Validation of LES-C turbulence models Batugedara, Yasasya; Labovsky, Alexander E.; Schwiebert, Kyle J.
Computer methods in applied mechanics and engineering,
01/2024, Volume:
418
Journal Article
Peer reviewed
Open access
A new family of turbulence models, Large Eddy Simulation with Correction (LES-C) has been proposed in Labovsky (2020), that reduces the modeling error by treating an LES model as a defect solution ...and then correcting it on the same spatial mesh. Herein, we investigate numerically several LES-C models, that stem from popular LES approaches: Approximate Deconvolution Model (ADM), Leray-α, NS-α, and NS-ω. The resulting LES-C models ADC, Leray-α-C, NS-α-C and NS-ω-C are tested on the two-dimensional problems (flow past a circular object, flow past a step) and on the three-dimensional benchmark problem of turbulent channel flow. In all the numerical tests all LES-C models are shown to outperform their LES counterparts on coarse spatial meshes.
Variability, duration and magnitude of stream temperature drives direct and indirect effects on aquatic ecosystems. Articles contained within this Special Issue provide an overview of the current ...modelling and field-based research on stream temperature in Canada, in addition to highlighting the need for better understanding of the ecological impacts of stream temperature. The nine papers in the Special Issue are grouped across four broad themes: river temperature and impoundments, monitoring of river temperature regimes at large scales, understanding river energy budgets, and river temperature and ecology. As a whole, the Special Issue provides commentary on the path forwards for enhanced collaboration and integration of complementary approaches, for better understanding of stream temperature regimes within Canada and further afield.
•Length required for fully developed flow through lattices.•Unsteady flow features through lattices.•Heat transfer and pressure loss for densely packed lattices.
As advanced manufacturing ...methodologies such as additive manufacturing become accessible and cost effective, more complex and tailored internal cooling schemes can be achieved. One family of cooling geometries that has recently garnered interest within the heat transfer community are lattice structures. These structures offer enhanced mixing and large surface area-to-volume ratios, but their application in advanced heat exchangers is in relative infancy. This study explored the performance of two types of lattice unit cells, specifically Kagome and body centered cubic (BCC), by identifying the flow development and unsteady characteristics using large eddy simulations (LES) at a Reynolds number of 20,000. Simulation results agree well with experimental data, and differences between the two methods was found to be a function of the as-printed quality of the experimental geometry. Results indicate that both lattices feature spatial periodicity in the local Nusselt number and friction factor, due to the changes in flow area and flow interactions in the wake of each lattice strut. LES results show that the flow through the BCC lattice became fully developed, both hydrodynamically and thermally, with fewer unit cells than through the Kagome. In the entry region, the flow in the Kagome lattice became biased towards one side of the channel due to local wakes and interactions with the lattice struts, resulting in a bias to the local heat transfer. The simulations also revealed that the instantaneous vortices shed from the BCC lattice struts interacted with the duct endwalls, pulling the boundary layer from the wall and enhancing heat transfer.
•Leaf phenology and plant age explained 38% and 28% of intraspecific trait variation.•Global leaf economic spectrum generally held at local scales.•Trait-trait relationships were strongly modulated ...by leaf phenology and plant age.
Intraspecific leaf economic spectrum (LES) traits vary considerably with leaf phenology and plant age, but whether these trait patterns significantly vary between species with different shade tolerances at local scales has rarely been examined. The presence of LES within species at local scales has recently been debated; however, the conclusions are far from universal, and whether the trait-trait relationships are modulated by leaf phenology and plant age needs to be tested. We measured six leaf traits (i.e., specific leaf area, leaf dry matter content, leaf thickness, mass-based leaf nitrogen content, leaf phosphorus content and ratio of nitrogen and phosphorus contents) among different leaf phenological stages (young, mature and old leaves) and plant ages (adult and sapling) for three temperate broadleaf species with different levels of shade tolerance. Intraspecific trait variation depended on the species and traits, and interspecies trait variation patterns were inconsistent with the LES prediction. Specific leaf area significantly decreased as the shade tolerance of a species increased, which was in contrast with the global LES prediction. Additionally, 38% and 28% of intraspecific trait variation was explained by leaf phenology and plant age, respectively, for the overall leaf traits of the three species. Generally, global LES held at the local scale, but trait-trait relationships were strongly modulated by leaf phenology and plant age. The intraspecific trait variation among the leaf phenology and plant age stages was driven by the LES axis and leaf thickness, respectively. We highlight the importance of leaf phenology and plant age on intraspecific trait variation and trait-trait relationships. We provide direct evidence of the LES at a local spatial scale and a seasonally temporal scale, but variations in LES traits are not always reliable for predicting the resource-use strategies of plants at local scales.
Wind loading is a major concern for solar array systems. To clarify the relations between flow field and wind pressure distributions on solar panels, large eddy simulations (LES) are performed to ...examine the flow characteristics around solar arrays mounted on a flat roof building for two normal wind directions, 0° and 180°. The mean, standard deviation and peak value of pressure and force coefficients obtained from LES and wind tunnel experiment are firstly compared to validate the accuracy of LES. Then the mean and unsteady flow fields around solar arrays are discussed to explain the corresponding wind pressure distributions. The local separation at the higher edges of solar panels located inside of both the separation bubble and the reattached flow are detected. The wind pressures on upper and lower surfaces of solar panels resulted by the local flow field are discussed accordingly for different scenarios. Ensemble-averaged flow fields on the condition of the occurrence of peak pressures at the higher edge of solar panels are also investigated. It is found that besides the large-scale separating and reattaching flow induced by the building, small-scale local separations at the higher edges of the solar panels are also responsible for the large peak of uplift.
•Large eddy simulation of flat-roof-mounted solar arrays in boundary layer flow.•Comparisons of wind pressure and force coefficients between LES and experiment.•Mean and unsteady flow characteristics of solar panels under different winds.•Interaction of separating and reattaching flow induced by building with solar panels.
A Sigfox Energy Consumption Model Gomez, Carles; Veras, Juan Carlos; Vidal, Rafael ...
Sensors (Basel, Switzerland),
02/2019, Volume:
19, Issue:
3
Journal Article, Publication
Peer reviewed
Open access
Sigfox has become one of the main Low-Power Wide Area Network (LPWAN) technologies, as it has attracted the attention of the industry, academy and standards development organizations in recent years. ...Sigfox devices, such as sensors or actuators, are expected to run on limited energy sources; therefore, it is crucial to investigate the energy consumption of Sigfox. However, the literature has only focused on this topic to a very limited extent. This paper presents an analytical model that characterizes device current consumption, device lifetime and energy cost of data delivery with Sigfox. In order to capture a realistic behavior, the model has been derived from measurements carried out on a real Sigfox hardware module. The model allows quantifying the impact of relevant Sigfox parameters and mechanisms, as well as frame losses, on Sigfox device energy performance. Among others, evaluation results show that the considered Sigfox device, powered by a 2400 mAh battery, can achieve a theoretical lifetime of 1.5 or 2.5 years while sending one message every 10 min at 100 bit/s or 600 bit/s, respectively, and an asymptotic lifetime of 14.6 years as the message transmission rate decreases.
The present study aims to elucidate the interplay among the interfacial dynamics, surfactant transport, and underlying flow structures inside a cylindrical stirred vessel equipped with a pitched ...blade turbine. To address this, massively parallel three-dimensional, interface-tracking, large eddy simulations of oil-in-water dispersions are deployed to provide detailed, realistic visualisations of the intricate interfacial dynamics coupled to the turbulent flow field. In particular, we isolate the effect of surfactant arising from interfacial tension reduction and Marangoni stress (related to surfactant concentration gradient) by comparing two surfactant-laden systems, one being a realistic and experiment-achievable case, and another a simulation-exclusive system where the Marangoni stress is turned off. This comparison consists of qualitative interface visualisation as well as quantitative statistics in terms of dispersed phases counts and their size distribution. Finally, surfactant elasticity is modified with the aim of exploring its effect on the targeted mixing system.
Complex adaptive systems Miller, John H; Miller, John H; Page, Scott E
2009., 20091128, 2009, 2007, 2007-01-01, 20070101, Volume:
14
eBook
This book provides the first clear, comprehensive, and accessible account of complex adaptive social systems, by two of the field's leading authorities. Such systems--whether political parties, stock ...markets, or ant colonies--present some of the most intriguing theoretical and practical challenges confronting the social sciences. Engagingly written, and balancing technical detail with intuitive explanations,Complex Adaptive Systemsfocuses on the key tools and ideas that have emerged in the field since the mid-1990s, as well as the techniques needed to investigate such systems. It provides a detailed introduction to concepts such as emergence, self-organized criticality, automata, networks, diversity, adaptation, and feedback. It also demonstrates how complex adaptive systems can be explored using methods ranging from mathematics to computational models of adaptive agents.
John Miller and Scott Page show how to combine ideas from economics, political science, biology, physics, and computer science to illuminate topics in organization, adaptation, decentralization, and robustness. They also demonstrate how the usual extremes used in modeling can be fruitfully transcended.
Understanding Writing Transfer Randall Bass, Jessie L. Moore / Randall Bass, Jessie L. Moore
2017, 2023-07-03, 2017-01-20
eBook
While education is based on the broad assumption that what one learns here can transfer over there across critical transitions what do we really know about the transfer of knowledge?The question ...is all the more urgent at a time when there are pressures to unbundle higher education to target learning particular subjects and skills for occupational credentialing to the detriment of integrative education that enables students to make connections and integrate their knowledge, skills and habits of mind into a adaptable and critical stance toward the worldThis book the fruit of two-year multi-institutional studies by forty-five researchers from twenty-eight institutions in five countries identifies enabling practices for, and five essential principles about, writing transfer that should inform decision-making by all higher education stakeholders about how to generally promote the transfer of knowledge.This collection concisely summarizes what we know about writing transfer and explores the implications of writing transfer research for universities institutional decisions about writing across the curriculum requirements, general education programs, online and hybrid learning, outcomes assessment, writing-supported experiential learning, e-portfolios, first-year experiences, and other higher education initiatives. This volume makes writing transfer research accessible to administrators, faculty decision makers, and other stakeholders across the curriculum who have a vested interest in preparing students to succeed in their future writing tasks in academia, the workplace, and their civic lives, and offers a framework for addressing the tensions between competency-based education and the integration of knowledge so vital for our society.
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