Anisotropic eddy-viscosity concept for strongly detached unsteady flows

The accurate prediction of the flow physics around bodies at high Reynolds number is a challenge in aerodynamics nowadays. In the context of turbulent flow modeling, recent advances like large eddy simulation (LES) and hybrid methods [detached eddy simulation (DES)] have considerably improved the physical relevance of the numerical simulation. However, the LES approach is still limited to the low-Reynolds-number range concerning wall flows. The unsteady Reynolds-averaged Navier–Stokes (URANS) approach remains a widespread and robust methodology for complex flow computation, especially in the near-wall region. Complex statistical models like second-order closure schemes [differential Reynolds stress modeling (DRSM)] improve the prediction of these properties and can provide an efficient simulationofturbulent stresses. Fromacomputational pointofview, the main drawbacks of such approaches are a higher cost, especially in unsteady 3-D flows and above all, numerical instabilities

Anisotropic Organised Eddy Simulation for the prediction of non-equilibrium turbulent flows around bodies

The unsteady turbulent flow around bodies at high Reynolds number is predicted by an anisotropic eddy-viscosity model in the context of the Organised Eddy Simulation (OES). A tensorial eddy-viscosity concept is developed to reinforce turbulent stress anisotropy, that is a crucial characteristic of non-equilibrium turbulence in the near-region. The theoretical aspects of the modelling are investigated by means of a phase-averaged PIV in the flow around a circular cylinder at Reynolds number 1.4×10^5. A pronounced stress–strain misalignment is quantified in the near-wake region of the detached flow, that is well captured by a tensorial eddy-viscosity concept. This is achieved by modelling the turbulence stress anisotropy tensor by its projection onto the principal matrices of the strain-rate tensor. Additional transport equations for the projection coefficients are derived from a second-order moment closure scheme. The modification of the turbulence length scale yielded by OES is used in the Detached Eddy Simulation hybrid approach. The detached turbulent flows around a NACA0012 airfoil (2-D) and a circular cylinder (3-D) are studied at Reynolds numbers 105 and 1.4×10^5, respectively. The results compared to experimental ones emphasise the predictive capabilities of the OES approach concerning the flow physics capture for turbulent unsteady flows around bodies at high Reynolds numbers

The relationships between total, electricity and biofuels residential energy consumption and income in Latin America and the Caribbean Countries

Controlling residential energy consumption in Latino America and the Caribbean countries is crucial to reduce CO2 emissions, as it has an important energy-saving potential, and its environmental controls are difficult to displace offshore. The aim of this study is to analyze the relationships between residential energy consumption and income for 22 Latin America and the Caribbean countries in the period 1990-2013. For this purpose, residential energy environmental Kuznets curves (EKC) are estimated by taking into account the heterogeneity among the countries by including two control variables: one representing the possible effect of urbanization on residential energy use and the second representing the possible effect of petrol production. The EKC are estimated for total residential energy consumption, for residential electricity consumption and for biofuels and waste energy consumption. The elasticities of total, electricity and biofuels residential energy consumption with respect to income are calculated for each year and country, analyzing the different behavior between countries. Obtained results show that the EKC hypothesis is confirmed for the residential sector when the biofuels energy consumption is considered. Moreover, the results also show that the turning point has been reached in some countries. Nevertheless, the EKC is not confirmed when electricity or total residential energy consumption is considered. Thus, for total residential energy consumption, the elasticity is always positive, growing also as the income does. For electricity energy consumption, the elasticity is also always positive, since although the elasticity decreases until a threshold, from an per capita income value it begins to grow

Thickness effect of Naca foils on hydrodynamic global parameters, boundary layer states and stall establishment

The present study investigates experimentally the hydrodynamic behavior of 2D NACA (15, 25, 35%) symmetric hydrofoils at Reynolds number 0.5 106 . A particular attention is paid on the hysteretic behavior at static stall angle and a detailed cartography of boundary layer structures (integral quantities and velocity profiles) is given in order to put in evidence the mechanism of the detachment and the onset of von Karman instability for thick profil

The relationship between public and private bicycle use: the case of Seville

Despite the success achieved by Public Bicycle Sharing Systems (PBSS) across the world, several researchers provide evidence on their limitations and constraints in a medium-long term, and bicycle ownership may be considered as a complementary tool to promote a 'bicycle-culture'. This paper aims to cover the gap about the interaction between both systems (public bicycle / private bicycle) and which are the key aspects to explain the bicycle-buying decision. After a fieldwork based on surveys conducted in Seville (Spain), one of the cities currently acknowledged worldwide for its successful policy of promoting cycling, we apply a Discrete Choice Model. Our findings show that among the socio-demographic factors that favor the move from the PBSS to the private bicycle are: having a higher level of education, being more progressive ideologically-speaking, and being a resident of the city itself; while age and gender do not appear to be conclusive. Experienced users, for whom the bicycle is a part of his /her healthy lifestyle, state a greater willingness to buy a bicycle. And the main obstacles to make the jump from the PBSS to the private bicycle, and that any action plan to support private bicycle usage should take into account, are: the lack of proper parking at the origin/destination, and fear of theft

Language skills, peer rejection, and the development of externalizing behavior from kindergarten to fourth grade

Background: Children with poorer language skills are more likely to show externalizing behavior problems, as well as to become rejected by their peers. Peer rejection has also been found to affect the development of externalizing behavior. This study explored the role of peer rejection in the link between language skills and the development of externalizing behavior. Methods: Six hundred and fifteen (615) children were followed from kindergarten to grade 4. Receptive language skills were measured with the Peabody Picture Vocabulary Test in grade 2. Teachers reported externalizing behavior and peer reports of social rejection were measured annually. Results: Children with poorer receptive language skills showed increasing externalizing behavior, while children with better receptive language skills showed decreases in externalizing behavior. Children with poorer receptive language skills experienced peer rejection most frequently. The link between receptive language skills and the development of externalizing behavior was mediated by the development of peer rejection. Findings suggested that this mediational link applied mostly to boys. Conclusion: Children with poorer language skills are at increased risk of becoming rejected by mainstream peers, which adds to the development of externalizing behavior. © 2010 The Authors. Journal of Child Psychology and Psychiatry. © 2010 Association for Child and Adolescent Mental Health

Evaluating the impact of an active labour market policy on employment: short- and long-term perspectives

The Labour Market Insertion Contract was an Active Labour Market Policy introduced in Spain. It was aimed at individuals who had difficulties entering the labour market, and it was introduced with the purpose of reducing the rate of unemployment. This article provides an estimation of the average impact that this contract had on the employability of individuals in the short and long term. A microeconomic analysis was carried out based on causal statistical inference by using propensity score matching and kernel and radial estimators. Data was taken from the most comprehensive database available, which is the Continuous Sample of Work Histories. Results are consistent with literature reports and show that the employability of participants was inferior to that of individuals with similar, temporary-type contracts. This research contributes to the literature by evaluating whether there was empirical evidence to support the political decision to revoke or replace this kind of direct employment programme.Junta de Andalucía proyecto SEJ-132Universidad Autónoma de ChileUniversidad de Sevilla. Departamento de Análisis Económico y Política Económic

Three dimensionality in the wake of the flow around a circular cylinder at Reynolds number 5000

The turbulent flow around a circular cylinder has been investigated at Re=5000Re=5000 using direct numerical simulations. Low frequency behavior, vortex undulation, vortex splitting, vortex dislocations and three dimensional flow within the wake were found to happen at this flow regime. In order to successfully capture the wake three dimensionality, different span-wise lengths were considered. It was found that a length LZ=2pDLZ=2pD was enough to capture this behavior, correctly predicting different aspects of the flow such as drag coefficient, Strouhal number and pressure and velocity distributions when compared to experimental values. Two instability mechanisms were found to coexist in the present case study: a global type instability originating in the shear layer, which shows a characteristic frequency, and a convective type instability that seems to be constantly present in the near wake. Characteristics of both types of instabilities are identified and discussed in detail. As suggested by Norberg, a resonance-type effect takes place in the vortex formation region, as the coexistence of both instability mechanisms result in distorted vortex tubes. However, vortex coherence is never lost within the wake.Peer ReviewedPostprint (author's final draft

Taxonomy and phylogeny of the Old World jumping plant-louse genus Paurocephala (Insecta, Hemiptera, Psylloidea)

Fifty-one species are recognized in the genus Paurocephala, with an additional 14 species which remain unnamed. Thirty-five species are described as new, and five species are synonymized: P. pumilae and P. zhejiangensis with P. chonchaiensis, P. debregeasiae with P. sauteri, and P. guangxiensis and P. tremae with P. trematos. Two varieties, P. psylloptera maculipennis and P. psylloptera setifera, are raised to species level. P. bifasciata is reinstated from former synonymy with P. chonchaiensis, and Anomoterga kleinhofiae is transferred back to Paurocephala. Lectotypes are designated for P. brevicephala, P. chonchaiensis, P. psylloptera, P. sauteri, P. seti/era and P. wilderi. The four New World species of Paurocephala are not considered to be congeneric with the Old World species and will be transferred to Diclidophlebia. Two South African species, P. bicarinata and P. hottentotti, are removed from Paurocephala and have to be accommodated in a new genus in the Diaphorininae. Thus Paurocephala is an Old World genus with nine Afrotropical and 42 Indo-Australian described species. Keys for the identification of adults and fifth instar larvae are provided. All 51 named species are diagnosed and illustrated, and information is given on distribution and host plants. Based on two cladistic analyses, one using adult characters only, and one using both adult and larval characters, four monophyletic species groups are recognized. In both analyses a basal group of 10 species, the brevicephala-group, forms the sister group to all other Paurocephala spp. The Afrotropical species are monophyletic and, together with one Oriental species constitute the gossypiigroup. In the analysis with adult characters only, the gossypii-group is the sister taxon of the kleinhofiae-group and, both together, are the sister group of the psylloptera-group, the largest species group with 27 species. In the analysis of adult and larval characters, the relationships between the last three species groups are not resolved. The result of the phylogenetic analysis confirms the synonymy of the subgenus Thoracocorna with Paurocephala. Known host plants of Paurocephala spp. belong to the Malvifiorae with the exception of the Afrotropical P. insolita which develops on Theifiorae (Theales, Clusiaceae). The brevicephala-, kleinhofiae- and gossypii-groups are associated with hosts of the order Malvales (Malvaceae and Sterculiaceae), whereas the psylloptera-group is with Urticales (Urticaceae, Moraceae and Ulmaceae).peer-reviewe