Editorial to special issue: ISROMAC 2017
Résumé
The International Symposium on Transport Phenomena and Dynamics of Rotating Machinery (ISROMAC), which is organized every two years in Hawaii, has a long history of scientific exchanges in all areas related to rotating machinery. Initially devoted to the scientific community of the Pacific Basin, it has become also popular in Europe, and it regularly attracts about 300 researchers from more than 25 countries. The two forums related to Acoustics and Non-Linear Structural Dynamics have been especially successful in the last two events, receiving about 70 contributions in total for ISROMAC 16 and ISROMAC 17. This has resulted in a number of high-quality papers, some of them being recommended by the conference reviewers for publication in a peer-reviewed Journal. It has thus been decided to group the best papers presented in these two forums at the last conference, which was held in Maui from December 16 to 21, 2017, in a special issue of the Journal of Sound and Vibration.
Aeroacoustics is a major concern in various turbomachinery applications such as aeronautical propulsion systems and cooling/air-conditioning devices. It differs from structural-vibration noise in that it is an essential signature and by-product of unsteady flows in blade or vane rows. In aeronautics the growing interest for aeroacoustics is justified by the emergence of more and more stringent ICAO standards and the targeted reduction of community noise around airports. In low-speed air-engineering applications new regulations are also defined to meet the everyday-life comfort required by populations. Noise is one of the features to be reduced in multidisciplinary optimization approaches, together with pollutant emissions and energy losses/consumption. Aeroacoustics also requires the most demanding extensions of the computational resources presently used to produce realistic predictions of unsteady flows in turbomachinery stages. The Aeroacoustic Forum of the ISROMAC 17 conference has been focused on the recent advances in rotating-blade aeroacoustics, including (i) aerodynamic noise prediction strategies based on analytical and/or numerical methods, (ii) experimental studies dedicated to the characterization of aerodynamic noise sources, and (iii) the physical understanding and the connection with unsteady flows in turbomachines.
Modern turbomachines should also reach an optimal trade-off between performance and operating costs. For aircraft applications, such requirements shall be partly met through designs which minimize operating clearances between stationary and rotating components, lighter and thus more flexible blades, and fewer compressor stages with comparable compression rates. Overall, modern designs enjoy improved energy efficiency and lower greenhouse signature, but shall also give rise to harmful side effects involving possibly catastrophic unilateral contact and friction occurrences between blades and surrounding casings, for instance. Currently, such complexities are not adequately addressed even though the proper understanding of the corresponding nonlinear dynamics is a primary concern to ensure reliable and safe operating conditions. In the same line, subsequent vibratory phenomena and associated resonances should be accurately predicted since excessive vibration in structures can cause high-cycle fatigue and fracture. Starting from these considerations, the non-linear structural dynamics forum has been devoted to all possible manifestations of structural nonlinearities in turbomachines with emphasis placed on (i) prediction tools based on analytical and numerical techniques, (ii) experimental set-ups and investigations devoted to the characterization of nonlinear phenomena, and (iii) realistic large-scale engineering applications and multi-physics modelling.
It is our pleasure to introduce the 12 new contributions of this special issue based on papers presented in these two forums, which have been combined with 11 other works published previously in the JSV, to form a coherent collection of papers in the area of acoustics and vibrations in Turbomachinery.
We would like to thank the current and previous Editors of the Journal of Sound and Vibration, Andrei Metrikine and Matthew Cartmell, for their initial acceptance of this idea and their continuous support, the Deputy Editor-in-Chief in charge of the special issue, Li Cheng, and the Managing Editor, Margaret Howls, for their assistance during the course of this special issue publication. We also would like to thank the authors of the papers for their efforts in preparing these contributions, and all reviewers for their help to improve the papers and identify the most suitable contributions for this special issue.