Fluid Gravity Engineering (United Kingdom)

The study explores plume-surface interactions (PSI) under Martian atmospheric conditions using a specialized large-volume plume-regolith facility. The experiments were carried out with a scaled rocket nozzle (Mach 5.8) on a porous surface representative of Mars soil characteristics. Measurements included impingement pressures and heat distribution profiles. The results revealed distinct variations in pressure and thermal impacts between steady and pulsed nozzle operations, with anomalies such as transducer response to hot plumes. Infrared imaging indicated differences in heat diffusion patterns across porous aluminum witness plates, which simulate Martian regolith characteristics. These findings contribute valuable data to the design of Mars landers, addressing critical challenges like regolith erosion, spacecraft stability, and thermal management.

Understanding the dynamics of rocket plume impingement on flat surfaces is critical for designing effective and sustainable landing pads. The current near vacuum study measures the surface pressures and temperature profiles arising on a flat surface due to highly underexpanded, axisymmetric plume impingement. The experiments were conducted in a dedicated, large-volume plume-regolith facility situated at the University of Glasgow. A total of eight tests were conducted, comprising of both constant and pulsed firing modes. The impingement plate is located at stand-off distances equal to 4 and 16 times the nozzle exit diameters and plate inclinations of 0° and 30°. Reduced stand-off distance increases impingement pressure, with a transient peak in the early stages of impingement indicating the presence of a primary shock wave. Higher stand-off distance resulted in decreased impingement pressure without an initial peak, but with a spike at the end of impingement once the nozzle had stopped firing. For inclined plates, the centerline impingement pressure magnitude decreased by around 40% compared with the 0° inclination. The measured pressures at lower stand-off height are then compared with the results of both a two-way coupled direct simulation Monte Carlo/Navier–Stokes–Fourier solver and an analytical theory. The results from all methods are in good agreement with each other, with the simulation and experimental centerline pressures being within 1% of each other. As the optical thickness of the gas is very low in the experimental case, the numerical method is used to generate a Schlieren image to analyze the shock structure.

Virtual reality (VR) displays have become increasingly popular in recent years, however, the nonidealities of these displays can hinder the users from experiencing a truly immersive experience. In this paper, we review the compensation process for micro‐organic light‐emitting diode (uOLED) displays and the associated optical modules. We discuss the full procedure of the panel compensation method, as well as the process of distortion correction for the optical modules. Additionally, we provide remarks on the mass‐production‐compatible metrology at the end.

Two-dimensional simulations of transpiration cooling in a laminar, hypersonic boundary layer were performed using the thermochemical implicit nonequilibrium algorithm (TINA): a Navier–Stokes solver. Coolant concentration and heat flux results are compared to data obtained from laminar transpiration cooling experiments conducted in the Oxford High Density Tunnel employing a flat-plate geometry at Mach 7. TINA successfully predicts the mixing rate at the wall as a function of the streamwise direction for all blowing ratios. The simulations are more successful in predicting the mixing downstream of the injector as compared to the mixing on the injector: especially at low blowing ratios. A collapse of the thermal effectiveness values calculated from TINA simulation data is achieved, which agrees with laminar correlations within an absolute value of . It is shown that, when the concentration effectiveness is close to one at the injector, the temperature gradient becomes negative at locations immediately downstream of the injector, resulting in a negative heat flux. The acceleration of the coolant in the streamwise direction downstream promotes dissipation of energy, which results in a reduction in the temperature of the coolant, and thereby induces a negative temperature gradient close to the injector.

Abstract We present here a coupled experimental and numerical modelling study to compare the underwater performance of different explosive charge types in simple geometries with a view to having confidence in the use of these models in the design of more complex warheads. Numerical modelling is used to predict the shock and bubble performance of underwater detonated charges and is intended to be used for comparison of the performance of different charge compositions. Model predictions are compared to experimental data from the underwater detonation of 1 kg cylindrical charges. It is shown that a simple 1D spherical geometry Eulerian hydrocode solution is suitable for comparison of the performance of different charge types provided that gauges are located on the radial axis of the charge and located a sufficient distance from the charge. Predictions using our chosen explosive models are shown to accurately capture the shock and bubble performance of ideal and non‐ideal charges tested and the effects of charge casing so that these models can be used in more complex warhead design studies at a later date.

Experiments show that when a high-explosive charge with embedded particles or a charge surrounded by a layer of liquid or granular material is detonated, the flow generated is perturbed by the motion of the particles and the blast wave profile differs from that of an ideal Friedlander form. Initially, the blast wave overpressure is reduced due to the energy dissipation resulting from compaction, fragmentation, and heating of the particle bed, and acceleration of the material. However, as the blast wave propagates, particle–flow interactions collectively serve to reduce the rate of decay of the peak blast wave overpressure. Computations carried out with a multiphase hydrocode reproduce the general trends observed experimentally and highlight the transition between the particle acceleration/deceleration phases, which is not accessible experimentally, since the particles are obscured by the detonation products. The dependence of the particle–blast interaction and the blast mitigation effectiveness on the mitigant to explosive mass ratio, the particle size, and the initial solid volume fraction is investigated systematically. The reduction in peak blast overpressure is, as in experiments, primarily dependent on the mass ratio of material to explosive, with the particle size, density, and initial porosity of the particle bed playing secondary roles. In the near field, the blast overpressure decreases sharply with distance as the particles are accelerated by the flow. When the particles decelerate due to drag, energy is returned to the flow and the peak blast overpressure recovers and reaches values similar to that of a bare explosive charge for low mass ratios. Time–distance trajectory plots of the particle and blast wave motion with the pressure field superimposed, illustrate the weak pressure waves generated by the motion of the particle layer which travel upstream and perturb the blast wave motion. Computation of the particle and gas momentum flux in the multiphase flow generated during explosive particle dispersal indicates that the particle momentum flux is the dominant term in the near field. Both the gas and particle loading must be taken into account when determining the damage to nearby structures following the detonation of a high-explosive charge surrounded by a material layer.

This paper presents the conceptual design and performance analysis of a partially reusable space launch vehicle for small payloads. The system uses a multi-stage vehicle with rocket engines, with a reusable first stage capable of glided or powered flight, and expendable upper stage(s) to inject a 500 kg payload in different low Earth orbits. The space access vehicle is designed to be air-launched from a modified aircraft carrier. The aim of the system design is to develop a commercially viable launch system for near-term operation, thus emphasis is placed on the efficient use of high TRL technologies. The vehicle design are analysed using a multi-disciplinary design optimisation approach to evaluate the performance, operational capabilities and design trade-offs.

The explosive compaction, fracture and dispersal of aluminum particles contained within a cylinder were investigated experimentally and computationally. The aluminum particles surrounded a central, cylindrical high explosive burster charge and were weakly confined in a cardboard tube. The compaction and fracture of the particles were visualized with flash radiography and the subsequent fragment dispersal was recorded with high-speed photography. The aluminum fragments produced were much larger than the original aluminum particles and similar in shape to those generated from the explosive fracture of a solid ductile metal cylinder, suggesting that the shock transmitted into the aluminum compacted the powder to near solid density. The presence of a casing on the burster explosive had little influence on the fragmentation behavior. The effect of an air gap between the burster and the aluminum particles was also investigated. The expansion and fracture of the aluminum were compared with the predictions of a multi-material hydrocode which indicated that the first appearance of cracks through the compacted aluminum layer occurred approximately when the release wave reached the inner surface of the compacted powder.

Abstract There are many application areas, where the ability to accurately predict the speed of expansion of fragments from explosively disseminated porous shells is important. For inert materials this speed in part determines the size of the resulting cloud. For reactive materials this speed in part determines the ability to ignite the material and determines the trade‐off between reactive and inertial fragment effects. Gurney analysis has been used extensively for many years to approximate the speed of fragmenting solid material shells. This work investigates the behavior of HE driven porous shells in spherical and cylindrical geometry and identifies factors to use to multiply solid shell Gurney velocity by to predict the speed of a porous shell.