Association Between Particulate Matter Exposure and Preterm Birth in Women With Abnormal Preconception Thyrotropin Levels: Large Cohort Study.

Background: Prior research has linked exposure to particulate matter with an aerodynamic diameter of ≤2.5 µm (PM2.5) with preterm birth (PTB). However, the modulating effect of preconception thyroid stimulating hormone (TSH) levels on the relationship between PM2.5 exposure and PTB has not been investigated. Objective: This study aimed to assess whether preconception TSH levels modulate the impact of PM2.5 exposure on PTB. Methods: This cohort study was conducted in Guangdong, China, as a part of the National Free Pre-Pregnancy Checkups Project. PM2.5 exposure was estimated by using the inverse distance weighting method. To investigate the moderating effects of TSH levels on trimester-specific PM2.5 exposure and PTB, we used the Cox proportional hazards model. Additionally, to identify the susceptible exposure windows for weekly specific PM2.5 exposure and PTB, we built distributed lag models incorporating Cox proportional hazards models. Results: A total of 633,516 women who delivered between January 1, 2014, to December 31, 2019, were included. In total, 34,081 (5.4%) of them had abnormal preconception TSH levels. During the entire pregnancy, each 10-µg/m3 increase in PM2.5 was linked to elevated risks of PTB (hazard ratio [HR] 1.559, 95% CI 1.390-1.748), early PTB (HR 1.559, 95% CI 1.227-1.980), and late PTB (HR 1.571, 95% CI 1.379-1.791) among women with abnormal TSH levels. For women with normal preconception TSH levels, PM2.5 exposure during the entire pregnancy was positively associated with the risk of PTB (HR 1.345, 95% CI 1.307-1.385), early PTB (HR 1.203, 95% CI 1.126-1.285), and late PTB (HR 1.386, 95% CI 1.342-1432). The critical susceptible exposure windows were the 3rd-13th and 28th-35th gestational weeks for women with abnormal preconception TSH levels, compared to the 1st-13th and 21st-35th gestational weeks for those with normal preconception TSH levels. Conclusions: PM2.5 exposure was linked with a higher PTB risk, particularly in women with abnormal preconception TSH levels. PM2.5 exposure appears to have a greater effect on pregnant women who are in the early or late stages of pregnancy.

Correlation Between Dynamic Spray Plume and Drug Deposition of Solution-Based Pressurized Metered-Dose Inhalers.

Background: The lack of visual dynamic spray characterization has made the understanding of the physical processes governing atomization and drug particle formation difficult. This study aimed to investigate the changes in the spray plume morphology and aerodynamic particle size of solution-based pressurized metered-dose inhalers (pMDIs) under different conditions to achieve better drug deposition. Methods: Solution-based pMDIs were studied, and the effects of various factors, such as propellant concentration, orifice diameters, and atomization chamber volume, on drug deposition were examined by analyzing the characteristics of spray plume and aerodynamic particle size. Results: Reducing the actuator orifice and spray area led to a concentrated spray plume and increased duration and speed. Moreover, the aerodynamic particle sizes D50 and D90 decreased, whereas D10 remained relatively unchanged. Decreasing the atomization chamber volume of the actuator led to reduced spray area and an increased duration but a decreased plume velocity. D90 exhibited a decreasing trend, whereas D10 and D50 remained relatively unchanged. Reducing the propellant concentration in the prescription, the spray area and the plume velocity first decreased and then increased. The duration initially increased and then decreased. The values of D50 and D90 showed an initial decreasing followed by an increasing trend, whereas D10 remained relatively unchanged. Conclusions: During the development process, attention should be paid to the changes in the spray area, spray angle, duration, and speed of the spray plume. This study recommended analyzing the characteristics of the spray plume and combining the data of two or more aerodynamic particle size detection methods to verify the deposition in vitro to achieve rapid screening and obtain high lung deposition in vivo.

Aerodynamic Investigation on a Coaxial-Rotors Unmanned Aerial Vehicle of Bionic Chinese Parasol Seed.

Aerodynamic investigation of a bionic coaxial-rotors unmanned aerial vehicle (UAV) is performed. According to Chinese parasol seed features and flight requirements, the bionic conceptual design of a coaxial-rotors UAV is described. A solution procedure for the numerical simulation method, based on a multi-reference frame (MRF) model, is expressed, and a verification study is presented using the typical case. The aerodynamic design is conducted for airfoil, blade, and coaxial-rotors interference. The aerodynamic performance of the coaxial rotors is investigated by numerical simulation analysis. The rotor/motor integrated experiment verification is conducted to assess the performance of the coaxial-rotors UAV. The results indicate that the UAV has excellent aerodynamic performance and bionic configuration, allowing it to adapt to task requirements. The bionic UAV has a good cruise power load reach of 8.36 kg/kw, and the cruise flying thrust force is not less than 78 N at coaxial-rotor and rotor-balloon distance ratios of 0.39 and 1.12, respectively. It has the "blocks stability phenomenon" formed by the rotor downwash speed decreases and the balloon's additional negative pressure. The present method and the bionic configuration provide a feasible design and analysis strategy for coaxial-rotors UAVs.

Aerodynamic Effects of Time-Varying Corrugations on Dragonfly Wings in Flapping Flight.

The aerodynamic effects of wing corrugation on insect flight have received widespread attention. However, there has hardly been any specific focus on dynamic changes to corrugation angle in the models. The flexible vein joints containing resilin in the wings of dragonflies and damselflies enable the longitudinal veins to rotate and thereby change the corrugation angles throughout flapping cycles. Therefore, a two-dimensional corrugated airfoil with time-varying corrugation angles is proposed and the aerodynamic performance is evaluated in terms of aerodynamic force, power and efficiency. The results indicate that the airfoil with time-varying corrugations outperforms the rigid one in terms of enhancing thrust and reducing power consumption. The aerodynamic performance of time-varying corrugated airfoils is optimal when the angle varies in a specific range, and an excessively large angle variation may have negative effects. In addition, excessive height or a negative leading edge of the corrugation can lead to a reduction in the thrust. A design concept for the 2D airfoil with time-varying corrugations is provided and the findings are of significance for enhancing the aerodynamic performance of biomimetic flexible flapping-wing vehicles.

Aerodynamic thermal breakup droplet ionization combined with a ß-irradiation source for mass-spectrometric analysis of samples in a nonpolar solvent.

A method is proposed for increasing the number of ions during mass-spectrometric analysis of samples in a nonpolar solvent (benzene). For this purpose, aerodynamic thermal breakup droplet ionization (ATBDI) with the impact of ß-radiation on the aerosol droplets used in ATBDI was evaluated. This modification of the method, which we named ß-ATBDI, allows to shift a nonvolatile analyte (trinitrotoluene in the negative ionization region and cocaine in the positive ionization region, as an example) into a gas phase as an aerosol at room temperature (in contrast to atmospheric pressure chemical ionization). In addition, ß-ATBDI enables a researcher to distinguish mass spectrometric peaks of the compounds located in an aerosol droplet from compounds located outside the droplet, i.e., to identify background peaks. Also briefly discussed the ionization of two antibiotics-azithromycin in methylene chloride and sulfadiazine in salt water with ß-ATBDI, ATBDI and electrospray ionization source.

Characteristics of radioactive aerosols during the pre-decommission phase of the experimental shielding reactor.

The decommissioning of nuclear reactors is a global concern, in part because of the generation of radioactive aerosols that can lead to internal radiation exposure. At present, radioactive aerosols generated during nuclear decommissioning have not been actively studied, and data collected from the actual decommissioning are limited. This paper presents a study of radioactive aerosols generated during the pre-decommission phase of an experimental shielding reactor. Among all the on-site operations, cutting resulted in the highest levels of radioactivity. Plasma arc cutting, in particular, had a maximum gross α and ß radioactivity over 0.10 and 0.14 Bq/m3, respectively. Assumed AMAD (activity median aerodynamic diameter) values are employed to assess the impact of particle size on the internal exposure dose resulting from the inhalation of 137Cs aerosols. This assessment is based on the Human Respiratory Tract Model of International Commission on Radiological Protection. When cutting stainless steel by plasma arc, the internal exposure dose caused by 137Cs aerosols with an AMAD of 0.1 µm is estimated to be nearly four times as that of aerosols with an AMAD of 10 µm. Results show that the internal exposure dose is highly dependent on the AMAD, implying the importance of measuring size-related parameters of radioactive aerosols in the future nuclear decommissioning. This study has revealed some characteristics of radioactive aerosols released in decommissioning operations, which can serve as a valuable reference for controlling and removing aerosols during the decommissioning of nuclear facilities.

Oral inhalation of dacomitinib nanocarriers as a therapeutic strategy for non-small cell lung cancer.

Background: Development of an inhalable nanoformulation of dacomitinib (DMB) encapsulated in poly-(lactic-co-glycolic acid) nanoparticles (NPs) to improve solubility, facilitate direct lung delivery and overcome the systemic adverse effects. Methods: DMB-loaded poly-(lactic-co-glycolic acid) NPs were prepared using solvent evaporation and characterized for particle size, polydispersity index and zeta-potential. The NPs were evaluated for in vitro drug release, aerosolization performance and in vitro efficacy studies. Results: The NPs showed excellent particle characteristics and displayed a cumulative release of ∼40% in 5 days. The NPs demonstrated a mass median aerodynamic diameter of ∼3 µm and fine particle fraction of ∼80%. Further, in vitro cell culture studies showed improved cytotoxic potential of DMB-loaded NPs compared with free drug. Conclusion: The study underscores the potential of DMB-loaded NPs as a viable approach for non-small cell lung cancer treatment.

Hybrid SPEAK OUT! protocol improves aerodynamic measurements and PROMs in Parkinson's disease.

BACKGROUND: SPEAK OUT! has been shown to enhance various aspects of voice such as intensity, prosody, voice quality and perception of voice. However, their impacts on expiration and communication effectiveness have not yet been evaluated. This study aimed to evaluate the effectiveness of the Hybrid SPEAK OUT! method on aerodynamic measurements and patient-reported outcome measures (PROMs) in individuals with Parkinson's disease (PD). METHODS: This study included 157 participants with PD who underwent an intensive 8-week multidisciplinary treatment program. The Hybrid SPEAK OUT! method consisted of three sessions per week, including two group sessions and one individual treatment session. Voice-related aerodynamic measures included maximum phonation time (MPT), vocal cord function using the S/Z ratio, and expiratory flow measures including peak expiratory flow (PEF) and peak cough flow (PCF). Two PROMs were included: the Hebrew version of the voice handicap index-10 and communication effectiveness questionnaire. RESULTS: The results of 111 participants were analysed. MPT duration increased, PEF and PCF increased, and better scores were found in PROMs. CONCLUSION: These findings would appear to support the effectiveness of the Hybrid SPEAK OUT! methods improving function, activity and participation in individuals with PD. However, further research is needed. WHAT THIS PAPER ADDS: What is already known on the subject Prior research has demonstrated the effectiveness of behavioral therapies, including the SPEAK OUT! program, in managing speech symptoms in individuals with Parkinson's disease (PD). These therapies have shown improvements in voice intensity, fundamental frequency, voice quality, and voice perception. However, the impact on aerodynamic measures, expiratory flow, and patient-reported outcome measures has not been extensively studied. What this paper adds to existing knowledge This study adds to the existing knowledge by demonstrating that a Hybrid SPEAK OUT! approach, can lead to improvements in aerodynamic measures, including maximum phonation time (MPT), expiratory and cough peak flow. In terms of motor learning, we found that two non-speech exhalation-related tasks that were not directly trained improved following the intensive speech training protocol. Furthermore, it shows positive changes in patient-reported outcome measures, with reduced voice-related disability and improved communication efficiency. What are the potential or actual clinical implications of this work? The findings of this study have important clinical implications for the management of speech symptoms in individuals with PD. The Hybrid SPEAK OUT! program, which combines group and individual sessions, can effectively improve voice, aerodynamic measurements and patient-reported outcome measures (PROMs), ultimately enhancing the overall quality of life for patients. These findings support the effectiveness of the Hybrid SPEAK OUT! methods for improving function, activity, and participation in individuals with PD.

Study on the Pumping Performance and Structure Parameters Optimization of High-Speed Small Compound Molecular Pump.

A molecular pump is the core component of vacuum systems in portable mass spectrometers and other analytical instruments. The forms of the existing molecular pumps mainly are the combinations of vertical bleed and compression channel, which have the shortcomings of heavy mass and large volume, which seriously restricts the application and development of portable mass spectrometers. Aiming at the problems of low strength and insufficient pumping performance under the miniaturization constraints (mass of 1.8 kg; exhaust diameter of 25 mm) of molecular pumps, a compound pump consisting of a horizontal bleed channel and multi-stage spiral compression channel is proposed. The pumping principle of the compound molecular pump is analyzed to obtain its preliminary structural size parameters. The test particle Monte Carlo method is presented for establishing an aerodynamic model for a high-speed small compound molecular pump, which can be used to investigate the pumping performance of bleed blades and compression channels in a thin air environment. On the basis of the aerodynamic model, the NNIA multi-objective optimization algorithm is presented to optimize the structural parameters of the compound molecular pump. After structural parameter optimization, the maximum flow rate and compression ratio of the compound molecular pump are increased by 13.6% and 41.6%, respectively. The experimental results of the pumping performance show that the predicted data of the aerodynamic model are in good agreement with the experimental data, with an error of 12-27%. Namely, the established aerodynamic model has high accuracy and the optimized structural parameters of the compound molecular pump can provide basic conditions for the large-scale application and promotion of portable mass spectrometers.

Preparation and Evaluation of Inhalable Microparticles with Improved Aerodynamic Performance and Dispersibility Using L-Leucine and Hot-Melt Extrusion.

Dry-powder inhalers (DPIs) are valued for their stability but formulating them is challenging due to powder aggregation and limited flowability, which affects drug delivery and uniformity. In this study, the incorporation of L-leucine (LEU) into hot-melt extrusion (HME) was proposed to enhance dispersibility while simultaneously maintaining the high aerodynamic performance of inhalable microparticles. This study explored using LEU in HME to improve dispersibility and maintain the high aerodynamic performance of inhalable microparticles. Formulations with crystalline itraconazole (ITZ) and LEU were made via co-jet milling and HME followed by jet milling. The LEU ratio varied, comparing solubility, homogenization, and aerodynamic performance enhancements. In HME, ITZ solubility increased, and crystallinity decreased. Higher LEU ratios in HME formulations reduced the contact angle, enhancing mass median aerodynamic diameter (MMAD) size and aerodynamic performance synergistically. Achieving a maximum extra fine particle fraction of 33.68 ± 1.31% enabled stable deep lung delivery. This study shows that HME combined with LEU effectively produces inhalable particles, which is promising for improved drug dispersion and delivery.

Experimental Study on Aerodynamic Characteristics of Downwind Bionic Tower Wind Turbine.

The vibrissae of harbor seals exhibit a distinct three-dimensional structure compared to circular cylinders, resulting in a wave-shaped configuration that effectively reduces drag and suppresses vortex shedding in the wake. However, this unique cylinder design has not yet been applied to wind power technologies. Therefore, this study applies this concept to the design of downwind wind turbines and employs wind tunnel testing to compare the wake flow characteristics of a single-cylinder model while also investigating the output power and wake performance of the model wind turbine. Herein, we demonstrate that in the single-cylinder test, the bionic case shows reduced turbulence intensity in its wake compared to that observed with the circular cylinder case. The difference in the energy distribution in the frequency domain behind the cylinder was mainly manifested in the near-wake region. Moreover, our findings indicate that differences in power coefficient are predominantly noticeable with high tip speed ratios. Furthermore, as output power increases, this bionic cylindrical structure induces greater velocity deficit and higher turbulence intensity behind the rotor. These results provide valuable insights for optimizing aerodynamic designs of wind turbines towards achieving enhanced efficiency for converting wind energy.

Effect of Trough Incidence Angle on the Aerodynamic Characteristics of a Biomimetic Leading-Edge Protuberanced (LEP) Wing at Various Turbulence Intensities.

A series of wind tunnel tests were performed to investigate the effect of turbulent inflows on the aerodynamic characteristics of variously modified trough incident leading-edge-protuberanced (LEP) wing configurations at various turbulence intensities. A self-developed passive grid made of parallel arrays of round bars was placed at different locations of the wind tunnel to generate desired turbulence intensity. The aerodynamic forces acting over the trough incidence LEP wing configuration where obtained from surface pressure measurements made over the wing at different turbulence intensities using an MPS4264 Scanivalve simultaneous pressure scanner corresponding to a sampling frequency of 700 Hz. All the test models were tested at a wide range of angles of attack ranging between 0°≤α≤90° at turbulence intensities varying between 5.90% ≤ TI ≤ 10.54%. Results revealed that the time-averaged mean coefficient of lift (CL) increased with the increase in the turbulence intensity associated with smooth stall characteristics rendering the modified LEP test models advantageous. Furthermore, based on the surface pressure coefficients, the underlying dynamics behind the stall delay tendency were discussed. Additionally, attempts were made to statistically quantify the aerodynamic forces using standard deviation at both the pre-stall and the post-stall angles.

Influence of air intake from existing shafts on the safety of operating trains.

Given the influence of air intake from inclined shafts in existing tunnel ventilation systems on train comfort and aerodynamic safety, a numerical analysis method is used to study the comfort and aerodynamic safety of operating trains under three conditions-inclined shaft closed and inclined shaft open without and with air intake-and to explore the variation law of transient pressure and aerodynamic force (lift coefficient, transverse force coefficient, and overturning moment coefficient). Combined with practical engineering and requirements, the influence of inclined shaft air intake on train operation comfort and aerodynamic safety is analyzed. Through this research, the influence of using air intake from the inclined shaft of an existing tunnel, a ventilation scheme of the new Wushaoling Tunnel, on the comfort and aerodynamic force of trains is revealed, and the comfort and aerodynamic safety of trains in an actual project are evaluated, verifying the rationality of the ventilation scheme of the Wushaoling Tunnel.

Numerical analysis of aerodynamic performance of the Ram Air Turbine in an aircraft.

A rotor design of a Ram Air Turbine (RAT) for a commercial aircraft was created taking three sections with different airfoils along the blade; those sections were assessed to evaluate their performance at different critical velocities (41, 81 and 251 m/s) and choose the best profile configuration generating a new proposal to increase the glide ratio by reducing the drag, which is helpful in emergency cases. The Blade Element Momentum (BEM) theory and Computational Fluid Dynamics (CFD) were used to analyze an initial design, then validating these results with the open software QBlade. For the BEM theory a program was created for the design and performance of the RAT adding the Viterna methodology for airfoil analysis. 16 designs were proposed by strategically interchanging wing profiles in different blade sections. These designs were analyzed by CFD, using the complete rotor and the S S T k - ω turbulence model. An optimal geometry was found, presenting a significant drag reduction of 25% generating an increase in the glide ratio and improving aircraft control in addition to maintaining the power generation above the desired values; therefore, it recommends using different airfoils for each section of a RAT's rotor blade.

Contrasting effects of urban trees on air quality: From the aerodynamic effects in streets to impacts of biogenic emissions in cities.

Urban trees are often not considered in air-quality models although they can significantly impact the concentrations of pollutants. Gas and particles can deposit on leaf surfaces, lowering their concentrations, but the tree crown aerodynamic effect is antagonist, limiting the dispersion of pollutants in streets. Furthermore, trees emit Biogenic Volatile Organic Compounds (BVOCs) that react with other compounds to form ozone and secondary organic aerosols. This study aims to quantify the impacts of these three tree effects (dry deposition, aerodynamic effect and BVOC emissions) on air quality from the regional to the street scale over Paris city. Each tree effect is added in the model chain CHIMERE/MUNICH/SSH-aerosol. The tree location and characteristics are determined using the Paris tree inventory, combined with allometric equations. The air-quality simulations are performed over June and July 2022. The results show that the aerodynamic tree effect increases the concentrations of gas and particles emitted in streets, such as NOx (+4.6 % on average in streets with trees and up to +37 % for NO2). This effect increases with the tree Leaf Area Index and it is more important in streets with high traffic, suggesting to limit the planting of trees with large crowns on high-traffic streets. The effect of dry deposition of gas and particles on leaves is very limited, reducing the concentrations of O3 concentrations by -0.6 % on average and at most -2.5 %. Tree biogenic emissions largely increase the isoprene and monoterpene concentrations, bringing the simulated concentrations closer to observations. Over the two-week sensitivity analysis, biogenic emissions induce an increase of O3, organic particles and PM2.5 street concentrations by respectively +1.1, +2.4 and + 0.5 % on average over all streets. This concentration increase may reach locally +3.5, +12.3 and + 2.9 % respectively for O3, organic particles and PM2.5, suggesting to prefer the plantation of low-emitting VOC species in cities.

Thermal modal analysis of hypersonic composite wing on transient aerodynamic heating.

Considering the influence of thermal stress and material property variations, this study employs the Navier-Stokes equations and Fourier heat conduction law to establish a semi-implicit time-domain numerical analysis method for hypersonic aerothermal-structural coupling. Study the temporal variation pattern of different regions of the composite material wing under aerodynamic heating. Using the obtained transient temperature field of the wing, the thermal modal of the wing at different time points is calculated using the finite element method. Additionally, it conducts an analysis and discussion on the factors influencing the thermal modal. Composites can be effectively utilized as thermal protection materials for aircraft. During the aerodynamic heating process, the leading edge temperature reaches thermal equilibrium first, followed by the trailing edge, and the belly plate experiences a slower thermal response. Temperature rise significantly affects higher-order modes, with the change in material properties during the early stages of heating being the dominant factor. This leads to a faster decrease in natural frequency. As heat conduction progresses, the influencing factors of thermal stresses gradually increase, and the natural frequency decreases slowly or even rises.

The Relationship Between Voice Parameters and Speech Intelligibility: A Scoping Review.

OBJECTIVE: To synthesize existing evidence of the relationship between voice parameters and speech intelligibility. METHODS: Following Preferred Reporting Items for Systematic Reviews and Meta-Analysis extension for Scoping Review (PRISMA-ScR) guidelines, 13 databases were searched and a manual search was conducted. A narrative synthesis of methodological quality, study characteristics, participant demographics, voice parameter categorization, and their relationship to speech intelligibility was conducted. A Grading of Recommendations Assessment, Development, and Evaluation (GRADE) assessment was also performed. RESULTS: A total of 5593 studies were retrieved, and 30 eligible studies were included in the final scoping review. The studies were given scores of 10-25 (average 16.93) out of 34 in the methodological quality assessment. Research that analyzed voice parameters related to speech intelligibility, encompassing perceptual, acoustic, and aerodynamic parameters, was included. Validated and nonvalidated perceptual voice assessments showed divergent results regarding the relationship between perceptual parameters and speech intelligibility. The relationship between acoustic parameters and speech intelligibility was found to be complex and the results were inconsistent. The limited research on aerodynamic parameters did not reach a consensus on their relationship with speech intelligibility. Studies in which listeners were not speech-language pathologists (SLPs) far outnumbered those with SLP listeners, and research conducted in English contexts significantly exceeded that in non-English contexts. The GRADE evaluation indicated that the quality of evidence varied from low to moderate. DISCUSSION: The results for the relationship between voice parameters and intelligibility showed significant heterogeneity. Future research should consider age-related voice changes and include diverse age groups. To enhance validity and comparability, it will be necessary to report effect sizes, tool validity, inter-rater reliability, and calibration procedures. Voice assessments should account for the validation status of tools because of their potential impact on the outcomes. The linguistic context may also influence the results.

Airfoil aerodynamic performance prediction using machine learning and surrogate modeling.

In recent times, machine learning algorithms have gained significant traction in addressing aerodynamic challenges. These algorithms prove invaluable for predicting the aerodynamic performance, specifically the Lift-to-Drag ratio of airfoil datasets, when the dataset is sufficiently large and diverse. In this paper, we delve into an exploration of five machine learning algorithms: Random Forest, Gradient Boosting Regression, Decision Tree Regressor, AdaBoost Algorithm, and Linear Regression. These algorithms are scrutinized within the context of various train/test ratios to predict a crucial aerodynamic performance metric-the lift-to-drag ratio-for different angle of attack values. Our evaluation encompasses an array of metrics including R2, Mean Square Error, Training time, and Evaluation time. Upon analysis, the Random Forest Method, with a train/test ratio of 0.2, emerges as the frontrunner, showcasing superior predictive performance when compared to its counterparts. Conversely, the Linear Regression algorithm distinguishes itself by excelling in training and evaluation times among the algorithms under scrutiny.

Experimental Investigation on Aerodynamic Performance of Inclined Hovering with Asymmetric Wing Rotation.

This study presents a model experiment method that can accurately reproduce the flapping motion of insect wings and measure related unsteady aerodynamic data in real time. This method is applied to investigate the aerodynamic characteristics of inclined hovering, which distinguishes it from normal hovering by having asymmetric wing rotation during the two half strokes. In the study of the aerodynamic influence of the downstroke rotational angle, it is found that the rotational angle affects lift generation by changing the angle between the wing surface and the horizontal plane in the mid-downstroke. When the wing is almost parallel to the horizontal plane in the mid-downstroke, the vortex structure can maintain structural integrity and a large magnitude, which is conducive to the generation of high lift. In the study of the aerodynamic effect of the upstroke rotational angle, the windward conversion mechanism is proposed to explain the influence of the upstroke rotational angle on the direction and magnitude of thrust. Obtaining the rotational angle that is most conducive to maintaining the flight state of hovering in the present study can provide guidance for the structural design and kinematic control of micro aerial vehicles.

Numerical Analysis of Broadband Noise Generated by an Airfoil with Spanwise-Varying Leading Edges.

Here, the single-target parameterization of alternatives to leading-edge noise is carried out using analytical models based on the Wiener-Hopf technique. Four leading-edge serration profiles with different frequencies, amplitudes, and phases are implemented to aid the understanding of sound suppression mechanisms. The effects of the serrated shape factor, wavelength, and amplitude are analyzed at tip-to-root ratios of 0.5, 1, and 2, respectively. An effective double-wavelength sinusoidal serration design can substantially reduce the noise emissions of 5.2 dB at h¯ = 2. Additionally, compared to single-wavelength serrations, an additional 1.47 dB noise reduction effect can be obtained by double-wavelength serrations under the appropriate design parameters. The surface pressure and phase distribution of different spanwise-varying leading edges indicate that the phase interference effect affected by source-radiated noise reduction is enhanced by this serration at the hills for serrations with a small curvature, and noise emission in the low-frequency band is more effectively suppressed. The sharper the serration is, the more conducive it is to a reduction in high-frequency noise. Nevertheless, the effectiveness of serrations is usually partially limited by the non-negligible trailing-edge self-noise. The sound source intensity of the root is decreased by the ogee-shaped serrations with a large curvature transition. A secondary noise reduction mechanism with a local source cut-off effect caused by nonlinearity is demonstrated.