Pablo Fajardo

• PhD Aeronautical Engineer
• Professor at University Carlos III de Madrid

Plasma chemistry of main air components is implemented in a hybrid 2D axisymmetric simulation code to assess the air-breathing concept in an electrodeless plasma thruster. Relevant electron-heavy species collisions for diatomic molecules are included: rotational and vibrational excitation, dissociation and dissociative ionization. Plasma-wall inter...

The dynamics of xenon atoms and ions expanding in the magnetic nozzle of a Helicon plasma thruster is studied by means of near-infrared laser-induced fluorescence spectroscopy on resonant and metastable states. Fluorescence spectra are measured for several operating conditions inside and outside the thruster discharge chamber. In the near-field plu...

Numerical simulations of the HT20k, a high power magnetically-shielded Hall effect thruster, developed by SITAEL, are carried out with HYPHEN, a two-dimensional axisymmetric hybrid PIC/fluid code with a magnetized and diffusive electron transport model. The model includes a phenomenological anomalous transport parameter, which is adjusted with expe...

The dynamics of atoms and ions expanding in the magnetic nozzle of a Helicon plasma thruster is experimentally studied by means of near-infrared laser-induced fluorescence spectroscopy and a retarding potential analyzer. The two techniques are compared in measuring Xe and Kr ion velocity for different thruster working parameters. Fluorescence spect...

Lunar Zebro’s mission is heading the race for deploying the world’s smallest and lightest swarm of nanorovers on the surface of Moon. The concept validation of a single nanorover is of crucial importance, as it will be the launching pad for deploying a swarm of those nanorovers thereafter. Then, they will get connected in a network, acting as a sin...

An axisymmetric fluid model for weakly-collisional, magnetized electrons is introduced and coupled to a particle-in-cell model for heavy species to simulate electrodeless plasma thrusters. The numerical treatment of the model is based on a semi-implicit time scheme, and specific algorithms for solving on a magnetic field aligned mesh. Simulation re...

Numerical simulations of a magnetically shielded Hall effect thruster with a centrally mounted cathode are performed with an axisymmetric hybrid particle-in-cell/fluid code and are partially validated with experimental data. A full description of the plasma discharge inside the thruster chamber and in the near plume is presented and discussed, with...

A radial particle-in-cell model of the weakly-collisional plasma discharge in a Hall thruster, provides the non-Maxwellian velocity distribution functions (VDF) of ions and electrons. The model considers a radial magnetic field, secondary electron emission from the two walls, and phenomenological models of anomalous electron scattering. The electro...

The effects of heavy particle-wall interaction on a cylindrical plasma source discharge are investigated, through hybrid particle-in-cell/fluid simulations. The bulk plasma is considered quasineutral with isothermal electrons, and with no secondary electron emission from the walls. The neutral gas wall reflection model is shown to play a major role...

The near plume of an SPT100-like Hall thruster is simulated with a hybrid particle-in-cell/fluid code to assess the three-dimensional effects of the neutralizer for two different asymmetric positions. The electron fluid model accounts for the effects of both magnetization and collisions, and closes the momentum equation with a simple polytropic clo...

Multiple simulations of a Cylindrical Hall Thruster (CHT) are performed using the hybrid PIC/fluid plasma code HYPHEN. This numerical research attempts to explore the effect of isolated (important) parameters. The design of a test prototype is introduced for a future comparison of experimental and computational results.

This paper reports a comparison between wind-tunnel measurements and numerical simulations to assess the capabilities of Reynolds-Averaged Navier-Stokes models to estimate the wind load over solar-panel arrays. The free airstream impinging on solar-panel arrays creates a complex separated flow at large Reynolds number, which is severely challenging...

Direct thrust measurements by means of a thrust balance are the golden standard for measuring thrust and concurrently the specific impulse in electric thrusters. To measure these properties in the novel class of electrode-less plasma thrusters a new thrust balance based on the VAHPER (Variable Amplitude Hanging Pendulum with Extended Range) concept...

HIPATIA (HelIcon PlasmA Thruster for In-Space Applications) is a project recently awarded with an European Commission H2020 grant for the development of the Helicon Plasma Thruster and the technologies associated to it. The goal of the HIPATIA Project is to verify the function and performances of an Electric Propulsion System based on the HPT techn...

A central challenge in the modeling of the near-collisionless expansion of a plasma thruster plume into vacuum is the inadequacy of traditional fluid closure relations for the electron species, such as isothermal or adiabatic laws, because the electron response in the plume is essentially kinetic and global. This work presents the validation of the...

A linear stability analysis of the thermoconvective problem of a thin liquid film contained in an annular domain has been conducted. The influence of the horizontal aspect ratio on the solution has been considered by keeping a fixed external wall while the internal radius of the annular domain was modified. The parameter used in the study, h , has...

Plasma discharges in electromagnetic thrusters often operate with weakly-collisional, magnetized electrons. Macroscopic models of electrons provide affordable simulation times but require to be solved in magnetically aligned meshes so that large numerical diffusion does not ruin the solution. This work discusses suitable numerical schemes to solve...

In this research, the plasma response of the Helicon Plasma Thruster experimental prototype is characterized for different operational parameters (Prf,m,B). The system sensitivity against variation of these parameters is monitored as part of the closed loop control design for the HPT Engineering Model (EM). The plasma impedance at each working poin...

This work aims to describe the observed structures of the plasma beam exhausted by an Helicon Plasma Thruster. Experimental data has been acquired through an intense experimental campaign on the HPT05M prototype, which has been operated nominally at 20 sccm of Argon, 450 W of RF power, and magnetic field strengths about 1000 G. This work explores t...

This paper begins with a brief review of the HPT technology development within the fruitful join-venture between UC3M and SENER Aerospacial. Starting from the first experimental platform, rated at 1 kW, passing through different modifications of the initial breadboard, until the last design, scaled down to 450 W of nominal power, called the HPT05M...

A three-dimensional hybrid PIC/fluid code is used to simulate a Hall Effect thruster plume, starting from a known injection profile at the annular exit section. The electron model features magnetized electrons and considers both anomalous transport and a polytropic closure for the electron temperature. Simulations with a varying anomalous transport...

Currently, the main problem for Helicon Plasma Thrusters (HPTs) is the lack of knowl- edge about its operation, and thus there are not proper guidelines for its design. In this paper, a novel 2D asymmetric code is proposed as a tool that could improve the understat- ing of the physics behind and acts as a guidance that leads to a competitive design...

HYPHEN is a new two-dimensional axisymmetric hybrid, particle-in-cell (PIC)/fluid multi-thruster simulation platform under development. This work presents the last modeling advances, outlining the recent improvements incorporated in both the PIC and the electron-fluid segments, and shows the code capabilities regarding the simulation of Hall efect...

A new algorithm for simulating the effect of an axial source of particles is implemented in a 1D radial particle-in-cell model of an annular Hall effect thruster discharge with secondary electron emission from the walls. New particles are generated into the domain from a prescribed axial source with a self-adjusted injection frequency so that a sus...

Direct thrust measurements by means of a thrust balance are the golden standard for measuring thrust and concurrently the specific impulse in electric thrusters. To measure the thrust of a medium power (300-1000W) Helicon Plasma Thruster (HPT) we propose a thrust balance design based on the VAHPER concept. The thrust balance is designed to measure...

An investigation on the influence of relevant parameters on an annular Hall effect thruster plasma discharge is performed using a radial particle-in-cell simulation code with secondary electron emission from the walls and prescribed axial electric and radial magnetic fields. A simulation with true-secondary electrons only is taken as reference. Fir...

In this work, we study numerically with large eddy simulation, the effects induced by the three-dimensional geometry of the channel on the flow topology that exists when the three-dimensional intrinsic instabilities appear in a backward facing step flow with low aspect ratio for Reynolds in the transitional regime (Re = 1,000–1,600), and its impact...

This article reviews the linear stability of a thermoconvective problem in an annular domain. The flow is heated from below, with a linear decreasing horizontal temperature profile from the inner to the outer wall. The top surface of the domain is open to the atmosphere and the two lateral walls are adiabatic. The effects of several parameters in t...

Diagnostics of plasma plumes are indispensable for both characterizing thruster performance and investigating the underlying physics of new thruster technologies. Most existing diagnostics either provide local or line-of-sight information and often require the assumption of axi-symmetry. Tomography does not have these limitations. By combining imag...

The expansion of a rarefied axisymmetric plume emitted by a plasma thruster is analyzed and compared with a 3D Cartesian-type and a 2D cylindrical-type simulation code, both based on a particle-in-cell formulation for the heavy species and a simple Boltzmann-type model for the electrons. The first part of the paper discusses the 2D code numerical c...

This manuscript studies the forced-mixed convective flow on a three-dimensional backward facing step with low aspect ratio (AR = 4) and expansion ratio ER = 2 for Reynolds number in the laminar and beginning of transitional regime (Re 100–1200). The analysis is performed using large eddy simulations, with the main objective assessing the effect of...

The plasma discharge inside a Helicon Plasma Thruster (HPT) chamber is studied. A preliminary version of a novel two-dimensional asymmetric code under development for HPT is used for the analysis. The dynamics of the plasma is described with a hybrid approach: a particle-in-cell method for the heavy species and a fluid model for electrons. Re- gard...

A Helicon Plasma Thruster has been tested in the 500-1000 W radio-frequency power range, at 13.56 MHz. In order to determine its propulsive performances, a parametric study of some operational parameters has been carried out, including the exploration of the magnetic field topology and strength, the mass flow rate, and different propellants. The pl...

An experimental Helicon Plasma Thruster developed by EP2 and SENER has been tested in the 300-1000 W radiofrequency power range. Several operational sets have been tried with the goal of determining the HPT performances envelope. This has included: Argon and Xenon mass flow rates about 35-100 sccm and 1-30 sccm respectively, different magnetic topo...

The new 2D and 3D hybrid particle-in-cell (PIC) fluid codes under development by the EP2 group are presented and compared in this manuscript through the simulation of an unmagnetized gridded ion thruster (GIT) plasma plume as benchmark case. The main innovations focused on improving PIC statistics are presented including a new population control al...

The manuscript presents development updates on a new two-dimensional, axisymmetric, hybrid particle-fluid code for simulation of plasma discharges, particularly, in Hall Effect thrusters. The overall code structure and main design rationale are introduced; par- ticularities for the particle segment are commented, including the algorithms for partic...

El análisis presentado en este artículo se enmarca en una serie de trabajos de prospectiva tecnológica en eí area espacial dentro del programa Horizontes ISDEFE. El presente estudio se centra en eí area Vigilancia y Seguimiento espaciales (VSE, SST en sus siglas en inglés). La creciente dependencia de las actividades terrestres de capacidades espac...

This manuscript explores numerical errors in highly anisotropic diffusion problems. First, the paper addresses the use of regular structured meshes in numerical solutions versus meshes aligned with the preferential directions of the problem. Numerical diffusion in structured meshes is quantified by solving the classical anisotropic diffusion proble...

This manuscript addresses the linear stability analysis of a thermoconvective problem in an annular domain. The flow is heated from below, with a linear de-creasing horizontal temperature profile from the inner to the outer wall. The top surface of the domain is open to the atmosphere and the two lateral walls are ad-iabatic. The effects of several...

Flow visualization experiments and numerical simulations were performed on a narrow three-dimensional backward-facing step flow with the main objective of characterizing the secondary bubble appearing at the top wall. The backward-facing step (BFS) has been widely studied because of its geometrical simplicity as well as its ability to reproduce mos...

A linear stability analysis of a thin liquid film flowing over a plate is performed. The analysis is performed in an annular domain when momentum diffusivity and thermal diffusivity are comparable (relatively low Prandtl number, Pr=1.2). The influence of the aspect ratio (Γ) and gravity, through the Bond number (Bo), in the linear stability of the...

A short study on numerical errors for highly anisotropic diusion problems in propulsion plasmas is presented in order to address the use of magnetic eld aligned meshes versus regular structured meshes in numerical solutions. Numerical diusion in structured meshes is quantied by solving the classical anisotropic diusion problem. Meshing strategies a...

A comprehensive evaluation of erosion reduction mechanisms in Hall Eect Thrusters with dielectric walls is performed. Two physical mechanisms: plasma density reduction at key thruster wall positions and acceleration region displacement, are presented as the main mechanisms which must be exploited in order to achieve reduced thruster wall erosion ra...

This manuscript addresses the application of numerical simulations for assessing the error in the measurement of the bulk temperature along the laser beam of a 3D flow using a 2D Moiré deflectometry analysis. To analyze the effect of different flow parameters on the error, a 3D computational model of an experimental system was developed. The simula...

Magnetic nozzles (MNs) in advanced plasma thrusters and EP2 team and Facilities

This paper presents the development and validation of a one-dimensional radial turbine model able to be used in automotive turbocharger simulations. The model has been validated using results from a numerical 3D CFD simulation of stationary and pulsating flow in a variable geometry radial turbine. As the CFD analysis showed, the main non-quasi-stea...

Materials of viscoelastic nature are widely used for engineering applications such as vibration isolation or as devices to mitigate earthquake effects in buildings. In order to predict the behavior of such structures, the models must reproduce the response as ac-curately as possible. In the most general case, the structures that include viscoelasti...

A steady multiple reference frame segregated compressible solver and an unsteady sliding mesh one are developed using OpenFOAM® to simulate turbomachinery. For each of the two solvers, governing equations, numerical approach and solver structure are explained. Pressure and energy equation are implemented so as to obtain the best numerical propertie...

This paper proposes a CFD method for simulating radial turbocharger turbine flows. A review is presented of the computational model in terms of meshing, mesh movement strategy, and computational algorithm in turbomachinery CFD simulations. A novel local mesh independence analysis is developed for this purpose. This procedure is aimed at distributin...

This Brief Report studies the linear stability of a thermoconvective problem in an annular domain for relatively low (∼1) Prandtl (viscosity effects) and Biot (heat transfer) numbers. The four possible patterns for the instabilities, namely, hydrothermal waves of first and second class, longitudinal rolls, and corotating rolls, are present in a sma...

Nowadays, turbocharged internal combustion engines (ICEs) are very common in automotive powerplants, monopolizing the diesel sector and having a steadily increasing percentage in the gasoline one. In this frame, the interest in modeling the behavior of the turbomachinery components involved, with the ultimate goal of characterizing the performance...

Export Date: 16 August 2013, Source: Scopus, Art. No.: 015001

Numerical computations are commonly used for better understanding the unsteady processes in internal combustion engine components and their acoustic behavior. The acoustic characterization of a system requires that reflections from duct terminations are avoided, which is achieved either by using highly dissipative terminations or, when an impulsive...

In the present paper an unsteady approach to determine the performance of a small radial inflow turbine working under cold pulsating flow is presented. It has been concluded that a reasonably good characterization of turbine behavior working with pulsating flow can be obtained using in a quasi-steady way models of the turbine isentropic efficiency...

This paper details a physically based methodology to perform an extrapolation of the radial turbine performance maps, both mass flow characteristics and the efficiency curve. This method takes into account a narrow range of experimental data, which is usually the data available when such turbines are part of a turbocharger. Therefore, the extrapola...

This work focuses on the analysis of a structural element of MetOP-A satellite. Given the special interest in the influence of equipment installed on structural elements, the paper studies one of the lateral faces on which the Advanced SCATterometer (ASCAT) is installed. The work is oriented towards the modal characterization of the specimen, descr...

Satellites and space equipment are exposed to diffuse acoustic fields during the launch process. The use of adequate techniques to model the response to the acoustic loads is a fundamental task during the design and verification phases. Considering the modal density of each element is necessary to identify the correct methodology. In this report se...

During launch, satellite and their equipment are subjected to loads of random nature and with a wide frequency range. Their vibro-acoustic response is an important issue to be analysed, for example for folded solar arrays and antennas. The main issue at low modal density is the modelling combinations engaging air layers, structures and external flu...

This paper describes the methodology followed to perform a co-simulation between 1D (OpenWAM) and 3D (FLUENT) CFD codes. The Method of Characteristics (MoC) has been chosen to transfer the information between the two domains by properly updating the boundary condition at the shared interface. A short explanation of the MoC is provided, including th...

This paper presents a new representation of the turbine performance maps oriented for turbocharger characterization. The aim of this plot is to provide a more compact and suited form to implement in engine simulation models and to interpolate data from turbocharger test bench.The new map is based on the use of conservative parameters as turbocharge...

The spray characteristics and, consequently, the success of the Diesel combustion process is strongly ffected by the manner in which fuel is introduced in the combustion chamber. This work consists in studying the effect of needle motion of typical single-hole sac-type injectors on nozzle exit conditions. Three-dimensional moving mesh simulations h...

The spray characteristics and, consequently, the success of the Diesel combustion process is strongly affected by the manner in which fuel is introduced in the combustion chamber. This work consists in studying the effect of needle motion of typical single-hole sac-type injectors on nozzle exit conditions. Three-dimensional moving mesh simulations...

The Silences of the Archives, the Reknown of the Story. The Martin Guerre affair has been told many times since Jean de Coras and Guillaume Lesueur published their stories in 1561. It is in many ways a perfect intrigue with uncanny resemblance, persuasive deception and a surprizing end when the two Martin stood face to face, memory to memory, befor...