Reaction Engines (United Kingdom)

In situ synchrotron X-ray computed tomography enables dynamic material studies. However, automated segmentation remains challenging due to complex imaging artefacts - like ring and cupping effects - and limited training data. We present a methodology for deep learning-based segmentation by transforming high-quality ex situ laboratory data to train models for segmentation of in situ synchrotron data, demonstrated through a metal oxide dissolution study. Using a modified SegFormer architecture, our approach achieves segmentation performance (94.7% IoU) that matches human inter-annotator reliability (94.6% IoU). This indicates the model has reached the practical upper bound for this task, while reducing processing time by 2 orders of magnitude per 3D dataset compared to manual segmentation. The method maintains robust performance over significant morphological changes during experiments, despite training only on static specimens. This methodology can be readily applied to diverse materials systems, enabling the efficient analysis of the large volumes of time-resolved tomographic data generated in typical in situ experiments across scientificdisciplines.

Abstract Brush seals are utilized in turbines to minimize leakage flows and enhance thermal efficiency. Their widespread use faces challenges like pressure-stiffening and hysteresis, leading to unpredictable performance. This work introduces an advanced numerical model to simulate inter-bristle frictional contact, shaft and backing ring interaction, and three-dimensional bristle bending. The model is adopted to investigate multi-bristle brush seal's behavior under shaft radial movements and pressure loading. Backing ring friction emerges as a vital factor in hysteresis modeling, lessening the impact of shaft friction. When the shaft retracts, modeling the bristle tip clearance becomes important. The clearance greatly increases leakage flow rate and changes bristles' aerodynamic loading distribution. With clearance, the normal force on upstream bristles rises markedly, opposing bristle hang-up, while the axial force decreases in downstream bristles, alleviating the bristle pack compression. Considering these factors, an improved model for pressurized seals in the shaft retraction phase is developed and compared to experimental data in the literature. Frictional inter-bristle contact significantly modifies the distribution of local tip force through the pack. These effects would influence localized wear and heat generation across the brush seal pack, shedding light on the uneven wear patterns often observed in experiments. The present high-fidelity model can capture these complex interactions, offering a means to deepen our understanding of the physical mechanisms underpinning novel brush seal designs.

Abstract A key requirement to achieve sustainable high-speed flight and efficiency improvements in space access, lies in the advanced performance of future propulsive architectures. Such concepts often feature high-speed nozzles, similar to rocket engines, but employ different configurations tailored to their mission. Additionally, they exhibit complex interaction phenomena between high-speed and separated flow regions at the base, which are yet not well understood, but are critical in terms of pressure and viscous forces. This paper presents a numerical investigation on the aerodynamic performance of a representative novel exhaust system, which employs a high-speed, truncated, ideal contoured nozzle and a complex-shaped cavity region at the base. Reynolds-Averaged Navier-Stokes computations are performed for a number of Nozzle Pressure Ratios (NPRs) and free stream Mach numbers in the range of 2.7 < NPR < 24 and 0.7 < M∞ < 1.2 respectively. The corresponding Reynolds number lies within the range of 1.06 · 106 < Red < 1.28 · 106 based on the maximum diameter of the configuration. A decomposition of the drag domain forces exposes the major trends between the constituent elements. The impact of the cavity on the aerodynamic characteristics of the apparatus is revealed by direct comparison to an identical non-cavity configuration. Results show a consistent trend of increasing base drag with increasing NPR for all examined M∞ for both configurations. This is attributed to the jet entrainment effect and to the lower base pressure imposed by the higher jet flow expansion. The cavity region is found to have almost no impact on the incipient separation location of the nozzle flow. At low supersonic speeds of M∞ = 1.2 and high NPRs, the cavity has a significant effect on the aerodynamic performance, transitioning nozzle operation to under-expanded conditions. This results in approximately 12% higher drag coefficient compared to the non-cavity case and shifts the minimum NPR for which the system produces positive gross propulsive force to higher values.

Abstract Hydrogen continues to show significant promise as a zero-carbon energy carrier in the pursuit of global decarbonisation targets. Hydrogen has wide flammability limits which means it can operate at considerably leaner conditions for reduced NOx emissions. However, fuel-lean operation makes these systems more susceptible to thermoacoustic instabilities and flame blow-off. Combustor configurations such as jet-in-crossflow are gaining popularity in industry for 100% hydrogen as they can help mitigate risk of flashback, but detailed characterisation of flame dynamics is still necessary. In this study, the combustion dynamics of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor were investigated at atmospheric conditions. The combustor inlet consisted of nine circular air channels, with hydrogen injected inwards through two diametrically opposite holes into each air channel. Dynamic pressure and OH* chemiluminescence measurements were employed to study the effect of varying key parameters, such as Reynolds number and global equivalence ratio, on combustor dynamics. High-speed OH-PLIF imaging was conducted to understand flame dynamics. The results showed that self-excited oscillations were observed at all tested conditions and the dynamical behaviour of the combustor was complex with strong dependency on global equivalence ratio and bulk velocity conditions. The magnitude of self-excited thermoacoustic oscillations initially increased with a decrease in global equivalence ratio, but subsequently decreased at leaner conditions (below global equivalence ratio 0.3). Similar observations were noted for all bulk velocities. High speed OH-PLIF imaging indicated that the heat release oscillations were influenced by vortex-flame roll up and possible global lean extinction events. The results from this work have the potential to inform design efforts towards development of new architectures for stable, low-emission 100% hydrogen combustors.

This paper presents an experimental study of the interaction of turbulent spots with an initially laminar separation, using schlieren visualisation and dynamic measurements of surface heat transfer and pressure. The separation is generated on a blunt cylinder-flare body, tested at Mach 9, and entropy layer effects result in a boundary layer edge Mach number of 3.43 at separation. A single roughness element is used to produce isolated spots, defined such that separation collapse and re-establishment is completed before arrival of the next spot. On average the spot axial length, at the start of the interaction, is 2.5 times the separation length, growing to 6.8 times as the spot base passes the original reattachment position. As such the spot comprises a large perturbation. The local separation responds almost immediately with passage of the spot, so that the downstream region may be unaffected while the upstream part has already collapsed. Re-establishment of separation is slow, taking up to four times the total transit time of the spot. A basic model is presented to explore the transient wave processes during spot passage.

Este estudio tuvo como objetivo analizar la relación entre nivel de presión social con la percepción de la imagen corporal y las características sociodemográficas en adolescentes, con una muestra de 138 participantes de primero y segundo año de educación media diversificada de tres instituciones educativas públicas del municipio Campo Elías, estado Mérida, Venezuela, seleccionadas de forma intencional. Se realizó un estudio de campo descriptivo de corte transversal, la muestra estuvo representada por un 47,1 % del género masculino y un 52,9 % del género femenino. El promedio de edad para los adolescentes fue de 16,09 años. El 24,6 % se percibió delgado, el 66,7% normal y el 8,7 % con sobrepeso. Las diferencias encontradas en los niveles de presión en relación a las variables sociodemográficas (edad, género y condición socioeconómica) no fueron estadísticamente significativas. Sin embargo, las diferencias encontradas en el nivel de presión social con respecto a la percepción de la imagen corporal fueron estadísticamente significativas (F=8.099 p = 0.000). Conclusión: Los adolescentes con percepción de imagen corporal con sobrepeso son más susceptibles de sentir mayor presión social por la apariencia física.

Reusable vehicles are vital to make access to space more affordable, but conventional rocket engines have their limits. Oliver Nailard describes how UK firm Reaction Engines hopes to revolutionize space access with a new class of propulsion system, the Synergetic Air Breathing Rocket Engine (SABRE)

Aim The purpose of this study was to replicate and extend a pilot evaluation of the effectiveness of school-based humanistic counselling for psychological distress in young people. Method Data were available on 32 young people who were randomised to either school-based humanistic counselling or waiting list conditions for one school term. The primary outcome measure was of psychological distress using the Young Person's CORE (YP-CORE), at six and 12 weeks post-assessment. Secondary measures at these time-points were of psychological difficulties, self-esteem, levels of depression, and attainment of personal goals; with longitudinal evaluation of outcomes at six months post-assessment. Results On the primary outcome measure, participants who received counselling were significantly less distressed at six weeks than those in the waiting list group but not at 12 weeks, with effect sizes (Cohen's d) of 0.59 and 0.39 respectively. Reductions in psychological distress were maintained at follow-up. Discussion Although the present findings, in isolation, are equivocal, they contribute to a body of evidence that supports the effectiveness of school-based humanistic counselling. However, the principal lesson learnt from this study was the need for rigorous training of researchers, counsellors and pastoral care teachers to ensure adherence to protocols.

Supremo Tribunal Federal