Supersonic jet mixing enhancement by delta-tabs

The results of a continuing investigation of the effect of vortex generators, in the form of small tabs at the nozzle exit, on the evolution of a jet are reported. Primarily, tabs of triangular shape are considered, and the effect is studied up to an equivalent jet Mach number of 1.8. By changing the orientation of the tab with respect to the nozzle exit plane, streamwise vortex pairs of opposite sign were generated. This resulted in either an outward election of jet core fluid into the ambient or an inward indentation of the mixing layer into the core of the jet. A triangular shaped tab with its apex leaning downstream, referred to as a delta tab, was found to be the most effective in influencing the jet evolution. Two delta tabs, spaced 180 degrees apart, completely bifurcated the jet. Four delta tabs increased jet mixing substantially, more than by various other methods tried previously; the mass flux at fourteen jet diameters downstream from the nozzle increased by about 50 percent over that for the no tab case. The tabs were found to be effective in jets with laminar or turbulent boundary layers as well as in jets with low or high core turbulence intensities

Effect of tabs on the evolution of an axisymmetric jet

The effect of vortex generators, in the form of small tabs at the nozzle exit, on the evolution of an axisymmetric jet was investigated experimentally over a jet Mach number range of 0.34 to 1.81. The effects of one, two, and four tabs were studied in comparison with the corresponding case without a tab. Each tab introduced an indentation in the shear layer, apparently through the action of streamwise vortices which appeared to be of the trailing vortex type originating from the tips of the tab rather that of the necklace vortex type originating from the base of the tab. The resultant effect of two tabs, placed at diametrically opposite locations, was to essentially bifurcate the jet. The influence of the tabs was essentially the same at subsonic and supersonic conditions indicating that compressibility has little to do with the effect

External and Turbomachinery Flow Control Working Group

Broad Flow Control Issues: a) Understanding flow physics. b) Specific control objective(s). c) Actuation. d) Sensors. e) Integrated active flow control system. f) Development of design tools (CFD, reduced order models, controller design, understanding and utilizing instabilities and other mechanisms, e.g., streamwise vorticity)

Learners’ and teachers’ beliefs about learning tones and pinyin

This paper reports a study of the perceptions of English-speaking learners and teachers about the challenges and difficulties of Chinese as a Second Language (CSL) learning in England. The study involved a Likert-scale questionnaire and follow-up interviews with 37 university student learners, 443 school students and the 42 teachers of both groups. The questionnaires and interviews explored beliefs about language learning, about Chinese language learning and about language learning strategies. This paper focuses on the findings concerning the perceived challenges of speaking Chinese and of tones in learning Chinese. The findings of this study present a picture of teachers who are keen for their students to learn to speak and communicate in Chinese, and of students who are keen to take risks in speaking. However, in contrast to earlier findings about learners’ views about learning Chinese, the learners in this study claimed to be very tone aware and reported that they found listening and understanding Chinese more difficult than production. This is explored in relation to the pupils’ views about learning tones and pinyin and raises questions about the ways they address tones and pinyin learning in the context of their expressed aim of communicating and taking risks in speaking. The discussion raises issues about the possible effects of communicative teaching of languages in English schools. We ask whether an emphasis on communicative approaches may affect how learners address difficulties of the Chinese pronunciation system and the use of pinyin

Pseudo-shock waves and their interactions in high-speed intakes

In an air-breathing engine the flow deceleration from supersonic to subsonic conditions takes places inside the isolator through a gradual compression consisting of a series of shock waves. The wave system, referred to as a pseudo-shock wave or shock train, establishes the combustion chamber entrance conditions, and therefore influences the performance of the entire propulsion system. The characteristics of the pseudo-shock depend on a number of variables which make this flow phenomenon particularly challenging to be analysed. Difficulties in experimentally obtaining accurate flow quantities at high speeds and discrepancies of numerical approaches with measured data have been readily reported. Understanding the flow physics in the presence of the interaction of numerous shock waves with the boundary layer in internal flows is essential to developing methods and control strategies. To counteract the negative effects of shock wave/boundary layer interactions, which are responsible for the engine unstart process, multiple flow control methodologies have been proposed. Improved analytical models, advanced experimental methodologies and numerical simulations have allowed a more in-depth analysis of the flow physics. The present paper aims to bring together the main results, on the shock train structure and its associated phenomena inside isolators, studied using the aforementioned tools. Several promising flow control techniques that have more recently been applied to manipulate the shock wave/boundary layer interaction are also examined in this review

Mejora académica y profesional de la suficiencia oral: un seminario lingüístico-colaborativo para estudiantes no nativos en TESOL.

This article is based on a study which examined the effectiveness of a 10-week collaborative languagefocused graduate seminar, offered in the Ohio State University, to improve NNES students� academic and professional oral English communication skills. The study was a collaboration among a TESOL faculty member, a senior NNES TESOL graduate student, and an ITA (International Teaching Asistant) specialist in language training. The seminar focused on both theoretical and practical aspects of oral English communication skills. Using both qualitative and quantitative methods, the study collected multiple data to answer the research questions. The findings have significant pedagogical implications for TESOL programs, in particular, for helping NNES TESOL graduate students improve their oral proficiency and their sense of legitimacy in the TESOL community.AMÉLIORER ACADÉMIQUE ET PROFESSIONNELLEMENT L�ORAL: UN SÉMINAIRE LINGUISTIQUE - COLLABORATIF POUR ÉTUDIANTS NON NATIFS EN TESOL Cette étude a été réalisée dans le but d�examiner l�effectivité d�un seminaire en collaboratif de 10 semaines dirigé aux étudiants de Postgrado de l�Université d� Ohio dans, visant l�amélioration des habiletés orales de communication académique et professionnelle en anglais à des étudiants non-natifs. Nous avons établi une collaboration entre une professeur membre de la faculté, une étudiante de la dernière année et une assistante spécialiste en entraînement d�étudiants internationaux préparateurs de « cátedra». Le séminaire a couvert des aspects théoriques et pratiques des habiletés orales communicatives en anglais. Pour cela, nous avons utilisé de méthodes quantitatives et qualitatives dans le but de collecter les donnés des perspectives multiples. Les resultats ont des implications pédagogiques significatives pour les programmes de fomation en TESOL ( enseignement en anglais à de parlants d�autres langues) en particulier pour l� amélioration de la capacité orale et le sens de légitimité des étudiants de postgrado non-natiEste estudio se realizó con la finalidad de examinar la efectividad de un seminario colaborativo de 10 semanas dirigido a estudiantes de postgrado no nativos en la Universidad de Ohio, con el propósito de mejorar sus habilidades orales de comunicación en inglés. Se estableció una colaboración entre una profesora de la facultad, una estudiante del último año y una asistente especialista en entrenamiento de estudiantes internacionales preparadores de cátedra (International Teaching Asistants). El seminario cubrió aspectos prácticos y teóricos de las habilidades orales comunicativas en inglés. Se utilizaron métodos cuantitativos y cualitativos para recolectar los datos desde múltiples perspectivas. Los resultados obtenidos tienen implicaciones pedagógicas significativas para los programas de formación en TESOL (Enseñanza de Inglés a Hablantes de Otras Lenguas), en particular para la mejora de l

Dynamic compensator for a synthetic-jet-like compression driver actuator in closed-loop cavity flow control

Collection of Technical Papers - 45th AIAA Aerospace Sciences Meeting1510698-1071