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Special Issue on Instability and Control of Massively Separated Flows
Aerospace Science and Technology 44 (2015) 1–3
Contents lists available at ScienceDirect
Aerospace Science and Technology www.elsevier.com/locate/aescte
Editorial
Special Issue on Instability and Control of Massively Separated Flows The present volume contains work performed during the execution of an EU FP7 Marie Curie International Research Scientists Exchange Scheme (IRSES) grant in the period of January 1, 2011 till December 31, 2014. Under this scheme research interests of scientists from EU and non-EU organizations participating in the consortium were organized in work-packages and executed through travel grants (so-called secondments) supported by the EU, while the core research funding had been put in place in advance by the participating organizations. Travel support was provided for Experienced Researchers (ERs), typically faculty and senior staff members, and Early Stage Researchers (ESRs), typically Ph.D. students and early-career post-doctoral researchers, in order to visit members of the consortium other than their own, for a period of up to 12 months per person, thus broadening the scope of work pursued at the home institution. The Instability and Control of Massively Separated Flows (ICOMASEF) IRSES Grant, was coordinated by the author and was organized around the joint research interests of the groups led by Vassilis Theofilis (Universidad Politécnica de Madrid, Spain), Spencer Sherwin (Imperial College London, UK), Julio Soria and Hugh Blackburn (Monash University, Australia), Marcello de Medeiros and Julio Meneghini (Universidade São Paulo, Brazil), Rama Govindarajan (then at Jawaharlal Center for Advanced Scientific Research, India) and O.N. Ramesh (Indian Institute of Science, India) and a total of 33 researchers from the consortium members, shown in Table 1, who performed 120 months of secondments between January 1, 2011 and December 31, 2014. Progress was monitored through four annual review meetings, held at the Monash Center in Prato, Italy in July 2011, in parallel to the 5th Global Flow Instability and Control Symposium in Crete, Greece in September 2012, again in Prato in September 2013, this time in conjunction with an international conference on a topic synonymous with the IRSES project, and finally immediately after the 8th IUTAM Laminar–Turbulent Transition Symposium in Rio de Janeiro, Brazil in September 2014. Six new international grants jointly submitted by ICOMASEF partners were won, two joint Ph.D. degrees were awarded, while some 30 joint publications and an equal number of international conference contributions were generated by consortium members during the lifetime of the project; more activity is expected in the immediate future. In the following, a brief description of concrete results obtained in the framework of the project is presented, alongside the related publications. The overall theme of the ICOMASEF project was to combine the predominantly theoretical/numerical capabilities available to the EU side with state-of-the-art computational and experimental capabilities available to the overseas partners, with the aim of furthering understanding of separated flow, its instability and control. Researchers working primarily on theory were exposed to and gained experience from the experimental facilities of partner organizations, while experimentalists gained experience in flow instability analysis and high performance computing. A series of developments was planned and successfully completed, including:
• Theoretical and numerical methods development for the computation of optimal inflow perturbations in separated flows. • Development of the next-generation high-order computational tools for unsteady Computational Fluid Dynamics and instability analysis of incompressible separated flows.
• Development of algorithms necessary for the analysis of compressible separated flows and to model aeroacoustic behavior arising from separated flows such as undercarriages or wind turbines.
• Development of a simplified theoretical separated flow description, including results of local and global instability analysis and supported by experimentation.
• Experimental and theoretical study of instabilities in open cavity flows, including cavity acoustics. • Analysis and control of vortex-induced vibrations. The present volume reports some of the results obtained in the above mentioned areas. A number of experimental works have been dedicated to the subject of massively separated flow and its instabilities. Buchner and Soria use high resolution PIV in the range 1500 < Re < 10 000 to identify and document individual coherent structures in massively separated flow at the leading- and trailing edge of pitching plate and characterize the effect of Reynolds number on the topology of the wake. Martínez and Lazaro present a two-part experimental contribution of a flow analogous to that found in lean premixed combustors considered for large aeroengine applications. Hot-wire, LDV and PIV measurements are used to characterize coherent structures of swirling jets discharging in a rectangular enclosure at Re = O(105 ). In the measured spectra a precession instability of the swirling jet vortex breakdown is identified, as are high- frequency modes connected to the Kelvin–Helmholtz instability of the shear layer that develops in the swirling jet core. Serna and Lazaro employ non-intrusive laser-based diagnostics to investigate the reattachment region in a separated boundary layer undergoing laminar–turbulent transition. Subcritical and supercritical reattachment regimes, respectively characterized by short and long recirculation bubbles, are found to depend on the Reynolds number and a characteristic length associated with the imposed adverse pressure gradient. The phenomenological differences between flow regimes are discussed and a simplified model is proposed to estimate a critical Reynolds number of http://dx.doi.org/10.1016/j.ast.2015.05.004 1270-9638/© 2015 Published by Elsevier Masson SAS.
2
Editorial
Table 1 Researchers involved in the ICOMASEF travel grant. Asterisk denotes that the person acquired a PhD during the lifetime of the grant. Universidad Politécnica de Madrid (UPM, Spain)
ER
ESR
Theofilis V. Cordero M. De Vicente J. González L. Jiménez J. Valero E. Gómez F.∗ He W. Le Clainche S.∗ Liu Q. Martín J.A.∗ Meseguer F.∗ Paredes P.∗ Pérez J.M.∗ Tendero J.A.
Imperial College London (ICL, UK)
ER ESR
Sherwin S.J. Rocco G.
Monash University (Australia)
ER ER
Blackburn H. Soria J.
Universidade São Paulo (USP, Brazil)
ER
Assi G. Carmo B. Medeiros M. Meneghini J.R. Freire C. Gaviria A. Gennaro E.∗ Serson D.∗ Souza D.∗
ESR
Indian Institute of Science, Bangalore (IISC, India)
ER ESR
Ramesh O.N. Mitra A. Patwardhan S.
Jawaharlal Nehru Center for Advanced Scientific Research (JNC, India)
ER ESR
Govindarajan R. Jotkar M.
the observed phenomena. Le Clainche et al. present a two-part combined experimental and numerical investigation of flow around a hemisphere-cylinder at AoA = 20 deg and Re < 1000. Flow separation observed at these conditions is found to give rise to a pair of so-called horn-vortices. Proper Orthogonal and Dynamic Mode Decompositions are performed to analyze the experimental and numerical data. Unsteadiness is found to commence at Re = 350 and critical point theory is employed to describe the flow patterns observed on the body surface. The work presented by Rocco et al. on Floquet and transient growth stability analysis of a flow through a compressor passage is motivated by previous experimental and numerical investigations on a linear low-pressure (LP) compressor cascade, in an effort to understand the role of laminar separation of the boundary layers at Re = O(105 ). Floquet and non-modal stability analyses are performed on a flow the periodicity of which is restricted to a small region of the domain. Strong energy transient growth is documented to be associated with convective instabilities in the region downstream from the separation bubble. Theoretical work performed in the framework of the ICOMASEF grant included the study by Gómez et al. on matrix-free shift-invert strategies for global flow instability analysis, in which complex non-symmetric eigenvalue problems are solved using a matrix-free subspace creation. It was found that the proposed methodology, which is applicable to any type of spatial discretization, could be improved substantially by the use of a preconditioner. By contrast, Bergamo et al. discuss a matrix-forming approach for the creation of subspaces in which the solution to the eigenvalue problem governing compressible flow instabilities is sought. The square lid-driven cavity is used as demonstrator and the part of the eigenspectrum known from incompressible analysis, as well as a new branch introduced by compressibility and related with acoustic instability is documented. Souza et al. also discuss aeroacoustic instabilities arising in the slat cove using Lattice-Boltzmann-method based large-scale simulation to obtain full flow-field information. Results are used as input into the Ffowcs Williams–Hawkings analogy in order to predict acoustic radiation, while POD was used to investigate the dynamics of the cove flow. Two further theoretical contributions complete the present volume: the work by Martín and Martel on nonlinear intrinsic streaks in the flat plate boundary layer has employed a reduced Navier-Stokes formulation to describe numerically a family of Reynolds-number independent, fully nonlinear streaks, which exhibit a strong spanwise localization absent in the known linear counterparts of these structures. Finally, Tendero et al. discuss as systematic derivation of the classic equations governing linear instability of isolated- and systems of trailing vortices. They compare results of the inviscid vortex filament method with those delivered by viscous linear BiGlobal modal analysis and demonstrate the limitations of the former methodology. Work currently underway, which arose from the collaborations within the ICOMASEF grant will be reported elsewhere. Additional work performed as part of the ICOMASEF grant has appeared in several publications included in the peer-reviewed Volume 107 in the series “Fluid Mechanics and its Applications” of Springer [5], which resulted from an International Conference on “Instability and Control Massively Separated Flows” that took place in Prato, Italy, in the Fall of 2013. Further publications on the development of numerical methods for instability analysis of massively separated flows can be found in Refs. [2,3] and [7], that on experimentation and analysis of instabilities in spanwise homogeneous open cavities in incompressible flow in [1] and [6], including experimentation on cavity resonances [4]. The interested reader is referred to the above publications for further reading on the subject matters of the ICOMASEF project.
Editorial
3
Conflict of interest statement None declared. Acknowledgement Support of the EU 7th Framework Program under Marie Curie Grant PIRSES-GA-2009-247651 “FP7-PEOPLE-IRSES: ICOMASEF – Instability and Control of Massively Separated Flows” is gratefully acknowledged. References [1] J. De Vicente, J. Basley, F. Meseguer-Garrido, J. Soria, V. Theofilis, Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation, J. Fluid Mech. 748 (2014) 189–220. [2] E.M. Gennaro, D. Rodríguez, M.A.F. Medeiros, V. Theofilis, Sparse techniques in global flow instability with application to compressible leading-edge flow, AIAA J. 51 (9) (2013) 2295–2303. [3] F. Gómez, R. Gómez, V. Theofilis, On three-dimensional global linear instability analysis of flows with standard aerodynamics codes, Aerosp. Sci. Technol. 32 (1) (2014) 223–234. [4] L.M. González, P. Cobo, V. Theofilis, E. Valero, Acoustic resonances in 2D open cavities, Acta Acust. Acust. 99 (4) (2013) 572–581. [5] Instability and control of massively separated flows, in: V. Theofilis, J. Soria (Eds.), Proceedings of the International Conference on Massively Separated Flows, held in Prato, Italy, September 4–6, 2013, Springer, ISSN 0926-5112, ISBN 978-3-319-06259-4. [6] F. Meseguer-Garrido, J. De Vicente, E. Valero, V. Theofilis, On linear instability mechanisms in incompressible open cavity flow, J. Fluid Mech. 752 (2014) 219–236. [7] P. Paredes, M. Hermanns, S. Le Clainche, V. Theofilis, Order 104 speedup in global linear instability analysis using matrix formation, Comput. Methods Appl. Mech. Eng. 253 (2013) 287–304.
Editor Vassilis Theofilis E-mail address: vassilios.theofi[email protected] Available online 14 May 2015
Contents lists available at ScienceDirect
Aerospace Science and Technology www.elsevier.com/locate/aescte
Editorial
Special Issue on Instability and Control of Massively Separated Flows The present volume contains work performed during the execution of an EU FP7 Marie Curie International Research Scientists Exchange Scheme (IRSES) grant in the period of January 1, 2011 till December 31, 2014. Under this scheme research interests of scientists from EU and non-EU organizations participating in the consortium were organized in work-packages and executed through travel grants (so-called secondments) supported by the EU, while the core research funding had been put in place in advance by the participating organizations. Travel support was provided for Experienced Researchers (ERs), typically faculty and senior staff members, and Early Stage Researchers (ESRs), typically Ph.D. students and early-career post-doctoral researchers, in order to visit members of the consortium other than their own, for a period of up to 12 months per person, thus broadening the scope of work pursued at the home institution. The Instability and Control of Massively Separated Flows (ICOMASEF) IRSES Grant, was coordinated by the author and was organized around the joint research interests of the groups led by Vassilis Theofilis (Universidad Politécnica de Madrid, Spain), Spencer Sherwin (Imperial College London, UK), Julio Soria and Hugh Blackburn (Monash University, Australia), Marcello de Medeiros and Julio Meneghini (Universidade São Paulo, Brazil), Rama Govindarajan (then at Jawaharlal Center for Advanced Scientific Research, India) and O.N. Ramesh (Indian Institute of Science, India) and a total of 33 researchers from the consortium members, shown in Table 1, who performed 120 months of secondments between January 1, 2011 and December 31, 2014. Progress was monitored through four annual review meetings, held at the Monash Center in Prato, Italy in July 2011, in parallel to the 5th Global Flow Instability and Control Symposium in Crete, Greece in September 2012, again in Prato in September 2013, this time in conjunction with an international conference on a topic synonymous with the IRSES project, and finally immediately after the 8th IUTAM Laminar–Turbulent Transition Symposium in Rio de Janeiro, Brazil in September 2014. Six new international grants jointly submitted by ICOMASEF partners were won, two joint Ph.D. degrees were awarded, while some 30 joint publications and an equal number of international conference contributions were generated by consortium members during the lifetime of the project; more activity is expected in the immediate future. In the following, a brief description of concrete results obtained in the framework of the project is presented, alongside the related publications. The overall theme of the ICOMASEF project was to combine the predominantly theoretical/numerical capabilities available to the EU side with state-of-the-art computational and experimental capabilities available to the overseas partners, with the aim of furthering understanding of separated flow, its instability and control. Researchers working primarily on theory were exposed to and gained experience from the experimental facilities of partner organizations, while experimentalists gained experience in flow instability analysis and high performance computing. A series of developments was planned and successfully completed, including:
• Theoretical and numerical methods development for the computation of optimal inflow perturbations in separated flows. • Development of the next-generation high-order computational tools for unsteady Computational Fluid Dynamics and instability analysis of incompressible separated flows.
• Development of algorithms necessary for the analysis of compressible separated flows and to model aeroacoustic behavior arising from separated flows such as undercarriages or wind turbines.
• Development of a simplified theoretical separated flow description, including results of local and global instability analysis and supported by experimentation.
• Experimental and theoretical study of instabilities in open cavity flows, including cavity acoustics. • Analysis and control of vortex-induced vibrations. The present volume reports some of the results obtained in the above mentioned areas. A number of experimental works have been dedicated to the subject of massively separated flow and its instabilities. Buchner and Soria use high resolution PIV in the range 1500 < Re < 10 000 to identify and document individual coherent structures in massively separated flow at the leading- and trailing edge of pitching plate and characterize the effect of Reynolds number on the topology of the wake. Martínez and Lazaro present a two-part experimental contribution of a flow analogous to that found in lean premixed combustors considered for large aeroengine applications. Hot-wire, LDV and PIV measurements are used to characterize coherent structures of swirling jets discharging in a rectangular enclosure at Re = O(105 ). In the measured spectra a precession instability of the swirling jet vortex breakdown is identified, as are high- frequency modes connected to the Kelvin–Helmholtz instability of the shear layer that develops in the swirling jet core. Serna and Lazaro employ non-intrusive laser-based diagnostics to investigate the reattachment region in a separated boundary layer undergoing laminar–turbulent transition. Subcritical and supercritical reattachment regimes, respectively characterized by short and long recirculation bubbles, are found to depend on the Reynolds number and a characteristic length associated with the imposed adverse pressure gradient. The phenomenological differences between flow regimes are discussed and a simplified model is proposed to estimate a critical Reynolds number of http://dx.doi.org/10.1016/j.ast.2015.05.004 1270-9638/© 2015 Published by Elsevier Masson SAS.
2
Editorial
Table 1 Researchers involved in the ICOMASEF travel grant. Asterisk denotes that the person acquired a PhD during the lifetime of the grant. Universidad Politécnica de Madrid (UPM, Spain)
ER
ESR
Theofilis V. Cordero M. De Vicente J. González L. Jiménez J. Valero E. Gómez F.∗ He W. Le Clainche S.∗ Liu Q. Martín J.A.∗ Meseguer F.∗ Paredes P.∗ Pérez J.M.∗ Tendero J.A.
Imperial College London (ICL, UK)
ER ESR
Sherwin S.J. Rocco G.
Monash University (Australia)
ER ER
Blackburn H. Soria J.
Universidade São Paulo (USP, Brazil)
ER
Assi G. Carmo B. Medeiros M. Meneghini J.R. Freire C. Gaviria A. Gennaro E.∗ Serson D.∗ Souza D.∗
ESR
Indian Institute of Science, Bangalore (IISC, India)
ER ESR
Ramesh O.N. Mitra A. Patwardhan S.
Jawaharlal Nehru Center for Advanced Scientific Research (JNC, India)
ER ESR
Govindarajan R. Jotkar M.
the observed phenomena. Le Clainche et al. present a two-part combined experimental and numerical investigation of flow around a hemisphere-cylinder at AoA = 20 deg and Re < 1000. Flow separation observed at these conditions is found to give rise to a pair of so-called horn-vortices. Proper Orthogonal and Dynamic Mode Decompositions are performed to analyze the experimental and numerical data. Unsteadiness is found to commence at Re = 350 and critical point theory is employed to describe the flow patterns observed on the body surface. The work presented by Rocco et al. on Floquet and transient growth stability analysis of a flow through a compressor passage is motivated by previous experimental and numerical investigations on a linear low-pressure (LP) compressor cascade, in an effort to understand the role of laminar separation of the boundary layers at Re = O(105 ). Floquet and non-modal stability analyses are performed on a flow the periodicity of which is restricted to a small region of the domain. Strong energy transient growth is documented to be associated with convective instabilities in the region downstream from the separation bubble. Theoretical work performed in the framework of the ICOMASEF grant included the study by Gómez et al. on matrix-free shift-invert strategies for global flow instability analysis, in which complex non-symmetric eigenvalue problems are solved using a matrix-free subspace creation. It was found that the proposed methodology, which is applicable to any type of spatial discretization, could be improved substantially by the use of a preconditioner. By contrast, Bergamo et al. discuss a matrix-forming approach for the creation of subspaces in which the solution to the eigenvalue problem governing compressible flow instabilities is sought. The square lid-driven cavity is used as demonstrator and the part of the eigenspectrum known from incompressible analysis, as well as a new branch introduced by compressibility and related with acoustic instability is documented. Souza et al. also discuss aeroacoustic instabilities arising in the slat cove using Lattice-Boltzmann-method based large-scale simulation to obtain full flow-field information. Results are used as input into the Ffowcs Williams–Hawkings analogy in order to predict acoustic radiation, while POD was used to investigate the dynamics of the cove flow. Two further theoretical contributions complete the present volume: the work by Martín and Martel on nonlinear intrinsic streaks in the flat plate boundary layer has employed a reduced Navier-Stokes formulation to describe numerically a family of Reynolds-number independent, fully nonlinear streaks, which exhibit a strong spanwise localization absent in the known linear counterparts of these structures. Finally, Tendero et al. discuss as systematic derivation of the classic equations governing linear instability of isolated- and systems of trailing vortices. They compare results of the inviscid vortex filament method with those delivered by viscous linear BiGlobal modal analysis and demonstrate the limitations of the former methodology. Work currently underway, which arose from the collaborations within the ICOMASEF grant will be reported elsewhere. Additional work performed as part of the ICOMASEF grant has appeared in several publications included in the peer-reviewed Volume 107 in the series “Fluid Mechanics and its Applications” of Springer [5], which resulted from an International Conference on “Instability and Control Massively Separated Flows” that took place in Prato, Italy, in the Fall of 2013. Further publications on the development of numerical methods for instability analysis of massively separated flows can be found in Refs. [2,3] and [7], that on experimentation and analysis of instabilities in spanwise homogeneous open cavities in incompressible flow in [1] and [6], including experimentation on cavity resonances [4]. The interested reader is referred to the above publications for further reading on the subject matters of the ICOMASEF project.
Editorial
3
Conflict of interest statement None declared. Acknowledgement Support of the EU 7th Framework Program under Marie Curie Grant PIRSES-GA-2009-247651 “FP7-PEOPLE-IRSES: ICOMASEF – Instability and Control of Massively Separated Flows” is gratefully acknowledged. References [1] J. De Vicente, J. Basley, F. Meseguer-Garrido, J. Soria, V. Theofilis, Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation, J. Fluid Mech. 748 (2014) 189–220. [2] E.M. Gennaro, D. Rodríguez, M.A.F. Medeiros, V. Theofilis, Sparse techniques in global flow instability with application to compressible leading-edge flow, AIAA J. 51 (9) (2013) 2295–2303. [3] F. Gómez, R. Gómez, V. Theofilis, On three-dimensional global linear instability analysis of flows with standard aerodynamics codes, Aerosp. Sci. Technol. 32 (1) (2014) 223–234. [4] L.M. González, P. Cobo, V. Theofilis, E. Valero, Acoustic resonances in 2D open cavities, Acta Acust. Acust. 99 (4) (2013) 572–581. [5] Instability and control of massively separated flows, in: V. Theofilis, J. Soria (Eds.), Proceedings of the International Conference on Massively Separated Flows, held in Prato, Italy, September 4–6, 2013, Springer, ISSN 0926-5112, ISBN 978-3-319-06259-4. [6] F. Meseguer-Garrido, J. De Vicente, E. Valero, V. Theofilis, On linear instability mechanisms in incompressible open cavity flow, J. Fluid Mech. 752 (2014) 219–236. [7] P. Paredes, M. Hermanns, S. Le Clainche, V. Theofilis, Order 104 speedup in global linear instability analysis using matrix formation, Comput. Methods Appl. Mech. Eng. 253 (2013) 287–304.
Editor Vassilis Theofilis E-mail address: vassilios.theofi[email protected] Available online 14 May 2015