High Pressure Region Research Articles

Investigation of Intake Buzz Focusing on Shock Wave Movement and Inflow/Outflow Balance

The intake buzz is one of the most important matters to be overcome in supersonic and hypersonic airbreathing engines. However, the buzz mechanism has not been adequately revealed yet, and further investigation is required. During the pressure-increasing period of a buzz cycle, the inflow rate exceeds the outflow rate, so the high-pressure region expands upstream inside the intake, accompanied by the upstream movement of the terminal shock wave. In this paper, the mechanism of this period was investigated numerically by changing an exit nozzle blockage to vary the outflow rate. As a result, the novel idea that the buzz phenomenon is governed by the governing equations of the moving normal shock wave as well as the mass conservation law is introduced. This is because the intake backpressure waveform and the moving velocity of the terminal shock wave are revealed to be unaffected by the outflow rate during a certain portion of the pressure-increasing period.

Levitation Performance of Radial Film Riding Seals for Gas Turbine Engines

Turbomachinery in gas turbines uses seals to control the leakage between regions of high and low pressure, consequently enhancing engine efficiency and performance. A film riding seal hybridizes the advantages of contact and non-contact seals, i.e., low leakage and low friction and wear. The literature focuses on the leakage performance of these seals; however, one of their fundamental characteristics, i.e., the gap between the rotor and seal surface, is scarcely presented. The seal pad levitates due to the deflection of the springs at its back under the influence of hydrodynamic forces. This study develops a test rig to measure the levitation of film riding seals. A high-speed motor rotates the rotor and gap sensors measure the levitation of the seal pads. Measurements are also compared with the predictions from a Reynolds equation-based theoretical model. Tests performed for the increasing rotor speed indicated that, initially, until a certain rotor speed, the pads adjust their position, then rub against the rotor until another rotor speed is reached, before finally starting levitating with further increased rotor speeds. Moreover, both the measured and predicted results show that pads levitated the most when located 90° clockwise from the positive horizontal axis (bottom of seal housing) compared to other circumferential positions.

Modeling Investigation on Gas Backflow Performances in Screw Vacuum Pump

Rotor structure has a great influence on the gas backflow in a screw vacuum pump. The characteristics of the gas main flow along the spiral groove of the screw rotor and the gas reverse flow along the tooth-shaped, tooth side, radial, and circumferential clearances are investigated. A new mathematical model of the pumping flow and backflow involved in a flow balance model is proposed to investigate the actions of the shearing force and pressure difference force. The calculated backflow is verified by comparing the experimental measured results. The relationships of the structural parameters of the screw rotor are established. The effects of the rotor parameters, such as pitch, diameter, and compression ratio, on backflow are revealed. The results show that the rotor diameter and compression ratio remain constant and that the influence of pitch on the backflow is slightly weak, with backflow variations of less than 3%, whereas the pitch, rotor length, and compression ratio are constant and the rotor addendum diameter is directly proportional to the backflow. The addendum diameter of rotor #4 is the largest, and its backflow is about 1.5 times larger than that of rotor #1. When the rotor radial sizes and the pitch of the suction end are constant, the compression ratio is inversely proportional to the backflow in the low-pressure region and proportional to the backflow in the high-pressure regions. Therefore, for a vacuum pump operating in low-pressure areas, the use of the compression ratio of 2.2 or higher is favorable for the reduction in backflow.

Simulation of a Container Vessel Using Boundary Element Method for the Computation of Hydrodynamic Pressure and Forces

This study presents a comprehensive analysis of the hydrodynamic behavior of a containership under varying wave conditions using the Boundary Element Method (BEM). The hydrodynamic pressure distribution, as derived from BEM simulations, highlights critical pressure zones on the vessel’s hull, with maximum pressures reaching approximately 160 N/mm² near the bow. These high-pressure regions, caused by direct wave impacts, emphasize the structural vulnerability to fatigue, underscoring the need for reinforced designs in areas subjected to repeated loading. Additionally, the pressure mapping reveals patterns that align with expected wave-induced behaviors, validating the effectiveness of the BEM in capturing critical load distributions. The analysis also investigates wave excitation forces and diffraction/Froude-Krylov forces across six motion modes (surge, sway, heave, roll, pitch, and yaw). Translational modes exhibit peak forces of up to 8000 N at low wave frequencies (~0.1 Hz), while rotational modes encounter forces as high as 10^8 N, particularly in roll and pitch. These findings highlight the influence of wave characteristics, such as frequency and angle, on vessel stability and structural stress. The results provide valuable insights for vessel design and operational planning, advocating for enhanced stabilization systems, optimized structural reinforcements, and improved cargo placement strategies to ensure safety, performance, and longevity under various sea conditions.

Flame acceleration and detonation initiation in a non-uniform hydrogen–air mixture with a combination of fluid and solid obstacles

Flame acceleration and the deflagration-to-detonation transition (DDT) process in premixed combustible gases are complex phenomena involving both fluid dynamics and chemical reactions. However in practical scenarios, premixed combustible gases are often non-uniform. Based on the OpenFOAM platform, this numerical study examines the impact of combined fluid and solid obstacles on flame acceleration and DDT within various non-uniform concentration fields. The results indicate that in the initial stage of flame development, the absence of blockages on one side of the pipe and the presence of a higher concentration of hydrogen contribute to faster flame acceleration. Additionally, the narrow channel formed between obstacles and the wall, enhanced by the pressure gradient, produces a stronger suction effect, causing the flame to experience multiple zones of velocity enhancement. Furthermore, the detonation initiation can be categorized into two types: a) detonation initiated by the interaction between the flame surface and the reflected shock wave; b) detonation triggered by the coupling of the flame front with high-pressure regions. During the detonation wave's propagation, hydrogen levels below 12.7% cause detonation wave decoupling, affecting its shape based on hydrogen concentration distribution. From the perspective of flame evolution, fluid obstacles introduce more disturbances and vortices, promoting the formation of pressure gradients, which accelerates flame development and facilitates detonation initiation. The combination of fluid and solid obstacles can effectively reduce the initiation distance and time required for DDT. Also, a more uniform distribution of hydrogen concentration leads to faster changes in the flame state, enabling quicker detonation initiation.

Numerical simulation of the self-propelled swimming performances and mechanisms of a biomimetic robotic fish with undulating fins under different fin waveforms

To study the self-propelled swimming performances and mechanisms of biomimetic robotic fish with undulating fins (BRFUF) under different waveforms, a numerical simulation system coupled with body dynamics and fluid dynamics was established to study the starting, accelerating, and cruising processes of a biomimetic robotic fish in a median/paired fin swimming mode. A systematic parametric study was carried out on the swimming performance of a BRFUF under the cooperative propulsion of two fins, and the mechanism of thrust generation and the influence mechanisms of waveform and kinematic parameters of fins on swimming performance were analyzed based on the hydrodynamic performance, surface pressure distribution, vortex dynamics, and longitudinal velocity iso-surface of the flow field. The results showed that a larger fin ray oscillation angle amplitude increased the acceleration and cruising velocity of the BRFUF from the static state to the cruising stage. A highly concentrated vortex generated at the trough of the fin creates a jet mass that generates a reactive (added-mass) force perpendicular to the propulsive element, which is the mechanism by which the high pressure always covers the trough of the fin. Driven by the flexible fluctuations of the fins, the high-pressure region continuously moves toward the trailing edge along with the vortex. Along with the generation and shedding of the vortex, the high-pressure region is constantly generated, moving and disappearing on the surface of the fin and providing continuous thrust for BRFUF self-propulsion.

Large-scale turbulence effects on flow dynamics around and aerodynamic forces on a square cylinder

Turbulence effects on the aerodynamics of a square cylinder have been widely investigated due to their fundamental significance in both flow physics and engineering applications. However, the influence of large-scale turbulence on shear layer unsteadiness, and its consequences on flow structure and aerodynamic forces has received insufficient attention. The present study explores these effects, considering turbulent flows with turbulence intensities up to 20% and integral length scales up to four times the characteristic length of the obstacle. A reduced-order model and measurable indicators of flow dynamics are employed to investigate the underlying mechanisms quantitively. The findings reveal that large-scale, high-intensity freestream turbulence amplifies the root mean square (rms) flapping amplitudes of shear layers by provoking and superposing a set of low-frequency unsteadiness with energy levels comparable to that of Karman vortex shedding. The alteration in shear layer behavior results in (1) an extended region of high rms pressures around the square cylinder and (2) intermittent shear layer reattachment, followed by an intermittent weakening of the vortex shedding. These effects lead to a significant increase in rms pressure coefficients on the lateral and leeward surfaces, as well as an intermittent suppression of lift forces. Two new flow patterns were observed during periods of weakened flow dynamics: (1) vortices forming above the lateral surfaces shed downstream directly without interacting with the shear layer on the other side; and (2) Karman vortices in the wake region break down before shedding downstream.

Numerical research on the muzzle multiphase flow field produced by gas curtain launch.

Gas curtain launch is an innovative method for underwater gun firing that enhances efficiency by creating a gas curtain. This gas curtain interacts with post-projectile gas and the surrounding water, resulting in a complex multiphase flow field at the muzzle, which significantly impacts projectile accuracy. To investigate the evolution of this flow field, a three-dimensional numerical model was developed, focusing on the distribution of shock waves, temperature, and pressure at the muzzle. The study's findings reveal that after ignition, the gas curtain passes through the projectile and exits the muzzle, forming an initial bottle-shaped shock wave through repeated expansion and compression actions. As the projectile penetrates this shock wave and the post-projectile gas continues to exit, a radially expanding bottle-shaped shock wave is formed. The Mach disk diameter decreases exponentially over time. The gas temperature within the shock wave bottle rises sharply at the Mach disk and remains high in the downstream region, gradually expanding while the overall temperature decreases. The high-pressure region is located downstream of the Mach disk and, due to the swirling effect caused by projectile penetration, this region moves radially along the Mach disk towards the downstream, with the average pressure gradually decreasing.

Design of a custom metamaterial insert for improved pressure distribution within transtibial prosthetic sockets.

Uneven pressure distribution within a transtibial prosthetic socket can lead to discomfort, skin degradation, and suspended prosthesis use. Current custom interfaces to improve pressure distribution are often costly, time-intensive to fabricate, or cannot be incorporated into standard socket fabrication methods. In this technical note, we describe the design and preliminary clinical evaluation of a novel transtibial prosthetic socket insert with modifiable mechanical properties, which can be incorporated into the current clinical cycle of care. The custom insert (termed "inlay") relies on a triangular unit cell, which can be modified based on the desired stiffness profile. Inserts are 3D printed in a soft polymer material and inset into shape-matched voids in a socket creating regions of custom offloading. Preliminary clinical efficacy of the inserts was assessed in a pilot long-term cross-over evaluation. After Institutional Review Board approval, 3 pilot participants wore a shape-matched replica of their habitual socket modified for insert use and a shape-matched socket without. Sockets were worn for 4-week each, and inner socket pressures were measured with thin film pressure sensors at the end of the wear period. Peak pressures within the distal tibial region of interest were decreased for 2 of 3 participants during midstance of level-ground walking when wearing the socket with inlays. The technical methods and results presented provide a new method to address high pressure regions within a transtibial prosthetic socket. The 3D-printed inlays can be rapidly produced allowing for easy modification and replacement without require new socket fabrication.

Acoustic vortex-based dynamic lens for light focusing and steering.

This study explores a technique for light manipulation using an acoustic vortex generated by a high-intensity focused ultrasound transducer. The acoustic vortex forms a ring of bubble wall near the high-pressure region, creating a lens-like structure that can effectively focus a laser beam. The effects of varying acoustic pressures and dissolved oxygen content on the focused ultrasound and vortex waveforms were tested. Results showed that the vortex waveform could enhance the laser beam peak intensity by 55.6% and reduce its full width at half maximum from 1.16 mm to 0.91 mm. Additionally, the study demonstrated the capability to dynamically steer the laser beam at angles ranging from 0° to 0.7°, achieving precise control without the need for mechanical components. This technique offers a stable, real-time, and on-demand method for light manipulation, with potential applications in various liquid environments and heterogeneous media. The study also highlights current hardware limitations and suggests future improvements for optimizing parameters and further exploring related mechanisms.

On the large-scale vortices in an L/D = 2.30 serpentine diffuser with internal bump

In this paper, the generation and spatial evolution of large-scale vortices in an ultra-compact serpentine diffuser (L/D = 2.30) featuring an integrated internal bump are experimentally and numerically investigated. Due to reduction of the local flow area caused by the internal bump, a favorable streamwise pressure gradient is induced first and then followed by an adverse one. Concurrently, a high-pressure region exists on the side of the diffuser as it contracts, yielding a sideward circumferential pressure gradient and then an inward one. Such circumferential pressure gradients divert the boundary layer on the windward side of the internal bump to the side and induce a spanwise U-shaped vortex on the leeward side, which constrains the development of flow separation in this region. The circumferential pressure gradients further induce two pairs of streamwise vortices located at the top and bottom of the diffuser, respectively. These vortex pairs entrain the low-energy fluids and transport them to the aerodynamic interface plane (AIP), resulting in two pairs of low-total-pressure regions and swirling flows. Moreover, in the experimentally studied range of the exit Mach number MAIP from 0.293 to 0.546, the distributions of low-total-pressure regions and swirl angles at the AIP exhibit a small variation, indicating that the internal flow field structures are insensitive to MAIP.

Simulation study on the cavitation flow characteristics of liquid ammonia in the nozzle under high-pressure injection conditions

In this study, a non-isothermal compressible cavitating flow simulation model for liquid ammonia in high-pressure injector, accounting for the phase change properties, was established. The model was validated using experimental data from existing literature. The cavitation phase change process of liquid ammonia within the injector nozzle was investigated, and the differences in cavitation distribution between ammonia and diesel were explored. The results indicate that with increasing injection pressure, the vapor volume fraction of ammonia increases linearly, while that of diesel fuel shows a rapid initial rise followed by a decelerating trend. In terms of flow coefficient, ammonia is lower than diesel, though the two values converge at higher injection pressures. Under low injection pressure, the heat absorbed by the cavitation phase change of ammonia exceeded the heat generated by the high-speed friction of ammonia flow against the nozzle wall, leading to a temperature drop at the nozzle inlet. Conversely, at high injection pressure, the temperature of ammonia on the nozzle wall increases by more than 20 K, resulting in a rapid rise in saturated vapor pressure and significantly intensifying the cavitation effect. Compared to ammonia, diesel experienced a higher temperature rise within the nozzle but exhibited smaller variations in saturated vapor pressure, making the temperature effect on cavitation less pronounced. Diesel’s higher density and viscosity resulted in lower flow velocities compared to ammonia, leading to more developed cavitation in the lower wall region of the nozzle and creating a higher pressure region on the upper wall of the nozzle, which was more distant from the nozzle inlet and inhibited cavitation development there. The research results provide theoretical support for the design of liquid ammonia injectors.

Explosion limits of binary mixtures of ammonia and additives (hydrogen, natural gas, and diethyl ether)

This study investigates the explosion limits of ammonia (NH3) and the effect of three different active fuels, hydrogen (H2), natural gas (NG), and diethyl ether (C2H5OC2H5, DEE), on the explosive characteristics of NH3 through comprehensive chemical kinetics analysis. The results reveal that the explosion limits of NH3 exhibit the narrowest explosive range and display comparatively weakest explosive reactivity among the four fuels, presenting a monotonic changing trend. Reaction pathway analysis unveils that with increasing temperature, NH2 tends to oxidize more predominantly through the NH-N2H2-NNH-N2 pathway, while the conversion of NH2 to H2NO pathway decreases. Therefore, the introduction of active fuels significantly enhances the explosive reactivity of NH3. However, their impact under various temperature-pressure conditions presents nuanced and diversified characteristics. When a 0.5 % mole fraction of active fuel is added to NH3, DEE exhibits the most significant enhancement in medium to high-pressure conditions, while H2 predominates at low pressure, with NG consistently demonstrating the least pronounced enhancement. Upon the active fuel proportion being increased to 20 %, the promoting effect of DEE remains the most significant in the medium to high-pressure region, while NG has surpassed H2 as the secondary dominant fuel. In the low-pressure region, NH3-H2 still demonstrates the highest reactivity, followed by NH3-DEE, while NH3-NG exhibits the least reactivity. These findings provide valuable insights into the widespread utilization and scientific exploration of ammonia as a fuel source.

CNTs@fabric/Ni@PU piezoresistive sensor with enhanced interfacial contact resistance variation for motion detection and deep-learning-assisted recognition

Abstract Flexible piezoresistive sensors based on the mechanism of interfacial contact resistance change are receiving increasing attention in the fields of human-computer interaction, health monitoring, and behavior tracking. However, the high cost and complex manufacturing process limit the wide application and development of these flexible piezoresistive sensors. Here, a novel carbon nanotubes@fabric (CNTs@fabric)/Ni@polyurethane (Ni@PU) piezoresistive sensor (CNPS) with low-cost, simple-preparation and high-sensitivity was proposed. The effective contact area is obtained by synergizing the woven micro-convex structure of the fabric, the large specific surface area of the CNTs and the porous three dimensional electrodes. Within the small pressure (0–9.52 kPa) effect, the area of connection with the electrodes to the active layer plays a dominant role, resulting in a sensitivity of up to 6.39 kPa−1 for CNPS. In the high pressure region (9.52–44.92 kPa), where internal mechanism of change in the sensitive material dominants, the CNPS has a response time of 85 ms at a constant pressure of 28.31 kPa. Considering the excellent output electrical performances, a variety of body movements could be detected by fixing the CNPS to different joints. Significantly, the designed intelligent object recognition system implemented by the combination of matrix stress detection module and residual neural network (ResNet) algorithm has a recognition accuracy of 99.26%. Enhancing the interfacial contact resistance change mechanism using a simple fabrication process offers a promising strategy for the rapid development of flexible piezoresistive sensors.

Equatons of State for Regolith and Chondrite at High Pressure

Using the principle of additivity under shock compression, wide-range equations of state of regolith and ordinary chondrite for the high-pressure region are constructed.

Collapse of metallicity and high-Tc superconductivity in the high-pressure phase of FeSe0.89S0.11

We investigate the high-pressure phase of the iron-based superconductor FeSe0.89S0.11 using transport and tunnel diode oscillator studies using diamond anvil cells. We construct detailed pressure-temperature phase diagrams that indicate that the superconducting critical temperature is strongly enhanced by more than a factor of four towards 40 K above 4 GPa. The resistivity data reveal signatures of a fan-like structure of non-Fermi liquid behaviour which could indicate the existence of a putative quantum critical point buried underneath the superconducting dome around 4.3 GPa. With further increasing the pressure, the zero-field electrical resistivity develops a non-metallic temperature dependence and the superconducting transition broadens significantly. Eventually, the system fails to reach a fully zero-resistance state, and the finite resistance at low temperatures becomes strongly current-dependent. Our results suggest that the high-pressure, high-Tc phase of iron chalcogenides is very fragile and sensitive to uniaxial effects of the pressure medium, cell design and sample thickness. This high-pressure region could be understood assuming a real-space phase separation caused by nearly concomitant electronic and structural instabilities.

Spatial correlations and risk transmission of virtual water flow at city scale: A case study of the Yellow River Basin

By introducing virtual water (VW) flow correlation coefficients and risk indicators, this study examines the VW transmission relationship between urban agglomerations and cities in the Yellow River Basin (YRB) and its impact on regional water resources pressure. The results show that: except for the Shandong Peninsula Urban Agglomeration (SPUA) and Central Plains Urban Agglomeration (CPUA), the other urban agglomerations primarily act as VW exporting regions, while virtual water-importing cities are concentrated in the eastern regions. Notably, the Ningxia Urban Agglomeration (NUA) demonstrates significantly higher values in VW impact and sensitivity coefficients than the remaining six urban agglomerations. First-tier cities generally display lower virtual water impact and sensitivity coefficients, whereas emerging cities exhibit the opposite trend. Additionally, we observe uneven risk variations between VW importing and exporting regions. Taking NUA as an example, the risk increase resulting from VW exports significantly exceeds the risk reduction associated with VW imports in the corresponding regions. It's important to highlight that first-tier cities consistently decrease water resource risk through VW imports in both study years. However, among second and third-tier cities, only 38.9% experience reduced water resource risk through VW imports. Therefore, we recommend a focused examination of VW imports and exports in western region urban agglomerations, cities, and second and third-tier cities within the watershed. Leveraging virtual water's asymmetric and high-value transfer can alleviate water resource pressure and scarcity risks in high-pressure regions by shifting them to lower-pressure regions, thus mitigating water resource stress across regions.

Numerical investigation of vehicle water entry with angle of attack

This paper investigates the water entry of a vehicle with angle of attack (AOA) through numerical methods, employing the volume-of-fluid multiphase flow model and overset grid technique. The validity of the numerical model is confirmed through experimental verification. Building upon this, the study analyzes the motion characteristics, cavity evolution, and flow field distribution of the vehicle during water entry, considering the influence of AOA and falling velocity. Numerical findings indicate that the collapse of the right side of the cavity induces a transient lateral force on the vehicle, resulting in vehicle tilting. Moreover, an increase in initial velocity delays vehicle tilt, while an increase in AOA reduces vehicle motion stability, leading to earlier tilting. Initially, the vehicle rotates counterclockwise around the Oz axis of the projectile coordinate system. Subsequent to cavity collapse, the vehicle experiences an opposing moment, leading to a reduction in rotation speed and eventual rotation in the opposite direction. Water impact triggers sudden changes in the vehicle's lift and drag coefficients, while cavity sticking induces a minor abrupt change in the lift coefficient. Following cavity collapse, both lift and drag coefficients exhibit significant oscillations. Unlike typical cavity collapse phenomena, the flow field on the right side of the vehicle undergoes alternating high-pressure and low-pressure regions.

Stacking faults along the {111} planes seed pressure-induced phase transformation in single crystal silicon

We explore the onset of phase transformation, at the nanoscale, in single-crystal diamond-cubic silicon (dc-Si) subjected to pressures of 13 GPa using a diamond anvil cell with a methanol-ethanol pressure medium. Transmission electron microscopy reveals two distinct structural features along {111} planes: (1) thin bands of defective dc-Si and (2) thicker bands of body-centered cubic silicon (bc8), surrounded by defective dc-Si. We propose that these features are consistent with shear bands that have been formed by slip along the low energy {111} planes and have a range of thicknesses depending on how much plastic deformation has occurred. The presence of bc8-Si within the thicker bands can be explained by localized regions of high pressure or energy at their center facilitating phase transformation to the metastable metallic β-Sn phase, which in turn, transforms to bc8 on pressure release. Our observations reveal that phase formation in silicon can be shear-activated, the transformation is not nucleation-limited, and its sluggish nature may be due to the slow growth of the metallic phase.

Spectrally-broadened femtosecond vortex beams in air with longitudinal pressure distribution.

The spectral broadening of femtosecond vortex beams in air with different longitudinal pressure distributions is studied numerically. By introducing a symmetrical pressure distribution, a sufficiently broadened spectrum while preserving vortex characteristics of the beam for different input energies can be generated. The proposed pressure distribution involves an increase during the self-focusing stage, followed by a flat-top and symmetric decrease. This approach takes advantage of the mechanism that the strong Kerr nonlinearity in the high-pressure filamentation region results in a broader spectrum towards the blue side through the self-phase modulation and ionization, while the weak Kerr nonlinearity in the low-intensity regions before and after filamentation with low pressure leads to the decrease of the intensity fluctuation and the preservation of vortex characteristics due to weak modulation instability. Consequently, the resulting vortex beam exhibits a broad enough spectrum, and the transform-limit duration reaches a single cycle. This study provides a valuable approach for generating single-cycle vortex beams.