In a non-transferred plasma torch, the working gas becomes ionized and forms plasma as it interacts with the electric arc at the cathode tip. However, in certain cathode shapes, particularly flat ones, and under specific conditions, the gas flow can separate at the cathode tip, forming a vortex region. While this flow separation is influenced by geometric factors, it occurs in the critical zone where plasma is generated. Understanding the causes of this separation is essential, as it may significantly impact torch performance. If the separation proves detrimental, it is important to identify ways to mitigate it. This paper presents a computational analysis of a non-transferred plasma torch to investigate the physics behind flow separation. The results highlight the location and causes of the separation, as well as its potential advantages and disadvantages. Finally, the paper explores theoretical approaches to address flow separation in plasma torches, offering practical insights for enhancing their design and efficiency.

The plasma jet produced by a non-transferred plasma torch may initially appear steady and laminar, but it undergoes significant turbulence as it interacts with the surrounding atmosphere. Within the plasma torch, the jet begins as laminar; however, upon exiting, it transitions into a turbulent flow, extending into a long, wavy structure as it develops. This paper explores the complexities of computational modeling for non-transferred plasma torches, focusing on the challenges of simulating the multiphysics and multiphase interactions at the outlet and tracing the evolution of the plasma jet. The computational analysis uses COMSOL Multiphysics software on a 2D axisymmetric geometry, with steady-state simulations incorporating various turbulence models. A comparative assessment of the results from each turbulence model is provided, highlighting their respective strengths and limitations. Although the diffusion of the turbulent jet at the outlet is presented, the turbulence models employed in this study only offer time-averaged values, rather than a detailed breakdown of the complete jet structure. The paper concludes by validating the computationally obtained velocity magnitudes against experimental data, ensuring the accuracy and reliability of the simulation results.

Labyrinth seals, extensively used in space applications, serve to prevent the loss of liquid lubricants and shield satellite subsystems from contamination. These seals are essential for the reliable functioning of bearings and for protecting satellite subsystems from contamination. This study compares analytical predictions of lubricant loss against experimental measurements and computer simulations to optimize labyrinth seal configurations. Analytical models tend to overestimate mass loss by 5–8 times compared to experimental data, indicating limited reliability for complex seal geometries. Simulations using MolFlow+ and COMSOL Multiphysics align closely with experimental results, providing accurate mass loss predictions. Key findings highlight that labyrinth length, width, and surface roughness are critical factors in minimizing evaporative mass loss. Notably, stepped labyrinth seals with relief grooves and optimized step positioning effectively reduce molecular beaming effects and improve sealing performance compared to straight geometries. Effective sealing not only reduces mission failures but also helps to minimize space debris, thereby promoting safer satellite missions.

Unmanned aerial vehicles (UAVs) have emerged as practical and potentially advantageous tools for scientific investigation and reconnaissance of planetary surfaces, such as Mars. Their ability to traverse difficult terrain and provide high-resolution imagery has revolutionized the concept of exploration. However, operating drones in the Martian environment presents fundamental challenges due to the harsh conditions and the different atmosphere. Aerodynamic challenges include low chord-based Reynolds number flows and the presence of dust particles, which can accumulate on the airfoil surface. This paper investigates the accumulation of dust on cambered plates with 6% and 1% camber, suitable for the type of flow studied. The analysis is conducted for Reynolds numbers of around 20,000 as a result of dimension restrictions, assuming a wind speed ranging from 12 to 14 m/s. Computational simulations are performed using a 2D C-type mesh in ANSYS Fluent, employing the 𝛾γ-Re SST turbulence model. Dust particle modeling is achieved through the Discrete Phase Model (DPM), with one-way coupling between phases. The accumulation of particles is monitored over a 6-month period with monthly intervals, and the airfoil is set at a 0° angle of attack. A deposition model, developed using user-defined functions in Fluent, considers particle–airfoil interaction and forces acting on particles. Results indicate a decrease in airfoil performance for negative angles of attack due to geometric changes, particularly due to accumulation on the bottom side near the tip. The discussion includes potential model enhancements and future research directions arising from the assumptions made in this study.

The weldability of duplex stainless steels partly depends on the ferritization of the high-temperature heat-affected zone (HT-HAZ). This area is rather narrow, and it can be challenging to visualize and determine its actual impact on the properties. To address this, various methods were applied to study the grain growth and austenite reformation in the HT-HAZ of the lean duplex grade UNS S32101. Thermo-mechanical Gleeble® simulations were conducted at 1360 °C with different holding times and cooling rates. Subsequently, the grain size and ferrite content were measured on polished and etched cross-sections. Bead-on-plate welds were performed on the same heat of 6-mm plate thickness using the gas tungsten arc welding (GTAW) process. The shielding gas was Ar + 0–8% N2 to illustrate the effect of nitrogen additions on the HT-HAZ morphology. The arc was either stationary, welding at one spot for 0.5–120 s, or travelling at different speeds to generate varying heat inputs and temperature gradients. The thermo-mechanical simulations approximated the results obtained by travelling arc welding and allowed for a more comprehensive investigation. Stationary arc welding was not suitable for HT-HAZ studies as it quickly caused nitrogen depletion and resulted in significantly higher ferrite contents compared to the travelling arc welds.

In 2021, the Ingenuity helicopter performed the inaugural flight on Mars, heralding a new epoch of exploration. However, the aerodynamics on Mars present unique challenges not found on Earth, such as low chord-based Reynolds number flows, which pose significant hurdles for future missions. The Ingenuity’s design incorporated a Reynolds number of approximately 20,000, dictated by the rotor’s dimensions. This paper investigates the implications of flows at a Reynolds number of 50,000, conducting a comparative analysis with those at 20,000 Re. The objective is to evaluate the feasibility of using larger rotor dimensions or extended airfoil chord lengths. An increase in the Reynolds number alters the size and position of Laminar Separation Bubbles (LSBs) on the airfoil, significantly impacting performance. This study leverages previous research on the structure and dynamics of LSBs to examine the flow around a cambered plate with 6% camber and 1% thickness in Martian conditions. This paper details the methods and mesh used for analysis, assesses airfoil performance, and provides a thorough explanation of the results obtained.

A non-transferred plasma torch is a device used to generate a steady thermal plasma jet. Plasma torches have the potential to replace fossil fuel burners used as heat sources in the process industry. Today, however, the available plasma torches are of small scale compared to the power used in the burners in the process industry. In order to understand the effects of large scales on the plasma flow dynamics, it is essential to understand the operation of the plasma torch under different operating conditions and for different geometries. In this study, the analysis of a non-transferred plasma torch has been carried out using both computational and experimental methods. Computationally, the magnetohydrodynamic (MHD) equations are solved using a single-fluid model on a 2D axisymmetric torch geometry. The experiments are performed using emission spectroscopy to measure the plasma jet temperature at the outlet. This paper explains the changes in the arc formation, temperature, and velocity for different working gases and power inputs. Furthermore, the possibilities and disadvantages of the MHD approach, considering a local thermal equilibrium, are discussed. It was found that in general, the computational temperature obtained is supported by the experimental and equilibrium data. The computational temperatures agree by within 10% with the experimental ones at the center of the plasma torch. The paper concludes by explaining the significant impact of input properties like working gas and power input on the output properties like velocity and temperature of plasma jet. 

Plasma, a complex fluid consisting of electrons, ions, neutrals, and excited species, exhibits both fluid-like behavior and electrical conductivity due to the presence of charge carriers. Consequently, computational modeling of plasma requires the integration of fluid and electrical models. This research paper presents a study on the steady-state computational modeling of a plasma torch with a 2D axisymmetric geometry using single-fluid and two-fluid modeling approaches in the COMSOL Multiphysics® software. The single-fluid modeling (SFM) approach combines the individual equations governing the behavior of different particles into a unified equation. Specifically, the SFM approach utilized in this study focuses on a fully ionized plasma and employs the Magnetohydrodynamic equations whose adaptation is equilibrium discharge interface (EDI) model available in COMSOL Multiphysics®. The EDI model solves the magnetohydrodynamic (MHD) equations, encompassing electric and magnetic fields, heat transfer in solids and fluids, and laminar models. By employing this approach, the researchers simulated and analyzed the behavior of the plasma torch. In contrast, the two-fluid modeling (TFM) approach separates the fluid equations for electrons and ions, considering a weakly ionized plasma. The TFM model is developed by deriving fluid equations based on kinetic theory for neutrals, ions, and electrons. These equations are then implemented in COMSOL Multiphysics®, utilizing models for the transport of diluted species, laminar flow, heat transfer in solids and fluids, and electric and magnetic fields. By adopting the TFM approach, the researchers aimed to gain insights into the behavior of the plasma torch. Throughout the study, various properties such as temperature, velocity, current density, and particle concentrations are analyzed within the plasma torch. Results obtained from both the single-fluid and two-fluid modeling approaches are compared and evaluated. This comparative analysis allows the researchers to highlight the advantages and challenges associated with each modeling approach. In conclusion, this study contributes to understanding plasma behavior by employing computational modeling techniques. The research presents and compares the outcomes of single-fluid and two-fluid modeling approaches applied to a plasma torch. By examining the advantages and challenges of each approach, the study offers valuable insights for future plasma modeling endeavors.

During the last decade, the efforts in space exploration have increased massively and led to a need for new ways to examine planets and other celestial bodies. The modern tendency is to create spacecraft able to scout the surface from a higher point of view, where drones have shown to be most helpful. Even if the benefits brought by this type of technology are considerable, the challenges are still difficult to overcome. This article presents a comprehensive literature review on drone technologies for planetary exploration, focusing mainly on the difficulties encountered. Considerable complications derive from the unknown environment, affecting most of the design, the mathematical model of the body, its controllability, and overall levels of autonomy. Various solutions to these challenges are proposed based on past and future missions. Furthermore, a look into the future gives an idea of possible technological developments and ways to provide the most efficient aerial exploration of other planets.