Reduced-order representation of near-wall structures in the late transitional boundary layer

Sayadi, Taraneh; Schmid, Peter J.; Nichols, Joseph W.; Moin, Parviz

doi:10.1017/jfm.2014.184

Cited by 79 publications

(26 citation statements)

References 35 publications

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“…The eigenvalue decomposition of this linear transformation then provides frequency information as well as the corresponding spatial structures. Furthermore, a projection of the snapshots onto these structures gives the amplitude (contribution) information (Schmid 2010;Sayadi et al 2014). Eventually, the snapshots can be approximated using the DMD modes as in which Φ r , ψ k and b k , are the field reconstructed by the r DMD modes, the k-th spatial DMD mode (shape of the mode), and the magnitude of the k-th DMD mode, respectively.…”

Section: Dynamic Mode Decomposition Based Analysis Of the Three-dimenmentioning

confidence: 99%

Spatio-temporal dynamics of turbulent separation bubbles

Meneveau

Mittal

2019

J. Fluid Mech.

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The spatio-temporal dynamics of separation bubbles induced to form in a fully-developed turbulent boundary layer (with Reynolds number based on momentum thickness of the boundary layer of 490) over a flat plate are studied via direct numerical simulations. Two different separation bubbles are examined: one induced by a suction-blowing velocity profile on the top boundary and the other, by a suction-only velocity profile. The latter condition allows reattachment to occur without an externally imposed favorable pressure gradient and leads to a separation bubble more representative of those occurring over airfoils and in diffusers. The suction-only separation bubble exhibits a range of clearly distinguishable modes including a high-frequency mode and a low-frequency "breathing" mode that has been observed in some previous experiments. The high-frequency mode is well characterized by classical frequency scalings for a plane mixing layer and is associated with the formation and shedding of spanwise oriented vortex rollers. The topology associated with the low-frequency motion is revealed by applying dynamic mode decomposition to the data from the simulations and is shown to be dominated by highly elongated structures in the streamwise direction. The possibility of Görtler instability induced by the streamwise curvature on the upstream end of the separation bubble as the underlying mechanism for these structures and the associated low frequency is explored.

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Section: Dynamic Mode Decomposition Based Analysis Of the Three-dimenmentioning

confidence: 99%

Spatio-temporal dynamics of turbulent separation bubbles

Meneveau

Mittal

2019

J. Fluid Mech.

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“…The analysis is performed in a limited streamwise range before the start of fully turbulent flow (x/h < 45, 55 and 65 for Re h = 1170, 730 and 460 respectively), as the latter contains mostly uncorrelated turbulent fluctuations (Wu & Moin 2009;Sayadi et al 2014), making the modal decomposition less insightful by masking the features in the laminar and transitional states. The spanwise range of the domain is also truncated to the wake region, removing the effect of the measurement noise at the edge of the domain.…”

Section: Pod Analysismentioning

confidence: 99%

On Reynolds number dependence of micro-ramp-induced transition

Schrijer

Scarano

2018

J. Fluid Mech.

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The variation of transitional flow features past a micro-ramp is investigated when the Reynolds number is decreased approaching the critical regime. Experiments are conducted in the incompressible flow spanning from supercritical to subcritical roughness-height-based Reynolds number (Re h = 1170, 730, 460 and 320) with tomographic particle image velocimetry. The effect of Re h on three-dimensional flow behaviour is analysed in a domain encompassing 73 ramp heights in the streamwise direction. Above the critical Re h , the primary vortex pair and induced central low-speed region in the mean flow field are active over longer range when decreasing Re h . In the instantaneous flow, at Re h < 1000, the hairpin vortices induced by Kelvin-Helmholtz (K-H) instability progress gradually from close to the micro-ramp into the region where the overall shear layer is destabilized, indicating the correlation between the K-H instability and the onset of transition. The breakdown of K-H vortices as observed at Re h = 1170, does not occur at lower Re h . Decreasing Re h , the secondary vortex structures make their first appearance significantly downstream, postponing the formation of sideward disturbances, which destabilize the local shear layer by ejection events. Two major types of eigenmodes with symmetric and asymmetric spatial distribution of velocity fluctuations in the near wake are clearly identified by proper orthogonal decomposition. The symmetric and asymmetric modes correspond to the presence of vortex shedding and a sinuous wiggling motion respectively. It is found that Re h is the key factor determining the importance of the symmetric mode. At Re h = 1170, the disturbance energy of the symmetric mode decays before the onset of transition, suggesting that it is relatively insignificant in the process. However, decreasing Re h to 730 and 460, the symmetric mode produces continuous growth of high level disturbance energy, leading to transition.

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“…Through his calculations, Reynolds argued that separate modeling considerations should be used for the stresses due to the imposed deterministic waves and the remaining "random turbulence," and that the modeling of the fine-scale turbulence stresses should take into account the stresses due to wave motions. The triple decomposition of Reynolds and Hussain has been adopted in representing turbulent flows by mean, coherent modes, and random fluctuations in several later studies (see Sayadi et al 2014). Reynolds continued his experimental studies of imposed unsteady fluctuations in turbulent shear flows for several years (Acharya & Reynolds 1975, Norris & Reynolds 1975, Brereton et al 1990).…”

Section: Turbulence Subject To Imposed Periodic Disturbancesmentioning

confidence: 99%

An Appreciation of the Life and Work of William C. Reynolds (1933–2004)

Moin

Homsy

2017

Annu. Rev. Fluid Mech.

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Bill Reynolds was a remarkably creative scientist who combined a natural curiosity with enormous energy to make significant contributions to fluid mechanics research. In this article, we combine our own recollections with those of many others to capture the aspects of Bill's personality and sense of humor that made him the irrepressible person that he was. We discuss his works on turbulent flow and touch on others that illustrate the wide range of his interests. We survey his involvement in education through classroom teaching and mentoring of research students, and his lifelong support of the Division of Fluid Dynamics of the American Physical Society. And we cover his many contributions during his long career at Stanford University, where he spent his entire working life, especially his seminal role with the Center for Turbulence Research. He served as the chair of the mechanical engineering department on two separate occasions, for a total of 15 years, and cofounded both the Institute for Energy Studies (IES) and the Center for Turbulence Research (CTR) at Stanford.Bill was a gifted educator: He received the G. Edwin Burks Award for Outstanding Teaching from the American Society of Engineering Education (1972), the Tau Beta Pi Outstanding Teaching Award at Stanford (1974), and the Teaching Award from the Society of Women Engineers. The textbooks Thermodynamics (Reynolds 1968) and Engineering Thermodynamics (Reynolds & Perkins 1977) and Bill's computer program for property estimation, STANJAN, are used at over 100 universities in the United States, and worldwide, including Japan, Russia, Denmark, Germany, Italy, Sweden, Brazil, South Africa, and Australia. The book Energy: From Nature to Man (Reynolds 1974) was used in his course about energy and energy technology aimed primarily at nonengineering students. The book is a timely and cogent presentation of quantitative aspects of energy sciences, and the accompanying societal/policy choices.But these simple statements of facts and honors paint an incomplete picture of Bill.

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Reduced-order representation of near-wall structures in the late transitional boundary layer

Cited by 79 publications

References 35 publications

Spatio-temporal dynamics of turbulent separation bubbles

Spatio-temporal dynamics of turbulent separation bubbles

On Reynolds number dependence of micro-ramp-induced transition

An Appreciation of the Life and Work of William C. Reynolds (1933–2004)

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