Iraj Mortazavi

Conservatoire National des Arts et Métiers | CNAM · Laboratoire Modélisation Mathématique et Numérique (M2N)

Review of reduced-order models for online protection of WDNs

The main goal of this work is to develop a data-driven Reduced Order Model (ROM) strategy from high-fidelity simulation result data of a Full Order Model (FOM). The goal is to predict at lower computational cost the time evolution of solutions of Fluid–Structure Interaction (FSI) problems. For some FSI applications, the elastic solid FOM (often cho...

Stable partitioned techniques for simulating unsteady fluid-structure interaction (FSI) are known to be computationally expensive when high added-mass is involved. Multiple coupling strategies have been developed to accelerate these simulations, but often use predictors in the form of simple finite-difference extrapolations. In this work, we propos...

This paper presents a review of reduced-order models (ROMs) and digital twins, with a primary focus on their application to water distribution networks (WDNs). Initially, we concentrate on the physical modeling of WDNs. Following this, we introduce relevant programming, specifically addressing WDNs and solving equations for extended-period simulati...

This aerodynamic study is an attempt to build up efficient flow control computations on a detached high Reynolds number flow behind a 25°inclined ramp enabling to reduce the turbulence energy of recirculating zones. Flow control is performed with a synthetic jet row placed at the top edge of this inclined ramp. Baseline simulations are validated wi...

In this work, the aerodynamic performances of a reduced scale vehicle characterized by a fully detached flow on the rear end and measured in a wind tunnel, are investigated in order to check the efficiency of active flow control using pulsed jets, implemented on the rear bumper. Here, the pressure increase on the tailgate by the optimum blowing con...

Modeling of pressure-dependent users’ consumption is mandatory to simulate accurately the hydraulics of water distribution networks (WDNs). Several software solutions already exist for this purpose, but none of them actually permits the easy integration and test of new physical processes. In this paper, we propose a new Python simulator that implem...

In this study, we evaluate various Large Eddy Simulation (LES) models applied to turbulent flows in the framework of remeshed or semi-Lagrangian Vortex Methods. The models are tested on the Taylor Green Vortex and the decay of homogeneous isotropic turbulence. We find a good performance when applying the Smagorinsky model to the smallest resolved s...

Accurate modelling of the hydraulic grade line by recursive discretization of pipes presenting background leakage. Keywords Water distribution network (WDN), background leakage, pressure-dependent model (PDM), recursive discretization method Highlights-New model with more physical insights of losses in water distribution networks-Integrating pressu...

The simulation of the wake past porous obstacles is numerically challenging because since it requires both an accurate model of the porous medium and a good grid resolution in the fluid domain. In this study a single-domain Brinkman penalization technique in a LBM framework is employed to investigate wake prediction in 3D porous–fluid flows. First...

The main goal of this work is to develop a data-driven Reduced Order Model (ROM) strategy from high-fidelity simulation result data of a Full Order Model (FOM). The goal is to predict at lower computational cost the time evolution of solutions of Fluid-Structure Interaction (FSI) problems. For some FSI applications, the elastic solid FOM (often cho...

The main goal of this research is to develop a data-driven reduced order model (ROM) strategy from high-fidelity simulation result data of a full order model (FOM). The goal is to predict at lower computational cost the time evolution of solutions of Fluid-Structure Interaction (FSI) problems. For some FSI applications like tire/water interaction,...

In last decades, several mathematical models have been proposed to simulate background leakages in water distribution networks (WDNs). Some of these models already consider the dependence of leakages to pressure, but they still neglect the gradient of pressure along the pipes. In this article, new models to take into account of this gradient are pr...

In this work hybrid RANS/LES methods are adapted in order to simulate the flow around a realistic car geometry (estate vehicle). Numerical results are compared to in-house experiments. In order to achieve an accurate understanding of the flow behavior around the car geometry, a wide range of experiments are performed measuring forces, pressure coef...

We present here a new slow-transient model including pressure-dependent background leakages. This model permits to take inertia effects into account while keeping time execution acceptable. New mathematical formulations and numerical implementations were developed to make the model both stable and accurate. Keywords: RWC (rigid water column) model,...

The main goal of this study is to develop a reduced order model (ROM) strategy in order to predict at lower cost compared to a full order model (FOM) the time evolution of physical fields of interest in the context of Fluid-Structure Interaction (FSI). The proposed non-intrusive ROM approach is purely data-driven. In this work, the Dynamic Mode Dec...

Active flow control with jet devices is a promising approach for vehicle aerodynamics control. In this work an extended computational study is performed comparing three different actuation strategies for active flow control around the square back Ahmed body at Reynolds number 500,000 (based on the vehicle height). Numerical simulations are run usin...

Purpose The purpose of this paper is to study pressure measurement correlations, as the location of the pressure sensors should enable to capture variation of the drag force depending on the yaw angle and some geometrical modifications. Design/methodology/approach The present aerodynamical study, performed on a reduced scale mock-up representing a...

The semi-Lagrangian Vortex method (VM) and the Lattice Boltzmann method (LBM) are used to investigate flows simulations in the incompressible regime. In this study, a proven version of each method is used and compared on different three dimensional benchmarks in terms of numerical accuracy, convergence, numerical diffusion and dissipation. The firs...

When particle-laden freshwater is placed above clear saltwater, double-diffusive sedi- mentation can arise. Navier-Stokes direct numerical simulations by Burns and Meiburg showed that this process can be dominated by either Rayleigh-Taylor or double-diffusive fingering instabilities. Based on two-dimensional simulations, those authors identify a si...

This review paper presents an overview of Vortex Methods for flow simulation and their different sub-approaches, from their creation to the present. Particle methods distinguish themselves by their intuitive and natural description of the fluid flow as well as their low numerical dissipation and their stability. Vortex methods belong to Lagrangian...

A study of SST RANS and three hybrid approaches (SAS, DDES and SBES methods) is per- formed to analyse the flow around the 25◦ Ahmed body. The DDES approach is then selected as the reference model, based on comparison of numerical results. The main study is based on grid and time step influence over the simulation results. All results are compared...

To date, the hydraulics of water distribution networks are calculated using deterministic models. Because many of the parameters in these models are not known exactly, it is important to evaluate the effects of their uncertainties on the results through uncertainty analysis. For the propagation of uncertain parameters, this article for the first ti...

Water distribution networks are critical infrastructures that should ensure the reliable supply of high quality potable water to its users. Numerical models of these networks are generally governed by many parameters for which the exact value is not known. This may be due to a lack of precise knowledge like for consumer demand or due to a lack of a...

Background leakages in water distribution networks (WDNs) may represent important economic and environmental losses, and significant ones should be integrated in hydraulic models to help utilities making good decisions for better rehabilitation and operational management of water-related infrastructures. Nowadays WDN models either do not take inert...

A hybrid particle/mesh Vortex Method, called remeshed vortex method, is proposed in this work to simulate three-dimensional incompressible flows. After a validation study of the present method in the context of Direct Numerical Simulations, an anisotropic artificial viscosity model is proposed in this paper in order to handle multi-resolutions simu...

A remeshed Vortex method is proposed in this work to simulate threedimensional incompressible flows. The convection equation is solved on particles, using a Vortex method, which are then remeshed on a Cartesian underlying grid. The other differential operators involved in the governing incompressible Navier-Stokes equations are discretized on the g...

The aim of this work is to explore the efficiency of different improved Reynolds-Averaged Navier-Stokes (RANS) and hybrid LES/RANS approaches to study the external aerodynamics related to ground vehicles. These computational techniques should be able to build a bridge between accuracy and robustness in order to compute complex high Reynolds number...

Water distribution networks are critical infrastructures that should ensure the reliable supply of high quality potable water to its users. Numerical models of these networks are generally governed by many parameters for which the true value is unknown. This may be due to a lack of knowledge like for consumer demand or due to a lack of accessibilit...

The research on the external aerodynamics of ground vehicles can nowadays be related to sustainable development strategies, confirmed by the worldwide CO2 regulation target. Automotive manufacturers estimate that a drag reduction of 30% contributes to 10g/km of CO2 reduction. However, this drag reduction should be obtained without constraints on th...

Purpose This research paper presents numerical investigations of the flow dynamic characteristics of a 47° Ahmed Body in order to identify wake flow control strategy, leading to drag coefficient reduction, which could be tested later on Sport Utility Vehicles (SUV). Design/methodology/approach This study begins with a mean flow topology descript...

The flow around the \(25^{\circ }\) Ahmed body has been studied computationally by applying different methods including an improved URANS formulation, the SAS model and two popular hybrid RANS/LES formulations: DDES and SBES models. All of the turbulence models employ the underlying SST RANS formulation. These hybrid models show a good prediction f...

In this work, a hybrid particle-grid method coupled with a penalization technique is introduced in order to compute Direct Numerical Simulations in three dimensions. The method is validated with the literature for the flow past a sphere and a hemisphere. The approach is extented to solid-porous-fluid media and applied to passive flow control for th...

The calculation of hydraulic state variables for a network is an important task in managing the distribution of potable water. Over the years the mathematical modeling process has been improved by numerous researchers for utilization in new computer applications and the more realistic modeling of water distribution networks. But, in spite of these...

The hydraulic state of a water distribution network is governed by a large number of uncertain parameters. These parameters may be given by uncertain consumer demand, valves states, the value of pipe diameters or the roughness of the pipes. In practice, the influence of parameter variations is important in the decision-making process of water utili...

The aim of this work is to study the platooning of square-back vehicles on top of a road. When two or three bodies are following each other with a short distance between them, the presence of the preceding body changes significantly the pressure force in front of the following one as a weak flow is present in between. The preceding body plays the r...

The calculation of hydraulic state variables for a network is an important task in managing the distribution of potable water. Over the years the mathematical modeling process has been improved by numerous researchers for the utilization in new computer applications and the more realistic modeling of water distribution networks. But, in spite of th...

Current automotive trends lead to vertical shapes in the region of the rear tailgates, which induce high aerodynamical losses at the rear wall of vehicles. It is therefore important to work on turbulent wake in order to find drag reduction solutions for the current vehicle design. This paper focuses on flow control strategies, which are designed to...

The problem of sensor placement for early-warning detection system is a topical issue for industry and utilities who want to equip their networks with such technology. It consists of finding the best sensor locations that optimize a criterion such as detection rate or time to detection. Few methods exist concerning the sensor placement that optimiz...

In this work, a passive flow control study is proposed in order to regularize the flow dynamics around a hemisphere at a low and a higher Reynolds number in the wake transition regime. This passive control is realized by covering the projected curved surface of the hemisphere with a porous coating. The presence of such porous medium modifies the bo...

Water distribution networks are subject to potential intentional contaminations to cause harm to the consumer. Reliable transport models are needed to detect, trace and follow any contaminant transported inside the network. For now, the transport of contaminants in pipes has been mostly modeled assuming perfect mixing conditions at T-junction. Howe...

A square back Ahmed body is used to mimic a heavy vehicle, bus or truck, in order to derive control processes that yield a significant drag reduction. The first step is to analyse carefully the structures in the flow that have a strong impact on the drag forces. Then, active and passive controls using blowing jets or porous medium layers are presen...

In this work, the effect of three different active control strategies namely, pulsed blowing, pulsed suction, and synthetic jets, is studied for a square back Ahmed body. Using a LES numerical simulation, the efficiency of the synthetic actuation on the rear pressure distribution is highlighted.

A vortex method with penalization is proposed in order to simulate three-dimensional incompressible bluff body flows. This approach combines the robustness of vortex methods and the flexibility of penalization methods to impose boundary conditions on the obstacle. Far field boundary conditions are handled in a FFT-based Poisson solver. A validation...

In this work a particle sets of contours method is coupled to a streamline technique in order to obtain accurate approximations of transport problems. A modified particle method based on streamlines technique is proposed and some bench tests arising in porous media are then simulated to validate the new method. These results are complemented with t...

In this work, a hybrid particle-penalization technique is proposed to achieve accurate and efficient computations of 3D incompressible flows past bluff bodies. This immersed boundary approach indeed maintains the efficiency and the robustness of vortex methods and allows to easily model complex media, like solid-fluid-porous ones, without prescribi...

In this work a penalization method is discussed in the context of vortex methods for incompressible flows around complex geometries. In particular we illustrate the method in two cases : the flow around a rotating blade for Reynolds Numbers 1000 and 10000 and the flow past a semi-circular body consisting of a porous layer surrounding a rigid body a...

One critical enhancement needed to model contaminant intrusion in water distribution network is to take into account imperfect mixing at junctions. This paper completes previous work by conducting LES and DNS CFD calculation and laboratory experiments. Statistics were compiled on large-size networks in France and Germany to serve to design a test r...

This paper deals with the application of remeshed particle methods for the simulation and control of wakes behind obstacles. We consider passive as well as active control strategies. Active control consists of jets at the boundary and we show how enhancing natural 3D instabilities of the flow can reduce the drag. Passive control strategies consist...

The trend of automotive design induces vertical shape in the region of the rear tailgate, which leads to important aerodynamic losses in the rear back of vehicles. Experimental wake analysis performed behind a square back bluff body shows influence of the vortex transport in the mixing layers backward the detachment region. It is therefore importan...

A two-dimensional backward facing ramp is used to represent a car simplified rear window. Direct numerical simulations are performed to describe the flow behavior over the ramp. Constant blowing jets and synthetic jets are applied on the body to control the flow. The results presented in this work show a significant reduction of the recirculation z...

The control of two-dimensional flows around bluff-bodies is achieved using porous devices added to some parts of the body. The bodies can be square or circular cylinders as well as a moving Ahmed body on the top of a road. The flow in different media is modelled by means of the penalisation method. A good choice of the location of the porous interf...

The aim of this work is to optimize an actuator design so that the flow profile at its exit section is as close as possible to a target profile. The method is founded on the penalization and level-set methods to solve direct and inverse problems on Cartesian meshes The optimization process is written and applied both for Stokes and Navier-Stokes fl...

In this work, a coupling of vortex methods with penalization methods is proposed in order to accurately and easily handle solid-fluid-porous media. This immersed boundary approach indeed maintains the efficiency and the robustness of vortex methods and allows to model the three different media without prescribing any boundary condition. In this pap...

The aim of this work is on the one hand to show that the drag coefficient of a bluff body is mainly linked to the vortical structures in the close wake of the body. Thus an active control can be used to push away these structures to decrease the pressure forces at the back and consequently to reduce the drag coefficient. On the other hand a study o...

Security is an important concern for the water industry nowadays. It is particularly important to have tools that are able to determine the source of contamination once an alarm is raised by the sensor detection system. The objective of this paper is the development of such a model to locate potential sources of contamination. The model solution us...

In this work three branches of Immersed Boundary Methods (IBM) are described and validated for incompressible aerodynamics and fluid-structure interactions. These three approaches are: Cut Cell method, Vortex-Penalization method and Forcing method. The first two techniques are validated for external bluff-body flow around a circular obstacle. The l...

The passive control of flow past a semi-circular cylinder is carried out. This control is achieved by adding a porous layer between the solid obstacle and the incompressible uid. A vortex-penalization method is chosen to easily tackle the simulation of the flow in the diff erent media. Several con gurations of the porous layer are investigated in o...

The aim of this work is to better understand the impact of the vortical structures motion to the drag coefficient of a simplified ground vehicle. A theoretical study and numerical experiments show the strong relationship between the distance of the vortices to the back wall and the pressure forces. So a way to control the flow is to change the traj...

In this work a particle sets of contours method is coupled to a streamline technique in order to obtain accurate approximations of transport problems. A modified streamlines technique is proposed and several bench tests arising in porous media are then simulated to validate the new method. These results are complemented with the resolution of the d...

The aim of this work is to show that the drag coefficient of a bluff body is mainly linked to the circulation and the distance of the vortices in the close wake of the body. Thus an active control can be used to push away the vortices to decrease the pressure forces at the back. For the size of the vortices a passive control by means of porous laye...

In this work a particle sets of contours method is coupled with a streamline technique in order to obtain accurate approximations of transport problems. A modified streamline technique is proposed and several bench tests arising in the field of porous media are then simulated to validate the new method.

Leakage represents a large part of the supplied water in Water Distribution Systems (WDS). Consequently, it is important to develop some efficient strategies to manage such a phenomenon. In this paper an improved formulation of the hydraulic network equations that incorporate pressure-dependent leakage, is presented and validated. The formulation i...

The aim of this work is to control the flow around ground vehicles by active or/and passive strategies. The active control is achieved by steady, pulsed or closed-loop jets located at the backof the simplified car model. The passive control is performed using porous layers between the solid body and the fluid in order to modify the shear forces. Th...

The vortices generated behind a simplified vehicle induce presssure forces at the back wall that contribute to a significant part of the drag coefficient. The study shows the strong relationship between the distance of the vortices to the back wall and these pressure forces. In particular, control process can modify the trajectory of the vortices t...

The goal of this work is on the one hand to simulate the flow around a simplified ground vehicle called Ahmed body in order to identify the structures that contribute strongly to the drag coefficient and on the other hand to control the flow by an action on these main structures to reduce the drag forces.

Ahmed body with a 25° rear window is used to represent a simplified car geometry. Two- and three-dimensional simulations are performed to analyse the flow behaviour around such a vehicle. Sucking and blowing jets or slots are added on the body to control the flow. The results presented show that good drag reductions are achieved for a good choice o...

The aim of this work is to couple vortex methods with the penalization methods in order to take advantage from both of them. This immersed boundary approach maintains the efficiency of vortex methods for high Reynolds numbers focusing the computational task on the rotational zones and avoids their lack on the no-slip boundary conditions replacing t...