tool to estimate the distribution of the turbulence dissipation rate. In this work, two kinds of simulation have been performed: a simulation based on the URANS equations and a Large Eddy Simulation with the Smagorinski subgrid scale model. The aims of the present paper are (1) to compare URANS and LES simulations to PIV data in terms of velocity, kinetic energy and turbulence dissipation rate and (2) to study the influence of the constant in the subgrid scale model used in LES. In term of mean velocity, URANS simulation and especially LES are in good agreement with PIV experiments. In term of total kinetic energy, both simulations also give good results; however URANS simulation fails to predict the repartition of total kinetic energy between its periodic and turbulent components in the vicinity of the impeller. The mean velocity and the kinetic energy are shown to be independent of the value of the constant CS in the Smagorinski model. The overall dissipation rate is well predicted by URANS simulation but not its distribution in the impeller stream. For LES, the amplitude of local and overall dissipation rate is shown to be strongly dependent of the value of the constant CS. However, its distribution in the stream is similar regardless of the value of CS and best reproduced than by the URANS simulation. © 2008 The Institution of Chemical Engineers

Orientation and detachment dynamics of Bacillus spores from stainless steel under controlled shear flow: Modelling of the adhesion force

International audienceShear-flow induced spore detachment was performed under well-controlled laminar flow conditions, in a specially-designed shear stress flow chamber. By comparing detachment profiles of a panel of four strains, belonging to the B. cereus group (B. cereus and B. thuringiensis) and to less related Bacillus species (B. pumilus), it was shown that the spore ability of attaching to stainless steel, probed under dynamic conditions, was mainly affected by the presence (and number) of appendages. Adhesion force between the B. cereus 98/4 strain and stainless steel was quantified at nanoscale. To this aim, detachment results were combined with a theoretical modelling, based on the balance of hydrodynamic forces and torque exerted over a simplified spore model with a spherical form. The wall shear stress, required to remove 50% of the spores initially attached to stainless steel, was determined. On this basis, an adhesion force of 930 +/- 390 pN was obtained. Real-time re-orientation of B. cereus 98/4 spores was experimentally established, by using a high-speed camera for tracking the motions of individual spores with high temporal and spatial resolution. Even though tethered to stainless steel without any detachment occurring, spores kept mobile on the substratum, probably due to the existence of discrete bonds or local clusters of anchoring sites, and tended to re-orientate in the flow direction, for minimizing hydrodynamic forces and torque exerted by fluid flow. A significant heterogeneity within the population was also observed, with the co-existence of both moving and immobile spores. (C) 2011 Elsevier B.V. All rights reserved

Estimation of wind energy over roof of two perpendicular buildings

WOS:000349732100006International audienceWind energy development in a built up environment will be an important subject for future sustainable cities. Maturing CFD technology is making more wind flow simulation experiments available, which can be validated by in situ and wind tunnel measurements. Starting from research on wind accumulation by the Venturi effect in built environment, this paper tries to establish the relationship between wind energy potential and the configuration of two perpendicular buildings by performing parametric CFD wind tests. Two reference buildings (width x length x height = 6 m x 15 m x 10 m) forming a symmetrical corner are chosen and different building lengths, widths, heights, corner separation distances, angles of inlet and altitudes of assessment are considered. Results show that, in converging inlet mode, wind energy potential over the roof generally increases sensibly as the corner separation becomes larger, while in diverging inlet mode it decreases rather slowly with corner enlargement. Meanwhile, compared with a single, isolated reference building, most of the corner configuration cases studied here show greater wind energy density over the roof. (C) 2014 Elsevier B.V. All rights reserved