Inviscid supersonic minimum length nozzle design

An aerospace vehicle is accelerated by a propulsion system to a given velocity. A nozzle is used to extract the maximum thrust from high pressure exhaust gases generated by the propulsion system. The nozzle is responsible for providing the thrust necessary to successfully accomplish the mission while its design efficiency translates to greater payload and reduction in propellant consumption. Specifically, the nozzle is that portion of the engine beyond the combustion chamber. Typically, the combustion chamber is a constant area duct into which propellants are injected, mixed and burned. Its length is sufficient to complete the combustion of the propellant before the nozzle accelerates the gas products. The nozzle is said to begin at the point where the chamber diameter begins to decrease. This paper exploits the De Laval nozzle, a convergent divergent nozzle invented by Carl De Laval toward the end of the 19th century, and it tries to give a practical procedure to design the nozzle of minimum length. The basic assumption made is that the boundary layer thickness is small compared to the characteristic length, i.e. nozzle radius, so that the nozzle flow field can be treated as inviscid for the purpose of designing the aerodynamic lines. Ones the aerodynamic lines are determined, a correction can be made to account for the displacement thickness of the boundary layer. This second step of the designing procedure is not treated in here. This basic procedure has been applied successfully to many supersonic nozzle

Development of a partially premixed combustion model

In this work, a possible extensions of the TFC model to imperfectly premixed cases has been introduced and validated, even if in a purely qualitative way. The proposed IPM model has given results physically consistent and it seems able to describe in more correct terms actual combustor, in which it is far from real any assumption of having perfectly premixed mixtures feeding the combustion chamber. Nevertheless, a proper validation of the proposed IPM model and of the TFC model over a realistic industrial case is still to come and it will be an essential part of the future work. Finally, the quite general lines of how to get a partially premixed model (premixed plus diffusion) have been drawn, showing that, in principle, no new modeling is needed and that it would be probably enough to assembly already existent premixed and diffusion models. The actual implementation of the idea above into ARES could be also a future development of this work

Flusso tridimensionale e viscoso nei ventilatori assiali: confronto fra risultati sperimentali e numerici

La conoscenza del flusso tridimensionale a valle della girante dei ventilatori assiali è di fondamentale importanza per valutare la distribuzione delle perdite fluidodinamiche nella macchina e per intervenire con proposte di modifiche della conformazione dei condotti palari in fase di progettazione. Per raggiungere questo obiettivo è particolarmente utile poter affiancare ai metodi di indagine sperimentale codici di calcolo evoluti ed affidabili. Per verificare la validità di tale impostazione nel presente lavoro si è effettuato il confronto fra i risultati dell’indagine sperimentale condotta con sonde ad alta risposta in frequenza e quelli derivanti dalla simulazione del flusso con un codice di calcolo su un ventilatore assiale di tipo industriale.The knowledge of detailed 3-D flow field downstream of rotor blade in industrial axial flow fan is important both to evaluate the aerodynamic losses and to improve the aerodynamic design of these machines. To achieve these goals it is very important to use a reliable fluid dynamic computational code. In this paper a comparison between experimental and numerical results downstream an axial fan are presented

Development and implementation of turbulence models in the combustion code Ares

This report describes the R&D activities carried out under the ENEA-MURST programme , objective 4. Three more turbulence models (the RNG K – ε, the one-equation Spalart & Allmaras and the Wilcox K – ω) have been implemented into the Ares combustion code. They represent state-of-the-art models that have demonstrated over the past decade their superior accuracy , robustness as well as ease of implementation with respect to the class of K – ε models. The first chapter describes the models formulations. In chapter 2 the three models have been validated against three well known test cases. Particular attention has been dedicated to coupling the one-equation turbulence model by Spalart & Allmaras to the TFC premixed combustion model, for two computed turbulence scales are needed to evaluate the turbulent flame velocity and one-equation models provide one turbulent scale only. For validating the correct models implementations, two simple cold test cases have been chosen, namely the turbulent boundary layer over a flat plate, and a well documented turbulent flow over a backward facing step. Finally the Moreau combustor test case have been used for the validation of the models for premixed combustion flow. The state-of-the-art turbulence models implemented should allow the combustion code Ares to increase its ability to correctly compute complex turbulent premixed reactive flows in real combustors, which is the objective of the next project tasks

Particle-yield modification in jet-like azimuthal di-hadron correlations in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV

The yield of charged particles associated with high-pT trigger particles (8 3 GeV/c on the away-side drops to about 60% of that observed in pp collisions, while on the near-side a moderate enhancement of 20-30% is found

Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV

We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region (|eta|<0.8) and transverse momentum range 0.2< p_t< 5.0 GeV/c. The elliptic flow signal v_2, measured using the 4-particle correlation method, averaged over transverse momentum and pseudorapidity is 0.087 +/- 0.002 (stat) +/- 0.004 (syst) in the 40-50% centrality class. The differential elliptic flow v_2(p_t) reaches a maximum of 0.2 near p_t = 3 GeV/c. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow increases by about 30%. Some hydrodynamic model predictions which include viscous corrections are in agreement with the observed increase

Numerical simulation of premixed combustion flows: a comparative study

In this work four different commercial and research CFD codes have been compared for the simulation of two combustion test cases. The aim was to get an overview of the capabilities of these different tools to simulate combustion flows in premixed regimes. Codes tested were Fluent, CFX, StarCD and Tanit. Three combustion models have been applied, namely the Eddy Break Up, the Eddy Dissipation Model and the Turbulent Flame Closure, the turbulence model used being the standard k-epsilon. Numerical results have been found to fairly fit experiments and helped to show some drawbacks of combustion models. In its theoretically correct range of applicability the TFC model has been found to give the better agreement with experiments

Poems, Quotes, and Meanderings Related to “Pauses in Drifting and White Caves”

"Pauses in Drifting and White Caves" is the title of my artwork that is also the primary portion of my thesis work. It is an installation involving objects, sound, and video. I exhibited this work in the MFA thesis exhibition entitled "Outside In" in the CU Art Museum from April 6-19, 2007. The space containing "Pauses in Drifting and White Caves" measured approximately 16 feet wide, 36 feet long, and 12 feet high. &nbsp; In this piece, numerous connected abstract shapes cut out from 1/8" thick Styrofoam sheeting and vinyl translucent carpet covering lie on the ground with the Styrofoam overlapping the carpet covering pieces in some parts. The two materials form a visual pathway that begins from the right-hand side of the space where the viewer first walks in. It then curves to the back, splitting one pathway to the right back corner, the other leading to the left and close to the far and lengthwise wall in an organic formation. About half way into the space, the path begins to split up more like tributaries of a river. The tributaries go in different directions, around and under a flowing but sculpted mass of larger rectangular Styrofoam sheeting that begins from the right edge of a large video projection of about 5 by 9 feet on the back wall measuring 12 by 16 feet. The thin sheeting sculpted on the wall is layered densely and holds itself like spastic waves that are curling up into it, frozen, but spilling out from the corner of the wall and onto the floor. The mass comes out in combinations of waves and flows, pleats and layers of the Styrofoam material having been worked with like fabric. It comes out of the corner in the form of a large diagonal movement, from the right-hand side of the video and towards the back left area and up to a large white translucent plastic cave nestled in puffy white pillow surroundings. The cave is large enough for two people to sit comfortably inside.</p

Movimento - partido - Estado : os repertórios de ação de militantes do movimento negro do Rio Grande do Sul

A pesquisa aqui apresentada visa contribuir para a discussão sobre os repertórios de ação dos movimentos sociais. Contrapondo-se às teorias clássicas dos movimentos sociais, que partem do pressuposto da externalidade do movimento frente às esferas institucionais, essa pesquisa buscou apreender sobre a relação entre política extrainstitucional e a política institucional. Focando a análise na interpenetração entre movimento/partido/Estado, essa pesquisa teve o objetivo de compreender como, no âmbito do ativismo individual, a entrada dos ativistas dentro das esferas institucionais, modificava a sua atuação militante. Como objeto de pesquisa foi escolhido entrevistar ativistas de uma organização de movimento negro do Rio Grande do Sul, movimento conhecido pela sua trajetória de intersecção com a arena institucional. Foram entrevistados sete militantes ao todo. A hipótese norteadora do trabalho foi a seguinte: Disponibilizada aos ativistas oportunidades de ação por dentro das esferas estatais e partidárias acreditava-se que os ativistas abandonariam os repertórios de confronto, optando gradativamente por repertórios institucionais. Os dados obtidos nas entrevistas, porém, levaram-nos a abandonar essa hipótese. Foi observado que, ao contrário do que se esperava, os ativistas não abandonaram os repertórios de confronto, sendo o confronto utilizado por alguns como repertório principal enquanto para outros como um repertório complementar à ação institucional. A escolha desses repertórios, porém, estava, em maior medida, condicionada não às oportunidades de ação ofertadas aos militantes, mas sim às suas percepções de como eles ‘deveriam’ agir para alcançar os objetivos do movimento, condicionados às percepções dos ativistas sobre os partidos e o Estado e como o movimento deve agir com relação a essas esferas. A partir do referencial analítico da sociologia compreensiva weberiana, foi possível captar dois tipos de ação dos ativistas: uma que chamamos de valorativa, mais identificada com o tipo ideal weberiano de ação racional com relação a valores, sendo os repertórios utilizados pelos ativistas os repertórios extra institucionais, repertórios de confronto; e a ação estratégica, mais identificada com o tipo ideal weberiano da ação racional com relação à fins, onde os ativistas intercalariam ações tanto de confronto quanto institucionais, sendo observadas as oportunidades políticas oferecidas ao movimento.This research aims to contribute to the discussion about the repertoires of action of social movements. Despite the classical theories of social movements, which start from the assumption of the externality of the movement in face of the institutional spheres, this research sought to understand the relationship between both extra-institutional and institutional politics. Focusing on the analysis of interpenetration between movement/party/state, this research aimed to understand how, considering individual activism, the entry of activists within the institutional spheres modified their militant performance. As a research object, it was chosen to interview black movement’s activists of Rio Grande do Sul, which is known by its trajectory of intersection with the institutional arena. Seven militants were interviewed in the whole. The guiding hypothesis of the study was the following: the entry of activists on state and partisan spheres would stimulate the activists to abandon the confrontation repertoires, gradually opting for institutional repertoires discourses and actions. The data obtained in the interviews, however, led us to abandon this hypothesis. Contrary to expectations, it was observed that the activists did not abandon the confrontation repertoires, being the confrontation used by some of them as the main repertoire while as a complementary repertoire to the institutional action by some others. The choice of these repertories was conditioned, however, not by the action opportunities offered to the militants, but by their perceptions of how they 'should' act to achieve the movement’s goals, considering their insights about parties and state conditioning and about how the movement should act in relation to these spheres. From the analytical framework of Weberian sociology, it was possible to capture two types of activist action: the evaluative action, related to the ideal Weberian type of value-oriented rational action, in which the activists repertoires are the extra institutional repertoires, the confrontational repertoires; and strategic action, identified with the ideal Weberian type of end-oriented rational action, in which activists interposes both confrontational and institutional actions, observing the political opportunities offered to the movement

Análise econômica de alternativas para a segunda rotação em plantações de Eu-calyptus globulus no sudeste do Uruguai

Eucalyptus globulus is one of the most planted forest species in Uruguay. However, its high susceptibility to diseases has determined that in recent years most plantations reaching harvest are replaced by other species, mainly E. dunnii and E. smithii. The decision whether to maintain the plantation for an additional rotation as coppice crop or to carry out a replanting depends on the expected economic results of both alternatives. Therefore, the objective of this research was to estimate the profitability of a coppice crop of E. globulus and that of a new plantation, with two different species, E. dunnii and E. smithii. In addition, a sensitivity analysis was carried out to study the impact of eventual variations in plantation productivity, in distance to the point of sale, and in the price of wood. Results showed that the three alternatives analyzed are economically viable, but that the management as coppice crop and the replanting with E. smithii are more profitable than replanting with E. dunnii. On the other hand, the coppice management is the alternative that requires less investment and that presents fewer risks, since it is less sensitive to changes in the main variables that determine the economic result.Eucalyptus globulus es una de las especies forestales más plantadas en Uruguay. Sin embargo, su alta susceptibilidad a enfermedades ha provocado que en los últimos años la mayoría de las plantaciones que llegan a la cosecha son reemplazadas por otras especies, principalmente por E. dunnii y E. smithii. La decisión de mantener la plantación para una rotación adicional como rebrotes o de realizar una replantación depende del resultado económico esperado para ambas alternativas. Por lo tanto, el objetivo de este trabajo fue comparar la rentabilidad esperada en la siguiente rotación para el manejo de rebrotes de E. globulus y para la replantación con dos especies diferentes, E. dunnii y E. smithii. A su vez, se realizó un análisis de sensibilidad para estudiar el impacto de eventuales variaciones en la productividad de la plantación, en la distancia al punto de venta y en el precio de la madera. Los resultados obtenidos mostraron que las tres alternativas analizadas son económicamente viables, pero que el manejo de rebrotes y la replantación con E. smithii son más rentables que la replantación con E. dunnii. Por otro lado, el manejo de rebrotes es la alternativa que requiere menor inversión y que presenta menores riesgos, ya que es menos sensible frente a cambios en las principales variables que determinan el resultado económico.O Eucalyptus globulus é uma das espécies florestais mais plantadas no Uruguai. No entanto, sua alta suscetibilidade a doenças fez com que nos últimos anos a maioria das plantações que chegam à colheita sejam substituídas por outras espécies, principalmente por E. dunnii e E. smithii. A decisão de manter a plantação para rotação adicional como brotos ou para replantar depende do resultado econômico esperado para ambas alternativas. Portanto, o objetivo deste trabalho foi comparar a lucratividade esperada na próxima rotação para o manejo de rebrotas de E. globulus e para o replantio com duas espécies diferentes, E. dunnii e E. smithii. Paralelamente, foi realizada uma análise de sensibilidade para estudar o impacto de eventuais variações na produtividade da plantação, na distância até o ponto de venda e no preço da madeira. Os resultados obtidos mostraram que as três alternativas analisadas são economicamente viáveis, mas que o manejo das brotações e o replantio com E. smithii são mais lucrativos do que o replantio com E. dunnii. Por outro lado, o manejo de rebrota é a alternativa que requer menos investimento e apresenta menos riscos, por ser menos sensível a mudanças nas principais variáveis ​​que determinam o resultado econômico