3D Ray Tracing Solver for Communication Blackout Analysis in Atmospheric Entry Missions

During the atmospheric entry phase at hypersonic speed, the radio communication from/to a space vehicle can be disrupted due to the formation of a plasma sheath within the surrounding flow field. In order to characterize such communication blackout phases, this work presents a numerical methodology combining Computational Fluid Dynamic (CFD) simulations of ionized chemically reacting entry flows by means of Computational Object-Oriented Libraries for Fluid Dynamics (COOLFluiD) and a ray tracing analysis by means of the newly developed BlackOut RAy Tracer (BORAT). The latter is based on the numerical solution of the 3D Eikonal system of equations, offering a fast, efficient and accurate method to analyse the interaction between electromagnetic signals and weakly ionised plasmas. The proposed methodology, and BORAT in particular, is first verified on popular benchmark cases and then used to analyse the European Space Agency (ESA) 2016 ExoMars Schiaparelli entry flight into Martian environment. The corresponding results demonstrate the validity of the proposed ray tracing approach for predicting communication blackout, where signals emitted from the on-board antenna undergo reflection and refraction from the plasma surrounding the entry vehicle, and the advantage of a 3D approach for analysing real flight configuration

A Magnetohydrodynamic enhanced entry system for space transportation: MEESST

This paper outlines the initial development of a novel magnetohydrodynamic (MHD) plasma control system which aims at mitigating shock-induced heating and the radio-frequency communication blackout typically encountered during (re-)entry into planetary atmospheres. An international consortium comprising universities, SMEs, research institutions, and industry has been formed in order to develop this technology within the MEESST project. The latter is funded by the Future and Emerging Technologies (FET) program of the European Commission’s Horizon 2020 scheme (grant no. 899298). Atmospheric entry imposes one of the harshest environments which a spacecraft can experience. The combination of hypersonic velocities and the rapid compression of atmospheric particles by the spacecraft leads to high-enthalpy, partially ionised gases forming around the vehicle. This inhibits radio communications and induces high thermal loads on the spacecraft surface. For the former problem, spacecraft can sometimes rely on satellite constellations for communicating through the plasma wake and therefore preventing the blackout. On the other hand, expensive, heavy, and non-reusable thermal protection systems (TPS) are needed to dissipate the severe thermal loads. Such TPS can represent up to 30% of an entry vehicles weight, and especially for manned missions they can reduce the cost- efficiency by sacrificing payload mass. Such systems are also prone to failure, putting the lives of astronauts at risk. The use of electromagnetic fields to exploit MHD principles has long been considered as an attractive solution for tackling the problems described above. By pushing the boundary layer of the ionized gas layer away from the spacecraft, the thermal loads can be reduced, while also opening a magnetic window for radio communications and mitigating the blackout phenomenon. The application of this MHD-enabled system has previously not been demonstrated in realistic conditions due to the required large magnetic fields (on the order of Tesla or more), which for conventional technologies would demand exceptionally heavy and power-hungry electromagnets. High-temperature superconductors (HTS) have reached a level of industrial maturity sufficient for them to act as a key enabling technology for this application. Thanks to superior current densities, HTS coils can offer the necessary low weight and compactness required for space applications, with the ability to generate the strong magnetic fields needed for entry purposes. This paper provides an overview of the MEESST project, including its goals, methodology and some preliminary design considerations

A Magnetohydrodynamic enhanced entry system for space transportation: MEESST

This paper outlines the initial development of a novel magnetohydrodynamic (MHD) plasma control system which aims at mitigating shock-induced heating and the radio-frequency communication blackout typically encountered during (re-)entry into planetary atmospheres. An international consortium comprising universities, SMEs, research institutions, and industry has been formed in order to develop this technology within the MEESST project. The latter is funded by the Future and Emerging Technologies (FET) program of the European Commission’s Horizon 2020 scheme (grant no. 899298). Atmospheric entry imposes one of the harshest environments which a spacecraft can experience. The combination of hypersonic velocities and the rapid compression of atmospheric particles by the spacecraft leads to high-enthalpy, partially ionised gases forming around the vehicle. This inhibits radio communications and induces high thermal loads on the spacecraft surface. For the former problem, spacecraft can sometimes rely on satellite constellations for communicating through the plasma wake and therefore preventing the blackout. On the other hand, expensive, heavy, and non-reusable thermal protection systems (TPS) are needed to dissipate the severe thermal loads. Such TPS can represent up to 30% of an entry vehicles weight, and especially for manned missions they can reduce the cost- efficiency by sacrificing payload mass. Such systems are also prone to failure, putting the lives of astronauts at risk. The use of electromagnetic fields to exploit MHD principles has long been considered as an attractive solution for tackling the problems described above. By pushing the boundary layer of the ionized gas layer away from the spacecraft, the thermal loads can be reduced, while also opening a magnetic window for radio communications and mitigating the blackout phenomenon. The application of this MHD-enabled system has previously not been demonstrated in realistic conditions due to the required large magnetic fields (on the order of Tesla or more), which for conventional technologies would demand exceptionally heavy and power-hungry electromagnets. High-temperature superconductors (HTS) have reached a level of industrial maturity sufficient for them to act as a key enabling technology for this application. Thanks to superior current densities, HTS coils can offer the necessary low weight and compactness required for space applications, with the ability to generate the strong magnetic fields needed for entry purposes. This paper provides an overview of the MEESST project, including its goals, methodology and some preliminary design considerations

Effect of fuel-jet injection angle variation on the overall performance of a SCRAMJET engine

Air-fuel mixing in a SCRAMJET engine is augmented by the interaction of the transverse fuel jet with the incoming supersonic air. The strong bow shock created by this interaction aids in mixing and increases the fuel residence time, but it also leads to loss in performance of the SCRAMJET engine through the loss of stagnation pressure, and rise in entropy in the combustor. One of the ways to address this issue is to weaken the bow shock by changing the angle of injection of fuel into the combustor. In the present study, the effect of variation of the injection angle, measured in the direction of the cross-flow from a line perpendicular to it (and the wall), has been numerically studied and analyzed on a 3-D SCRAMJET combustor of generic design with dual injectors, using Menter's SST model for turbulence on an in-house 3-D unstructured grid RANS solver. The angle for each injector is independently varied between 0° and 45° with an increment of 15°, while the jet positions are kept fixed at locations previously found to be optimum for the chosen flow conditions and zero angle (i.e. transverse) injection. It is observed that in every case that positive non-zero angles of injection, in the direction of the crossflow, increase thermodynamic efficiency, while the negative non-zero angles, opposing the crossflow, augment mixing. As mixing is of paramount importance in the SCRAMJET engine, due to high speeds and low residence times, we conclude that the best option is to have the angle of fuel jet injection in the direction opposing the incoming flow – a recommendation that has not been seen yet in the research literature. The degree to which the injection is slanted towards the incoming flow can be decided on the basis of the desired rate of the simultaneous penetration of the fuel into the recirculating flame-holder, which increases with increasing angle

Influence of isolator section on the shock augmented mixing in SCRAMJET engine

The paper aims to numerically study the effect of isolator design on shock-augmented mixing in a generic supersonic Ramjet (SCRAMJET) engine and reduce what would be a very complicated thermodynamics+aerodynamic optimization in the design to a simpler aerodynamic one. Changing the length of the isolator section effectively varies the thickness of the boundary layer that is formed in the isolator, which then enters into the SCRAMJET combustor. The study is conducted on a three-dimensional geometry using the Menter's SST model for turbulence on an in-house unstructured grid RANS solver. In this paper, the authors quantify the effect of the incoming boundary layer thickness on the shock-augment air-fuel mixing in the SCRAMJET combustor. It is observed that for the maximum variation in the isolator length, the normalized mixing volume only improves by 7%, which is only a marginally better mixing of air and fuel obtained as with an increase in the isolator length. The authors conclude that the Prandtl-Meyer expansion fan (PMEF) formed at the flame-holder effectively isolates the combustor from the isolator section to a degree that the isolator dimensions can therefore be chosen entirely on considerations of flow homogenization of inlet air before it enters the combustor section of the SCRAMJET engine. Although, the paper analyses a generic SCRAMJET with specific dimensions, the results are more generally applicable than for the specific design actually considered in the paper. Thus this study is also relevant to SCRAMJET engines that may differ radically from our considered design in form and dimensions. © 2022 Elsevier Masson SA

Computational Analysis of Transverse Sonic Injection in Supersonic Crossflow Using RANS Models

Transverse injection at sonic speed from a rectangular slot into a supersonic crossflow is numerically explored with an indigenously developed parallel three-dimensional (3D) Reynold-averaged Navier-Stokes (RANS) solver for unstructured grids. The RANS models used for turbulence closure are the one-equation Spalart-Allmaras (SA) model and the two-equation shear stress transport (SST) model. For each model, the influence of compressibility corrections is assessed. Due to the presence of shock-turbulent boundary layer interaction (STBLI) in the flow, various STBLI corrections are assessed for both the models. Most of the simulations are two-dimensional (2D), but three-dimensional simulations are also performed to investigate the mismatch between the experimental dataset and the numerical results. The SA model is less sensitive to STBLI corrections, but some improvement in its prediction of the separation distance is found with the compressibility corrections. The SST model results are insensitive to the compressibility corrections, but the STBLI correction improves its results. Improved agreement with the experimental dataset is found when simulations are done in 3D, suggesting that the experiments were not so close to 2D as previously believed

Development and Validation of Jatayu -- an In-House CFD solver for High-Speed Aerospace Applications

This paper introduces Jatayu – the in-house parallel, three-dimensional, all-speed, finite-volume, unstructured-grid-framework-based Computational Fluid Dynamics (CFD) solver aimed specifically at high speed flow applications. Jatayu is written in C++ as an object oriented programming platform(O2P2), which creates each physics model as a separate library, that can be dynamically loaded during run-time. This makes Jatayu very modular and flexible, such that it can be easily extended to solve any arbitrary set of equations for multi-physics problems relevant to aerospace such as combustion, aero-acoustics, etc., without affecting other modules in the solver. Jatayu is also capable of harnessing the high-performance scientific computing by using MPI and the ATLAS library for solving complex aerospace applications. We present an overview of current capabilities of Jatayu along with their brief description in terms of physical models and numerical methods. The paper also presents two challenging benchmark problems solved using Jatayu, the first over a missile body at Ma = 7, the second over a DLR R − 6 aircraft at transonic speeds. © 2022, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved

Exploring impact, spreading, and bonding dynamics in molten metal deposition for novel drop-on-demand printing

This study delves into the dynamics of molten metal deposition (MMD)-based drop-on-demand (DoD) printing, focusing on the interaction between aluminum droplets and substrates. Nozzle-to-substrate distances below 20 mm prevent droplet pinch-off, while distances exceeding 40 mm result in no droplet-substrate adhesion. Operating within the substrate temperature range of 350–550 °C is crucial, avoiding delamination, and shrinkage pits at lower temperatures, and substrate deformation and heightened oxidation at higher temperatures. Droplet adhesion is impeded at nozzle temperatures below 700 °C. Impact-driven and inviscid, DoD-MMD exhibits spreading outpacing overall solidification, particularly at higher temperatures. Surface tension forces dominate, influencing droplet spreading and leading to underdamped interfacial oscillations. Weak droplet-substrate adherence, facilitated by Van der Waals forces, allows easy droplet detachment, beneficial for successive drop-on-drop deposition. Unique to DoD-MMD, ridges along the droplet periphery act as solidification paths, influenced by thermal contraction and surface tension. The spherical pancake shape of the droplet, characterized by a solidification angle >90°, is elucidated through Weber and Freezing numbers. The final deposited droplet width to initial diameter ratio increases with the droplet temperature and deposition height. In contrast to other metal DoD studies, the spreading factor decreases with a rise in substrate temperature, attributed to intensified oxidation at higher substrate temperatures

Effect of location of a transverse sonic jet on shock augmented mixing in a SCRAMJET engine

Transverse sonic injection into supersonic cross flow is a well-established technique to inject fuel into a SCRAMJET combustor. A SCRAMJET combustor with a backward facing step acting as a flame-holder has been used for this study. The jet is placed at various locations downstream of the step, where each location represents a distinct flow region. Three-dimensional simulations have been performed using Menter's SST model in our in-house parallel 3-D RANS unstructured grid CFD solver. In such a SCRAMJET configuration, mixing between air and fuel is augmented by shocks generated by the under-expanded jet injected into the supersonic cross flow, hence the jet location is expected to be critical. The performance and mixing of the combustor has been quantified for each of the distinct configurations. The length of the combustor required for complete mixing has also been estimated for the different cases. It is observed that the mixing and performance are strongly affected by the location of the jet in the combustor flow-field. From the results presented in this paper, the optimal location for the jet is somewhat before the end of the recirculation region behind the backward facing step