Second Announcement for the CISM Summer School on

Modelling, manipulation and Control of Transverse Jets

Udine/Italy, June 11-15 2001

Advanced School coordinated by

Luca Cortelezzi (McGill University, Canada) and Ann R. Karagozian (University of California, USA)

The study of jets in crossflow, or transverse jets, is of great practical relevance to both engineering applications and natural phenomena. Numerous examples can be found in industry and nature. These includes V/STOL aircraft during transition flight, gas turbine blade cooling and exhaust gas cooling, the roll-control of missiles, chimney plumes for the dispersion of pollutants in the atmosphere, sewerage outfalls and many biological systems.

Four types of coherent vortical structures can be identified in the near field of the transverse jet: (i) the jet shear-layer vortices; (ii) the system of horseshoe vortices; (iii) the counter-rotating vortex pair; and (iv) the wake vortices. The shear-layer vortices and the wake vortices are intrinsically unstable, while the counter-rotating vortex pair and the horseshoe vortices have mean flow definition although they may also have unsteady components. Because of these vortical structures, the jet in crossflow has been demonstrated to enhance molecular mixing and has been applied to improve a variety of energy-generating technological systems. In particular, dilution air jets are used for temperature pattern factor optimization and for NOx reduction through air-fuel mixture ratio control in gas turbine engines and industrial furnaces.

Limited experiments on pulsed or acoustically driven transverse jets demonstrate that temporally varying the jet velocity allows jet penetration and mixing to be enhanced, at specific conditions of excitation, due to control of the generation of jet vorticity. Consequently, intelligent manipulation and feedback control of transverse jets has a great potential for improving current industrial applications and for stimulating new engineering applications.

In general the problem of feedback control for an unsteady fluid flow is nonlinear. Especially challenging is the control of transverse jet flows in a hot, potentially reactive environment. Because of the high temperatures present, realistic actuators can operate mainly in cool regions, e.g., near the orifice of the jet, and currently realistic sensors (e.g., MEMS-based sensors) can be placed only in relatively cool regions, beyond the exhaust of the combustion chamber. Consequently, there is a large time lag between the time at which the actuator modifies the jet velocity and the time at which the sensor measures the effect of this action on the mixing (and possibly reaction) process.

The successful design of a controller for jets in crossflow is possible only if a model can be identified which is able to capture the dynamics of the flow processes. The size of the controller, however, is a crucial parameter in any engineering application because of the amount of hardware and computer power necessary to compute a real-time control law. Thus, it is essential to derive a reliable reduced-order model of the nonlinear flow processes to be able to develop a practically implementable controller. The aim of the present course is to provide an overview of the physics and state-of-the-art theoretical/numerical modeling of the vortical structures identifiable in the near field of the transverse jet, where the three-dimensional interaction between the jet and crossflow is most intense. Furthermore, the course intends to characterize the conditions that produce optimal entrainment and mixing in terms of the vortical structures produced by the pulsation or acoustic excitation of the jet. Particular attention will be given to model reduction techniques and sensors/actuators dynamics and placement, essential issues for the practical implementation of the controller. Finally, the course intends to review control design techniques based on robust control theory and genetics algorithms and provide examples of transverse jet manipulation and control for mixing optimization.

This course is addressed to a wide range of scientists and practitioners: postgraduates, postdoctoral researchers, mechanical, chemical and aeronautical engineers, and applied mathematicians in universities and industries.

WORKSHOP

This course will be complemented by a workshop co-organized by Prof. Alfredo Soldati(University of Udine). The scope of the workshop is to provide a fertile environment for discussions where participants to the course as well as academic and industry experts from fluids, combustion and control disciplines could present their recent results.

Course and Workshop Lecturers:

L. Cortelezzi - McGill University, Canada A. Glezer - Georgia Institute of Technology, USA A.R. Karagozian - U.C.L.A., USA P. Koumoutsakos - ETH, Zurich, Switzerland G. Mungal - Stanford University, USA Igor Mezic, Harvard University, USA Ellen Longmire, University of Minnesota, Minneapolis, MN, USA Clyde Warsop, British Aerospace Systems Advanced Technology Centers, Sowerby, UK Gaudenzio Mariotti, Centro Ricerche Termiche, ENEL, Pisa, Italy Alfredo Soldati , Università di Udine, Italy Maria Vittoria Salvetti, Università di Pisa, Italy Roberto Verzicco, Politecnico di Bari, Italy Hamid Johari, Worcester Polytechnic Institute, MA, USA ..... ..... For further information please contact: CISM: cism@cism.itURL: http://www.cism.it/CISM, Palazzo del TorsoPiazza Garibaldi 18 33100 Udine (Italy) tel. +39 0432 248511 (6 lines) fax +39 0432 248550

Registration Form Course: Modeling, Manipulation and Control of Transverse Jets

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(1). Thank you very much for the information about the summer course on "Jets in cross-flow". (2). I think, it is a very important and practical subject. The problem also has been studied by many CFD experts for some time. (3). The gas turbine HP blade cooling is one good example of application, where tiny jets are used to cool the blade in high temperature environment.