Department of Civil & Infrastructure Engineering

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IIT Jodhpur

The turbulence parameters over a water-worked gravel-bed (WGB) and a screeded gravel-bed (SGB) are studied, measuring the flow by a particle image velocimetry system in a rectangular flume keeping the flow conditions identical in both the beds. Owing to the water action, the orientation and the alignment of the surface gravels in the WGB were entirely different from those in the SGB. As a result, the WGB possesses higher roughness than the SGB. Analysis of vorticity contours infers that the gravels cause the fluid streaks to have both clockwise and counterclockwise motions in the near-bed flow zone. Besides, the double-averaged streamwise velocity, spatially averaged (SA) Reynolds and dispersive shear stress, SA and dispersive turbulent kinetic energy (TKE) fluxes, and SA TKE budget were analyzed in both the beds. Owing to the higher roughness in the WGB than in the SGB, the turbulence parameters, especially in the near-bed flow zone, remain higher in the former than in the latter. © Springer Nature Switzerland AG 2020.

World University root node

GeoPlanet: Earth and Planetary Sciences

Hydrodynamics of Water-Worked and Screeded Gravel-Bed Flows

The turbulence characteristics in flow over and within the interface of two-dimensional dunes are investigated experimentally. Besides the spatial flow and turbulence quantities, their double-averaged profiles are also analyzed. The flow over dunes is recognized to be a wake-interference flow, where the decelerated flow at the immediate downstream of the crest causes the kolk-boil effect. The flow reattachment can be explained from the perspective of the CoandÄ effect. The inner boundary layer edge follows the locus of the inflection points of velocity profiles having a velocity defect. The Reynolds shear stress profiles attain their respective peaks along this locus. In addition, the dispersive shear stress initiates from the edge of the form-induced sublayer being negative, indicating a spatially decelerated flow. The third-order correlations reveal that an inrush of rapidly moving fluid streaks coupled with a downward-downstream Reynolds stress diffusion prevails within the interfacial sublayer, while an arrival of slowly moving fluid streaks coupled with an upward-upstream stress diffusion governs the flow zone above the crest. The turbulent kinetic energy (TKE) flux results corroborate the similar findings. Concerning the TKE budget, the dispersive kinetic energy diffusion is found to be substantial within the roughness sublayer. The budget terms exhibit their respective peaks near the crest. The production rate is greater than the dissipation rate. However, the TKE diffusion and pressure energy diffusion rates are negative in the interfacial sublayer. The bursting analysis endorses that the sweeps and ejections govern within the interfacial sublayer and the flow zone above the crest, respectively. © 2020 Author(s).

Physics of Fluids

Hydrodynamics of flow over two-dimensional dunes

This experimental study brings the turbulent length scales and the Reynolds stress anisotropy into focus in wall-wake flow downstream of an isolated dunal bedform. The results reveal that wall-wake flow downstream of an isolated dune possesses a high-turbulence level having its peak value at the dune crest level. This level lasts up to the vertical distance until the effects of the dune on the flow disappears. Regarding the turbulent length scales, downstream of the dune, the Prandtl’s mixing length in wall-wake flow is greater than that in undisturbed upstream flow, while the Taylor microscale and the Kolmogorov length scale are smaller. In Reynolds stress anisotropy analysis, the anisotropy invariant maps demonstrate the data plots form a looping trend in wall-wake flow. Below the dune crest, the turbulence is characterized with an affinity to show a two-dimensional isotropy, while above the crest, the anisotropy has a tendency to reduce to a quasi-three-dimensional isotropy. © Springer Nature Switzerland AG 2020.

Turbulent Length Scales and Reynolds Stress Anisotropy in Wall-Wake Flow Downstream of an Isolated Dunal Bedform

Fluvial instabilities originate from an interplay between the carrier fluid and the erodible loose boundary at their interface, manifesting a variety of sedimentary architectures with length scales spanning from a few millimeters to hundreds of meters. This review sheds light on the current state-of-the-science of the subject, explaining the fluvial instabilities from three broad perspectives. They are micro-scale, meso-scale, and macro-scale instabilities. The interactions between the near-bed hydrodynamics and the sediment dynamics in generating various kinds of instabilities, including their natures and driving mechanisms, are thoroughly appraised in the light of laboratory experimental results, field observations, and theoretical backgrounds. Besides, this review addresses the current challenges, delineating key points as a future research scope. © 2020 Author(s).

Fulltext

Fluvial instabilities

Characteristics and sources of volatile organic compounds (VOCs) were investigated with highly time-resolved simultaneous measurements by two proton-transfer-reaction time-of-flight mass spectrometers (PTR-ToF-MS) at an urban and a suburban site in New Delhi, India, from January to March 2018. During the measurement period, high mixing ratios of VOCs and trace gases were observed, with high nocturnal mixing ratios and strong day-night variations. The positive matrix factorization (PMF) receptor model was applied separately to the two sites, and six major factors of VOCs were identified at both sites, i.e., two factors related to traffic emissions, two to solid fuel combustion, and two secondary factors. At the urban site, traffic-related emissions comprising mostly mono-aromatic compounds were the dominant sources, contributing 56.6% of the total mixing ratio, compared to 36.0% at the suburban site. Emissions from various solid fuel combustion processes, particularly in the night, were identified as a significant source of aromatics, phenols and furans at both sites. The secondary factors accounted for 15.9% of the total VOC concentration at the urban site and for 33.6% at the suburban site. They were dominated by oxygenated VOCs and exhibited substantially higher contributions during daytime. © 2020 BMJ Publishing Group. All rights reserved.

Atmospheric Chemistry and Physics

Source characterization of volatile organic compounds measured by proton-transfer-reaction time-of-flight mass spectrometers in Delhi, India

This chapter presents the seismic vulnerability of Kathmandu City (Nepal), based on Nepal 2015 earthquake, in terms of the ground response and liquefaction potential. The spatially well-distributed 10-boreholes and ground motions of Mw 7.8 Nepal 2015 earthquake recorded at five different stations were adopted for the analysis. The range of peak ground acceleration and peak spectral acceleration were in the order of 0.21g-0.42g and 0.74g-1.50g, respectively. Liquefaction potential of the sites were computed using both semi-empirical approach and liquefaction potential index (LPI). LPI shows that the 6 sites out of 10 sites are at high risk of liquefaction. Copyright © 2020, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited.

International Journal of Geotechnical Earthquake Engineering

Characterization of ground response and liquefaction for Kathmandu city based on 2015 earthquake using total stress and effective stress approach

EGU General Assembly Conference Abstracts

Modeling of Basin Scale Hydro-meteorological association by Hybrid Wavelet-ARX approach

Delhi, the capital of India, suffers from heavy local emissions as well as regional transport of air pollutants, resulting in severe aerosol loadings. To determine the sources of these pollutants, we have quantified the mass concentrations of 26 elements in airborne particles, measured by an online X-ray fluorescence spectrometer with time resolution between 30 min and 1 h. Measurements of PM10 and PM2.5 (particulate matter &lt;10 μm and &lt; 2.5 μm) were conducted during two consecutive winters (2018 and 2019) in Delhi. On average, 26 elements from Al to Pb made up ~25% and ~19% of the total PM10 mass (271 μg m−3 and 300 μg m−3) in 2018 and 2019, respectively. Nine different aerosol sources were identified during both winters using positive matrix factorization (PMF), including dust, non-exhaust, an S-rich factor, two solid fuel combustion (SFC) factors and four industrial/combustion factors related to plume events (Cr-Ni-Mn, Cu-Cd-Pb, Pb-Sn-Se and Cl-Br-Se). All factors were resolved in both size ranges (but varying relative concentrations), comprising the following contributions to the elemental PM10 mass (in % average for 2018 and 2019): Cl-Br-Se (41.5%, 36.9%), dust (27.6%, 28.7%), non-exhaust (16.2%, 13.7%), S-rich (6.9%, 9.2%), SFC1 + SFC2 (4%, 7%), Pb-Sn-Se (2.3%, 1.66%), Cu-Cd-Pb (0.67%, 2.2%) and Cr-Ni-Mn (0.57%, 0.47%). Most of these sources had the highest relative contributions during late night (22:00 local time (LT)) and early morning hours (between 03:00 to 08:00 LT), which is consistent with enhanced emissions into a shallow boundary layer. Modelling of airmass source geography revealed that the Pb-Sn-Se, Cl-Br-Se and SFC2 factors prevailed for northwest winds (Pakistan, Punjab, Haryana and Delhi), while the Cu-Cd-Pb and S-rich factors originated from east (Nepal and Uttar Pradesh) and the Cr-Ni-Mn factor from northeast (Uttar Pradesh). In contrast, SFC1, dust and non-exhaust were not associated with any specific wind direction. © 2020 The Authors

Department of Electrical Engineering

Science of the Total Environment

Real-time measurement and source apportionment of elements in Delhi's atmosphere

The results of an experimental study on the turbulence characteristics in flow over and downstream of an isolated bedform are presented. The vertical profiles of time-averaged streamwise velocity, Reynolds stresses and turbulent kinetic energy (TKE) fluxes at different horizontal locations over and downstream of a bedform are shown to demonstrate their variations. The experimental results signify a flow acceleration, separation and deceleration over the stoss-side, at the crest and in the leeside of a bedform. In addition, in the wall-wake region (far downstream of the bedform), the defects (uninterrupted upstream value minus downstream value at a given vertical distance) in time-averaged streamwise velocity, Reynolds shear stress (RSS), turbulence intensities and TKE fluxes demonstrate the self-preserving characteristics in their individual vertical profiles when they are scaled by their individual peak defects. For scaling the vertical distance to achieve the self-preserving characteristics, the defect profiles of velocity were scaled by the half-width of peak velocity defect, those of RSS and turbulence intensities by the half-width of peak RSS defect and those of TKE fluxes by the half-width of individual peak TKE flux defects. The peak defects of all the parameters lessen, as one moves toward the downstream, recovering their uninterrupted upstream profiles. © 2020, Springer Nature B.V.

Environmental Fluid Mechanics

Self-preserving characteristics in wall-wake flow downstream of an isolated bedform

The hydrodynamic force on sediment particles is decomposed into two components, hydrodynamic drag and lift, whose estimations are made semiempirically by the introduction of drag and lift coefficients. A remarkable agreement on the estimation of drag coefficient has been attained in the literature. However, a generic consensus on the determination of lift coefficient so far remains unachievable. This article presents a state-of-the-art review of the hydrodynamic lift on sediment particles at an entrainment, highlighting the present status of lift coefficient in light of experimental observations and the theoretical foundation. The uncertainty in the estimation of hydrodynamic lift and different components of hydrodynamic lift in modeling the entrainment threshold of sediments are discussed. This article shows, for the first time, that there remains a prospect to obtain a generic consensus on the lift coefficient. Compiling and analyzing the lift coefficient data obtained from theoretical predictions, experimental observations, and numerical simulations, it is revealed that the lift coefficient data are somewhat collapsed to a thick band. This band, although subject to inevitable uncertainties, is found to provide a general consensus on the lift coefficient over a wide range of the particle Reynolds number. Finally, the article offers an insight into open questions and sheds light on how these challenges could be resolved. © 2020 American Society of Civil Engineers.