Examining the dispersion of hazardous agents within complex environments, whether situated in urban or remote areas globally, requires a comprehensive analysis of evolving wind patterns and atmospheric stability in hazardous zones on an hourly basis. This investigation is essential to ensure that models employed for risk assessment can furnish a timely and effective response. However, modeling complex scenarios, especially those involving low wind conditions (wind speed < 1-2 m/s) and meandering, poses challenges due to the intricate dynamics of these phenomena.This study aims to conduct numerical modeling of wind flow in an urban area, characterized by sequences of weak winds and meandering. The computational analysis utilizes the atmospheric module of the Code_Saturne Computational Fluid Dynamics (CFD) software developed by EDF R&D. The inquiry originates from a measurement campaign conducted by LMEE (Laboratoire de Mécanique et d'Énergétique d'Évry) in Evry, south of Paris, France, spanning 16 months from September 2008 to December 2009. Statistical analysis of raw measurements from the campaign reveals that almost 45% of the winds are weak, with nearly 50% falling under very stable atmospheric conditions.The CFD model is evaluated against averaged observations obtained from micro-scale measurements using an ultrasonic anemometer. The study encompasses a 1x1 km grid covering the urban area. Subsequently, meso-scale hourly measurements from nearby Météo-France stations, providing essential outputs for the CFD model, are incorporated.

This article presents a novel approach for predicting vibration bandgaps in periodic composite plates with fluid–structure interaction (FSI) using a unit cell-based finite element model. The novelty of our approach lies in the formulation of a fluid-induced added mass matrix, which integrates the Bloch periodic boundary condition, allowing for the incorporation of the fluid’s inertial effect in the context of unit cell-based bandgap analysis. We therefore construct a unit cell model comprising a composite Mindlin plate which integrates periodic FSI effects with the simultaneous application of Bloch conditions on both the structure and the fluid domains. Subsequently, we studied a set of periodic composite plates with FSI effects on one or both sides, thereby assessing the influence of the fluid properties such as density and the fluid domain dimension on the structure vibration. The bandgap prediction is compared with the frequency response simulations which involve diversified microstructure designs. The obtained results provide indications regarding the effectiveness and applicability of the proposed numerical methodology.

Modeling the atmospheric dispersion of pollutants emitted from different types of sources under various atmospheric conditions is an essential prerequisite for risk assessment studies and emergency preparedness. In this study, we evaluate the performance of different turbulence models and velocity-scalar correlation models implemented in the Code_Saturne. The evaluation is done with observations of four trial cases of the Mock Urban Setting Test (MUST) campaign in an urban type environment and in neutral and stable atmospheric conditions. For all of the trials studied, the CFD model with a first-order closure model (k−ɛ) predicts 61.1% of the concentrations within a factor of two of the observations, which is higher than the percentage of predicted points (58.8%) when a second-order closure model (Rij−ɛ) is used. Overall, the CFD model underestimates observed concentrations, regardless of the turbulence model used. For the trial with slightly stable conditions, the results show that the k−ɛ model combined with an algebraic SGDH model predicts 75% concentrations within a factor of two of the observations. The performance of the k−ɛ model is compared to that of the Rij−ɛ model when used with the algebraic SGDH, GGDH models and with the scalar flux transport equation (DFM model). Under slightly stable atmospheric conditions, the DFM model predicts 69% of concentrations within a factor of two of observations, showing promise for modeling under these conditions, despite its relatively high computational cost.

A full-scale finite element model is presented for monolithic fluid-structure interaction (FSI) simulations of thin-walled piezoelectric fluid energy harvesters (PFEHs). Unlike widely used beam/plate-based models, our model employs a solid finite element discretization to precisely represent the complex PFEH designs involving microstructured transducers and non-uniform cantilevers. These features, plus the local FSI effects, are often ignored by simplified models. We applied the Galerkin method to formulate the weak form of the mixed equation system, integrating the flow dynamics, the geometrically nonlinear cantilever, the piezoelectric components, the electrode, and the output circuit within a closed-circuit electro-mechanical coupled system. The coupling of the multiple domains is achieved through boundary-fitted discretization within a monolithic scheme, using shifted-Crank-Nicolson temporal integration. This work explored implementing piezoelectric FSI systems within the FEniCS-based TurtleFSI library, and experimented techniques such as employing penalty functions for achieving electrode components with uniform electric potentials. We investigated various advanced PFEH features, including the baseplate design, the arrangement and microstructure of the piezoelectric components, and their influence on the system's dynamic and energy output behavior. The results confirmed the model's key advantages: full-scale modeling allows the integration of complex base structures and transducer microstructures in PFEH design. Combined with monolithic FSI coupling, it offers greater versatility, supporting a wider range of fluid environments and configurations in both wind and hydropower harvesting. Additionally, the modeling strategy can be intended not only to enhance power output, but also to minimize material usage, reduce mechanical fatigue, and extend the operational lifespan of PFEH systems.

The dual-bell nozzle (DBN) is a rocket nozzle concept that could provide a substantial payload gain. The present paper focuses on the impact of radial secondary injection on DBN behavior during its ascent and descent in the atmosphere. The influence of the secondary injection settling chamber (cavity) volume is discussed. The positive influence of the cavity volume on the DBN behavior during transition phases has been exposed, and its effects during retransition were shown to be negligible. The use of secondary injection allowed the transition nozzle pressure ratio to be increased by nearly 24%, and the lateral forces were reduced to less than 1% of the nozzle thrust. A first approach regarding secondary injection optimization is finally proposed.

The effect of rotational nonequilibrium on the macroscopic parameters of the flow behind a normal shock wave in oxygen gas flow has been examined. The electron thermal equilibrium was taken into account where the electron temperature was equal to the vibrational temperature according to Park’s assumption. Therefore, only the effect of rotational nonequilibrium on the translational and vibrational temperature was analyzed. Rotational and vibrational relaxation time for the O2-O2 and O2-O collisions proposed recently by Andrienko and Boyd are used. Also, the O2 dissociation rates proposed by Kim and Park are used. The results obtained with the three-temperature model well reproduce the data obtained in shock tube for the shock velocity of 4.44 km/s.

Low wind conditions (wind speed < 1-2m/s) are the most critical atmospheric states for the dispersion of a pollutant due to highly non-stationary and inhomogeneous diffusion conditions governed by the meandering, weak, sporadic and intermittent turbulence. These atmospheric conditions coupled with thermal stable conditions remain a challenge for the numerical modelling of turbulent flows and dispersion at local scale. Numerical simulation of a pollutant dispersion in these atmospheric conditions using the RANS (Reynolds Averaged Navier Stokes) equations is known to be highly dependent on selected turbulence models. On one hand, the modelling of turbulence and dynamic of wind field, by means of first order Eulerian closure models based on the turbulent viscosity hypothesis, lacks an adequate and complete representation of the anisotropic effect. On the other hand, the isotropic aspect attributed to the dispersion of the pollutant, through the simple gradient diffusion model, tends to underestimate the horizontal diffusion of the pollutant, thus overestimating the concentration along the plume axis near the source. Therefore, the purpose of this study is to investigate the behaviour of anisotropic RANS models for dispersion of a pollutant in low wind stable conditions. The models used to simulate the dynamic field are the second order RSM (Reynolds Stress models), whereas the algebraic models used to model the concentration turbulent flux of concentration are either the AFM (Algebraic Flux model) or the GGDH (Generalized Gradient Diffusion Model). The simulations are performed using a 3-dimensional CFD code, Code_Saturne® (EDF), in which these turbulence models are implemented. The models are validated with a well-known Idaho Falls experiment (USA) for the dispersion of a passive tracer under low-wind stable conditions. Various inflow boundary conditions for wind profiles and turbulence parameters are applied. In order to assess the predictive capacity of these models, a comparative statistical analysis is performed using standard statistical performance measures. The model results are also compared with the results from a Gaussian plume dispersion model.

Experiments on an axisymmetric dual-bell nozzle were performed at EDITH nozzle test facility of CNRS in Orléans, France. The main purpose of the study was to explore the possibility of controlling the flow regime transition by a secondary fluidic injection in the dual bell nozzle. The main focus of the present paper is to investigate the impact of the secondary injection parameters on the flow regimes transition in such nozzles. Secondary injection has been found to effectively control the flow regime transition and consequently to increase the propulsive performance of the device. It has also been pointed out that even a very low injected secondary mass flow rate leads to the control of the transition and contributes to reducing the lateral loads which can exist, moreover, when transitions are operated without injection.

In this study, the effect of rotational nonequilibrium on the macroscopic parameters of the flow behind a normal shock wave in oxygen and nitrogen gas flow has been examined. Comparison between three chemical kinetic models including Park89, Park93, and Dunn-Kang was used to describe the chemical nonequilibrium. The obtained results show the significant effect of the rotational nonequilibrium on the relaxation zone and also on the translational and vibrational temperatures and were found to be in a good agreement with the experimental data particularly when the Park89 model was used.

With the ever rising demands for cheaper payload delivery to orbit, dual bell nozzle with a potential theoretical performance gain of up to 10% can represents one of the major ways of advance to achieve the goal. The well-known transition unsteadiness in a dual-bell rocket nozzle represents one of the major concerns for the development of such altitude compensating type nozzle (ACN). The present study proposes and investigates the possibilities of secondary radial injection for flow regime transition control. Present experimental results demonstrate potential effects of secondary injection on transition and re-transition control even with a relatively low secondary injection mass flow rates. Doing so, the transition and retransition process were significantly delayed towards the ideal transition point. In addition, side loads have been found to be greatly decreased or even eliminated.

In this study, a one-dimensional post-normal shock solver in hypersonic ionized air flow was developed to study the effect of the physical-chemical phenomena that occur at high temperature. To simulate this case, the upstream air flow is considered with 2 species (21% of O2 and 79% of N2). Behind the shock wave, the Park’s chemical kinetics model with 11 species (O2, N2, NO, O2+, N2+, NO+, O, N, O+, N+, e−) and 49 chemical reactions is used. The vibration-dissociation coupling is taken into account according to the Park’s model for which the activation temperature of the dissociation reactions is \(T_{a} = T^{q} T_{v}^{1 - q}\). The energy exchange model between translation modes and vibration modes is described by the Landau-Teller formula where the species relaxation time is based on the Millikan-White formula, including Park’s high-temperature correction. The numerical model of the flows governed by the Euler equations supplemented by the equations of the chemical kinetics and the system of equations obtained is discretized by the finite difference method, good agreement between the relaxation zone obtained and those obtained by Panesi for the two trajectory points corresponding to t = 1634 s and t = 1643 s of the Fire II re-entry vehicle.

The aim of this study is to optimize sensor networks for fast deployment in order to reconstruct an unknown source of intentional or accidental release in local urban topography. In such emergency circumstances, only the meteorological conditions are available in real time and the network deployed must be efficient enough regardless of a source's position and intensity. To determine the optimal positions to be instrumented by the sensors, an adequate cost function is defined based on the renormalization inversion method. This function, named the entropic criterion, quantifies the amount of information contained in a network of the sensors to estimate the intensity and the location of an unknown source. The optimal design is approached as combinatorial optimization (NP‐Hard) and a stochastic algorithm (simulated annealing, SA) is employed to solve this problem. The computation is performed by coupling the CFD adjoint fields in an urban environment, the renormalization algorithm and the SA. The optimization is evaluated with 20 trials of the Mock Urban Setting Test (MUST) tracer field experiment for the reconstruction of a continuous point release in an idealized urban geometry using optimal networks of sizes 10 and 13 sensors. The process is achieved successfully and the results showed that the reduction of an original network of 40 sensors to one third (13) and one quarter (10) does not degrade the performance of this network. Also, a comparison of the optimal design efficiency based on apriori information and without apriori information about the source showed that the present entropic criterion leads to network design and performance that can accurately retrieve an unknown emission source in an urban environment.

In this study, the effects of different thermo-chemical models on the macroscopic parameters of the flow behind a strong shock wave have been examined. The effect of the geometric average temperature proposed by Park and the effect of the electronic energy are also presented, and two CVD vibration-dissociation coupling models including those of Park and Kuznetsov are also examined and used for comparison. The Park93 chemical kinetic model with 11 species and 49 elementary reactions was used to describe the non-equilibrium air chemistry. The energy exchange model between translational and vibrational modes is described by the Landau-Teller formula, where the species relaxation time is based on the Millikan-White formula including Park’s high-temperature correction. The theoretical model consisting of the Euler equations supplemented with the equation of molecular vibration and the equations of chemical kinetics using a two-temperature model (translational-rotational temperature and vibrational-electron-electronic temperature) is discretized by a finite difference scheme. Good agreement is found for the relaxation zone between the present results and those obtained by Panesi for the two trajectory point (1634 s and 1643 s) for the FIRE II reentry capsule.

The aim of this research is to optimize a methodology used in eco-design, that so-called Life Cycle Assessment (LCA), in order to increase its representativeness when evaluating systems. This optimization consists of introducing temporal factors in the environmental impact assessment. This process is called Dynamic Life Cycle Assessment (DLCA). It uses the Enhanced Structural Path Analysis (ESPA) method combined with OpenLCA software and an algorithm written under MATLAB. Then, the Life Cycle of the Inventory (LCI), carrying out the inventory of input and output masses of the controlled compounds (NO,,, 03, PM10, etc.) for relevant studied subsystems, takes the date of the process into account and breaks the amount of pollutants flows down. A double glazing bay was chosen to apply this method.

In the aeronautical and aerospace industries, the flow configurations where an incident oblique shock wave impinges upon a boundary layer are very common. The supersonic flow around an aircraft, in a rocket nozzle or in a supersonic inlet are some examples among others.

Dual-bell axisymmetric propulsive nozzle, as the most prominent altitude compensating nozzle concept has been investigated for transition modes and effects. Experimental and numerical investigations show that dual-bell nozzle can be very effective for desired large envelope launcher stage trajectories. Transition regimes are studied in the high altitude simulation wind-tunnel and supported by the numerical simulations. Analysis of the employed diagnostics shows an existing particular hysteresis between the transitioning modes and pinpoints to possibilities to control the early transition. Further numerical investigation on active flow control indicates the promising potentials of the proposed fluidic injection system.

The transverse injection in a supersonic cross-flow is problematic which can be encountered in several aerodynamic applications such as fuel injection in scramjet combustor, missile control, drag reduction, and thrust vector control. In recent years, an extended analytical, numerical, and experimental work has been carried out by the authors [1, 2] to investigate the vectoring performances of a supersonic axisymmetric nozzle using secondary fluid injection. Secondary gas injection thrust vector control (SITVC) or shock vector control (SVC) is considered as an alternative way to control the thrust direction of a rocket nozzle beside the classical use of mechanical device such as fluidic actuators. In the context of SITVC operation, the nature and source of injectant gas may raise efficiency-related issues. In previous studies [3–6], it is well established that injection of gas with low molar mass promotes better jet penetration and therefore will be a better choice for SITVC operation. To assess this point, an experimental test campaign has been conducted in the hypersonic test facility EDITH of the CNRS institute ICARE in Orléans, France. The focus of the study is to analyze the secondary injectant gas thermodynamic properties influence on the global vectoring performance of a supersonic nozzle. For this purpose, performance aspects of fluidic thrust vectoring concept have been experimentally investigated on a truncated ideal contour (TIC) nozzle model using a variety of gas species (with low to moderate molar mass) as injectant. Qualitative and quantitative diagnostics consisted of Z-Schlieren visualization, 3-axis force balance, and static and dynamic parietal pressure measurements. The experimental results are compared to the numerical and analytical findings.