bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of vortex regeneration mechanism in the self-sustaining process of wall-bounded flows using resolvent analysis
Authors: Jane Bae H. , McKeon Beverley J. 
Published: June 2020

Abstract
The regeneration mechanism of streamwise vortical structures in the self-sustaining process of wall-bounded turbulence is investigated. Resolvent analysis [1] is used to identify the principal forcing mode which produces the maximum amplification of the response modes in the minimal channel for the buffer [2] and logarithmic layer [3]. The identified mode is then projected out from the nonlinear term of the Navier-Stokes equations at each time step from the direct numerical simulations (DNS) of the corresponding minimal channel. The results show that the removal of the principal forcing mode is able to significantly inhibit turbulence for the buffer and logarithmic layer while removing the subsequent modes instead of the principal one only marginally affects the flow. Analysis of the dyadic interactions in the nonlinear term shows that the contributions toward the principal forcing mode come from a limited number of wavenumber interactions. Using conditional averaging, the flow structures that are responsible for generating the principal forcing mode, and thus the nonlinear interaction to self-sustain turbulence, are identified to be spanwise rolls interacting with meandering streaks.
Effect of bubble size on Lagrangian pressure statistics in homogeneous isotropic turbulence
Authors: Bappy M H , Vela-Martin A , Buscaglia G C , Carrica P M , Freire L S 
Published: June 2020

Abstract
The study of bubble’s behavior in turbulent flows is fundamental to the understanding of many engineering applications that are concerned with bubbly/two-phase flow. In turbomachinery, for example, tiny gas nuclei present in the liquid may grow to macroscopic size if the instantaneous pressure dips below the vapor pressure for a time long enough to incite cavitation events. In this paper, the Lagrangian pressure statistics of finite sized bubbles in homogeneous isotropic turbulence is investigated using highly-resolved direct numerical simulations of the Navier-Stokes equations at Reλ
= 150. A modified Maxey-Riley equation is used for Lagrangian tracking of bubbles in the turbulence field. The Lagrangian pressure statistics (probability density function, frequency of low-pressure events and their duration) are analyzed as functions of the bubble size. The overall picture that emerges is consistent with finite-sized bubbles being driven towards vortex cores, resulting in an average pressure further below the mean value and longer and more frequent low-pressure events as the considered size is increased.
Reynolds shear-stress carrying structures in shear-dominated flows
Authors: Gungor Taygun R , Maciel Yvan , Gungor Ayse G 
Published: June 2020

Abstract
Four direct numerical simulation (DNS) databases are examined to understand the effect of the wall and near-wall turbulence on the Reynolds shear-stress carrying structures in shear-driven flows. The first DNS database is of a non-equilibrium adverse-pressure-gradient (APG) turbulent boundary layer (TBL) with momentum thickness Reynolds number (Reg) reaching 8000. The second one is the same flow as the previous, but turbulence activity in the inner layer (y/S < 0.1) is artificially eliminated. The last two DNS databases are homogeneous shear turbulence (HST) with Taylor microscale Reynolds numbers (Re\) are 104 and 248. Results show that outer layer turbulence in the APG TBLs with large velocity defect is only slightly affected by the near-wall region turbulence which suggests outer layer turbulence sustains itself without necessitating near-wall turbulence. The Corrsin length scale (Lc) scales the size of the Reynolds shear-stress carrying structures in both APG TBLs and HSTs. The streamwise length of these structures is 1LC or larger in all cases. The aspect ratio of the structures behaves similarly in both APG TBLs and HSTs when the size of the structures are normalized with Lc. Sweeps and ejections tend to form side-by-side pairs in both flow types. The spatial properties of sweeps and ejections, such as aspect ratios or relative positions are not affected by near-wall turbulence activity or presence of the wall. This suggests that the structures mostly dependent on the local mean strain rates.
Global modes and large-scale structures in an Ekman boundary layer
Authors: Ortiz-Tarin J L , Lee S , Flores O , Sarkar S 
Published: June 2020

Abstract
Motivated by the dynamics of the atmospheric boundary layer, the present work examines the influence of Coriolis acceleration on wall-bounded turbulence. The large-scale structures of an Ekman boundary layer are compared to those of a channel. The distribution of energy across scales is studied by looking into the spectra of the velocity fluctuations. Linear stability analysis reveals the existence of an unstable range of wavenumbers which sustain the turbulence and lead to transverse “roll” structures observed in instantaneous snapshots of the flow.
Analysis of the spanwise extent and time persistence of uniform momentum zones in zero pressure gradient and adverse pressure gradient turbulent boundary layers
Authors: Senthil Shevarjun , Atkinson Callum , Soria Julio 
Published: June 2020

Abstract
Time-resolved velocity fields from direct numerical simulations (DNS) are used to investigate the spanwise extent and the time persistence of uniform momentum zones (UMZs) in a zero pressure gradient turbulent boundary layer (ZPG-TBL) and a self-similar adverse pressure gradient turbulent boundary layer (APG-TBL) at the verge of separation. The instantaneous detection methodology introduced by Adrian et al. [1] is used to detect the UMZs and is extended to take into account the spanwise domain length and the temporal evolution of the UMZs. The Reynolds number based on friction velocity (Reτ) ranges from 1176 to 1277 for the ZPG-TBL and from 1652 to 1745 for the self-similar APG-TBL within the domain of interest. For both the TBL cases, probability density functions (PDFs) of the number of UMZs are computed as a function of the streamwise extent, spanwise extent and time extent. For the ZPG-TBL, when the streamwise length of the domain is greater than or equal to 3 boundary layer thickness, the probability of finding 4 UMZs becomes almost negligible. For the APG-TBL, even when the streamwise domain length is taken as large as 1.3 boundary layer thickness, the probability of finding 4 UMZs is still significant. The spanwise extent of the UMZs is found to be shorter than their streamwise extent regardless of the pressure gradient in the flow. In the ZPG-TBL flow, the majority of the UMZs have a spanwise extent of the order of one-tenth of a boundary layer thickness while for the APG-TBL, it is found to be on the order of one-hundredth of a boundary layer thickness. In the ZPG-TBL, the probability of finding 2 UMZs that persist over a time period of 2 integral time scale is around 50%. Similarly, for the APG-TBL, the probability of finding 2 UMZs with a time persistence of 0.4 integral time scale is over 50%. In the case of the ZPG-TBL, it is observed that some of the UMZs with higher persistence in time have higher streamwise momentum and are found to be closer to the free-stream in general. This result is consistent with the previous observations by Laskari et al. [2]. In contrast, for the APG-TBL, UMZs with longer time persistence are found closer to the wall with lower streamwise momentum.
Wall-bounded turbulence control: statistical characterisation of actions/states
Authors: Pastor R , Vela-Martín A , Flores O 
Published: June 2020

Abstract
The present paper reports the results of a Monte Carlo experiment using a turbulent channel flow. Different actions are proposed, varying the size, duration and sign of a localised volumetric force that acts near one wall of a turbulent channel flow, running at a small Reynolds (ReT
= 165) in a small computational domain. The effect of each action is evaluated comparing the evolution of the flow with and without the action, gathering statistics over 1700 repetitions of the experiment for each action. The analysis of the results show that small/short forcings are equally likely to increase or decrease the skin friction drag, independently of the sign of the forcing (i.e., towards or away from the wall). When the size or the duration of the forcing increases, so does the probability of increasing the skin friction. Then, an a priori analysis is performed, evaluating the state of the flow just before the action, conditioned to actions that result in a decrease of the skin friction over a period of one eddy turn-over time. The resulting fields of velocity, wall shear stresses and wall pressure are consistent with an opposition control strategy, where the forcing is opposing the vertical motions near the wall. Finally, a preliminary analysis of the performance of actuation triggered by pressure or wall shear stresses sensors is evaluated (i.e., a posteriori analysis). Our results show that the actuation triggered by a wall shear sensor seems to be more effective than the actuation triggered by a wall pressure sensor, at least for the preliminary definitions of sensors and thresholds used here.
Flow structures and shear-stress predictions in the turbulent channel flow over an anisotropic porous wall
Authors: Le Clainche Soledad , Rosti Marco , Brandt Luca 
Published: June 2020

Abstract
This article identifies the main coherent structures driving the flow dynamics in the turbulent channel flow over anisotropic porous walls. Two different cases have been analyzed where the drag increases or decreases with respect to a channel with isotropic porous walls. Higher order dynamic mode decomposition (HODMD) is applied to analyze these data, identifying 20 and 15 high amplitude modes in the drag increasing (DI) and drag reducing (DR) cases, respectively, which well reflects the largest flow complexity in the former case. The frequency of 13 modes and the three-dimensional structure of the modes are similar in the DR and DI cases, suggesting the need of using more complex analyses to deepen our physical insight of these flows. The spatio-temporal HODMD analysis identifies a periodic solution along the spanwise direction (as imposed by the boundary conditions). The wavenumbers related to the modes with highest amplitude are β = 0 and β = 3 (Lz = 2
3
π ). The rollers, groups of spanwise correlated structures, are mostly identified in the DI case near the wall, with β = 0, while the presence of the streaks, streamwise correlated structures are mostly identified in the DR case. Although, in areas far away from the wall it is possible to identify these two types of structures with β = 3 in both cases, depending on the temporal frequency of the DMD modes, the rollers and the streaks are related to high and low frequency DMD modes, respectively. Finally, a model is constructed to predict the temporal evolution of the wall shear, using the 6 most relevant DMD modes interacting near the channel wall: 6 low frequency modes for DR and 3 low and 3 high frequency modes for DI. In the DR case the wall shear is predicted for almost 300 time units with relative error ∼ 2%, however, this error is larger in the DI case, ∼ 6%, suggesting the need of using a larger number of modes to represent this more complex flow.
Effect of limited near-wall inlet data on the direct numerical simulation of turbulent channel flow
Authors: Ezhilsabareesh K. , Atkinson Callum , Lozano-Duran Adrian , Schimd Peter J. , Jimenez Javier , Soria Julio 
Published: June 2020

Abstract
Direct numerical simulation (DNS) of turbulent flows require a large computational domain and a long simulation time to capture and evolve the large-scale structures and attain a statistically stationary state. In contrast, experimental measurements can relatively easily capture the large-scale structures, but struggle to resolve the dissipative flow scales. This study investigates the spatial extent required for the DNS of a turbulent channel flow to recover turbulent fluctuations and energy when using experimental inlet data which is typically unable to capture fluctuations down to the viscous sub-layer. Synthetic experimental fields from streamwise periodic channel flow DNS at Reτ = 180 are used as an inlet for a channel flow DNS with inlet-outlet boundary conditions. The effect of limited near-wall data at the inlet is examined by removing the near-wall energy and fluctuations in all but the zeroth Fourier mode. The influence of limited near-wall data on the convergence of mean and streamwise fluctuating velocity profiles is less significant when the fluctuations are removed at the inlet up to y+ = 5. However, the spanwise fluctuations are slightly weakened. The spanwise energy spectra suggest that at 1/16 of the domain length (x/h ≍ π/4) the flow scales are recovered. When the fluctuations are removed up to y+ = 17 or greater, recovery of full range of flow scales requires a domain larger than x/h = 4π.
Prediction of wall-bounded turbulence from wall quantities using convolutional neural networks
Authors: Guastoni Luca , Encinar Miguel P. , Schlatter Philipp , Azizpour Hossein , Vinuesa Ricardo 
Published: June 2020

Abstract
A fully-convolutional neural-network model is used to predict the streamwise velocity fields at several wall-normal locations by taking as input the streamwise and spanwise wall-shear-stress planes in a turbulent open channel flow. The training data are generated by performing a direct numerical simulation (DNS) at a friction Reynolds number of Reτ = 180. Various networks are trained for predictions at three inner-scaled locations (y+ = 15, 30, 50) and for different time steps between input samples Δt+
s. The inherent non-linearity of the neural-network model enables a better prediction capability than linear methods, with a lower error in both the instantaneous flow fields and turbulent statistics. Using a dataset with higher Δt+
s improves the generalization at all the considered wall-normal locations, as long as the network capacity is sufficient to generalize over the dataset. The use of a multiple-output network, with parallel dedicated branches for two wall-normal locations, does not provide any improvement over two separated single-output networks, other than a moderate saving in training time. Training time can be effectively reduced, by a factor of 4, via a transfer learning method that initializes the network parameters using the optimized parameters of a previously-trained network.
A note on the reconstruction of a 3D-3C velocity field for box turbulence
Authors: Sasaki Eiichi , Ohzeki Masayuki 
Published: June 2020

Abstract
We examine the reconstruction of a three-dimensional three-component (3D-3C) snapshot velocity field in a torus using a denoising method of compressed sensing. Using 30% of the total grid points, we could reconstruct the velocity with a relative error of approximately 10%.
Simulating interactions between topography, permafrost, and vegetation in Siberian larch forest
Authors: Sato Hisashi , Kobayashi Hideki , Beer Christian , Fedorov Alexander 
Published: June 2020

Abstract
In eastern Siberia, topography controls the abundance of the larch forest via both drought and flooding stresses. For the reconstruction of these topographical effects, we modified a dynamic vegetation model to represent soil water relocation owing to within-grid heterogeneity of elevation, over-wet-kill of trees, and air temperature differences within-grid. After calibration, the model reasonably reconstructed the geographical distributions of observation-based-estimates of fundamental properties of plant productivity and thermo-hydrology. Thus, the model appropriately responded to environmental gradients in eastern Siberia. The modified model also partially reconstructed the topography control on tree abundance and thermo-hydrology status in eastern Siberia, although its geographical distribution was not always good. In the modified model, soil water redistribution increased the risk of over-wet-kill in lower elevation classes, whereas it reduced the risk of over-wet-kill for larch trees in higher elevation classes. We demonstrated that without considering the latter effect, forest collapse due to over-wet stress would happen throughout eastern Siberia under a forecasted climatic condition during the 21st century, which will deliver a much moister environment throughout eastern Siberia. Therefore, modeling the over-wet-kill of trees without considering topographical heterogeneity would result in the overestimation of forest collapse caused by the over-wet-kill of trees under an expected climate trend in eastern Siberia.
Community engagement and public awareness on safe city program based on road safety initiatives
Authors: Mazlan Ain Naadia , Nor Lizan Mohd Hanif , Aminuddin Eeydzah , Shukor Lim Nor Hasanah Abdul , Warid Naqiuddin , Mohd Azman , Mohamed Mohd Firdaus 
Published: June 2020

Abstract
The Ministry of Housing and Local Government (KPKT) initiated Safe City Program in August 2004 as a move towards creating a safe communities and environment in urban areas to improve public quality of life. It served as a crime prevention measure in ensuring the crime rate in the city can be reduced and enables the residents to live, comfortably and safely without fear. To implement this program, each municipal council’s department of town and country planning lead the effort by designing a safe environment and reduce the chance to commit crimes. This study aims to evaluate public awareness of safe city program implementation in Johor Bahru district. Community engagement is important to make sure local community fully aware about safe city program and help in making the program successful. To determine the level of awareness, 80 questionnaires were distributed to public community around affected areas. The data were then analysed using spread sheet program and SPSS. Result has shown that public awareness is closely related with physical visibility for each safe city initiatives. The significant of the study is to provide strategy to increase public awareness for the continuation of safe city program in the future.
Design, Material Selection and Manufacturing for Sustainable Construction: An Analytical Network Process Approach
Authors: Haruna A , Shafiq N , Montasir O A , Haruna S , Mohammed M 
Published: June 2020

Abstract
Sustainable design, material selection and manufacturing of building materials serve as an important aspects of building project. Recent design decision, material selection and material manufacturing procedures fail to provide remedy to the environmental impacts caused in terms of carbon footprint and embodied energy. The research report in this paper was to address the issue in the Malaysia construction industry. This paper presented an Analytical Network Process (ANP) which is a multi-criteria decision-making technique to determine the effective strategy for material impact towards the environment with respect to design, selection and manufacturing of the building material to develop a less embodied energy profile buildings. An expert opinion survey was conducted using a well-structured questionnaire which was scaled according to saaty’s with (1) equal importance to (9) extreme importance. Three (3) responses were received which satisfies Saaty’s assertion on ANP. The retrieved questionnaire was then filled into the multi criteria decision making tools and findings showed that the most important priorities base on expert opinion were use of recyclable material at design stage, use of innovative material during manufacturing and maximize the use of local skills.
Bond behaviour of geopolymer concrete in structural application: A review
Authors: Abdul Sani M F A , Muhamad R 
Published: June 2020

Abstract
Sustainable manufacturing materials are being developed and utilized until now due to its remarkable reduction of carbon footprint along with significant structural and mechanical performances. To gain wide acceptance in the construction industries, the bond between geopolymer concrete and the reinforcing bar should be investigated beforehand. It is a critical factor that influences the behaviour of structures, specifically bond strength that will be very crucial for structural applications. Therefore, this paper review aims to describe and summarize the utilization of GPC on previous pull-out testing. A total of 10 papers on the pull-out test with different bond strengths and parameters have been summarized and discussed. Findings from the results show that effect of geopolymer blending, compressive strength, cover-to-diameter (C/D) ratio and embedment length of GPC specimens have a significant influence on the bond strength. Based on the parameters from previous experimental studies, GPC is comparable with OPC concrete, but further research needs to be carried out to investigate the structural behaviour utilizing GPC for construction application.
Review on interlocking compressed earth brick
Authors: Abdullah E S R , Mirasa A K , Asrah H , Lim C H 
Published: June 2020

Abstract
Soil is known as the most cost-effective material in construction since available locally and has been used for centuries. Soil widely used throughout the world in brick production including Malaysia. The used of soil in construction can reduce environmental issues and act as a green building material. In addition, high pressure of compression is used to produce the interlocking bricks and it is at high speed of production compared to conventional method which is firing process that can contribute to the environmental issues. To achieve sustainable development, interlocking compressed earth bricks have been developed which can reduce cost, environmental-friendly, and energy-efficient. This paper aims to review the interlocking compressed earth bricks (ICEB).
Study on removal of pollutant from batik wastewater using coal bottomash (CBA)
Authors: Jamaludin M Z 
Published: June 2020

Abstract
Batik, which is a hand-painted product which is richly colored pattern. It is a textile industrial wastewater and usually releases their industrial effluents into the river without any proper treatment. Coal bottomash (CBA) derived from coal combustion for electricity generation in power plants or some industries and the characteristic of CBA may depend upon the raw coal source, size, type of coal burner and the operating conditions of the burner. The main objectives of this study were to identify the efficiency treated and untreated CBA in the treatment of batik wastewater effluents and to determine the size of bottom ash suitable for the fixed-bed column treatment mechanism. CBA was washed, treated with HCl, HNO3, and H2O2 and dried for the preparation fixed bed column. Batik waste water treatment efficiency was enhanced by the use of treated CBA fixed-bed column with size 0.45 mm and reduced the TSS, BOD, and turbidity by 41.6%, 65.3% and 75.6%, respectively. CBA is an effective and inexpensive for the removal of color, BOD, TSS and turbidity due to its high porosity and adsorption capacity. Problems of environmental pollution can also be minimized by utilization of CBA-fixed bed column in batik industries waste water treatment.