Cavity Shape Research Articles

Analysis of particle dispersion and cavity formation during bulk particle water entry using fully coupled CFD-DEM-VOF approach

This paper presents the development and validation of a fully coupled computational fluid dynamics—discrete element method—volume of fluid (CFD-DEM-VOF) model to simulate the complex behavior of particle-laden flows with free surfaces. The coupling between the fluid and particle phases is established through the implemented continuity, momentum, and alpha transport equation. The coupled particle forces such as drag, pressure gradient, dense virtual mass, viscous, and interface forces are also integrated, with drag and dense virtual mass forces being dependent on local porosity. The integrated conservative alpha transport equation ensures phase volume conservation during interactions between particles and water. Additionally, we have implemented a trilinear interpolation method designed to operate on unstructured hexahedral meshes. This method has been tested for its ability to properly resolve the coupling effects in the numerical simulations, particularly in cases with a relatively low cell-size ratio. The model is validated through three distinct test cases: single particle water entry, dam break with particles, and water entry of a group of particles case. The experimental setup is built to study the dynamics of the water entry of a group of particles, where three key flow features are analyzed: the evolution of average particle velocity, cavity shape, and particle dispersion cloud profiles in water. The tests involve four different scenarios, including two different water levels (16.1 and 20.1 cm) and two different particle densities (2650 and 4000 kg/m3). High-speed videometry and particle tracking velocimetry (using ImageJ/TrackMate) methods are employed for experimental data acquisition. It is demonstrated that numerical results are in excellent agreement with theoretical predictions and experimental data. The study highlights the significance of vortices in cavity shaping and particle dispersion. The validated CFD-DEM-VOF model constitutes a robust tool for simulating particle-laden flows, contributing valuable insights into the complex interplay between particles and fluids.

Numerical Analysis of Laminar Natural Convection Inside Enclosed Squared and Trapezoidal Cavities at Different Inclination Angles

The effects of cavity shape by inclination angle on laminar natural convection inside trapezoidal and square-shaped cavities have been numerically investigated in this work. Several simulations had been conducted for various inclinations of the trapezoidal cavity at Rayleigh numbers (Ra) =105 to 106 in a laminar flow regime. The walls at the left and right sides of the cavities were heated isothermally, while the walls at the top and bottom sides were adiabatic. The problem was assumed to be 2-D and solved using the software package ANSYS Fluent 16.2. Cavity filled with air is examined in two distinct instances; varying boundary layers and the flow generated for the natural convection. This numerical study analyzed the flow characteristics, temperature distribution, and Nusselt number. The analysis reveals that as the Rayleigh number increases, the Nusselt number also increases, with a more pronounced effect at higher Rayleigh numbers. It has been observed that there is a substantial effect of cavity shapes on the Nusselt number. The presence of an angled wall inhibits convection resulting in stronger flow in the squared cavity compared to the trapezoidal cavity. From numerical results, it is also found that the temperature distribution at Ra = 105 is wider than the temperature distribution at Ra= 106.

Magnetic field effect on mixed convection flow inside an oval-shaped annulus enclosure filled by a non-Newtonian nanofluid

The phenomenon of flow around a static or rotating circular cylinder has significant applications in various engineering fields, such as building, bridge, and structure engineering. It can be used to control flow-induced vibration, blowing or suction, moving surfaces, acoustic thriller, and synthetic jet. Additionally, there is a need to enhance heat transfer rates in many life and industrial applications, including cavity shape enhancement, heating or cooling spread inside a cavity, heat dissipation in electronic devices, thermal mixing in storage units, solar collectors, desalination, and journal bearing lubrication. This study explores the effect of a horizontal magnetic field and a rotating inner circular cylinder on mixed convection within a two-dimensional oval-shaped enclosure filled with a non-Newtonian nanofluid. The Galerkin Finite Element Method (GFEM) is utilized for analysis, with the enclosure undergoing differential heating and cooling on the inner cylinder wall and the enclosure wall, respectively. The nanofluid consists of water infused with copper nanoparticles. The study explores various simulation parameters, including the Richardson number (Ri), Hartmann number (Ha), the inclination angle of the enclosure (β), power-law index (n), circle center eccentricity (e), and nanoparticles volume fraction (φ). It has been observed that as the Ha and n index increase for different Ri values, a wavy trend in local Nusselt number (Nu) profiles along the heat source surface is observed. Additionally, the heat transfer rate decreases with increasing Ri for various combinations of Ha and n index. Under specific conditions, such as Ri = 0.001, Ha = 60, e = 0, φ = 0.09, and β = 90, the results show that, compared to a Newtonian fluid (n = 1), the heat transfer rate exhibits percentage gains of approximately 6.31% for a pseudo-plastic fluid (n = 0.6) and 8.47% for a Dilatant fluid (n = 1.4). The convective heat transfer was significantly enhanced when the eccentricity of the cylinder was positioned in the lower or upper regions of the oval-shaped enclosure, particularly at e = - 0.3. The highest heat transfer rates were observed at β = 60 and 240.

Semi-self-similar fractal cellular structures with broadband sound absorption

Honeycomb core materials, recognized for their excellent sound absorption and load-bearing capabilities, are widely employed in engineering applications. The back cavity shape of honeycomb structure absorbers plays a crucial role in their sound absorption performance. In this study, the honeycomb structure absorbers are re-designed using fractal design principles, enabling a modification of the acoustic properties of traditional honeycomb-type absorbers and a significant enhancement in the sound absorption frequency band. The theoretical predictions of the semi-self-similar fractal honeycomb absorber structure are validated through finite element simulations and experimental studies, exhibiting remarkable consistency. The findings indicate that compared to single-layer first-order structures, the performance of dual-layer second-order fractal element Helmholtz resonators is significantly improved. Relative to conventional honeycomb panel structures, the fractal design approach markedly enhances the semi-absorption bandwidth of the absorbers, with an increase in the fractal order further broadening the sound absorption frequency band. The innovation of achieving broadband absorption through fractal resonators not only represents a new direction in the design of advanced honeycomb core materials but also holds substantial promise in the field of noise control.

PREPARATION AND IN-VITRO ESTIMATION FOR GASTRORETENTIVE FLOATING HOLLOW – MICROSPHERES OF FAMOTIDINE

Objective: The present study’s objectives were to prepare and evaluate gastroretentive floating hollow-microspheres (HM) of the selected Famotidine (FM) to enhance its retention time within the stomach. Methods: HM was prepared by solvent emulsion diffusion technique utilizing various polymers such as ethyl cellulose, eudragit L100, eudragit S100 as polymers, and Dichloromethane and methanol as solvents. The formulated HM was estimated for their particle-size, entrapment efficiency, floating ability, scanning electron microscopy, and in vitro drug release of drug. Results: The average particle-size of the formulated HM was within the range of 262.3±3.5 to 323.1±2.1μm. The SEM confirmed the smooth surface, sphere shape, and hollow cavity within it. The formulated microspheres showed good floating behavior for up to 8 h because of their low particle size. The invitro release profile of the HM displayed a controlled-release of FM microspheres in pH1.2 for up to 8 h. Conclusion: The result depicts that the formulated HM of FM by virtue of good floating time and sustained release properties is likely to improve the retention time within the stomach and thereby the oral bioavailability.

Effects of cage topology on ethylene adsorption mechanism in silver exchanged CHA and RHO zeolites: An Inelastic Neutron Scattering and Density Functional study

Zeolite-based adsorbents have been successfully used for many challenging separations due to their tunable properties. A particularly notable application involves the separation of light olefins from paraffins, wherein the molecular sieving properties of zeolites play a pivotal role. Additionally, the selective interaction of alkenes with transition metal cations, positioned within the channels and cavities of microporous zeolites, further enhances separation capabilities.This study aims to comprehensively characterize the interactions between ethylene and Ag+ exchanged zeolites, employing a multidisciplinary approach, combining Inelastic Neutron Scattering (INS), Infrared (IR) spectroscopy, Nuclear Magnetic Resonance (NMR), UV–Vis and Density Functional Theory (DFT) calculations. CHA and RHO, zeolites largely applied in gas separation processes, were chosen due to their similar small pore sizes and pore volume, but different cavity shapes and flexibilities.The interpretation of derived DFT Electron Density Difference, experimentally supported by 13C Solid State NMR results, provide an understanding of each framework’s role during the charge transfer mechanisms between ethylene and transition metal species. Specific deformations in the flexible framework of zeolite RHO explain a blueshift of the band at 400 cm−1 in the librational region of INS spectra compared to CHA. This structural change in RHO, represented by the conic shape of the cage 8-ring side pockets, increases steric effects over the adsorbate while rendering the metallic adsorption center less exposed within the zeolite’s cavity, finally leading to a weaker adsorption energy. The redshift of C=C stretching frequencies observed by IR spectroscopy and DFT calculations, as well as C=C and C-H bond lengthening of ethylene confirm the formation of π-complexes on silver in both zeolites and allowed a further evaluation of the effects of the different frameworks cages on the aforementioned interaction.

Research on snow prevention in the bogie region based on active blowing method

To reduce excessive snow accumulation on bogie surfaces during high-speed train operations in cold regions, two active blowing schemes are designed in this study based on the shape of the bogie cavity and the relative position of the brake caliper. The unsteady Reynolds-averaged Navier–Stokes algorithm coupled with a discrete phase model was used to calculate the airflow and snow flow under the train. Moreover, the algorithm is employed to explore the impact of active blowing on the flow field characteristics and snow accumulation in the bogie region. Results show that active blowing changes the upward airflow in the bogie region, causing air at the bottom of the train to flow outwards, carrying off numerous snow particles from the bogie region. Active blowing accelerates the surface friction velocity on the bogie, increases the shear force on snow particles, and effectively reduces the snow accumulation on the bogie surface. The foregoing observation indicates that active blowing has considerable potential for snow accumulation prevention.

Using Bayesian optimization for warpage compensation in injection molding

AbstractIn injection molding, shrinkage and warpage lead to a deformation of the produced parts with respect to the cavity shape. One method to mitigate this effect is to adapt the cavity shape to the expected deformation. This deformation can be determined using appropriate simulation models, which then also serve as a basis for determining the optimal cavity shape. Shape optimization usually requires a sequence of forward simulations, which can be computationally expensive. To reduce this computational cost, we use Bayesian optimization which uses Gaussian process regression as a reduced order model. Additionally, Gaussian process regression has the benefit that it allows to account for uncertainty in the model parameters and thus provides a means to investigate their influence on the optimization result. We present a Gaussian process regression trained with samples from a finite‐element solid‐body model. It predicts the deformation of the product after solidification and, together with Bayesian optimization, allows for efficient cavity optimization.

The influence of the void shape in the bearing capacity of rock mass with a superficial void

In this study is proposed a chart that allow estimating the reduction of bearing capacity due to the existence of a superficial void in a rock mass. It is contemplated the influence of different shapes and size of the void in relation to the foundation. The reduction of the bearing capacity is analyzed through the Finite Difference Method. In the numerical model, six possible cavity shapes are considered, with three different sizes and depths. Calculations are made considering eighteen types of rock masses, modelled by the H&B failure criterion. The results demonstrate that the critical depth where the cavity no longer influences the bearing capacity varies considerably depending on the geometric variables (size, shape and location of the void). In addition, it is observed that the relation between the bearing capacity obtained considering the rock mass with and without void is not affected by the geotechnical parameters of the H&B failure criterion. According to the results analyzed and graphic output, the variation in the stress distribution in the rock mass and the change of the failure mechanism under the different hypotheses studied can be observed. The results are presented in chart that facilitate to directly estimate the reduction of the bearing capacity of a rock mass with void based on geometric parameters.

Programmable synthesis of organic cages with reduced symmetry.

Integrating symmetry-reducing methods into self-assembly methodology is desirable to efficiently realise the full potential of molecular cages as hosts and catalysts. Although techniques have been explored for metal organic (coordination) cages, rational strategies to develop low symmetry organic cages remain limited. In this article, we describe rules to program the shape and symmetry of organic cage cavities by designing edge pieces that bias the orientation of the amide linkages. We apply the rules to synthesise cages with well-defined cavities, supported by evidence from crystallography, spectroscopy and modelling. Access to low-symmetry, self-assembled organic cages such as those presented, will widen the current bottleneck preventing study of organic enzyme mimics, and provide synthetic tools for novel functional material design.

Study and simulation of cryogenic bi-periodic accelerating structure with TM02 mode

To further enhance the accelerating gradient of accelerators, we designed a cryogenic C-band standing wave bi-periodic accelerating structure for the Shanghai Soft X-ray Free Electron Laser Facility (SXFEL). According to the low-temperature environment, material characteristics and technological conditions, the design is completed and it is decided to design the accelerating structure into a bi-periodic magnetic coupling structure. It is a 17-cell structure consisting of 9 accelerating cavities and 8 coupling cavities. To guarantee the symmetry of the field, the structure is doubly-fed. Operating with the π/2 mode standing wave, it is much less sensitive than the standing-wave structure of π-mode. Additionally, the microwave mode is TM02 in coupling cavities that are larger and even less sensitive than the traditional bi-periodic structure. The shape of the coupling cavity can be redesigned to make it tunable.

Клинический случай мембранозной дисменореи у женщины с синдромом поликистозных яичников

Aim. To present a case report of membranous dysmenorrhoea in woman with polycystic ovary syndrome. Key points. Membranous dysmenorrhea is defined as sudden sloughing of thickened endometrium as a whole with the shape of the uterine cavity. It’s more common in young females who were on either combined hormonal contraceptive or progestagen. Membranous dysmenorrhea is a rare gynecologic disorder with only a few documented cases. Because this entity is rarely mentioned in the medical literature, the purpose of this report is to describe such case. In presented clinical case report 30-year-old woman with polycystic ovary syndrome at the end of first cycle of treatment with combined oral contraceptive, containing ethynilestradiol and dienogest, developed acute cramping hypogastric pain followed by discharge a tissue from vagina. It's histopathological exam was performed with a clear diagnosis of membranous dysmenorrhoea. Conclusion. The medical knowledge, due to the lack of description of this entity in current textbooks, contributes to its underdiagnosis. More studies are needed to clarify the aetiology and the pathophysiology of this pathologic condition. Keywords: membranous dysmenorrhea, women, polycystic ovary syndrome.

The counteracting influence of 2-hydroxypropyl substitution and the presence of a guest molecule on the shape and size of the β-cyclodextrin cavity.

The aqueous solubility of β-cyclodextrin (β-CD), a cyclic carbohydrate comprising seven α-D-glucose molecules, is enhanced by 2-hydroxypropyl (2-HP) substitution of the hydroxyl groups at the CD rims. Our thorough analysis of the structural and solvation properties with different degrees of 2-hydroxypropyl substitution on β-CD using molecular dynamics simulations reveals that the solubility is enhanced at the cost of the structural distortion of the CD cyclic structure. Substitution at the secondary rim predominantly enhances the favourable interactions between CD and water by decreasing CD-CD hydrogen bonding and promoting CD-water hydrogen bonding. However, the effect of substitution at the primary rim on the CD-water interactions is minimal; the hydrogen bonds between water and the primary hydroxyl group in native CD merely get replaced by those between water and 2-HP, since the substitution makes the primary hydroxyl oxygen (O6 atom) inaccessible to water. In contrast, substitution at the primary rim maintains the structural integrity of CD, while substitution at the secondary rim results in structural distortion due to the disruption of the intramolecular hydrogen bond belt, even leading to cavity closure. Certain strategic substitutions of the primary hydroxyl groups can help in the reduction of structural distortion, depending upon the degree of substitution at the secondary hydroxyl rim. A detailed inspection of the simulation trajectory revealed that the tilting of glucose units with the primary hydroxyl oxygen (O6) pointing inward is the primary driver for cavity closure. Even though the dynamics of glucose tilting can influence the kinetics of host-guest complex formation, once the guest is well incorporated into the cavity, glucose tilting is inhibited and the cavity opens up as in native β-CD.

THE RELATIONSHIP OF THE PITCH OF THE TEETH AND THE AREA OF THE DEPTHS WITH THE FEED TO THE SAW TOOTH DURING CUTTING WOOD OF HARD LEAVED BREEDS

The article covers issues related to the sawing of hard hardwoods. In particular, attention is focused on the relationship between the pitch of the teeth and the area of the cavity with the feed per tooth of the frame saw. It is noted that the physical, chemical, physico-mechanical and operational properties of hardwood differ significantly from coniferous and soft hardwood. The wood of hard deciduous species has increased physical and mechanical indicators and has a beautiful texture, which makes it a valuable species of wood. The physical, chemical, physico-mechanical and operational properties of hardwood hardwood are given. It is shown that these properties of wood significantly affect its processing by cutting and determine certain requirements for the structural parameters of the wood-cutting tool. Formulas are given for calculating the productivity of sawmill frames, the technical linear productivity of a frame saw and the productivity of one saw tooth. It is noted that the feed per tooth of the frame saw depends on the shape of the cavity between the teeth, its area, as well as on the hardness of the teeth, their sharpness and the quality of the surface obtained during sawing. Formulas for calculating the feed per saw tooth, the stress coefficient of the cavity, the largest height of the cut in the middle of the length of the log, the coefficient of chip compaction of the cavity, the area of the cavity and the reference value of the log are also given. It is noted that when sawing hardwood, the size of the log reference depends on the pitch of the teeth and the coefficient of the cavity shape. In the process of research, it was concluded that the amount of feed per tooth during sawing of hardwood should be lower by 24 - 29% compared to the amount of feed per tooth for pine.

Optimization of Rotor Tip Cavity Shapes for Mitigating Aerodynamic Tip Leakage Losses

Rotor blade tip leakage loss influences turbine stage efficiency. A parametric optimization method based on five design variables combined with Non-Linear Programming by Quadratic Lagrangian to optimize the turbine efficiency estimated from computational fluid dynamics analysis has been used to obtain estimates of the optimal cavity depth and split rib location within the tip cavity, which appears to improve the stage efficiency by 1.5%. Besides the design point, the influence of the optimized tip cavity shape impacts the performance of the rotor at different rotational speeds and pressure ratios. In this study, by comparing different tip cavity shapes, it is shown that a dual-cavity shape on the rotor blade tip with a stream-direction split rib can effectively control the air flow bending angle inside the tip clearance and improve the aerodynamic performance. The compressible unsteady Reynolds-averaged Navier–Stokes model is used to verify the adaptability of the optimized tip cavity shape to periodic wake disturbances, and the results demonstrate that the time-averaged estimate of the efficiency can be improved by 1.3% compared to that of the flat rotor tip.

Large eddy simulation of cavitating flow around a pitching hydrofoil

This numerical investigation employs advanced computational fluid dynamics techniques to examine the intricate physics of cavitating flows around a pitching NACA 66 hydrofoil. Unsteady simulations are conducted using both large eddy simulation (LES) and K-Omega SST turbulence models. The pitching motions range from 0 to 15°, encompassing four cavitation numbers (3.25, 3.5, 3.75, 4) and a Reynolds number of 750,000. The study comprehensively analyzes various flow field characteristics, including pressure distribution, velocity, vorticity, shear stress, vapor volume fraction, and turbulence kinetic energy. The kinematics of pitching significantly influence hydrodynamic loads and the surrounding flow structures in cavitating conditions. Flow visualizations illustrate the evolution of sheet/cloud cavitation, reentrant jet, and vortex dynamics throughout a pitching cycle. Notable findings demonstrate the impact of cavitation number on cavity shape and the relationship between angle of attack, reentrant jet location, and vortex size. Additionally, negative vorticity dilatation is observed to be correlated with cavity size.

Detection of erosion damage on airfoils by means of thermographic flow visualization

Cavity-type defects on a wind turbine rotor blade due to erosion lead to an sub-optimal boundary layer flow behavior and result in a reduced annual energy production. To enable an indirect defect detection from far distances, with no contact and no wind turbine stop, the thermographic visualization of the defect wake flow is studied. Experimental investigations and complementary flow simulations on two different airfoil shapes show that the detection is possible above a critical Reynolds number. Furthermore, the wake flow depends on multiple influencing quantities such as the airfoil geometry and the associated chord Reynolds number as well as the cavity position, the cavity shape and the associated cavity Reynolds number. Adjacent cavities can also influence the wake flow behavior. For instance, the cavity position has an influence on the turbulent flow region even after the natural laminar–turbulent flow transition line, and many cavities close to each other shift the transition line towards the leading edge. With increasing aspect ratio as well as increasing inflow velocity, the wake flow turbulence and, thus, the visibility of the wake in the thermographic images becomes higher. However, even if the wake flow from the cavity to the transition line is not continuously visible, a change in the natural transition can still be observed. As a result, thermographic flow visualization enables the indirect detection of cavity-type defects on airfoils and can provide further information about the cavity features.

Cyclization mechanism of monoterpenes catalyzed by monoterpene synthases in dipterocarpaceae

Monoterpenoids are typically present in the secretory tissues of higher plants, and their biosynthesis is catalyzed by the action of monoterpene synthases (MTSs). However, the knowledge about these enzymes is restricted in a few plant species. MTSs are responsible for the complex cyclization of monoterpene precursors, resulting in the production of diverse monoterpene products. These enzymatic reactions are considered exceptionally complex in nature. Therefore, it is crucial to understand the catalytic mechanism of MTSs to elucidate their ability to produce diverse or specific monoterpenoid products. In our study, we analyzed thirteen genomes of Dipterocarpaceae and identified 38 MTSs that generate a variety of monoterpene products. By focusing on four MTSs with different product spectra and analyzing the formation mechanism of acyclic, monocyclic and bicyclic products in MTSs, we observed that even a single amino acid mutation can change the specificity and diversity of MTS products, which is due to the synergistic effect between the shape of the active cavity and the stabilization of carbon-positive intermediates that the mutation changing. Notably, residues N340, I448, and phosphoric acid groups were found to be significant contributors to the stabilization of intermediate terpinyl and pinene cations. Alterations in these residues, either directly or indirectly, can impact the synthesis of single monoterpenes or their mixtures. By revealing the role of key residues in the catalytic process and establishing the interaction model between specific residues and complex monoterpenes in MTSs, it will be possible to reasonably design and engineer different catalytic activities into existing MTSs, laying a foundation for the artificial design and industrial application of MTSs.

Performance and parameter optimization design of microchannel heat sink with different cavity and rib combinations

Microchannel heat sinks play a crucial role in dissipating heat in microelectronic systems in computer data centers. To enhance their thermal performance, this study proposes a combined microchannel design consisting of various cavity shapes and straight ribs, and analyzes its heat transfer and flow performance through numerical simulation. The heat transfer characteristics of microchannel heat sink with different straight rib structures are compared. Moreover, the four parameters including the relative length (α), relative width of the cavity (β), relative length of straight ribs (γ) and relative width of straight ribs (λ) are investigated, and the effects of Reynolds number variation on heat sink Nusselt number (Nu), friction coefficient (f) and thermal enhancement efficiency (η) are studied. The optimization process employs an artificial neural network and a multi-objective genetic algorithm to determine the optimal compromise solution and heat sink model, utilizing the Nusselt number and friction coefficient as evaluation indices. The results show that rectangular rounded straight rib is the straight rib structures with the best comprehensive thermal performance, with an average η approximately 9.7 % higher than that of the non-straight ribbed heat sink model. Furthermore, the variation in the four studied parameters yields distinct effects on the Nusselt number, friction coefficient, and thermal enhancement efficiency. Notably, the optimal performance is achieved when Nu = 13.59679 and f = 0.11855, with corresponding parameter values of α = 0.1575, β = 0.3931, γ = 0.0714, and λ = 1.2149. Ultimately, these results provide valuable insights into the structural optimization of microchannel heat sink cavity and straight rib combination models.

Cavity effects on spontaneous ignition of pressurized hydrogen jets

The release of pressurized hydrogen jets can lead to spontaneous ignition, which poses a major challenge to the safe utilization of hydrogen energy. Previous studies have primarily focused on the spontaneous ignition of pressurized hydrogen released into tubes. However, in real industrial scenarios, pressurized hydrogen is usually released into the atmosphere or a complex equipment environment. Therefore, the effect of obstacles on spontaneous ignition needs to be considered. In this study, the spontaneous ignition of sudden releases of pressurized hydrogen entering various cavity shapes was modeled using the standard k-ω turbulence model, the eddy dissipation concept (EDC) model and a detailed 21-step chemistry model. The effects of the cavities on the jet flow fields and the spontaneous ignition were analyzed for various cavity shapes and release pressures. For the pressures considered in this study, the cylindrical cavity did not lead to ignition. The highest hydrogen jet temperature occurred in the contact region due to the shock wave reflection, after which spontaneous ignition could not occur due to the flow divergence. The pressurized hydrogen entering hemispherical and conical cavities enhanced the hydrogen-air mixing which led to combustible regions and the formation of multidimensional shock waves, which significantly increased the spontaneous ignition probability. The cavities created a high-temperature region inside the cavity that experienced ignition but the flames did not spread out of the cavity. The conical cavity produced lower flame temperatures than the hemispherical cavity but prolonged the flame lifetime. Higher initial hydrogen release pressures resulted in more violent multidimensional shock wave interactions and higher contact surface temperatures, which lead to earlier ignition times but with little impact on the initial location of the spontaneous ignition. The results of this study provide a scientific foundation for hydrogen safety codes, safe equipment designs and the development of industry codes and standards.