Turbulent Air Research Articles

Identification of Emission Source Using a Micro Sampler Carried by a Drone

A micro needle trap sampler (NTS) was carried by a mini quadrotor drone (Mavic Pro, DJI) to collect volatile organic compounds (VOCs) from industries. The NTS was fabricated using a 7 cm long, 22-gauge stainless steel needle by packing powdered divinylbenzene (DVB) adsorbents (60–80 mesh diameters). The telescoping sampling shaft was installed on the drone to extend the NTS beyond the downward air turbulence that was caused by the rotation of its propellers. The total mass of the sampling device, including an NTS, a telescoping shaft, a mini-air pump, and an ABS (acrylonitrile butadiene styrene) rack, was not more than 200 g. The emitted VOCs, those from a steel processing plant, including aromatic hydrocarbons (toluene of 15 ppb, ethylbenzene of 9 ppb and p-xylene 12 ppb), and those from a semiconductor processing factory, including trace amounts of methanol (1.96–2.00 ppm), acetone (0.05–0.10 ppm), and toluene (1.04–2.00 ppm), were extracted by the NTS on the drone and identified using a gas chromatography-mass spectroscopy (GC-MS) system in the laboratory. According to the results of VOC detection during the sampling flight of a drone, the stationary pollution sources were successfully identified.

Airborne lifetime of respiratory droplets

We formulate a model for the dynamics of respiratory droplets and use it to study their airborne lifetime in turbulent air representative of indoor settings. This lifetime is a common metric to assess the risk of respiratory transmission of infectious diseases, with a longer lifetime correlating with higher risk. We consider a simple momentum balance to calculate the droplets' spread, accounting for their size evolution as they undergo vaporization via mass and energy balances. The model shows how an increase in the relative humidity leads to higher droplet settling velocity, which shortens the lifetime of droplets and can, therefore, reduce the risk of transmission. Emulating indoor air turbulence using a stochastic process, we numerically calculate probability distributions for the lifetime of droplets, showing how an increase in the air turbulent velocity significantly enhances the range of lifetimes. The distributions reveal non-negligible probabilities for very long lifetimes, which potentially increase the risk of transmission.

The effects of turbulent air streams and corrugated surfaces on the output of a wind turbine

It is challenging to select the area that best fit the installation of wind turbines within complex and forestry terrains. This study aims to highlight the effects of corrugated surfaces on the characteristics of a turbulent wind flow, and on the performance of a wind turbine installed within this topography. It is hypothesized that a sinusoidal wave can be utilized to describe a corrugated surface. The physical stance was analytically modeled based on conservation principles of mass and mechanical energy. Model’s mathematical equation was then solved, by adopting finite difference method and MATLAB’s Bvp4c algorithm. The results show that wind and turbine related parameters are affected by the evolved atmospheric Boundary Layer (ABL) and differed according to the location within the boundary layer (BL) from the leading part to the edge, where BL’s retarding effects diminishes. The study also proves that velocity and turbine harvested power are inversely proportional to the corrugated surface’s amplitude, and to the wind’s turbulence ratio. On the other hand, it demonstrates a direct proportion between boundary layer thickness (BLT) and corrugated surfaces-related parameters. To the contrary of previous works, this study concentrated on capturing interaction effects between wind turbine, atmospheric inflow, and complex terrains.

Aeroscapes and the Sensory Ecology of Olfaction in a Tropical Dry Forest

Aeroscapes—dynamic patterns of air speed and direction—form a critical component of landscape ecology by shaping numerous animal behaviors, including movement, foraging, and social and/or reproductive interactions. Aeroecology is particularly critical for sensory ecology: air is the medium through which many sensory signals and cues propagate, inherently linking sensory perception to variables such as air speed and turbulence. Yet, aeroscapes are seldom explicitly considered in studies of sensory ecology and evolution. A key first step towards this goal is to describe the aeroscapes of habitats. Here, we quantify the variation in air movement in two successional stages (early and late) of a tropical dry forest in Costa Rica. We recorded air speeds every 10 seconds at five different heights simultaneously. Average air speeds and turbulence increased with height above the ground, generally peaked midday, and were higher overall at the early successional forest site. These patterns of lower air speed and turbulence at ground level and overnight have important implications for olfactory foraging niches, as chemotaxis is most reliable when air movement is low and steady. We discuss our results in the context of possible selective pressures and observed variation in the foraging ecology, behaviors, and associated morphologies of resident vertebrates, with a focus on mammals. However, these data also have relevance to researchers studying socioecology, invertebrate biology, plant evolution, community ecology and more. Further investigation into how animals use different forest types, canopy heights and partition activities across different times of day will further inform our understanding of how landscape and sensory ecology are interrelated. Finally, we emphasize the timeliness of monitoring aeroecology as global wind patterns shift with climate change and human disturbance alters forest structure, which may have important downstream consequences for biological conservation.

Do Red-cockaded Woodpecker (Dryobates borealis) cavity locations provide olfactory concealment from predators?

Nest site selection is crucial for survival and fecundity of birds. Predators find nests using visual, aural, thermal, and olfactory cues, yet few studies have evaluated olfactory concealment of nests. Rat snakes (Pantherophis spp.) are common nest predators that use ground-level olfactory cues to detect nest locations. In Arkansas, USA, we evaluated if cavity locations of the Red-cockaded Woodpecker (Dryobates borealis, RCW), a species that experiences nest predation by rat snakes, were associated with airflow conditions known to provide olfactory concealment for other bird species. We used a 3-dimensional sonic anemometer to measure ground-level air velocity, turbulence, and turbulence intensity at cavity trees and unused trees, and at cavity and opposite orientations on trees. For all airflow variables, we found no differences between used and unused trees and orientations. Other factors such as landscape-scale vegetation cover, forest stand structure, and tree characteristics may be more important for providing visual concealment or optimal foraging conditions. However, it remains possible that such factors also convey olfactory concealment. For example, savannah-like forests preferred by RCWs may have greater air turbulence than closed forests. Further research on RCWs and other bird species to address additional aspects of olfactory concealment, and relationships between different dimensions of concealment (e.g., between visual and olfactory concealment), would give insight into how habitat management could provide multiple benefits to birds.

Coupling of Mouse Olfactory Bulb Projection Neurons to Fluctuating Odor Pulses.

Odours are transported by turbulent air currents, creating complex temporal fluctuations in odour concentration that provide a potentially informative stimulus dimension. Recently, we have shown that mice are able to discriminate odour stimuli based on their temporal structure, indicating that information contained in the temporal structure of odour plumes can be extracted by the mouse olfactory system. Here, using in vivo extra- and intracellular electrophysiological recordings, we show that mitral and tufted cells (M/TCs) of the male C57BL/6 mouse olfactory bulb can encode the dominant temporal frequencies present in odour stimuli up to at least 20 Hz. A substantial population of cell-odour pairs showed significant coupling of their subthreshold membrane potential with the odour stimulus at both 2Hz (29/70) and the supra-sniff frequency 20Hz (24/70). Furthermore, M/TCs show differential coupling of their membrane potential to odour concentration fluctuations with tufted cells coupling more strongly for the 20Hz stimulation. Frequency coupling was always observed to be invariant to odour identity and M/TCs that coupled well to a mixture also coupled to at least one of the components of the mixture. Interestingly, pharmacological blocking of the inhibitory circuitry strongly modulated frequency coupling of cell-odour pairs at both 2Hz (10/15) and 20Hz (9/15). These results provide insight into how both cellular and circuit properties contribute to the encoding of temporal odour features in the mouse olfactory bulb.

Ability of the WRF-ARW and HARMONIE-AROME models to detect turbulence related to mountain waves over Central Iberia

Aircraft turbulence is one of the most dangerous meteorological phenomena that can affect aviation safety. This study is focused on the turbulence associated to mountain lee waves in the vicinity of Adolfo Suárez Madrid-Barajas airport (Spain). Sixty-eight mountain lee waves events are selected to simulate the turbulence with the Weather Research and Forecasting (WRF-ARW) and the HARMONIE-AROME numerical weather prediction models. To study and characterize the turbulence associated, the vertical wind speeds are selected as an important variable and the Eddy Dissipation Rate is estimated. Both models have properly simulated the turbulence and the clear air turbulence, obtaining higher values of turbulence intensity by WRF-ARW than HARMONIE-AROME in the mountain lee waves events. Finally, these results are used to enhance a mountain wave warning decision tree, including the turbulence warning which is validated through several turbulence reports.

Enhancement of multi-filament generation and filament-induced fluorescence by turbulence

Exploring the influence of atmospheric turbulence on remote sensing based on filament-induced fluorescence is still challenging. In this study, we applied artificial turbulence during remote filamentation and recorded the enhanced backward fluorescence of nitrogen. At the strongest turbulence, the nitrogen fluorescence signal was higher than that obtained when no turbulence was applied. The air turbulence introduces random noise in the laser profile, which is subsequently amplified by self-focusing effect and causes multiple filamentation. Moreover, by lowering the threshold for multiple filaments generation, turbulence led to an increase in the number of filaments, thereby enhancing fluorescence.

Calibration of phase-only liquid-crystal spatial light modulators by diffractogram analysis

Phase-only spatial light modulator (SLM) is a key device for light manipulation. It is critical to calibrate the grayscale-phase response to the driving voltage of SLM, namely the look-up table (LUT), before use. The conventional calibration methods, which rely on interference, diffraction, or polarization to extract the phase, require extra optical devices and are sensitive to mechanical vibration, air turbulence, and systematic aberrations. To overcome these shortcomings, here we develop a novel method, which is based on the diffractogram analysis. By analyzing the intensity distribution of the diffractogram as a function of the specific SLM hologram, we identify both the global and the localized LUTs of SLM at high accuracy. Compared with the other ones, our method allows in-situ SLM calibration and is more tolerant to the exogenous factors.

Transport dynamics of SARS-CoV-2 under outdoor conditions.

This study aimed at estimating the transport dynamics of a single severe acute respiratory syndrome corona-virus 2 (SARS-CoV-2)-laden droplet of 1 to 500 μm in diameter at a wind speed from 1 to 4 m/s. Motion dynamics of SARS-CoV-2-laden respiratory droplets under calm or turbulent air conditions were quantified using a combined model. Dalton’s law was implemented to estimate their evaporation. One-factor-at-a-time procedure was applied for the sensitivity analysis of model of deposition velocity. The transport distance of the single virus ranged from 167 to 1120 m as a function of the droplet size, wind speed, and falling time. The evaporation times of the droplets ≤ 3 and ≤ 14 μm in diameter were shorter than their settling times from 1.7 m in height at midnight and midday, respectively. Such droplets remained in the air for about 5 min as the droplet nuclei with SARS-CoV-2. The minimum transport distance of the respiratory droplets of 1–15 μm varied between 8.99 and 142 m at a wind speed range of 1–4 m/s, based on their deposition velocity. With their short transport distance, the larger droplet (30 to 500 μm) was not suspended in the air even under the windy conditions. The deposition velocity was found most sensitive to the droplet diameter. The droplets < 15 μm in diameter completely evaporated at midday and the droplet nuclei with the single virus can travel a minimum distance of 500 m under a horizontal wind speed of 3 m/s.

Вентиляционные течения в турбулизированной среде производственных помещений

The turbulent air environment in industrial premises intensively affects the characteristics of air and heat and gas jets and thereby the effectiveness of various industrial ventilation devices. This effect manifests itself in the accelerated expansion of the main sections of the jets and in the reduction of their range of action. Until recently, the influence of the intensity of air turbulence was not taken into account in the corresponding calculation and design methods. The article proposes methods for calculating air jets and the efficiency of open local suction, taking into account the influence of a turbulized air environment.

Performance analysis of multi-hop underwater wireless optical communication system with space-time block codes considering the impact of beam spread function

The average bit error rate (ABER) performance of the decode-and-forward-based multiple-input multiple-output (MIMO) multi-hop underwater wireless optical communication (UWOC) systems has been investigated over the composite exponential-generalized gamma (EGG) fading channel with space-time block coding (STBC). The impacts of absorption, scattering, and the misalignment caused by spatial spreading in the sea, which are modeled by the beam spread function, as well as the turbulence-induced fading are all taken into account in this work. With the help of the moment generating function, Meijer’s-G function, and Gauss–Laguerre quadrature numerical methods, the approximate closed-form expressions of ABER for the UWOC system with binary phase shift keying are mathematically derived. Furthermore, numerical analyses are provided to investigate the effects of various hops, temperature gradients, air bubbles levels, STBC schemes, and turbulence severity on the performance of the multi-hop MIMO UWOC system. In addition, Reed–Solomon (RS) codes are adopted to improve the UWOC system performance. Results reveal that the ABER performance of this multi-hop UWOC system would degrade as the temperature gradients, hop numbers, and bubble levels (BLs) increases, which could be improved considerably by employing the STBC scheme. The ABER performance over the composite EGG distribution is mainly limited by the environmental parameters, whereas the fading can be significantly improved by RS codes. The ABERs of EGG distribution are compared with exponential-gamma and exponential-lognormal distributions in oceanic turbulence under different temperature gradients and BLs, respectively. These analytical results are also verified by Monte Carlo simulations. This work is beneficial for the design of UWOC system.

Investigation and Analysis of Air Curtains for the Improvement of Refrigeration Energy Efficiency

The purpose of this research is to present a warm air infiltration simulation for a cold room, considering the effects of an air curtain. At present, there exist a large number of retail businesses, operating within an industry entailing high investment and competition. Therefore, retail operators must distinguish factors that are essential to lowering their costs, one of which is energy reduction. A survey of energy consumption in stores found that most used energy is due to the cooling system. Therefore, we tested the protection of cold rooms against air inflow by conducting three simulations: 1. Without an air curtain; 2. using an air curtain having a common grille; and 3. using an air curtain with a honeycomb grille. The cold room temperature was set to 1 °C, the cold room door was 200 × 100 m2, and the air curtain was installed 5 cm above the cold room door; furthermore, the velocity of air emitted from the air curtain was 6.5 m/s. Warm air infiltration simulations were carried out using SolidWorks Flow Simulation software, in order to determine the temperature change in the cold room and the airflow direction. From the results of the comparative experiments, when using the different wind grilles, there were differences in the infiltration of warm air. The honeycomb grille reduced air turbulence in the cold room more effectively than the common grille. As a result, the temperature in the cold room was consistent, and the temperature inside the cold room was maintained 10.62% lower when using a honeycomb grille compared to a common grille.

Phase combining of radiation from a two-channel explosively pumped photodissociation iodine laser with an SBS mirror

A two-channel double-pass iodine explosively pumped photodissociation laser (EPPL) with an explosively pumped master oscillator (MO) and an SBS mirror is studied. The radiation source, determined by an aperture 6 mm in diameter, through which the radiation from MO enters the turbulent surface air path, is located at a distance of 2.5 km from the amplifier unit input. An SBS mirror with a kinoform raster of microlenses is used to compensate for the amplifier and path optical inhomogeneities and to match the phases in the EPPL channels. The energy and spatial characteristics of the EPPL output radiation are studied experimentally and numerically. Good agreement is obtained between the experimental and calculated distribution of the energy density of the output EPPL radiation in the plane of the MO aperture, which is a pattern of interference between the two channels. The maximum energy density in the aperture plane is by more than 4 times greater than in the case of a single-channel EPPL.

Performance improvement of an air gap membrane distillation process with rotating fan

The current paper presents an experimental study on the performance of a novel air gap membrane distillation (AGMD) desalination system where a fan blade is installed within the air gap to improve the system’s productivity and energy utilization. The installed blade creates suction inside the air gap behind the membrane and increases the air turbulence, thereby reducing the vapor mass transfer resistance across the membrane and improving the productivity and energy efficiency of the system. Results revealed that the proposed design and process improve the vapor permeate flux by about 250% when compared to the conventional AGMD module. Furthermore, the average improvement in the gained output ratio of the system is about 67%, with a corresponding 77% reduction in the specific thermal energy consumption. Influences of the feed temperature and the motor speed are dominating the performance of the new system.

Numerical simulation of water spray evaporation in a turbulent air flow

Water spray evaporation in a hot air flow is a common process for many industrial applications. Spray nozzles should be well adjusted and distributed specifically to achieve efficient evaporation. The present study addressed simulation of the process within the Eulerian-Lagrangian workframe with k-∈ turbulence model. Simulation was carried out via OpenFOAM and postprocessed with ParaView. SprayFOAM solver was used to obtain a solution for 2D and 3D representations of the wind tunnel. Custom JANAF-based approximations were introduced for thermophysical properties of working mediums (air and water vapor). Obtained results were accurate enough to validate the presented model against adopted experimental data. Drift eliminator was modelled with virtual interfaces (baffles), which were tested in two scenarios: accumulating and removing droplets from the computational domain.

Analysis of Turbulent Air Flow Characteristics Due to the Presence of a 13 × 30 Threads·cm−2 Insect Proof Screen on the Side Windows of a Mediterranean Greenhouse

Insect-proof screens are a frequent passive method to restrict the entrance of insects into greenhouses. However, the installation of these screens also has a negative effect on natural ventilation, which is reflected in the turbulence and velocity of the airflow inside the greenhouse. The turbulent characteristics of airflow through an insect-proof screen installed in the greenhouse windows have not been studied thoroughly in the literature. The present work focuses on the use of two simultaneous 3D sonic anemometers to study the impact of the use of a 13 × 30 threads·cm−2 insect-proof screen on the turbulence properties of the micro and microscale airflow turbulence. Four tests have been carried out in windward-oriented side windows of a Mediterranean greenhouse. Results demonstrate that the approach of using two simultaneous 3D sonic anemometers for the first time allows one to observe that the effect is different for the three components of the velocity vector field, and there is a strong connection between the simultaneous conditions inside and outside of the greenhouse. Useful information and data on the effect of using a 13 × 30 threads·cm−2 insect-proof screen are also provided. To give details on the impact of screens in the turbulent properties of ventilation is essential for any commercial distribution, as well as providing important data in the design and development of more efficient insect-proof screens.

Clear Air Turbulence Observed Across a Tropopause Fold Over the Drake Passage—A Case Study

AbstractAn aircraft turbulence encounter over the Drake Passage is investigated by combining unique high‐frequency flight level data, vertical profiles of a near‐simultaneous radiosonde profile and numerical results from global and regional numerical weather prediction (NWP) models. Meteorological analysis reveals an intense polar low propagating from the Bellinghausen Sea toward the Drake Passage. A small and deep stratospheric intrusion formed a tropopause fold that promoted strong upper‐level frontogenesis and enhanced shear and horizontal deformation of the upper tropospheric and lower stratospheric (UTLS) airflow. In this region, the Basic HALO Measurement and Sensor System (BAHAMAS) aboard the HALO research aircraft flying at FL450 detected large peak‐to‐peak variations in all meteorological parameters. The computed Energy dissipation rate (EDR) values (cubic root of the eddy dissipation rate) indicate moderate to severe turbulence. The location of this turbulence encounter was well‐predicted by the clear air turbulence (CAT) indices derived from the NWP results. The enhanced CAT indices emphasize the large shear and horizontal deformation of the airflow as the cause of the turbulence. Horizontal and vertical energy spectra calculated from the 10 Hz BAHAMAS data show a well‐defined energy cascade toward small scales with Kolmogorov scaling. Maximum EDR values of about 0.35 derived both from the spectra and structure functions for the wind speed agree quantitatively very well. In addition, the structure functions support the detection of turbulent atmospheric conditions with signatures of flow anisotropy generated by enhanced thermal stratification in the UTLS. The scales involved are between the buoyancy length scale LB ≈ 1,500 m and the Ozmidov scale LO ≈ 111 m.

Exergy-Based Thermo-Hydraulic Performance of Roughened Absorber in Solar Air Heater Duct

This paper presents the thermo-hydraulic performance of small conical ribs on the absorber plate of a solar energy air heater (SAH) using exergy analysis. Application of conical protrusion ribs on the absorber is an attractive solution for enhancing the thermal performance of a SAH. However, these ribs are also responsible for high friction losses and increased fan power consumption caused by the turbulent air flow. To optimize the rib design, it is vital to consider both thermal and hydraulic performance at the same time. The SAH was assessed using an analytic method which predicts the exergy efficiency under operating parameters (e.g., Reynolds number, solar insolation and temperature increase parameter). The following geometric quantities of ribs were evaluated for optimum exergy efficiency: the relative rib height (e/D), which was in the range between 0.200 and 0.044, and the relative rib pitch (p/e), which was in the range between 6 and 12. The combination of a relative rib height of 0.044 and relative rib pitch of 10 exhibits the highest exergy efficiency of 0.0202. The optimization of the rib geometric quantities parameters was performed by considering the temperature increase parameter, aiming to achieve maximum exergy efficiency. The combination of rib parameters e/D = 0.044 and p/e = 10 are noted to yield best performance when operating at a temperature increase parameter above 0.0141 K∙m2/W.

Calculating Terahertz Channel Capacity Under Beam Misalignment and User Mobility

In this letter, we consider the terahertz (THz) wireless communication between an unmanned aerial vehicle (UAV) and a base station. The beam alignment is interrupted by some unpredictable factors, such as air turbulence, and the UAV recovers the beam alignment via flying maneuver. Here, we propose a new method to obtain the closed-form channel capacity under the beam misalignment, where a classical control model is used to capture the trajectory of the UAV maneuver. This allows us to obtain a much accurate channel capacity compared with the conventional methods that treat the misalignment as a random variable. The numerical results show that the proposed method reduces almost 80% calculation error compared to the conventional method.