Interaction Of Airflow Research Articles

Finite element simulations of free reed instrument operation

To facilitate research into the acoustical properties of free reed instruments, there is a need for a quick and inexpensive way to prototype new geometries. It is here that a computational model with easily adjustable parameters offers a substantial advantage over an experimental apparatus if it can sufficiently resolve the essential acoustic features. Simulations using the finite element method have been utilized to solve the fluid dynamics, pressure acoustics, structural mechanics, and the multi-physics couplings underpinning various free reed systems. These phenomena include attack transients and frequency-pressure dependence of Western free reeds, fluid-structure interaction of turbulent airflow in an Asian free reed, effects of air compressibility on reed vibration, and the acoustic impedance of a reed-driven khaen pipe. Results consistent with experimental and analytical models were obtained and methods of optimizing the computational cost while maintaining realism are proposed. The models fail, however, to capture the essential feature of free reed sound production via the periodic interruption of airflow through the reed plate. Ways for future research to achieve this benchmark are suggested. [Research supported by National Science Foundation, Grant NSF-REU-1950337.]

Decoupling transient effects of factors affected by air recirculation devices on contaminant distribution in ventilated spaces

The use of indoor air recirculation devices, such as air cleaners and air curtains, results in an airflow interaction between air supply jets and recirculated airflows. It is essential to quantify the independent effects of supply air, contaminant source, and initial condition in a ventilated room with air recirculation. In this paper, the transport process of a contaminant with air recirculation is mathematically derived based on a fixed flow field. A linear expression is established to describe the transient contributions of different influencing factors. The indices of revised transient accessibility of supply air (RTASA), contaminant source (RTACS), and initial condition (RTAIC), are defined to quantify the effect of each factor by incorporating the effect of air recirculation. The prediction accuracy is verified through a comparison with simulation results. The proposed indices are applied to evaluate a ventilated room with an air cleaner and recirculated air curtain. The results indicate that the recirculated airflows from both the air cleaner and air curtain increase the RTASA of each air supply inlet to distant areas. The purification effect (30%) occurs only after a certain period for RTASA and RTACS, while it operates from the initial stage for RTAIC owing to the initial high contamination. The RTACS in the protected zone is reduced significantly owing to the air curtain, with a decrease from 1.33 to 0.77 at 600 s at a height of 1.2 m in the curtain jet. The proposed method can be used to evaluate indoor environments with various air recirculation devices.

Numerical investigation on transport characteristics of high-temperature fine particles generated in a transiently welding process

The motion feature of particulate pollutants in industrial buildings, has a significant impact on the indoor environment and workers' health. In this study, the numerical simulations are performed to investigate the transport characteristics of high-temperature fine particles generated during the welding processes, influenced by four different factors (i.e, release temperature (T0), release velocity (v0), operation time (t0), and particle diameter (dp)). Specifically, the movement mechanism of particles is clarified through the conservation of energy and Newton's second law. The maximum horizontal diffusion distance of particles (ΔRmax) has been proposed to assess the exposure risk of particles. Results show that the transformation between heat energy and kinetic energy drives the two-phase flow to move up. The temperature of particles drops sharply and reaches the environmental temperature at 3.0 s approximately, while their velocity increases first before decreasing slowly. The gravity acting on particles and vortex interaction of airflow result in different motion behaviors of particles in both vertical and horizontal directions. Moreover, ΔRmax is positively correlated with T0, v0, and t0, but negatively correlated with dp, and has a maximum value of 6.4 m. Generally, the motion and exposure risk of particles are dependent on the heat exchange amount and particle size. The results can contribute to health risk assessment and ventilation system design in the industrial plants.

Process enhancement of organic pollutant removal by micro channel excited dielectric barrier discharge

In this study, a micro-channel excited DBD plasma water treatment system is proposed to enhance the discharge and gas-liquid mass transfer processes simultaneously. As the core of the reactor, the micro-channel plays a crucial role in the process intensification. On the one hand, the micro-channel can reduce the initial discharge voltage and enhances the discharge intensity, because of the increased space charge density initiated by the transverse electric field formed by the charges accumulated on the micro-channel wall, as a result, the generation efficiency of active particles can be improved. On the other hand, the micro-channel can also reduce the air pressure resistance and enhance the bubbling process, due to the exciting effect of micro-channel discharge on air flow and plasma-water interaction, as a result, the utilization efficiency of active particles can be improved. Tetrabromobisphenol-S (TBBPS) is used as the target pollutant, with the initial condition of 500 mL, 0.2 mmol/L, the maximum removal is over 98 % after a 30 min treatment under an applied voltage of 18.4 kV. Applied voltage, air flow rate and water flow rate are the key parameters affecting the treatment efficiency. It can be concluded from the results of this study that the micro-channel excited DBD plasma is of significance favorable for the treatment of wastewater.

Identification of Wind-Induced Hazard Zones Impacting UAS Bridge Inspection

Unmanned Aerial Systems (UAS) continue to grow in both popularity and utility within the national airspace system. The use of commercial UAS for civil inspection, specifically that of bridge structures, is becoming commonplace among practitioners and academics alike. The development of an integrated bridge-inspection hazard model provides a way for UAS operators to prepare for and respond to changing environmental conditions that could otherwise prevent a successful UAS flight. The interaction of wind-induced airflow with bridge surfaces creates an aerodynamic wake that can result in hazardous conditions for a UAS platform operating in close proximity. An analysis of this airflow surrounding an overpass bridge using computational fluid dynamic (CFD) models shows where these hazardous areas exist, based on initial wind conditions, existing functionality of UAS platforms, and mitigating systems that exist within current UAS technology. Altering the initial conditions by modifying wind velocities allows for a baseline understanding of which areas surrounding an overpass bridge structure are not suitable for successful UAS flight. Hazard zones range from severe, moderate, and mild, to no appreciable hazard. Moderate to extreme hazard zones are located in areas where high levels of wind shear, vorticity, or general turbulence exist, making UAS operations difficult. This study develops a practical model that may be utilized by UAS operators to better understand and potentially avoid unsafe flight environments during bridge structure inspections.

Albatross and Falcon inspired Bionic UAV: An Aerodynamic Analysis

The drone industry yearns for enhanced aerodynamic performance. In order to achieve this feat, researchers and engineers are trying to mimic the natural flyers due to their aerodynamic optimality. One such flyer, the Albatross is an inspiration for many marine drones due to its planform and aerodynamic efficiency. The wing of the plan form is designed and simulated to study its properties. The Bell-Shaped Lift Distribution is incorporated for higher efficiency and elimination of the total downwash produced in case of an Elliptical Lift Distribution. A blended wing body inspired by the Falcon is used for smoother airflow interactions. Furthermore, a tilt-rotor design provides an efficient combination of hovering and cruising modes of flight. Design choices and changes are discussed and tested to obtain an efficient tilt-rotor UAV inspired by the Albatross.

A review on the applied techniques of exhaled airflow and droplets characterization.

In the last two decades, multidisciplinary research teams worked on developing a comprehensive understanding of the transmission mechanisms of airborne diseases. This article reviews the experimental studies on the characterization of the exhaled airflow and the droplets, comparing the measured parameters, the advantages, and the limitations of each technique. To characterize the airflow field, the global flow‐field techniques—high‐speed photography, schlieren photography, and PIV—are applied to visualize the shape and propagation of the exhaled airflow and its interaction with the ambient air, while the pointwise measurements provide quantitative measurements of the velocity, flow rate, humidity and temperature at a single point in the flow field. For the exhaled droplets, intrusive techniques are used to characterize the size distribution and concentration of the droplets' dry residues while non‐intrusive techniques can measure the droplet size and velocity at different locations in the flow field. The evolution of droplets' size and velocity away from the source has not yet been thoroughly experimentally investigated. Besides, there is a lack of information about the temperature and humidity fields composed by the interaction of the exhaled airflow and the ambient air.

Wind loads on buildings in tandem arrangement

The paper presents the research results of the distribution of the local and integral pressure coefficients over the sides of the square prisms arranged in tandem and experiencing the airflow. The correlation is shown between the obtained airflow patterns and the pressure coefficient distribution; the dependences are obtained between the building arrangement and the distribution of the pressure coefficients; the phenomena caused by the airflow interaction are described in this paper.

Multiphase CFD modeling and laboratory testing of a Vortecone for mining and industrial dust scrubbing applications

Dust exposure-related occupation diseases are irreversible and have led to debilitating outcomes in personnel. Particles like coal dust generated in mines and accumulated above a critical concentration are explosive. Fibrous type multi-layered filters are the primary dust particle capturing element in flooded-bed dust scrubbers. However, these filters get clogged due to prolonged dust accumulation. This paper investigates the interaction of dust, water, and airflow in CFD in a non-clogging Vortecone filter. The Vortecone accelerates the particle-laden fluid, forces it into rapid swirling fluid motion, and pushes particles to separate and capture them. Filter capture performance in several air and water quantities regimes with aerosol particles exceeding 2.0 μm from a coal-dust laden airstream is described here. Detailed computational fluid dynamics models mimicking steady-state flow regime and transient-state air-water interface motion are presented. Particle tracking and their capture on water film using volume of fraction approach to determine the cleaning efficiency for different particle sizes is presented. Experimental cleaning efficiency results obtained from iso-kinetic sampling and optical particle counting agree with the computer models. Laboratory tests run on the Vortecone showed coal-dust cleaning efficiency exceeding 75% for particles 2.8 μm in size and 90% for 4.7 μm for all airflows.

Integration of Time and Spatially Resolved In-Situ Temperature and Pressure Measurements With Soft Ionisation Mass Spectrometry Inside Burning Superslim and King-Size Cigarettes

Summary Background Combustion as well as pyrolysis of tobacco greatly affect the type and levels of toxicants in cigarette smoke. We previously developed an approach to combine simultaneous temperature and pressure measurements with fast in-situ microprobe chemical sampling inside a burning cigarette, producing a series of temperature and gas-flow velocity maps that characterize this dynamic system in response to externally applied air flow. Aim Two cigarette types differing only in diameter were puffed under ISO 3308 and Health Canada Intense (HCI) regimes to further understand the dynamic interaction of air flow and cigarette design parameters on tobacco combustion and pyrolysis by applying the thermophysical and thermo-chemical mapping approach. Methods Three types of sampling probes were inserted, which are thermocouple arrays for gas-phase temperature, quartz tubes for pressure measurement, and a heated sampling microprobe coupled to a single-photon soft ionisation mass spectrometer for chemical analysis. Two kinds of similarly constructed cigarettes with the same blend were analysed: superslim (17 mm circumference) and king-size (24 mm circumference). Synchronization among the sampled signals was achieved by mapping two probes (e.g., temperature/chemistry or temperature/pressure) at a time. The physical and chemical events were visualised and compared between the cigarettes and puffing regimes. Results A series of temperature, pressure, and chemical maps were obtained for the superslim and king-size cigarettes under ISO and HCI conditions. The pressure in the burning cigarette was higher in the superslim cigarette, and the temperature distribution differed between the two cigarette formats. As expected, temperatures and pressures were higher under HCI puffing than under ISO puffing for both cigarette formats. Thermochemical maps for e.g., benzene and nitric oxide formation were qualitatively similar between the superslim and king-size cigarettes. For other substances the distribution was markedly different. Conclusion The application of multi-probe in-situ chemical sampling is suitable to analyse highly dynamic combustion and pyrolysis processes occurring inside the two types of cigarettes. Ultimately, a direct comparison of cigarette circumferences on the complex combustion processes and formation of smoke constituents was achieved. [Beitr. Tabakforsch. Int. 29 (2020) 44–54]

Aerodynamic and thermal interference between two building models

the paper considers aerodynamic and thermal interference of separated flows between two square prisms arranged at a short distance from each other. It is shown how relative positions of the square prisms affect the specific phenomena caused by the airflow interactions. This work is the experimental study of aerodynamic and thermal interference effects on two square prisms or building models depending on their relative positions. A strong difference is shown between aerodynamic and thermal interferences observed in the airflow behind two tandem models. The thermal interference effect turns to be rather conservative as compared to the aerodynamic. Using the interference parameters one can easily analyze the extreme values of the pressure and thermal flows interfering with the building models depending on many factors, including relative model positions.

A Meteorological Study of the Port Hills Fire, Christchurch, New Zealand

AbstractIn February 2017, a wildfire occurred in the Port Hills on the southern boundary of Christchurch city in New Zealand. It was one of the country’s most severe fires of the last decade in terms of the scale of evacuation, infrastructure damage, and property loss. On the third day of the fire, fire behavior was unexpectedly active, and two rapid downhill fire-spread events took place, creating a dangerous situation for firefighters. The aim of this paper is to explore the atmospheric processes that influenced the fire behavior at a range of meteorological scales, from the synoptic to meso- and microscales. Meteorological and fire data analyzed include observed data together with model simulations of weather conditions at different scales: 1) the Weather Research and Forecasting (WRF) numerical weather prediction model, which provided the regional context of the fire; and 2) the California Meteorological (CALMET) diagnostic model, which was used to undertake a higher-resolution investigation of atmospheric processes near the fire. Results indicate that the fire was not strongly seasonally influenced. Instead, it appears the fire conditions were the effect of a specific combination of synoptic weather conditions and local meteorological conditions. The first rapid downhill fire-spread event was the result of airflow interaction with the intricate terrain of the Port Hills under stable nocturnal conditions. The second downhill fire-spread event bears similarities to vorticity-driven lateral spread, because the downhill component of the spread happened on a broad fire flank perpendicular to the surface wind direction and characteristic pyrocumulus convection occurred.

Computational Predictions of Velocity Ratio and Ejection Angle on Purge Flow in a Linear Turbine Cascade with Upstream Disturbance

Secondary air bled from the compressor which bypasses the combustion chamber is used to seal the turbine components from incoming hot gas. Interaction of this secondary air or purge flow with the mainstream can alter the flow characteristics of turbine blade passage. An in depth analysis of secondary loss generation by purge flow in the presence of upstream disturbances has huge relevance. The objective of present study is to understand the aerodynamic and thermal effects caused by the purge coolant flow in the presence of an upstream wake. A linear turbine cascade is selected for the computational study and a stationary cylindrical rod which resembles the trailing edge of nozzle guide vane is kept 20 mm before the leading edge to generate the upstream wake (or disturbance). Purge flow disturbances includes strong formation of Kelvin-Helmholtz vortices at trailing edge and additional roll-up vortices at leading edge. Detailed analysis is carried out by varying the velocity ratios as well as the ejection flow angle. Higher velocity ratio and perpendicular coolant ejection reduces the mainstream axial momentum which enhances the passage cross flow. Even though the mass averaged total pressure loss is linearly dependent on the velocity ratio, a reduction in the ejection angle brings down the loss coefficient at the blade exit. A lower ejection angle will improve the film cooling effectiveness also. The presence of purge flow causes an increase in the overturning and underturning.

Interaction of Vibration and Air Flow-Accelerating Droplet Emission from the Gas Diffusion Layer of Proton Exchange Membrane Fuel Cell

In order to explore the influence of vibration that the vehicles are often subjected on water management of PEMFC, the dynamic characteristics of vibrating droplet on gas diffusion layer (GDL) surface were investigated through a high-speed image technology. The operating condition of vertical and horizontal excitations separately or coupled with air flow under different frequencies and amplitudes are applied on the substrate, so that the laws for the transition from Wenzel-Cassie regime to Cassie regime and the contact angle, the deformation rate for the width and height are obtained. It is observed that the wetting diameter of the droplet is smaller than the initial value under vertical vibration, making it easier for the gas to discharge the water droplets from the PEMFC. For the horizontal excitation, the droplet is pulled apart when the applied energy exceeded the cohesive energy at elevated frequency and amplitude. Moreover, as to the interaction of vibration and air flow, the droplet was more likely to move forward under the gas-driven force.

A Monocular SLAM-based Controller for Multirotors with Sensor Faults under Ground Effect.

Multirotor micro air vehicles can operate in complex and confined environments that are otherwise inaccessible to larger drones. Operation in such environments results in airflow interactions between the propellers and proximate surfaces. The most common of these interactions is the ground effect. In addition to the increment in thrust efficiency, this effect disturbs the onboard sensors of the drone. In this paper, we present a fault-tolerant scheme for a multirotor with altitude sensor faults caused by the ground effect. We assume a hierarchical control structure for trajectory tracking. The structure consists of an external Proportional-Derivative controller and an internal Proportional-Integral controller. We consider that the sensor faults occur on the inner loop and counteract them in the outer loop. In a novel approach, we use a metric monocular Simultaneous Localization and Mapping algorithm for detecting internal faults. We design the fault diagnosis scheme as a logical process which depends on the weighted residual. Furthermore, we propose two control strategies for fault mitigation. The first combines the external PD controller and a function of the residual. The second treats the sensor fault as an actuator fault and compensates with a sliding mode action. In either case, we utilize onboard sensors only. Finally, we evaluate the effectiveness of the strategies in simulations and experiments.

Dynamic and thermal interference effects on two neighbouring building models

The paper considers the dynamic and thermal interference effects on two neighbouring building models in the form of square prisms arranged at a short distance from each other. It is shown how relative positions of the models affect the specific phenomena caused by the airflow interactions.

Otdelkin N.S., Adamov E.I., Sikarev S.N., Smirnov S.G. Development of a mathematical model for the study of the dynamics of changing the character of interaction of air flow and dust flow at collision with a dust asylum wall

Otdelkin N.S., Adamov E.I., Sikarev S.N., Smirnov S.G. Development of a mathematical model for the study of the dynamics of changing the character of interaction of air flow and dust flow at collision with a dust asylum wall

Numerical Investigation of Electrostatic Spray Painting Transfer Processes for Vehicle Coating

<div class="section abstract"><div class="htmlview paragraph">In this study we examined numerically the electrostatic spray transfer processes in the rotary bell spray applicator, which is this case implemented in a full 3D representation. Instead of an experimental approach [Stevenin et al., 2015, Fluids Eng., 137 (11)], here an algorithm implemented and developed for this simulation includes airflow, spray dynamics, tracking of paint droplets and an electrostatic modularized solver to present atomization and in-flight spray phenomena for the spray forming procedure. The algorithm is implemented using the OpenFOAM package. The shaping airflow is simulated via an unsteady 3D compressible Navier-Stokes method. Solver for particle trajectory was developed to illustrate the process of spray transport and also the interaction of airflow and particle that is solved by momentum coupling. As the numerical results in this paper indicates dominant operating parameter voltage setting, further the charge to mass ratio and air-paint flow rate deeply effect the spray shape and the transfer efficiency (TE). The spin of the bell forced the paint to fall off from the bell edge into the high-velocity airflow. By increasing the shaping airflow more uniform distribution of mass of paint is produced but the TE decreases. The size distribution is highly sensitive to the bell rotational speed. Our results demonstrate the validity of the numerical procedure and also the applicability of it in reducing the production costs for painting. Unsteady and dynamic treatment of the flow is described using Large eddy simulation (LES) turbulence models, whereas the movement of the paint particles is modeled by the approach of tracking droplet size distribution, also the electrical potential effect on its size and form can be predicted. Using this advanced numerical simulation the efficiency and quality of the program can be evaluated precisely for industrial robots of paint over Off-Line Programming (OLP). Further, the paint spraym structure obtained from the numerical simulations is compared with the experimental data at the same working condition with appropriate quantitative accuracy.</div></div>

Blowing in the wind: Increasing social presence with a virtual human via environmental airflow interaction in mixed reality

In this paper, we describe two human-subject studies in which we explored and investigated the effects of subtle multimodal interaction on social presence with a virtual human (VH) in mixed reality (MR). In the studies, participants interacted with a VH, which was co-located with them across a table, with two different platforms: a projection based MR environment and an optical see-through head-mounted display (OST-HMD) based MR environment. While the two studies were not intended to be directly comparable, the second study with an OST-HMD was carefully designed based on the insights and lessons learned from the first projection-based study. For both studies, we compared two levels of gradually increased multimodal interaction: (i) virtual objects being affected by real airflow (e.g., as commonly experienced with fans during warm weather), and (ii) a VH showing awareness of this airflow. We hypothesized that our two levels of treatment would increase the sense of being together with the VH gradually, i.e., participants would report higher social presence with airflow influence than without it, and the social presence would be even higher when the VH showed awareness of the airflow. We observed an increased social presence in the second study when both physical–virtual interaction via airflow and VH awareness behaviors were present, but we observed no clear difference in participant-reported social presence with the VH in the first study. As the considered environmental factors are incidental to the direct interaction with the real human, i.e., they are not significant or necessary for the interaction task, they can provide a reasonably generalizable approach to increase social presence in HMD-based MR environments beyond the specific scenario and environment described here.

Резонансное взаимодействие воздушного потока с изгибными колебаниями конечной упругой пластины

Резонансное взаимодействие воздушного потока с изгибными колебаниями конечной упругой пластины