A combined oscillation cycle involving self-excited thermo-acoustic and hydrodynamic instability mechanisms

The paper examines the combined effects of several interacting thermo-acoustic and hydrodynamic instability mechanisms that are known to influence self-excited combustion instabilities often encountered in the late design stages of modern low-emission gas turbine combustors. A compressible large eddy simulation approach is presented, comprising the flame burning regime independent, modeled probability density function evolution equation/stochastic fields solution method. The approach is subsequently applied to the PRECCINSTA (PREDiction and Control of Combustion INSTAbilities) model combustor and successfully captures a fully self-excited limit-cycle oscillation without external forcing. The predicted frequency and amplitude of the dominant thermo-acoustic mode and its first harmonic are shown to be in excellent agreement with available experimental data. Analysis of the phase-resolved and phase- averaged fields leads to a detailed description of the superimposed mass flow rate and equivalence ratio fluctuations underlying the governing feedback loop. The prevailing thermo-acoustic cycle features regular flame liftoff and flashback events in combination with a flame angle oscillation, as well as multiple hydrodynamic phenomena, i.e., toroidal vortex shedding and a precessing vortex core. The periodic excitation and suppression of these hydrodynamic phenomena is confirmed via spectral proper orthogonal decomposition and found to be controlled by an oscillation of the instantaneous swirl number. Their local impact on the heat release rate, which is predominantly modulated by flame-vortex roll- up and enhanced mixing of fuel and oxidizer, is further described and investigated. Finally, the temporal relationship between the flame “surface area,” flame-averaged mixture fraction, and global heat release rate is shown to be directly correlated

Large eddy simulation of an oscillating flame using the stochastic fields method

Large eddy simulation (LES) of a partially pre-mixed, swirl-stabilised flame is performed using atransported Probability Density Function approachsolved by the stochastic fields method to accountfor turbulence-chemistry interaction on the sub-gridscales. The corresponding sub-grid stresses and scalarfluxes are modelled via a dynamic version of theSmagorinsky model and a gradient diffusion approx-imation, respectively.A 15-step reduced methanemechanism including 19 species is employed for thedescription of all chemical reactions. The test case in-volves a widely studied gas turbine model combustorwith complex geometry and the simulation is carriedout for a specific operating condition involving an os-cillating flame. Overall, results of the velocity, temper-ature and major species mass fractions as well as theinstantaneous thermochemical properties are shown tobe in good agreement with experimental data, demon-strating the capabilities of the applied stochastic fieldsmethod. The inclusion of wall heat transfer in the com-bustion chamber is found to improve temperature pre-dictions, especially in the near-wall regions. In sum-mary, this work showcases the LES method’s accuracyand robustness - none of the default model parametersare adjusted - for an application to complex, partiallypremixed combustion problem

Electrostatic fields for the control of evaporating charged fuel sprays

The current socio-economic shift towards electrification of the transport sector and development of hybrid thermal–electric propulsion systems provides new opportunities for the development of ‘clean’ aviation technologies. In this work, the use of electrostatic fields to control the location of electrically charged fuel droplets is proposed as a novel technology to enhance pre-evaporation of liquid sprays in confined spaces. An electrospray in cross-flow is numerically investigated using large-eddy simulations for a range of flow and droplet conditions in order to study the feasibility of the approach. A deterministic model is further introduced to compute the trajectory of single droplets in a steady cross-flow. This enables a separation of the effects of turbulence, droplet repulsion and evaporation through comparison with data obtained from the large-eddy simulations, and at the same time provides a cheap computational tool to explore a wider range of operating conditions. It is shown that external electrostatic fields below the breakdown threshold of air can significantly change the trajectory of charged droplets at moderate flow velocities. Moreover, electrostatic forces acting in the opposite direction of the mean cross-flow can potentially be used to stabilise the spray position within a confined region, hence allowing for an increase of the residence time available for full evaporation. The application and modulation of such electrostatic forces is envisioned as a new paradigm to achieve ‘targeted evaporation’ in next-generation hybrid thermal–electric aero-engines and to improve the fuel-oxidiser mixing quality. The electrical power associated with the external electrostatic field to achieve droplet stabilisation is negligible compared to the thermal power released by complete combustion of the injected fuel. In addition, it is shown that stabilisation of the droplets enhances the evaporation rate (by more than 30%) and mixing quality due to an increase of the relative velocity between the droplets and the gas flow, as well as the turbulence induced by the stagnating spray cloud. The results of this work offer new insights for the development of advanced fuel injection strategies based on electrohydrodynamics

Definição da folha a ser amostrada para monitoramento de Mosca Branca (Bemisia tuberculata) na cultura da mandioca (Manihot esculenta Crantz).

A mandioca (Manihot esculenta Crantz) é uma cultura com crescente importância no mundo tropical, sendo a terceira fonte de calorias, atrás apenas do arroz e do milho, sendo utilizada na alimentação de cerca de 600 milhões de pessoas. No Brasil, aproximadamente 90% da produção da mandioca é obtida em propriedades de base familiar, sendo o país o terceiro produtor mundial, depois da Nigéria e da Tailândia, com uma produção de 26,52 milhões de toneladas de raízes, obtidas em uma área de cerca de 1,89 milhão de ha, o que corresponde a 12,37% da produção mundial e 10,20% da área, respectivamente (FAOSTAT, 2009). Essa é provavelmente a espécie vegetal mais disseminada pelo país, numa demonstração da profunda identificação entre essa cultura e o povo brasileiro. A cultura se caracteriza pela baixa necessidade de uso de insumos e agroquímicos, tem alta tolerância a períodos de seca, além de poder permanecer no solo até seu consumo, desempenhando papel importante na alimentação da população brasileira (CAMARGO, 2009). No entanto, por apresentar um longo ciclo vegetativo, está sujeita a uma grande diversidade de artrópodes que dela se alimentam (BELLOTTI et al., 1999). Dentro do complexo de insetos praga que atacam a cultura atualmente no Brasil, relata-se o crescimento da importância das espécies de mosca branca. Os gêneros mais importantes descritos atacando a cultura da mandioca no Brasil são Aleurothrixus aepim, Bemisia tuberculata, Trialeurodes variabilis e Bemisia tabaci biótipo B (OLIVEIRA & LIMA, 2006). No Centro-Sul do Brasil a espécie predominante é B. tuberculata, enquanto que no Nordeste destaca-se a espécie A. aepim (OLIVEIRA & LIMA, 2006). As moscas brancas causam danos diretos e indiretos, resultantes da sucção da seiva e transmissão de viroses, respectivamente (OLIVEIRA & LIMA, 2006). Para a supressão das populações desses insetos, apesar da existência de diversos inimigos naturais (BELLOTTI et al., 1999), tem-se predominado a utilização de inseticidas químicos, ainda que sem registros para essa cultura (AGROFIT, 2013) e ineficientes no controle do complexo de moscas brancas (MOREIRA et al., 2006). A utilização de variedades resistentes é outra estratégia de controle dessa praga, pois a mandioca é uma das poucas culturas onde se têm identificado níveis de resistência ao complexo de moscas brancas (CARABALI et al, 2010; OMONGO et al, 2012). Esta estratégia apresenta baixo custo e longa manutenção da população da praga abaixo do nível de dano econômico, além de reduzir perdas no rendimento, sendo uma importante ferramenta para ser incluída em um programa de manejo integrado de pragas (BELLOTTI et al., 1999). Para o estabelecimento de um eficiente programa de manejo integrado de pragas, além de utilizar várias estratégias de controle, é de suma importância um bom monitoramento da população da praga, visando à adoção de medidas de controle no momento ideal. Para a cultura da mandioca não se tem estabelecido um método de monitoramento preciso, eficiente e de baixo custo, principalmente para mosca branca. Observa-se que na cultura da mandioca os adultos de moscas brancas são encontrados principalmente nos ponteiros das plantas, onde se observa que o número de adultos presentes nas três primeiras folhas abertas, onde estes se alimentam e depositam seus ovos, é maior. Já as ninfas e 'pupas' são encontradas no terço apical e médio. Visando estabelecer um método de amostragem, que efetivamente seja representativo da população de mosca branca na cultura da mandioca, e considerando as características de localização dos adultos, se realizou este trabalho, cujo objetivo foi definir qual folha de mandioca deve ser amostrada durante o monitoramento de mosca branca em cultivos comerciais de mandioca, que expressem o nível populacional desta praga no cultivo

Aplicação de manipueira no controle da Cochonilha-da-Raiz (Dysmicoccus sp.).

Na região Centro-Sul do Brasil, onde o cultivo da mandioca é destinado principalmente à indústria, o Paraná se destaca ocupando o segundo lugar na produção nacional e o primeiro na produção de fécula (GROXKO, 2013). Com o grande avanço tecnológico nesse cultivo, possibilitando o plantio de grandes áreas, surgiram novos problemas fitossanitários. Das 200 espécies de artrópodes estimadas que estejam em associação com a cultura da mandioca, citadas por Bellotti et al. (2002), muitas tem elevado potencial para atingirem o status de pragas, dentre essas estão as cochonilhas. A cochonilha-das-raízes da mandioca (Dysmicoccus sp.) tem sido amplamente encontrada alimentandose do pedúnculo e raiz de mandioca nas áreas produtoras do Paraná, se tornado uma preocupação ao setor produtivo, seja pela perda direta ocasionada pela sua alimentação ou indireta, abrindo porta de entrada para fungos que causam podridão radicular. A busca de alternativas para o controle de insetos de solo é de extrema importância, uma vez que estes são de difícil controle, necessitando muitas vezes a adoção de produtos com alto poder residual, o que para a cultura da mandioca, na qual se tem o consumo direto das raízes, é um fator limitante. A possibilidade de uso da manipueira, resíduo do processamento da mandioca, no controle desses insetos é uma alternativa interessante, considerando a alta disponibilidade deste produto nas indústrias. Diante desta perspectiva, o objetivo deste trabalho foi comparar a eficiência de aplicação de manipueira oriunda de diferentes cultivares de mandioca, em diferentes concentrações, para o controle de cochonilha da raiz da mandioca (Dysmicoccus sp.)

Large Eddy simulation of a reacting kerosene spray in hot vitiated cross-flow

The evaporation and combustion characteristics of a kerosene spray injected perpendicularly into a cross-flow of high-temperature vitiated air is investigated. This fundamental flow configuration has wider implications for the future development of ultra-low emission aeronautical combustors, particularly with respect to technologies involving MILD combustion. Large eddy simulations with a Eulerian–Lagrangian framework are performed to investigate the spray evolution and the characteristics of the reaction zone for a range of conditions. For the closure of turbulence-chemistry interactions at the sub-grid scales, a transported probability density function approach solved by the Eulerian stochastic fields method is applied. A configuration based on the use of airblast atomisation is assessed first and compared with experimental observations. The effect of the atomiser air-to-liquid mass flow ratio is studied in greater detail, both in terms of the resulting gas-phase properties and the droplet evaporation process. Then, the effect of ambient pressure on the global spray flame behaviour is examined. For this part of the study, no atomising air is included in the simulation to separate the effects of ambient pressure on the spray from the interaction with the air jet. Analysis of the flame and spray properties at cross-flow operating pressures of 1 atm, 2 bar and 4 bar highlights the strong coupling between the reacting flow and droplet evaporation characteristics, which are highly affected by the penetration of the spray into a flow field characterised by relatively large gradients of temperature. The results reported in this work provide fundamental understanding for the development of novel low-emission combustion technologies and demonstrate the feasibility of applying large eddy simulation with detailed chemistry for the investigation of reacting aviation fuel sprays in hot vitiated cross-flow

Geologically constrained evolutionary geomechanical modelling of diapir and basin evolution: a case study from the Tarfaya basin, West African coast

We systematically incorporate burial history, sea floor geometry and tectonic loads from a sequential kinematic restoration model into a 2D evolutionary geomechanical model that simulates the formation of the Sandia salt diapir, Tarfaya basin, NW African Coast. We use a poro-elastoplastic description for the sediment behaviour and a viscoplastic description for the salt. Sedimentation is coupled with salt flow and regional shortening to determine the sediment porosity and strength and to capture the interaction between salt and sediments. We find that temporal and spatial variation in sedimentation rate is a key control on the kinematic evolution of the salt system. Incorporation of sedimentation rates from the kinematic restoration at a location east of Sandia leads to a final geomechanical model geometry very similar to that observed in seismic reflection data. We also find that changes in the variation of shortening rates can significantly affect the present-day stress state above salt. Overall, incorporating kinematic restoration data into evolutionary models provides insights into the key parameters that control the evolution of geologic systems. Furthermore, it enables more realistic evolutionary geomechanical models, which, in turn, provide insights into sediment stress and porosity

Assessment of risk of introduction of Echinococcus multilocularis to mainland Norway

Source at https://vkm.no/In the light of the recent findings of the tapeworm Echinococcus multilocularis (EM) in four red foxes from three different locations in Sweden, the Norwegian Scientific Committee for Food Safety (Vitenskapskomiteen; VKM), Panel of Biological Hazards (Faggruppe hygiene og smittestoffer) took the initiative to undertake a risk assessment regarding the probability of this parasite being introduced to mainland Norway and thus becoming a threat to public health in the country.Med bakgrunn i funnet av bendelorm Echinococcus multilocularis (EM) i fire rødrev fra tre forskjellige steder i Sverige, har VKM ved Faggruppe hygiene og smittestoffer tatt initiativ til å foreta en vurdering av sannsynligheten for at EM kan bli introdusert til fastlands Norge og sannsynligheten for at mennesker i så fall også kan bli smittet

Intersectin associates with synapsin and regulates its nanoscale localization and function.

Neurotransmission is mediated by the exocytic release of neurotransmitters from readily releasable synaptic vesicles (SVs) at the active zone. To sustain neurotransmission during periods of elevated activity, release-ready vesicles need to be replenished from the reserve pool of SVs. The SV-associated synapsins are crucial for maintaining this reserve pool and regulate the mobilization of reserve pool SVs. How replenishment of release-ready SVs from the reserve pool is regulated and which other factors cooperate with synapsins in this process is unknown. Here we identify the endocytic multidomain scaffold protein intersectin as an important regulator of SV replenishment at hippocampal synapses. We found that intersectin directly associates with synapsin I through its Src-homology 3 A domain, and this association is regulated by an intramolecular switch within intersectin 1. Deletion of intersectin 1/2 in mice alters the presynaptic nanoscale distribution of synapsin I and causes defects in sustained neurotransmission due to defective SV replenishment. These phenotypes were rescued by wild-type intersectin 1 but not by a locked mutant of intersectin 1. Our data reveal intersectin as an autoinhibited scaffold that serves as a molecular linker between the synapsin-dependent reserve pool and the presynaptic endocytosis machinery