Asymmetric Air Research Articles

Study on the flame behavior of ethanol spill fire on base plate with different width in longitudinal ventilation environment

The intricate flame behavior of spill fire in a ventilated tunnel significantly aggravates the severity of accident consequences. Flame height, flame tilt angle, and combustion area were measured by conducting ethanol spill fire experiments in model tunnel with different wind speeds in base plates of different width. Furthermore, critical transition wind speed, dimensionless analysis of burning rate and heat transfer analysis were performed. The findings reveal that, in windy conditions, wind speed linearly lowers flame height, while baseplate width’s impact is irregular. Longitudinal ventilation notably causes flame inclination, base plate width and wind speed jointly affect inclination at low wind speed, however, in high wind speeds, the inclination is mainly determined by the wind speed. With the increase of wind speed, the burning rate firstly increases and then decreases, resulting in an initial decline followed by an increase in the combustion area. The increase in base plate width not only leads to a continuous increase in the combustion area, but also results in a decrease of the critical transition wind speed at which the burning rate changes. An equation for the dimensionless burning rate in upwind environments has been developed, revealing that burning rate is significantly higher in longitudinal wind conditions compared to still air. Furthermore, the difference becomes more pronounced as the baseplate width decreases. By taking into account the asymmetric air entrainment of the spill fire flame, a revised model for flame height and inclination has been introduced, utilizing a dimensionless array (2n+1/n). This model effectively predicts the morphological changes of spill fire flames under windy conditions, and the dimensionless flame height of spill fires is approximately 0.18 to 0.36 times that of pool fires.

Assessment of flat, symmetric, and asymmetric CPC photovoltaic thermal air solar collectors for building façades using artificial Neural Network Modelling

This study aims to develop and evaluate the performance of an asymmetric compound parabolic concentrator (ACPC) PV/T designed for building façade configuration, addressing the limitations of conventional symmetric compound parabolic concentrators (CPC) and flat type, double-pass photovoltaic thermal (PV/T) air solar collectors. The ACPC enhances solar incidence angle within the full acceptance angle for optimal performance in a façade configuration. However, accurately predicting the performance of the solar collectors remains a challenge due to the variations in ambient parameters. To overcome this, an Artificial Neural Network (ANN) model was developed and validated to predict system performance based on input ambient variables, such as solar radiation and temperature, with outputs representing the electrical and thermal performance of the PV/T collector. The validated ANN model was then used to conduct a simulation case study for the tropical climate of Malaysia. The simulation results demonstrated that the ACPC PV/T collector outperformed both symmetric CPC and flat-type PV/T collectors regarding electrical and thermal performance. Additionally, the ACPC PV/T had a shorter payback of 5.4 years, approximately 1 year shorter than the CPC and 2 years shorter than the flat-type PV/T. These findings suggest that the ACPC PV/T system offers a more efficient and cost-effective solution for façade-integrated systems. This study contributes to the body of knowledge on photovoltaic/thermal systems with three key contributions: first, an investigation of the underexplored asymmetric CPC for building façades; second, the utilization of a data-driven ANN model as a predictive tool, demonstrated through a simulation case study in combination with TRNSYS; and third, a comparative analysis of asymmetric CPC, symmetric CPC, and flat PV/T air solar collectors specifically for façade applications. This study, therefore, provides a comprehensive platform for further research on CPC PV/T systems for building façades.

An Investigation of Internal Drag Correction Methodology for Wind Tunnel Test Data in a High-Speed Air-Breathing Vehicle Using Numerical Analysis

AbstractAccurate understanding of aerodynamic characteristics is critical for air vehicle design. This study applies the impulse-momentum theorem to estimate internal drag of an asymmetric air vehicle. Both computational fluid dynamics (CFD) and wind tunnel tests were employed. Numerical analysis using STAR-CCM + was conducted across various Mach numbers, while wind tunnel tests were conducted under only specific Mach number conditions. The measured data from wind tunnel tests, which is considered representative, were compared with CFD plane-averaged values, indicating fairly good agreement. However, discrepancies arose when comparing CFD cell-averaged values with the plane-averaged values. To address this, a correction function was developed to describe the differences. It was observed that the ratio of internal drag coefficient from the cell-averaged values to that of the plane-averaged values followed an exponential function of Mach number. This approach allows wind tunnel data to be transformed into a form akin to cell-averaged values, enhancing internal drag estimation accuracy. Future research will explore additional methodologies to further refine and validate the proposed approach.

Singularity-free practical finite-time force control for a compliant grinding mechanism subject to hysteresis nonlinearity and asymmetric time-varying air pressure constraints

Singularity-free practical finite-time force control for a compliant grinding mechanism subject to hysteresis nonlinearity and asymmetric time-varying air pressure constraints

A novel high-sensitivity sensor with asymmetric elliptical shaped exposed core and gold coating for sucrose and chemical concentration detection

The article introducing an innovative exposed core SPR biosensor employing an asymmetrical elliptic air hole PCF known for remarkable sensitivity. Gold-plated fiber sensor detects changes in refractive index. This sensor effectively covers a RI scale of 1.28 to 1.42 for analytes, showcasing its versatility in simultaneous detection. Taking into account the RI change at the outer surface, attractive sensing implementations such as optimal wavelength sensitivity of 97,000 nm/RIU and optimal amplitude sensitivity of 529.20 RIU−1 are attained. Furthermore, with a resolution of 9.09 × 10−6 RIU, a figure in merit of 170 RIU−1, an FWHM of 570 nm, and a detection accuracy of 0.0166 nm−1, the suggested sensor is impressive. This suggested sensor finds application in monitoring sucrose solutions across a spectrum ranging from 0% to 45% chemical concentration over time. It has an ideal amplitude sensitivity of 530.95 RIU−1 and an ideal wavelength sensitivity of 10,000 nm/RIU for sucrose solutions at the 40% concentration level. Furthermore, the sensor shows an ideal wavelength sensitivity of 35,000 nm/RIU and an ideal amplitude sensitivity of 793.80 RIU−1 for the detection of 2-propanol. Nevertheless, beyond sucrose noticing auspicious sensing qualities by the suggested sensor its feasibility for impact fully identifying a range of biochemical and organic samples. As a result, the proposed sensor holds promise as an exemplary choice the realms in biomedical sensing, the detection of lower RI analyses as well as chemical analysis. Streamlining practical application, the sensor's structure incorporates eight elliptical air holes, uncomplicated readily manufactural with existing technologies.

Impact of ventilated tunnels on smoke peculiarities in train carriage fires with multiple lateral openings

This research investigates the dynamics of smoke dispersion in a subway train carriage with multiple lateral openings within a ventilated subway tunnel. Numerous extensive full-scale numerical simulations were conducted to analyze the thermal plume distribution within multiple lateral openings of a train carriage, and the longitudinal and transverse maximum excess ceiling temperature. The results reveal that the heat release rates have a greater impact on the airflow in the carriage than velocities ,even when the longitudinal ventilation velocity reaches 8 m/s or the heat release rate reaches 15 MW. The multiple lateral openings cause significant differences in smoke flow characteristics compared to tunnels with both ends open. Additionally, the transverse maximum ceiling excess temperature inclines towards the lateral opening side due to asymmetrical air entrainment. The analysis of longitudinal maximum ceiling excess temperature identified two regions based on the dimensionless heat release rate, showing a linear increase followed by a constant phase dependent on the heat release rate, with a maximum longitudinal excess gas temperature of 1242 K. Additionally, a relationship between the dimensionless heat release rate and the transverse dimensionless maximum ceiling excess temperature was established. This study can be used as a guide for smoke exhaust mitigation and fire safety measures in the event of subway train carriage fires.

ЧИСЕЛЬНЕ МОДЕЛЮВАННЯ ПРОЦЕСУ ВПЛИВУ ПРОДУКТІВ ДЕТОНАЦІЇ НА НАДЗВУКОВИЙ ПОТІК ПОВІТРЯ

Currently, there is a large number of control bodies used in modern rocket technol-ogy. Gasdynamic systems are usually used in rocket engines to change the thrust vector, less often - to create asymmetric air flow around the case. But the application of the det-onation process for such scheme can have better energy and dynamic characteristics compared to existing systems. The driving force in such scheme is created not only by the reactive mass force of detonation products ejected from the gas generator, but also by the effect of an intense shock wave on the pattern of supersonic flow around the rocket. Therefore, it is necessary to evaluate the performance and efficiency of the experiment. The purpose of the study is a priori numerical study of the detonation wave effect on the supersonic flow in the nozzle. Modeling was carried out in the Solid Works application software package. The geometric parameters of the model coincide with the experimental model. It is a flat nozzle, one of the walls is longer than the other and imitates the surface of the rocket. Air, accelerating in the nozzle to supersonic speeds with Mach number M=1.3...2, flows around this wall. Setting devices affecting the flow in it, it is possible to investigate their influence and the possibility of creating a lateral (controlling) force. When detonation is used to disturb the flow, an intense shock wave is generated in it, which changes the pres-sure distribution on the wall surface. Some holes for pressure sensors are made in the wall to fix this disturbance over time. A priori numerical modeling was carried out in order to estimate the parameters of the interaction of detonation products with the supersonic air flow. The pressure range and duration of the process have been determined, which allows selection of equipment and planning of the experiment. Patterns of velocity and pressure distribution in the model over time were obtained.

Highly birefringent photonic crystal fibers with near-zero flattened dispersion for polarization-maintaining terahertz transmission

In this work, we present a novel hexagonal lattice porous-core photonic crystal fiber (PCF) exhibiting high birefringence, low loss, and near-zero flattened dispersion in the terahertz regime. The core design incorporates asymmetric rectangular and triangular air holes to achieve enhanced birefringence performance. The background material, TOPAS, is carefully selected to minimize dispersion and transmission losses. Furthermore, by employing the finite element method, the guiding properties of the proposed PCF are comprehensively investigated. Our simulation results reveal a near-zero flattened dispersion value of ±0.2ps⋅THz−1⋅cm−1 within a broad frequency range of 0.8−1.6THz, accompanied by an impressive birefringence value of 0.072. Additionally, the PCF demonstrates outstanding characteristics in terms of confinement loss, effective material loss, effective mode area, core power fraction, and bending loss. Considering its exceptional attributes, the proposed PCF holds significant promise for polarization-maintaining applications and terahertz communication systems.

Birefringence characterization in a dual-hole microstructured optical fiber using an OFDR method.

The birefringence in a dual-hole microstructured optical fiber is numerically calculated and characterized with an optical frequency domain reflectometry (OFDR) method. Due to the asymmetric dual air holes in the cross-section, the polarized L P01x and L P01y modes propagate with different group velocities and time delays. Through a polarized coherent OFDR system in experiment, the Fresnel reflection peaks for each mode are separated in the frequency domain with their corresponding beat frequency. Thus, the group birefringence -9.68×10-4 is calculated with a beat frequency difference of 50.03Hz between the L P01x and L P01y modes at a 6.2m fiber end, which is in good agreement with that of -9.54×10-4 from the theoretical simulation. Our demonstration provides an accurate and flexible method for group birefringence characterization in microstructured optical fibers with complex cross-sectional structures.

Surface lattice resonance in an asymmetric air environment of 2D Au near-spherical nanoparticle arrays: impact of nanoparticle size and its sensitivity

2D Au nanoparticle (NP) arrays with larger NP size displayed an obvious surface lattice resonance (SLR) peak in an asymmetric air environment, indicating that, if the NP size was large enough, index-matching was not necessary for forming SLR.

Force modeling of a reluctance motion system with multi-axial asymmetrical air gaps

Semiconductor photolithography equipment requires an actuation system that can satisfy high acceleration and precision demands on the nanoscale in order to operate with high throughput and efficiency. Reluctance actuators, which offer greater acceleration and force output than conventional Lorentz actuators, are one option. The photolithography technique uses a floating stage with air bearings to reduce friction; nonetheless, vibration transfer is not completely prevented, potentially causing misalignment and asymmetries between the actuator components. The output force can be significantly impacted by unequal offsets between the mover and stator. In the paper that follows, a technique for calculating the force of various asymmetrical instances for the C-core reluctance actuator is demonstrated. This paper looks into the effect of rotational offsets in all rotational degrees of freedom occurring simultaneously. Previously, only each degree of freedom was analyzed. Analytical models are developed and compared to Comsol Multiphysics (COMSOL) simulations, and experimental findings show accuracy to be within almost 10% for the ranges examined. The findings presented can allow for future control systems to be designed to counteract multi-axial asymmetric issues.

Pushing Optical Virus Detection to a Single Particle through a High-Q Quasi-bound State in the Continuum in an All-dielectric Metasurface.

Bound states in the continuum (BICs) have emerged as a powerful platform for boosting light-matter interactions because they provide an alternative way of realizing optical resonances with ultrahigh quality factors, accompanied by extreme field confinement. In this work, we realized an optical biosensor by harnessing a quasi-BIC (qBIC) supported by an all-dielectric metasurface with broken symmetry, whose unit cell is composed of a silicon cuboid with two asymmetric air holes. Thanks to the excellent field confinement within the air gap of a metasurface enabled by such a high-Q qBIC, the figure of merit (FOM) of the biosensor is up to 2136.35 RIU-1. Futhermore, we demonstrated that such a high-Q metasurface can push the detection limit to a few virus particles. Our results may find exciting applications in extreme biochemical sensing like COVID-19 with ultralow concentrations.

Asymmetric air gap fault detection in linear permanent magnet Vernier machines

PurposeThe aim of this paper is to introduce an accurate asymmetric fault index for the diagnosis of the faulty linear permanent magnet Vernier machine (LPMVM).Design/methodology/approachThree-dimensional finite element method is applied to model the LPMVM. The geometrical and physical properties of the machine, the effect of stator and translator teeth, magnetic saturation of core and nonuniform air gap due to asymmetric fault are taken into account in the simulation. The air gap asymmetric fault is proposed. This analytical method estimates the air gap flux density of an LPMVM.FindingsThis paper presents an analytical method to predict the performance of a healthy and faulty LPMVM. The introduced index is based on the frequency patterns of the stator current. Besides, the robustness of the index in different loads and fault severity is addressed.Originality/valueIntroducing index for air gap asymmetry fault diagnosis of LPMVM.

Parallel water entry: Experimental investigations of hydrophobic/hydrophilic spheres

This study aims to experimentally investigate the vertical parallel water entry of two identical spheres (in geometry and material) with different surface wettability (hydrophilic or hydrophobic) pairings. The spheres simultaneously impact the water surface with velocities ranging from 1.71 to 4.32 m s−1. The corresponding ranges of the impact Froude, Weber, and Reynolds numbers are 3.87–9.75, 816–5167, and 38.5×103 to 96.8×103, respectively. The spheres' lateral distances vary from 1.0 to 5.0 times the diameter. A high-speed photography system and image processing technique analyze the event dynamics, focusing on air-entrainment cavity behavior (shapes, closure, shedding), water flow features (Worthington jets, splashes), and sphere kinetics. Results for hydrophobic/hydrophobic cases show that even at the maximum lateral distance, a slightly asymmetric cavity forms, but deep-seal pinching occurs at a single point, similar to a single water entry scenario. As the lateral distance decreases, the spheres significantly influence each other's behavior, leading to the formation of a highly asymmetric air cavity and an oblique Worthington jet. In the case of a hydrophobic/hydrophilic pairing, vortices generated behind the hydrophilic sphere influence the air cavity development of the hydrophobic sphere. This can cause a secondary pinch-off, especially at low lateral distances. This effect becomes more pronounced at higher impact velocities. Additionally, at higher impact velocities and minimum lateral distance (direct contact between the spheres), a smaller cavity detaches from the hydrophobic sphere's cavity, attaches to the hydrophilic sphere, and moves with it. These different regimes result in varying descent velocities for the spheres.

Experimental study on the morphology of turbulent diffusion flames with different aspect ratios under slope conditions

In this paper, the morphology of turbulent diffusion flames with varying aspect ratios under slope conditions was investigated. A simulated fire source using propane gas with an area of 80 cm2 was utilized. The influences of slope angle and aspect ratio of the fire source on the flame tilt angle (between the plume centerline and the slope), flame length, and flame height were systematically studied. The aspect ratio of the fire source (L/W) was changed from 1 to 8, and the slope angle was changed from 0° to 40°. Results indicate that the presence of a slope causes asymmetrical air entrainment on both sides of the fire plume, causing a pressure difference that leads to a decrease in the flame tilt angle as the slope angle increases. Additionally, the flame length increases monotonically with the slope angle due to the enhanced component of thermal buoyancy along the slope. Under the same slope condition, the flame tilt angle and flame height (perpendicular to the slope) decrease as the aspect ratio increases. This phenomenon is attributed to the increased entrainment restriction effect of the slope on the fire plume. New models for calculating flame tilt angle, flame length, and flame height, which consider the slope angle and aspect ratio of the fire source were established by using the equivalent perimeter of plume entrainment. To further verify the reliability of the newly established models, reference data with wide heat release rate (6.15 kW–231 kW), different slope inclination angle (0°–80°), pool size (equivalent diameter: 9 cm–44.1 cm), and different fuels (propane, ethylene) were used to against with the predicted values of our correlations. It is found that the maximum error of all correlations is within 15–20%, their universality and accuracy are further verified.

Flame and burning dynamics of pool fire inside semi-confined compartment under external cross wind

In this paper, experimental and theoretical studies of the flame shape and burning rate of pool fire inside a semi-confined compartment (with one sidewall and ceiling open) under the cross wind were investigated. The effects of fuel pool size and cross wind velocity on the flame morphological parameters and burning rate were obtained. Three typical bending behavior of the tilted flame was observed during the experiments. The dimensionless burning rate m˙″* decreased slightly when Frw<1, and increased linearly with Frw when Frw≥1. An air gap (δair) between the flame and sidewall was observed because of the restriction of the sidewall and blow-off by strong airflow recirculation. Theoretical analysis of wind-blown pool fire inside the semi-confined compartment was conducted based on the asymmetrical air entrainment and the buoyancy length scale. A dimensionless parameter (sm˙fρ∞uwlb2) considering the burning rate and cross wind velocity was proposed to predict the flame height, flame tilted angle and air gap thickness. The flame morphological characteristic parameters and the thickness of the air gap were correlated linearly well with the dimensionless parameter in exponent expression.

Controlling the Influence of an Asymmetric Air Gap in a Synchronous Electrical Machine on the Unidirectional Attractive Force

Controlling the Influence of an Asymmetric Air Gap in a Synchronous Electrical Machine on the Unidirectional Attractive Force

Design of a broadband dual-cladding PCF polarization filter via triple surface plasmon resonance effects

Photonic crystal fiber (PCF) polarization filters are widely utilized due to high integrity and flexible tunability. However, most filters still face the challenges from intricate structure and limited bandwidth. Here, we propose a dual-cladding PCF polarization filter with a large bandwidth by triple surface plasmon resonance (SPR) effects. Asymmetric Au-filled air holes are arranged in the dual-cladding lattice to excite the triple SPR effects with enhanced birefringence, therefore extending the operating bandwidth. The results show that the triple SPR phenomena occur in the y-polarized direction at resonance wavelengths of 1212.8, 1347.5, and 1567 nm with confinement losses of 946.63, 826.79, and 737.13 dB/cm, respectively. In contrast, the x-polarized direction shows extremely low confinement losses of only 0.20, 1.94, and 2.03 dB/cm. With the fiber length (L) of only 300μm, the filter achieves the maximum crosstalk (CT) of 246.62 dB, and the bandwidth above 20 dB extends to 830 nm. High performance filter based on multiple SPR effects may has the potential applications in optical communication and optical sensing.

Measurement of Local Void Fraction of Air-Water Flow in an 8 × 8 Rod Bundle Using High-Resolution Gamma-Ray Tomography

High-resolution two-phase flow data in the rod bundle are important in the development and validation of high-fidelity models for computational fluid dynamics and subchannel codes, in particular, those pertaining to light water reactor cooling systems. The Michigan Adiabatic Rod Bundle Flow Experiment (MARBLE) has been constructed as a modular assembly of an 8 × 8 lattice rod bundle to simulate scaled pressurized water reactor and boiling water reactor subchannel assemblies. To establish a high-spatial resolution database of the void fraction in the reactor fuel assembly geometries, tomographic measurements were performed with the High-Resolution Gamma-ray Tomography System, which was designed and built in house; the detector system has a spatial resolution of less than 1.0 mm using 240 LYSO (Lu1.8Y0.2SiO5) scintillators with a fan-beam array. In the present study, the local void fraction was measured with the MARBLE facility under various air-water flow conditions (jg = 0.04 to 0.85 m/s and jl = 0.12 to 0.77 m/s) covering from bubbly to cap-turbulent flows. The local void fraction was also successfully measured under nonuniform and asymmetric air bubble distribution conditions with an investigation of the effect of spacer grids and mixing vanes on void drift across subchannels.

Design to Reduce Cogging Torque and Irreversible Demagnetization in Traction Hybrid Motor Using Dy-free Magnet

The PMSM (Permanent Magnet Synchronous Motor) is being studied a lot in traction motors for high efficiency and high performance. Usually, magnets containing rare earth elements are used. However, since rare earth elements are not suitable for future industries due to their limited reserves, many studies on magnets excluding rare earth elements are being conducted. Magnets excluding rare earth elements have a low coercive force and are vulnerable to irreversible demagnetization, so their design must be robust. Additionally, the design used for reducing the cogging torque, which is a major variable of traction motors, is also important. Therefore, in this study, a design process for reducing irreversible demagnetization and cogging torque is proposed. There are three methods for this process. The first one is the application of the tapering structure, and the second one is the tapering skew structure. The third one is the application of an asymmetric air hole. As a result of these methods, the target irreversible demagnetization ratio was satisfied and the cogging torque was reduced. This was proven through FEA (Finite Element Analysis) and verified by comparing and analyzing the experimental results and simulation results of actual manufacturing.