Anderson, William
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/5767
William Anderson joined the Erik Jonsson School of Engineering and Computer Science in 2014 as an Assistant Professor of Mechanical Engineering. He is currently an Associate Professor of mechanical engineering and a Fellow, Eugene McDermott Professor. His work on fluid dynamics helped him and a colleague propose a solution to the mystery of Martian crater mountains formation. His research interests include:
- Computational fluid dynamics,
- Turbulent flows,
- Environmental fluid dynamics,
- High-performance computing, and
- Boundary layer meteorology
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Recent Submissions
Item Numerical Study of Turbulent Channel Flow Perturbed by Spanwise Topographic Heterogeneity: Amplitude and Frequency Modulation Within Low- and High-Momentum Pathways(American Physical Society) Awasthi, Ankit; Anderson, William; Awasthi, Ankit; Anderson, WilliamWe have studied the effects of topographically driven secondary flows on inner-outer interaction in turbulent channel flow. Recent studies have revealed that large-scale motions in the logarithmic region impose an amplitude and frequency modulation on the dynamics of small-scale structures near the wall. This led to development of a predictive model for near-wall dynamics, which has practical relevance for large-eddy simulations. Existing work on amplitude modulation has focused on smooth-wall flows; however, Anderson [J. Fluid Mech. 789, 567 (2016)10.1017/jfm.2015.744] addressed the problem of rough-wall turbulent channel flow in which the correlation profiles for amplitude modulation showed trends similar to those reported by Mathis et al. [Phys. Fluids 21, 111703 (2009)10.1063/1.3267726]. For the present study, we considered flow over surfaces with a prominent spanwise heterogeneity, such that domain-scale turbulent secondary flows in the form of counter-rotating vortices are sustained within the flow. (We also show results for flow over a homogeneous roughness, which serves as a benchmark against the spanwise-perturbed cases.) The vortices are anchored to the topography such that prominent upwelling and downwelling occur above the low and high roughness, respectively. We have quantified the extent to which such secondary flows disrupt the distribution of spectral density across constituent wavelengths throughout the depth of the flow, which has direct implications for the existence of amplitude and frequency modulation. We find that the distinct outer peak associated with large-scale motions - the "modulators" - is preserved within the upwelling zone but vanishes in the downwelling zone. Within the downwelling zones, structures are steeper and shorter. Single- and two-point correlations for inner-outer amplitude and frequency modulation demonstrate insensitivity to resolution across cases. We also show a pronounced crossover between the single- and two-point correlations, a product of modulation quantification based upon Parseval's theorem (i.e., spectral density, but not the wavelength at which energy resides, defines the strength of modulation). © 2018 American Physical Society.Item Langmuir Turbulence In Coastal Zones: Structure and Length Scales(American Meteorological Society) Shrestha, Kalyan; Anderson, William; Kuehl, J.; Shrestha, Kalyan; Anderson, WilliamLangmuir turbulence is a boundary layer oceanographic phenomenon of the upper layer that is relevant to mixing and vertical transport capacity. It is a manifestation of imposed aerodynamic stresses and the aggregate horizontal velocity profile due to orbital wave motion (the so-called Stokes profile), resulting in streamwise-elongated, counterrotating cells. The majority of previous research on Langmuir turbulence has focused on the open ocean. Here, we investigate the characteristics of coastal Langmuir turbulence by solving the grid-filtered Craik-Leibovich equations where the distinction between open and coastal conditions is a product of additional bottom boundary layer shear. Studies are elucidated by visualizing Langmuir cell vortices using isosurfaces of Q. We show that different environmental forcing conditions control the length scales of coastal Langmuir cells. We have identified regimes where increasing the Stokes drift velocity and decreasing surface wind stress both act to change the horizontal size of coastal Langmuir cells. Furthermore, wavenumber is also responsible in setting the horizontal extent Ls of Langmuir cells. Along with that, wavenumber that is linked to the Stokes depth δ_s controls the vertical extent L_h ^{SSV} of small-scale vortices embedded within the upwelling limb, while the downwelling limb occupies the depth of the water column H for any coastal surface wave forcing (i.e., L{_h ^d} =H and L{_h^{ssv} ~δ_s). Additional simulations are included to demonstrate insensitivity to the grid resolution and aspect ratio.Item Turbulent Flow Over Craters on Mars: Vorticity Dynamics Reveal Aeolian Excavation Mechanism(American Physical Society, 2017-10-27) Anderson, William; Day, Mackenzie; Anderson, WilliamImpact craters are scattered across Mars. These craters exhibit geometric self-similarity over a spectrum of diameters, ranging from tens to thousands of kilometers. The late Noachian-early Hesperian boundary marks a dramatic shift in the role of mid-latitude craters, from depocenter sedimentary basins to aeolian source areas. At present day, many craters contain prominent layered sedimentary mounds with maximum elevations comparable to the rim height. The mounds are remnants of Noachian deposition and are surrounded by a radial moat. Large-eddy simulation has been used to model turbulent flows over synthetic craterlike geometries. Geometric attributes of the craters and the aloft flow have been carefully matched to resemble ambient conditions in the atmospheric boundary layer of Mars. Vorticity dynamics analysis within the crater basin reveals the presence of counterrotating helical vortices, verifying the efficacy of deflationary models put forth recently by Bennett and Bell . . . and Day et al. . . . We show how these helical counterrotating vortices spiral around the outer rim, gradually deflating the moat and carving the mound; excavation occurs faster on the upwind side, explaining the radial eccentricity of the mounds relative to the surrounding crater basin.