Recent Developments in Turbulence Management

The European Drag Reduction Meeting has been held on 15th and 16th November 1990 in London. This was the fifth of the annual European meetings on drag reduction in engineering flows. The main objective of this meeting was to discuss up-to-date results of drag reduction research carried out in Europe. The organiser has adopted the philosophy of discussing the yesterday's results rather than the last year's results. No written material has therefore been requested for the meeting. It was only after the meeting the submission of papers was requested to the participants, from which 16 papers were selected for this proceedings volume. The meeting has attracted a record number of participants with a total of 52 researchers from seven European countries, U. K. , France, Germany, the Netherlands, Italy, Switzerland and U. S. S. R. as well as from Japan, Canada and Australia. The subjects covered in this proceedings volume include riblets, LEBUs (Large Eddy Break-Up device), surface roughness, compliant surfaces and polymer additives. Riblets seem to be one of the most extensively studied devices in the past years. Reflecting this situation in the European community, there are six papers on riblets covering their practical applications to aircraft and to a model ship, near-wall coherent structure of the boundary layer and effects of flow three-dimensionality. Possibility of heat-transfer enhancement with riblets and potential use in the laminar flow are also investigated. An analytical model is developed for the boundary-layer with a LEBU device.

Contenu

I. Riblets.- Experiments with a 1:4.2 model of a commuter aircraft with riblets in a large wind tunnel.- Heat transfer study of riblets.- Performances of internal manipulators in subsonic three-dimensional Flows.- High resolution conformal mesh computations for V, U or L groove riblets in laminar and turbulent boundary layers.- Coherent structures over a smooth and a triangular riblet drag reducing surface.- Some further experiments on riblet surfaces in a towing tank.- II. LEBUs.- Analytical and experimental study of energy density spectra of the outer region of a manipulated turbulent boundary layer.- Review: effect of the OLDs on near wall coherent structures; discussion and need for future work.- III. Surface Roughness.- Turbulent drag reduction of a d-type rough wall boundary layer with longitudinal thin ribs placed within the traverse grooves.- The correlation of added drag with surface roughness parameters.- IV. Compliant Surfaces.- The optimisation of compliant walls for drag reduction.- Nonlinear evolution of modes in the flow over compliant surfaces.- On conditions of modelling and choice of viscoelastic coatings for drag reduction.- Experimental investigation of one-layer viscoelastic coatings action on turbulent friction and wall pressure pulsations.- V. Polymer Additives.- The pulseless injection of polymeric additives into near-wall flow and perspectives of drag reduction.- Initial section of time-dependence of the Toms effect for solutions of poly (ethylene oxide).- Panel discussions.- List of Referees.- List of Participants.- Author Index.