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

International audienceDirect numerical simulations (DNS) of controlled H- and K-type transitions to turbulence in an M=0.2 (where M is the Mach number) nominally zero-pressure-gradient and spatially developing flat-plate boundary layer are considered. Sayadi, Hamman & Moin (J. Fluid Mech., vol. 724, 2013, pp. 480-509) showed that with the start of the transition process, the skin-friction profiles of these controlled transitions diverge abruptly from the laminar value and overshoot the turbulent estimation. The objective of this work is to identify the structures of dynamical importance throughout the transitional region. Dynamic mode decomposition (DMD) (Schmid, J. Fluid Mech., vol. 656, 2010, pp. 5-28) as an optimal phase-averaging process, together with triple decomposition (Reynolds & Hussain, J. Fluid Mech., vol. 54 (02), 1972, pp. 263-288), is employed to assess the contribution of each coherent structure to the total Reynolds shear stress. This analysis shows that low-frequency modes, corresponding to the legs of hairpin vortices, contribute most to the total Reynolds shear stress. The use of composite DMD of the vortical structures together with the skin-friction coefficient allows the assessment of the coupling between near-wall structures captured by the low-frequency modes and their contribution to the total skin-friction coefficient. We are able to show that the low-frequency modes provide an accurate estimate of the skin-friction coefficient through the transition process. This is of interest since large-eddy simulation (LES) of the same configuration fails to provide a good prediction of the rise to this overshoot. The reduced-order representation of the flow is used to compare the LES and the DNS results within this region. Application of this methodology to the LES of the H-type transition illustrates the effect of the grid resolution and the subgrid-scale model on the estimated shear stress of these low-frequency modes. The analysis shows that although the shapes and frequencies of the low-frequency modes are independent of the resolution, the amplitudes are underpredicted in the LES, resulting in underprediction of the Reynolds shear stress

Monitoring the Planned Restoration of Streambeds following Damage from Hurricane Irene and Tropical Storm Lee

SUNY Cobleskill has a long history of monitoring water quality in the Schoharie Valley in New York\u27s northern Catskill region. Catastrophic damage to creeks throughout the region affected by Hurricane Irene and Tropical Storm Lee was exacerbated by some anthropogenic fixes immediately following. As these waterways still threaten the life and livelihood of a good portion of the county, a $20+M federal project to restore these streams and creek is well underway. Our longitudinal studies continue to monitor water quality before and during this comprehensive restoration project. Our results show that some creeks have recovered naturally over the last three years, but others remain unstable and essentially unsustainable environmentally as seen by lack of biological diversity, low alkalinity and high turbidity. We plan to continue monitoring throughout 2015 as the restoration projects conclude

The Role of the Honors College Dean in the Future of Honors Education

In this chapter, four honors deans reflect on the unique aspects of the honors dean\u27s role. The authors argue that by being responsive to the challenges, opportunities, and responsibilities they face daily, honors deans can enable honors to deliver on its promises to students and to serve the whole university community. Attentive to changing dynamics in honors education nationwide, the authors address how deans must confront myths about honors that bear the legacy of past realities while actively tending to justice in the admissions process, to recruiting and serving diverse populations, and to supporting an honors environment that addresses the needs of the whole student. Doing so, honors deans can be at the forefront of transforming higher education. The authors explore the honors dean’s transformative role of promoting interdisciplinarity, institutional nimbleness, and innovative approaches to fundraising, in addition to the imperative of developing powerful new strategies for telling the story of honors and the value it provides. The authors argue, finally, that honors deans have the critical task of leading honorably, which means that a modern concept of honor, focusing on justice, accessibility, well-being, and empowerment, should lie at the heart of every honors enterprise

Stability and Control of Spiral Vortex Breakdown

The physical origin of spiral vortex breakdown is investigated using the direct and adjoint Navier-Stokes equations linearized around axisymmetric vortex breakdown. The wave modes region, defined as the overlap region between adjoint and direct global mode, allows us to determine whether the wake of the recirculation region or the recirculation region itself causes the spiral vortex breakdown

Sparsity-promoting dynamic mode decomposition

International audienceDynamic mode decomposition (DMD) represents an effective means for capturing the essential features of numerically or experimentally generated flow fields. In order to achieve a desirable tradeoff between the quality of approximation and the number of modes that are used to approximate the given fields, we develop a sparsity-promoting variant of the standard DMD algorithm. Sparsity is induced by regularizing the least-squares deviation between the matrix of snapshots and the linear combination of DMD modes with an additional term that penalizes the l(1)-norm of the vector of DMD amplitudes. The globally optimal solution of the resulting regularized convex optimization problem is computed using the alternating direction method of multipliers, an algorithm well-suited for large problems. Several examples of flow fields resulting from numerical simulations and physical experiments are used to illustrate the effectiveness of the developed method. (C) 2014 AIP Publishing LLC

NDE Software Developed at NASA Glenn Research Center

NASA Glenn Research Center has developed several important Nondestructive Evaluation (NDE) related software packages for different projects in the last 10 years. Three of the software packages have been created with commercial-grade user interfaces and are available to United States entities for download on the NASA Technology Transfer and Partnership Office server (https://sr.grc.nasa.gov/). This article provides brief overviews of the software packages

X-Atlas: An Online Archive of Chandra's Stellar High Energy Transmission Gratings Observations

The high-resolution X-ray spectroscopy made possible by the 1999 deployment of the Chandra X-ray Observatory has revolutionized our understanding of stellar X-ray emission. Many puzzles remain, though, particularly regarding the mechanisms of X-ray emission from OB stars. Although numerous individual stars have been observed in high-resolution, realizing the full scientific potential of these observations will necessitate studying the high-resolution Chandra dataset as a whole. To facilitate the rapid comparison and characterization of stellar spectra, we have compiled a uniformly processed database of all stars observed with the Chandra High Energy Transmission Grating (HETG). This database, known as X-Atlas, is accessible through a web interface with searching, data retrieval, and interactive plotting capabilities. For each target, X-Atlas also features predictions of the low-resolution ACIS spectra convolved from the HETG data for comparison with stellar sources in archival ACIS images. Preliminary analyses of the hardness ratios, quantiles, and spectral fits derived from the predicted ACIS spectra reveal systematic differences between the high-mass and low-mass stars in the atlas and offer evidence for at least two distinct classes of high-mass stars. A high degree of X-ray variability is also seen in both high and low-mass stars, including Capella, long thought to exhibit minimal variability. X-Atlas contains over 130 observations of approximately 25 high-mass stars and 40 low-mass stars and will be updated as additional stellar HETG observations become public. The atlas has recently expanded to non-stellar point sources, and Low Energy Transmission Grating (LETG) observations are currently being added as well