In the flamelet approach of turbulent premixed combustion, the flames are modeled as a wrinkled surface whose propagation speed, termed the {open_quotes}displacement speed, {close_quotes} is prescribed in terms of the local flow field and flame geometry. Theoretical studies suggest a linear relation between the flame speed and stretch for small values of stretch, S{sub L}/S{sub L}° = 1 - MaKa, where S{sub L}° is the laminar flame speed, Ka = [kappa][delta]{sub F}/S{sub L}° is the nondimensional stretch or the Karlovitz number, and Ma = L/[delta]{sub F} is the Markstein number. The nominal flame thickness, [delta]{sub F}, is determined as the ratio of the mass diffusivity of the unburnt mixture to the laminar flame speed. Thus, the turbulent flame model relies on an accurate estimate of the Markstein number in specific flame configurations. Experimental measurement of flame speed and stretch in turbulent flames, however, is extremely difficult. As a result, measurement of flame speeds under strained flow fields has been made in simpler geometries, in which the effect of flame curvature is often omitted. In this study we present results of direct numerical simulations of unsteady turbulent flames with detailed methane/air chemistry, thereby providing an alternative method of obtaining flame structure and propagation statistics. The objective is to determine the correlation between the displacement speed and stretch over a broad range of Karlovitz numbers. The observed response of the displacement speed is then interpreted in terms of local tangential strain rate and curvature effects. 13 refs., 3 figs.

A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.

The inaugural Symposium on Turbulent Shear Flows was held at The Pennsylvania State University in 1977. Thereafter the locations for the biennial symposium have alternated between the USA and Europe. However, the ninth Symposium on Turbu lent Shear Flows was awarded to Japan in recognition of the strong support researchers of the Pacific Rim countries have given previous symposia. The University of Kyoto was the host institution and the meeting was held in the Inter national Conference Hall. The Local Arrangements Committee did a superb job scheduling traditional Japanese dinners and arranging visits to the many cultural treasures in the Kyoto region. The meeting attracted more than 260 offers of papers. Thirty-three sessions were scheduled to accommodate the 138 papers accepted for oral presentation. In addition a poster session was scheduled on each of the three days to accommodate a total of 42 poster presentations. From the presentations at the symposium 24 have been selected for inclusion in this volume. The authors of these papers have revised them taking into consideration comments made during their oral presentation and recommendations made by the Editors. Four subject areas are identified, namely closures and fundamentals, free flows, wall flows, and combustion and recirculating flows. Eminent authorities have prepared introductory articles fot each topic to put the individual contributions in context with each other and with related research.

This book consists of papers prepared for and presented at a NATO sponsored Advanced Study Institute which was held in Montechoro, Portugal during the period 16-27 April, 1990. This Institute was attended by approximately ninety delegates from fifteen countries and followed from a related Institute held in Vimeiro, Portugal in 1987 (see the book entitled "Instrumentation for Combustion and Flow in Engines", edited by D. F. G. Dur~o, J. H. Whitelaw and P. O. Witzel. The purposes of the first Institute related closely to instrumentation for use in gas-turbine combustors and the cylinders of internal-combustion engines. These topics were also addressed in the second Institute, though in a manner which was wider ranging and chosen to demonstrate and explain the development and application of measurement methods to combusting flows in general. The papers contained in this boo~ were selected to provide the reader with a comprehensive and up-to-date view of the variety of experimental techniques available to measure in combusting flows. Included are discussions of their range and applicability, potential accuracy and ease of use. Thus, the first paper provides a brief overview and the second an indication of those aspects of combustion which should influence the choice of flow property to be measured and the technique to be used.