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Aerodynamic noise from rigid trailing edges with finite porous extensions
- A. Kisil, L. J. Ayton
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- Journal:
- Journal of Fluid Mechanics / Volume 836 / 10 February 2018
- Published online by Cambridge University Press:
- 11 December 2017, pp. 117-144
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This paper investigates the effects of finite flat porous extensions to semi-infinite impermeable flat plates in an attempt to control trailing-edge noise through bio-inspired adaptations. Specifically the problem of sound generated by a gust convecting in uniform mean steady flow scattering off the trailing edge and the permeable–impermeable junction is considered. This set-up supposes that any realistic trailing-edge adaptation to a blade would be sufficiently small so that the turbulent boundary layer encapsulates both the porous edge and the permeable–impermeable junction, and therefore the interaction of acoustics generated at these two discontinuous boundaries is important. The acoustic problem is tackled analytically through use of the Wiener–Hopf method. A two-dimensional matrix Wiener–Hopf problem arises due to the two interaction points (the trailing edge and the permeable–impermeable junction). This paper discusses a new iterative method for solving this matrix Wiener–Hopf equation which extends to further two-dimensional problems, in particular those involving analytic terms that exponentially grow in the upper or lower half-planes. This method is an extension of the commonly used ‘pole removal’ technique and avoids the need for full matrix factorisation. Convergence of this iterative method to an exact solution is shown to be particularly fast when terms neglected in the second step are formally smaller than all other terms retained. The new method is validated by comparing the iterative solutions for acoustic scattering by a finite impermeable plate against a known solution (obtained in terms of Mathieu functions). The final acoustic solution highlights the effects of the permeable–impermeable junction on the generated noise, in particular how this junction affects the far-field noise generated by high-frequency gusts by creating an interference to typical trailing-edge scattering. This effect results in partially porous plates predicting a lower noise reduction than fully porous plates when compared to fully impermeable plates.
A roadmap for Antarctic and Southern Ocean science for the next two decades and beyond
- M.C. Kennicutt II, S.L. Chown, J.J. Cassano, D. Liggett, L.S. Peck, R. Massom, S.R. Rintoul, J. Storey, D.G. Vaughan, T.J. Wilson, I. Allison, J. Ayton, R. Badhe, J. Baeseman, P.J. Barrett, R.E. Bell, N. Bertler, S. Bo, A. Brandt, D. Bromwich, S.C. Cary, M.S. Clark, P. Convey, E.S. Costa, D. Cowan, R. Deconto, R. Dunbar, C. Elfring, C. Escutia, J. Francis, H.A. Fricker, M. Fukuchi, N. Gilbert, J. Gutt, C. Havermans, D. Hik, G. Hosie, C. Jones, Y.D. Kim, Y. Le Maho, S.H. Lee, M. Leppe, G. Leitchenkov, X. Li, V. Lipenkov, K. Lochte, J. López-Martínez, C. Lüdecke, W. Lyons, S. Marenssi, H. Miller, P. Morozova, T. Naish, S. Nayak, R. Ravindra, J. Retamales, C.A. Ricci, M. Rogan-Finnemore, Y. Ropert-Coudert, A.A. Samah, L. Sanson, T. Scambos, I.R. Schloss, K. Shiraishi, M.J. Siegert, J.C. Simões, B. Storey, M.D. Sparrow, D.H. Wall, J.C. Walsh, G. Wilson, J.G. Winther, J.C. Xavier, H. Yang, W.J. Sutherland
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- Journal:
- Antarctic Science / Volume 27 / Issue 1 / February 2015
- Published online by Cambridge University Press:
- 18 September 2014, pp. 3-18
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Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to ‘scan the horizon’ to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone.
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