Turbulent Velocity Components Research Articles

Modeling wind-driven seed dispersal using a coupled Lagrangian particle tracking and 1-D [formula omitted]-[formula omitted] turbulence model

We present a one-dimensional k-ɛ model and a Markov chain stochastic Lagrangian particle tracking model to study wind-driven dispersal of forest and grassland seeds. The turbulence model within and above the canopy is implemented for transient winds so that time series of profiles of mean velocity, turbulence kinetic energy, dissipation rate, and the root-mean-square of fluctuating velocity components can be modeled. We validate the model for steady state conditions using observations in a wide range of canopies, and apply the model for predicting time series of seed dispersal of Andropogon gerardii in a tall grass prairie in Missouri, United States. The stochastic seed dispersal model is validated against experimental data from a Quercus-Carya (oak-hickory) forest where seeds were released from different heights for a range of wind speeds. Using the model, we explore the detailed seed movement trajectories, instantaneous velocities, and investigate the relationship between dispersal distance and the seed falling duration and the mean fluctuating velocity during the falling. Moreover, examining the role of individual turbulent velocity components, we elucidate the different roles of horizontal and vertical velocity fluctuations, i.e., the horizontal component mainly contributes to the seed spreading in the wind direction, while the vertical component enhances the long tail of the distribution in the downstream direction, i.e., promoting long-distance-dispersal of seeds by wind.

POD analysis of the turbulent boundary layer flow downstream of miniature vortex generators

In this study we investigate the influence of an array of miniature vortex generators (MVGs) in a zero-pressure-gradient turbulent boundary layer (ZPG TBL) by means of a large-eddy simulation of rectangular MVGs in a spatially evolving moderate Reynolds number ZPG TBL up to Reτ=1350. The MVG array consists of pairs of rectangular blades arranged in spanwise oriented arrays in the flow. The turbulent intensities and streamwise inclination angles related to the large streamwise extent high-momentum regions (HMRs) and low-momentum regions (LMRs) induced by the MVGs are presented. The instantaneous velocity fluctuation is decomposed into a turbulent velocity component and a spatial velocity component based on the triple velocity decomposition, where the spatial velocity component represents a spatial variation of the time-averaged flow induced by the MVGs. The streamwise turbulent velocity fluctuation associated with the HMRs and the LMRs is further investigated using proper orthogonal decomposition (POD), where we further examine a reduced-order reconstruction of the HMRs and the LMRs, using two-dimensional data. POD has also been used to determine the streamwise inclination angle of wall-attached structures in the HMRs and the LMRs. An examination of the streamwise inclination angle associated with the POD modes has been performed. Results suggest that the streamwise inclination angle of higher energy POD modes may be related to that of the relatively large wall-attached structures reported in the literature. In addition, if the lower energy POD modes are also retained, the value of the streamwise inclination angle tends to approach the value of mean streamwise inclination angle of wall-attached structures. The results suggest that the decreasing trend in streamwise inclination angle may be related to the contributions of the small-scale wall-attached motions.

Limits on non-canonical heating and turbulence in the intergalactic medium from the low redshift Lyman α forest

ABSTRACT We examine the column density distribution function (CDDF) and Doppler parameter distribution from hydrodynamical simulations and Cosmic Origins Spectrograph (COS) observations of the Ly α forest at redshift 0 ≤ z ≤ 0.2. Allowing for a factor of two uncertainty in the metagalactic H $\, \rm \scriptstyle I \, $ photoionization rate, our hydrodynamical simulations are in good agreement (1–1.5σ) with the shape and amplitude of the observed CDDF at H $\, \rm \scriptstyle I \, $ column densities $10^{13.3}\rm \, cm^{-2}\le N_{\rm H\,{\small I}}\le 10^{14.5}\rm \, cm^{-2}$. However, the Doppler widths of the simulated lines remain too narrow with respect to the COS data. We argue that invoking AGN feedback does not resolve this discrepancy. We also disfavour enhanced photoheating rates as a potential solution, as this requires an unphysically hard UV background spectrum. If instead appealing to a non-canonical source of heating, an additional specific heat injection of $u \lesssim 6.9\rm \, eV\, m_{\rm p}^{-1}$ is required at z ≲ 2.5 for gas that has $N_{\rm H\,{\small I}}\simeq 10^{13.5}\rm \, cm^{-2}$ by z = 0.1. Alternatively, there may be an unresolved line of sight turbulent velocity component of $v_{\rm turb}\lesssim 8.5\rm \, km\, s^{-1}(N_{\rm H\,{\small I}}/10^{13.5}\rm \, cm^{-2})^{0.21}$ for the coldest gas in the diffuse IGM.

Analysis of Turbulent Flow Structure with Its Fluvial Processes around Mid-Channel Bar

Researchers have recognized that the successive growth of mid-channel bar deposits can be entertained as the raison d’être for the initiation of the braiding process, which is closely interlinked with the growth, decay, and vertical distribution of fluvial turbulent kinetic energy (TKE). Thus, focused analysis on the underlying mechanics of turbulent flow structures in the proximity of a bar deposit occurring in the middle of the channel can afford crucial scientific clues for insight into the initiating fluvial processes that give rise to braiding. In the study reported herein, a physical model of a mid-channel bar is constructed in an experimental flume to analyze the turbulence parameters in a region close to the bar. Notably, the flow velocity plays an important role in understanding the flow behavior in the scour-hole location in the upstream flow divergence zone as well as near the downstream zone of flow convergence in a mid-channel bar. Therefore, the fluctuating components of turbulent flow velocity are herein discussed and analyzed for the regions located close to the bar. In the present study, the impact of the mid-channel bar, as well as its growth in turbulent flow, on higher-order velocity fluctuation moments are investigated. For near-bed locations, the results show the dominance of ejection events in upstream zones and the dominance of sweep events at locations downstream of the mid-channel bar. In scour-hole sections, the negative value of the stream-wise flux of turbulent kinetic energy and the positive value of the vertical flux of turbulent kinetic energy indicate energy transport in downward and forward directions, respectively. The downward and forward energy transport processes lead to scouring at these locations. The maximum turbulent production rate occurs in the wake region of the bar. The high rate of turbulence production has occurred in that region, which can be ascribed to the process of shedding turbulent vortices. The results show that the impact of the presence of the bar is mainly restricted to the lower layers of flow. The turbulent dissipation rate monotonically decreases with an increase in the vertical distance from the bed. The turbulent production rate first increases and then decreases with successive increases in the vertical distance from the bed. The paper concludes with suggestions for the future potential use of the present research for the practical purpose of examining braid bar occurrences in alluvial rivers to develop an appropriate response through training measures.

Experimental investigation of 90° intake flow patterns with and without submerged vanes under sediment feeding conditions

In this study, two experiments were conducted in a 90° water intake to study 3D flow patterns and sediment distribution using submerged vanes under sediment feeding and live-bed conditions. One column three vanes were installed at a 20° angle maintaining for a water discharge ratio of qr ≈ 0.1. Three-dimensional mean and turbulent velocity components of flow in a 90° channel intake were measured using acoustic Doppler velocimetry (ADV). Flow characteristics of the intake structure area with no vanes were compared with these conditions. Results showed that three vanes with a single column reduced the amount of sediment by 20% during intake diversion. In the downstream corner of the intake, high velocities were measured where scouring occurred. The vanes affected the intensity of secondary flow, turbulence energy, flow separation, and moved sediment deposition downstream of the main channel.

Investigation of the influence of nonbreaking waves on the turbulence using PIV methods within laboratory modelling of the upper layer ocean dynamics

The influence of nonbreaking waves on the mixing processes in the upper layer of the ocean during wind-wave interaction was investigated under the conditions of laboratory modeling at the Thermostratified Wind Wave Tank (TSWiWaT) of IAP RAS. Experiments of three types were performed. In the first experiment, shear flow in water was induced using a weak wind to avoid the excitation of surface waves. In the second experiment, in the absence of wind, only a long smooth surface wave was generated using an underwater paddle wavemaker. The third type of experiment combined the conditions of the previous two, i.e. at the same time the wave generator was working and the wind was blowing. In all experiments, the underwater flow characteristics were measured using the PIV method. Vertical profiles of the mean velocity and fluctuations for two components were obtained. It was shown that the presence of waves leads to an increase in the average drift current, as well as, more importantly, on the level of fluctuations over the entire depth of the recorded profile by more than 3 times. This was observed for horizontal and vertical turbulent velocity components both.

The influence of wall heating on turbulent boundary layer characteristics during mixed convection

An investigation on the modification of turbulent boundary layer characteristics by wall heating was conducted on the mixed convection turbulent boundary layer flow. The multi-plane particle image velocimetry (PIV) technique was used to characterize turbulent boundary layer dynamics. Experiments were performed over a range of mixed convection flow conditions, quantified by the Richardson number (Ri), from inertia dominant flow (RiL=0.01) to buoyancy-influenced flow (RiL=0.3). The implemented PIV technique produced multiple two-dimensional velocity fields from two orthogonal planes with respect to the mean-flow direction. From the computed velocity fields, the low-order turbulent statistics were computed where a significant modification to the wall normal stress was observed. The cause of this modification was investigated via the probability density function (PDF) of the turbulent wall-normal velocity component (v'). Results show that the PDF of v' is multi-modal in the presence of wall heating, demonstrating that the buoyancy-driven phenomena influence the turbulent boundary layer flow via intermittent bursting and rising of thermals through the boundary layer.

Measurement of forced convection subcooled boiling flow through a vertical annular channel with high-speed video cameras and image reconstruction

ABSTRACT In order to develop models regarding subcooled boiling flow and its heat transfer, we conducted subcooled boiling experiments to investigate subcooled bubble formation and measured development process of the bubbles using a test loop with a vertical annulus flow path under atmospheric conditions. Two-phase flow parameters regarding subcooled boiling, such as instantaneous bubble velocity, turbulent velocity components, void fraction, onset of nucleate boiling (ONB) and onset of significant void (OSV), were obtained with two high-speed video cameras in high resolution in temporally and spatially. The identical bubbles were identified from the two video images taken by the high-speed video cameras, and the trajectories were reconstructed in three-dimensional. The instantaneous bubble velocities and turbulence velocity components regarding bubble transport were quantified with the trajectory data. It was observed that the bubbles were rising along the surface of the heater rod moved largely in the circumferential direction, and it was found from the result that velocity component for circumferential direction was enough large compared with that for radial direction.

Measurement of forced convection subcooled boiling flow and rod surface temperature distribution

In order to obtain high-resolution data for modelling of boiling two-phase flow and its validation, we designed and constructed a test loop with a vertical annulus flow path and conducted subcooled boiling experiments to investigate subcooled bubble incipience and its development process under atmospheric condition. Three kinds of the state-of-the art measurement techniques were applied to quantify key parameters such as radial and vertical distributions of void fraction, bubble velocity, interfacial area concentration (IAC), Sauter mean diameters, high-resolution temperature distribution on rod surface, bubble transport behavior, and turbulent velocity components as well as onset of nucleate boiling (ONB), and onset of significant void (OSV).

Genesis of Antibiotic Resistance LV: Validity Contexture of Mixing Length Hypothesis Turbulence Modelling (MLH ‐ TM) in an exacerbated mortality rate of Early Resuscitation Protocol ‐ Early Goal‐Directed Therapy (ERP‐EGDT) for sepsis.

To decipher the validity of Prantel’s Mixing Length Theory (MLH‐TM) in ERP‐EGDT for sepsis with comorbidity (CC) Capillary Leakage Syndrome ( CLS), also called as Vascular Leak Syndrome ( VLS); Systemic Capillary Leak Syndrome ( SCLS); Sepsis Induced Coagulopathy ( SIC); Sepsis‐induced Disseminated Intravascular Coagulation syndrome ( DIC)) a hypothesis that MLH could be of the valid diagnostic tool in clinical stratification of symptoms pertaining to sepsis with comorbidity, in real‐time scale to determine the onset of “Critical Closing Pressure” (CCP), and consequent collapse of vasculature is presented. Per contexture of the aforementioned objectives, NCT01663701 was chosen because of the case selection criteria and clinical case presentation, to the point data analysis, accessibility of data sets in the public domain and follow‐up care of both primary outcome of in‐hospital mortality and secondary efficacy outcome including 28‐day mortality and time to death. As per MLH, that a lump of fluid particles in one layer of the fluid flow, retains its original momentum at a specific location prior to the transition. During the transition from laminar viscous sublayer to buffer layer to turbulent zone, the turbulent velocity component and viscosity of the lump is dependent on a turbulent fluctuation. The universal velocity distribution law for smooth pipes: laminar viscous sublayer, buffer zone, and the turbulent zone is correlated with intact capillary bed. As indicated, this profile and eq:10.45 to 10.47, for rough pipe where protrusion extending outside of the laminar viscous sublayer, is correlated with dysfunctional vascular endothelium scramming the turbulent zone, escalating an adverse pressure gradient (ISBN: 9780070667624; 2008). It is known that such an adverse pressure gradient can plausibly induce an alteration in antibiotic resistance gene repertoire (ARGR) expression profile augmenting a selection pressure on AR persisters. Diagnostic index such as platelet aggregation, activation of the coagulation cascade and endothelial cell damage in sepsis‐induced coagulopathy originating from comorbidities are known to promote DIC and subsequent loss of capillary bed by glycocalyx shedding (J.Clin.Med.2019, 8,728; Crit.Care (2019) 23:259). Taken together, loss of vascular autoregulation and loss of the intravascular net filtration pressure (~25mmHg) gradient in the capillary bed revives MLH as imperative. It is our interpretation that subsequent to ERP‐EGDT, within the four hour period of admitting to ER/ICU/medical ward, a decrease in arterial pressure leading to increase the resistance with a gradual collapse of capillary bed, due to reduced distending pressure below a critical level (≤ 20mmHg) referred to as Critical closing pressure exacerbating the mortality rate in ERP‐EGDT for sepsis. With the turbulence modeling, in particular, the time scale, knowledge on its viscosity profile of fluid bolus along the damaged endotheliam (rough wall boundary layer), would benefit patient care by mitigating the mortality rate.Support or Funding InformationSupported by the professional development funds by SWTJC to Subburaj Kannan

Measurements of fluctuating lift forces on rectangular cylinders in turbulent flow

The fluctuating lift on a rectangular cylinder induced by turbulent flow is investigated by force measurement experiments. A square uniform grid is installed downstream of the entrance of the working section of the wind tunnel to generate approximately homogeneous and isotropic turbulence. The rectangular cylinder models of two different cross sections (width to depth ratio B/D = 5, 10) are tested in the experiments. Each rectangular cross section has two aspect ratios (length to width ratio θ = 1, 7) and a fixed width (B = 0.15 m). The measurements include the spectra of fluctuating lift force and vertical turbulent velocity component. From these measurements, the experimental values of generalized transfer functions of these rectangular cylinder models are obtained, which are compared with the calculated values based on three aerodynamic force theories. The one-wavenumber transfer functions and the spanwise influence terms of these rectangular cylinders are used in the calculations, which were determined by the pressure measurement experiments in the previous work. Comparisons of the measured and calculated values of generalized transfer functions demonstrate that the three-dimensional theory is satisfactory and confirm that the one-wavenumber transfer functions and spanwise influence terms determined by the pressure measurements are valid. The results also show that both the two-dimensional theory and the strip theory would overestimate the generalized transfer function, but for the rectangular cylinder with the larger aspect ratio, the strip theory is very close to the three-dimensional theory. The one-wavenumber transfer functions of these rectangular cylinders are therefore determined based on the strip theory. This indicates that the approximate approach to determination of the one-wavenumber transfer function, which was proposed for an airfoil in the previous work, could also be applicable to bluff bodies.

IABSE Task Group 3.1 Benchmark Results. Part 2: Numerical Analysis of a Three-Degree-of-Freedom Bridge Deck Section Based on Experimental Aerodynamics

IABSE Task Group 3.1 has the mandate to define reference results for the validation of methodologies and programs used to study both stability and buffeting responses of long-span bridges. To this end, the working group set up a benchmark procedure consisting of several steps with increasing complexity to define reference results useful for this validation. The simplest step (1.1a) was presented in Part 1. In this paper (Part 2), the contributions and reference results of the second sub-step (1.1c) are discussed. It consists of the simulation of the aeroelastic response of a three-degree-of-freedom bridge deck section forced by turbulent wind, using experimental aerodynamic coefficients measured in a wind tunnel. The increase in complexity, compared to the previous step, involves the experimental definition of unsteady force coefficients that are defined in a limited range of reduced velocities, and inclusion of the lateral motion and horizontal turbulent wind velocity components. Comparison of the different outputs, obtained by Task Group 3.1 participants with the same input data, is presented, revealing differences that are not always negligible. Moreover, the increase in complexity of the test case results in larger spreads of the results compared to the fully analytical case, analysed in Part 1.

Distributed Turbulence Model with Rigorous Spatial Cross-Correlation for Simulation of Helicopter Flight in Atmospheric Turbulence

This paper presents a distributed turbulence model with rigorous spatial cross-correlation for helicopter flight simulation in atmospheric turbulence and for future handling-quality analysis. First, digital filters with longitudinal correlations of the von Kármán turbulence are developed to generate discrete turbulence velocity components. Meanwhile, transverse turbulence correlations are considered by relating the filters in different positions with mathematically rigorous spatial cross-correlation. Then, the distributions of the related filters on the transverse plane in front of helicopter and their velocity components in the longitudinal direction of airspeed, as well as turbulence models of helicopter aerodynamic surfaces, are established. Finally, a flight dynamics model coupled with the turbulence model is developed and validated against the flight-test data. The proposed model can achieve accurate real-time simulations of helicopter response to atmospheric turbulence in the frequency range of interest of handling qualities. The effect of transverse turbulence correlations on helicopter frequency response is also analyzed. The results show that the simulation model regardless of transverse turbulence correlations would aggravate the "rotor-to-body attenuation" effect of the main rotor and therefore underpredict the helicopter roll, pitch, and heave rate responses to atmospheric turbulence in the frequency range of interest.

Turbulence velocity spectra and intensities in the inflow of a turbine rotor

The changes in spectra and intensities of the streamwise component of turbulent velocity are calculated in the inflow of a turbine rotor. The flow is initially calculated in the limit when the turbulence is of small scale compared with the rotor diameter. Rapid distortion theory (RDT), Batchelor & Proudman (Q. J. Mech. Appl. Maths, vol. 7 (1), 1954, pp. 83–103) (BP), for small-scale turbulence is combined with the effect of the fluctuating potential flow field on the turbulence caused by the direct interaction of the incident turbulence with the rotor as a sheet of resistance. A second computation is then carried out for turbulence of larger length scale. The results of the calculations are compared with velocity measurements in the inflow of both a commercial wind turbine and a tidal turbine rotor.

A method for reducing mean flow in oscillating-grid turbulence

Oscillating-grid turbulence (OGT) is an experimental tool that has been widely used to study the role of turbulent fluctuations under conditions of small mean flow. We report experiments to investigate the structure of the turbulent flow produced by an oscillating grid, using velocity measurements obtained through the application of two-dimensional particle image velocimetry in the vertical plane through the centre of the grid. Ensemble averages of the fluid velocity measurements at specific stages of the grid’s oscillation indicate that mean flow is induced in OGT by the merging of grid-induced jets close to the tank sidewalls. The installation of an open-ended ‘inner box’ (with its top edge positioned just below the bottom of the grid’s oscillation) is shown to inhibit the merging of the jets, thereby resulting in a reduction in the magnitude of the mean flow within the interior of the inner box region. Measurements of the time-averaged root-mean-square turbulent velocity components and the time-averaged turbulent kinetic energy flux indicate that the installation of the inner box results in turbulence that is in good agreement with the well-established models of OGT across the central 50% of the inner box’s width, but that distinct anisotropic regions exist adjacent to the vertical sidewalls. We anticipate that this simple amendment to reduce the mean flow present in OGT can be readily used in future work that utilises OGT to isolate the effects of turbulent fluctuations from those of the mean flow.Graphical abstract

Ejective and Sweeping Motions Above a Peatland and Their Role in Relaxed-Eddy-Accumulation Measurements and Turbulent Transport Modelling

The three turbulent velocity components, water vapour ( $$\text {H}_2\text {O}$$ ), carbon dioxide ( $$\text {CO}_{2}$$ ), and methane ( $$\text {CH}_{4}$$ ) concentration fluctuations are measured above a boreal peatland and analyzed using conditional sampling and quadrant analysis. The overarching question to be addressed is to what degree lower-order cumulant expansion methods describe transport efficiency and the relative importance of ejections and sweeps to momentum, $$\text {CH}_{4}$$ , $$\text {CO}_{2}$$ and $$\text {H}_2\text {O}$$ fluxes across a range of atmospheric flow regimes. The patchy peatland surface creates distinctly different source and sink distributions for the three scalars in space and time thereby adding to the uniqueness of the set-up. The measured and modelled fractional contributions to the momentum flux show that sweep events dominate over ejections in agreement with prior studies conducted in the roughness sublayer. For scalar fluxes, ejections dominate the turbulent fluxes over sweeps. While ejective motions persist longer for momentum transport, sweeping events persist longer for all three scalars. Third-order cumulant expansions describe many of the results detailed above, and the results are surprising given the highly non-Gaussian distribution of $$\text {CH}_{4}$$ turbulent fluctuations. Connections between the asymmetric contributions of sweeps and ejections and the flux-transport term arising in scalar turbulent-flux-budget closure are derived and shown to agree reasonably well with measurements. The proposed model derived here is much simpler than prior structural models used to describe laboratory experiments. Implications of such asymmetric contributions on, (i) the usage of the now proliferating relaxed-eddy-accumulation method in turbulent flux measurements, (ii) the constant-flux assumption, and (iii) gradient-diffusion closure models are presented.

Synthetic turbulence methods for computational aeroacoustic simulations of leading edge noise

A leading edge noise prediction methodology that uses an advanced digital filter method to generate synthetic turbulence is presented for efficient two- and three-dimensional simulations. The digital filter method combines the advantages of the Random Particle-Mesh method, for the mathematical background, and synthetic eddy methods, for the numerical implementation. This allows the generation of non-periodic turbulence without explicitly filtering white noise signals, and gives a significant reduction in the number of constraint parameters and random numbers involved in comparison with previous methods. A new eddy profile is defined through a superposition of Gaussian eddies that matches a target isotropic energy spectrum. The method is used in a linearised Euler equation solver to predict turbulence-aerofoil interaction noise from a number of configurations, including variations in aerofoil thickness, angle of attack and Mach number. A comparison with stochastic turbulence based on Fourier modes indicates that noise predictions are independent of the choice of synthetic turbulence method, provided that streamwise and transverse turbulent velocity components are included. Nevertheless, the advanced digital filter method is advantageous due to its reduced computational cost. This paper also extends the advanced digital filter method to realise a two-dimensional turbulent flow with the key statistics of three-dimensional turbulence, which is suitable to perform low-cost leading edge noise predictions that can be compared with experiments. Tests show that this approach is capable of reproducing experimental noise measurements to within an accuracy of 3 dB, and predicts similar noise levels to fully three-dimensional simulations.

FLOW DYNAMICS OF WAVES PROPAGATING OVER DIFFERENT PERMEABLE BEDS

The analysis of the hydrodynamics over porous media is of interest for many coastal engineering applications as the wave propagation over permeable structures or gravel beaches. The study of a boundary layer evolving over permeable beds is important to a better understanding of the interactions between the flow over and inside the porous medium. An experimental study has been performed to analyze the dynamics produced when waves propagate over two kinds of permeable beds: spheres (regular permeability) and natural stones. For comparative purposes the same analysis has been extended to two rough beds made, respectively, by a single layer of spheres and natural stones. We here focus on the correlation between the wave energy reduction induced by a porous bed and the flow resistance. An experimental law for the prediction of the friction factor is found by using the log-fit method in analogy to that reported in Dixen et al. (2008) for rough beds. Moreover, inspection of the turbulent velocity components allows one to evaluate the bottom shear stress. The latter analysis has been performed for different permeable beds (regular and irregular beds). A good agreement between the bottom shear stress behavior and the wave height attenuation over rough and permeable beds (Corvaro et al. 2010 and Corvaro et al. 2014a) has been observed.

Modelling airborne dispersion for disaster management

Industrial disasters, like any other disasters, can happen anytime, anywhere and in any form. Airborne industrial disaster is a kind of catastrophic event involving the release of particles such as chemicals and industrial wastes into environment in gaseous form, for instance gas leakages. Unlike solid and liquid materials, gases are often colourless and odourless, the particles are too tiny to be visible to the naked eyes; hence it is difficult to identify the presence of the gases and to tell the dispersion and location of the substance. This study is to develop an application prototype to perform simulation modelling on the gas particles to determine the dispersion of the gas particles and to identify the coverage of the affected area. The prototype adopted Lagrangian Particle Dispersion (LPD) model to calculate the position of the gas particles under the influence of wind and turbulent velocity components, which are the induced wind due to the rotation of the Earth, and Convex Hull algorithm to identify the convex points of the gas cloud to form the polygon of the coverage area. The application performs intersection and overlay analysis over a set of landuse data at Pasir Gudang, Johor industrial and residential area. Results from the analysis would be useful to tell the percentage and extent of the affected area, and are useful for the disaster management to evacuate people from the affected area. The developed application can significantly increase efficiency of emergency handling during a crisis. For example, by using a simulation model, the emergency handling can predict what is going to happen next, so people can be well informed and preparations works can be done earlier and better. Subsequently, this application helps a lot in the decision making process.

Experimental study of oscillating-grid turbulence interacting with a solid boundary

The interaction between oscillating-grid turbulence and a solid, impermeable boundary (positioned below, and aligned parallel to, the grid) is studied experimentally. Instantaneous velocity measurements, obtained using two-dimensional particle imaging velocimetry in the vertical plane through the centre of the (horizontal) grid, are used to study the effect of the boundary on the root-mean-square velocity components, the vertical flux of turbulent kinetic energy (TKE) and the terms in the Reynolds stress transport equation. Identified as a critical aspect of the interaction is the blocking of a vertical flux of TKE across the boundary-affected region. Terms of the Reynolds stress transport equations show that the blocking of this energy flux acts to increase the boundary-tangential turbulent velocity component, relative to the far-field trend, but not the boundary-normal velocity component. The results are compared with previous studies of the interaction between zero-mean-shear turbulence and a solid boundary. In particular, the data reported here are in support of viscous and ‘return-to-isotropy’ mechanisms governing the intercomponent energy transfer previously proposed, respectively, by Perot & Moin (J. Fluid Mech., vol. 295, 1995, pp. 199–227) and Walkeret al.(J. Fluid Mech., vol. 320, 1996, pp. 19–51), although we note that these mechanisms are not independent of the blocking of energy flux and draw parallels to the related model proposed by Magnaudet (J. Fluid Mech., vol. 484, 2003, pp. 167–196).