Aerodynamic Considerations Research Articles

Blockchain-Driven Demand Response System for Resilient and Sustainable MicroGrids Integrating Wind Energy Conversion Systems

This study introduces the B-DDR system, leveraging blockchain technology for real-time, decentralized energy management in MicroGrids. By integrating Vertical Axis Wind Turbines (VAWTs), including a novel H-Darius VAWT-PMSG model with magnetic levitation and aerodynamic considerations, the proposed approach addresses challenges in optimizing energy supply and demand. Blockchain smart contracts facilitate peer-to-peer energy trading among WECS owners and users, promoting efficient renewable energy utilization. The system, analyzed through optimization models, demonstrates a notable reduction in peak demand rate from 40% to 15%, an improvement in energy efficiency from 7% to 12%, and a remarkable 92% increase in utilization efficiency. With a transaction speed of 5s during outages, the B-DDR system proves its capability to enhance MicroGrids, ensuring a robust, efficient, and sustainable energy environment. The incorporation of H-Darius VAWT-based PMSGs and blockchain technology enables precise demand response, achieving effective grid energy state equilibrium while minimizing losses. The self-executing agreements, monitored by H-Darius-PMSG nodes, provide real-time tracking and balancing, addressing the dynamic challenges posed by fluctuating demand requirements in a decentralized and efficient manner.

Effects of body angles on the aerodynamic characteristics in the flight period of ski jumping: a simulation study

ABSTRACT The flight period of ski jumping involves aerodynamic considerations. Reasonable controls and adjustments of in-flight body attitudes are beneficial to improve the aerodynamic performance of athletes, thus obtaining a longer flight distance. Here, the aerodynamic forces and moments of a simplified body-ski model in the flight period are calculated via the computational fluid dynamics (CFD) method, considering influences of head angle, hip angle, and body-ski angle, and the contributions of each body part are discussed. Results show that the hip angle and body-ski angle dominate the aerodynamic performance, and the skis and the trunk contribute most to the aerodynamic force and moment. In addition, based on CFD results, the hip angle and body-ski angle are selected as design variables, and optimisations for lift area and lift-to-drag ratio are conducted via the combination of Kriging models and genetic algorithm. When the lift-to-drag ratio reaches its peak (which is beneficial to the early flight), the athlete should keep a flatter body attitude, leading to a relatively low lift area and drag area. Properly raising the posture of the body can get a higher lift area, which is beneficial to balance the gravity and prolong the athletes’ flight distance in the late flight.

Layout and yaw optimisation of an offshore wind farm through analytical modelling

In this work, a computational tool for analytical large scale modelling of offshore wind farms is presented. Using Horns Rev 1 as a reference baseline, an optimal layout and yaw angle setting for one wind direction based on aerodynamic considerations is proposed. Based on a wake model presented by Qian & Ishihara, flow velocities as well as turbulence intensities are predicted when several wake flows are superimposed. Subsequently, the aerodynamic performance of the wind turbines is calculated. The proposed tool shows good agreement with measurement and LES data. The influence of performance-driving parameters, namely turbine spacing, ambient turbulence intensity and yaw angle are investigated. The axial spacing and ambient turbulence are identified as the most significant factors. Based on these results, the proposed optimal layout solution suggests a higher power yield of up to 57 %, while the optimal yaw angles found in this work show a power increase of over 6% compared to the baseline layout.

Investigation of the Effect of the Wind Speed on the Aerodynamic and Architectural Design of Tall Buildings

The magnitude, speed, direction, and distribution of the wind are known to have a negative impact on high-rise buildings, particularly when the building is extremely tall. As the height of the building increases, the effect of the wind increases significantly. This results in a high wind pressure exerted on the building which causes the wind loads subjected by the buildings to increase considerably. Thus, this study investigates the wind effect on tall buildings and proposes a solution to reduce the aerodynamic drag through a design that meets both architectural and aerodynamic considerations. Investigation of wind effect on tall buildings with different wind speeds, heights and shapes is carried out. Numerical methods are utilized to study the wind pressure, drag coefficient and pressure distribution on different types of buildings. ANSYS Fluent is used for computational fluid dynamics (CFD) simulation to assess the drag coefficient of the buildings. The drag coefficient of the building is determined in Reynold’s number range of 1×106 to 2×106. The study is conducted in low subsonic speed (Ma < 0.3). The result shows that the drag coefficient of the building tends to be constant at low subsonic speeds. Besides, the study found that the drag coefficient increases by 1% to 3% for every 0.1 m increment in the height of the building. The study also found that a cylindrical building has the lowest drag coefficient because of its more streamlined shape. Overall, this study provided guidance and recommendations for wind resistance which can be taken into consideration when designing tall buildings. Hence, the building can be built even taller while maintaining its rigidity and stability.

The relationship of moult timing, duration and sequence to the aerial lifestyle of the Little Swift (Apus affinis)

Feather moult is an important and energy‐demanding avian life‐history trait that is necessary to maintain the function of the plumage by replacing abraded feathers with new ones. However, during moult, aerodynamic capacity is temporarily impaired by the reduction and shape change of the flight surface. Therefore, among aerial birds, adaptations may evolve to reduce this impairment. Here, we studied the timing, duration and sequence of the annual complete moult of adult Little Swifts Apus affinis in northern Israel by examining the plumage of 55 individuals monthly in their colony. Primary moult occurs over 191.7 ± 24.0 days, representing 52.5 ± 6.6% of the annual cycle, and overlaps with the breeding season, a rare occurrence among small Palaearctic bird species. In addition, primary moult duration was significantly affected by its timing such that individuals that started to moult later had a shorter moult duration than those that started to moult earlier. This relationship is most likely to be a result of the time available for moult, which is limited by breeding and also by the cold season and the expected decline in food availability. Moult overlap with breeding or cold seasons may involve energetic and functional costs. Our results indicate two strategies that appear sequentially: (1) a slow and long moult that largely overlaps with breeding, and (2) a shorter moult that overlaps less with breeding (both strategies avoid moulting during the cold season). Most Little Swifts (85.7%) moulted their rectrices in a centripetal sequence starting with the outermost pair of rectrices inward. This moult was later in relation to wing feather renewal and had almost no overlap with primary moult. Finally, we tested a method for non‐invasively monitoring moult of small species by collecting and sampling shed feathers without the need to capture the birds themselves, as has been successfully used for larger bird species. This work demonstrates the importance of aerodynamic considerations in the evolution of life‐history traits. Moult‐related aerodynamic costs may be an important evolutionary factor shaping moult strategy, including timing, duration and sequence, mainly among species, like swifts, that are highly dependent on their aerodynamic ability.

The impact of shape and attachment position of biologging devices in Northern Bald Ibises

BackgroundThe impact of biologging devices on the aerodynamics or hydrodynamics of animals is still poorly understood. This stands in marked contrast to the ever more extensive use of such technologies in wild-living animals. Recently, increasing concerns have been raised about the impairing effects of these devices on the animals concerned. In the early days of biotelemetry, attention was focused solely on reducing weight, but now aerodynamic effects are also increasingly being considered. To investigate these effects, we trained Northern Bald Ibises to fly in a wind tunnel in which we measured heart rate and dynamic body acceleration (VeDBA) as proxies for energy expenditure in relation to different logger shapes and wind flow directions.ResultsOur data provide evidence that the position of biologging devices significantly influence the flight distances, and the shape of biologging devices has a considerable effect on heart rate and VeDBA, both of which have been used as proxies for energy expenditure. Unfavorable shape and positioning go beyond merely affecting the effort required during flapping flight. The energetically probably more important effect is that the devices impair the bird’s ability to glide or soar and thus force them to perform the energetically much more demanding flapping flight more frequently. This effect was more pronounced in rising air than in horizontal airflow. A complementary study with wild Northern Bald Ibises during spring migration provides evidence that the position of the devices on the bird’s back affects the length of the flight stages. Birds carrying the devices on the upper back, fixed by wing-loop harnesses, had significantly shorter flight stages compared to birds with a more caudally positioned device, fixed by leg-loop harnesses.ConclusionThe attachment of biologging devices on birds affects their performance and behavior and thus may influence their fitness and mortality. Our results show that detrimental effects can be reduced with relatively little effort, in particular through a strictly aerodynamic design of the housing and increased consideration of aerodynamics when attaching the device to the body. In birds, the attachment of biologging devices via leg loops to the lower back is clearly preferable to the common attachment via wing loops on the upper back, even if this affects the efficiency of the solar panels. Nevertheless, the importance of drag reduction may vary between systems, as the benefits of having a biologging devices close to the center of gravity may outweigh the increase in drag that this involves. Overall, more research is required in this field. This is both in the interest of animal welfare and of avoiding biasing the quality of the collected data.

Resuspension of microplastics and microrubbers in a semi-arid urban environment (Shiraz, Iran)

Although airborne urban particles are a concern for air quality and human health, little information exists on the levels and characteristics of microplastics (MPs) and microrubbers (MRs) in this setting. In the present study, MPs and MRs are quantified and characterised in road dusts and accumulations captured passively (and up to elevations of 177 cm above road level) in the steps of utility poles at 18 locations throughout the city of Shiraz, southwest Iran. Dust accumulation rates were greatest at road level (median = 45 g m−2 month−1) and declined with elevation (median = 2.0 g m−2 month−1 at 177 cm). The accumulation rates and concentrations (per g of dust) of MPs and MRs were more variable between locations but accumulation declined with elevation for both particle types and MR concentration (up to ∼27,000 MR g−1) was always greater than corresponding MP concentration (up to ∼3300 MP g−1). Increasing elevation was also accompanied by an increasing proportion of fine (≤100 μm) and fibrous particles, and in particular for MPs. Fractionation in the quantities and characteristics with elevation above road level are attributed to the extent of resuspension of MPs and MRs from the road surface by wind and passing traffic, with aerodynamic considerations predicting the greatest and most widespread resuspension of fibrous MPs. The fractionation of MPs and MRs with elevation above road level also results in different exposures for adults and children.

3D printed rotor blades for a research wind turbine: Aerodynamic and structural design and testing

This study combines the design, the 3D printing and the testing of a small 3-bladed wind turbine rotor for research and teaching purposes. The objective is the additive manufacturing of a rotor with a radius of one meter, as an alternative to subtractive methods, such as computerized milling. The blade design is developed using freely available software packages. The aerodynamic considerations include the airfoil selection, the calculation of the blade geometry and the simulation of the ultimate load cases. The structural considerations are focussed on the printable materials, the infill structures and the retrofit of a load-carrying spar. The rotor blades are 3D printed with the BigRep One at the maker space of the TH Wildau. The structural integrity of the prototype blade is tested in terms of the ultimate root bending moments and the centrifugal forces at the HTW Berlin. The aerodynamic run-up tests are performed at the large wind tunnel of the TU Berlin measuring the power curves. The successful prototype paves the way for follow-up projects, such as open field tests and the 3D printing of larger rotor blades.

Virtual four sensor fast response aerodynamic probe (FRAP®)

This paper introduces the new fast response aerodynamic probe (FRAP®), which was recently developed at the ETH Zurich. The probe provides time-resolved, three-dimensional flow measurements using the virtual four sensor technique. Two probes work in tandem, being comparable to a pair of pneumatic needle probes. The first probe, being yaw angle sensitive, is positioned in three circumferential positions. The second probe being pitch angle sensitive is brought into exactly the same position as the first probe. The resulting set of four measurements is phaselock-averaged to one specific rotor trigger position. Then the reduced data sets are combined to four calibration coefficients, which are then further processed to determine the unsteady flow vector. The results consist of yaw and pitch flow angles as well as the total and static pressure. The outer diameter of the cylindrical probe head was miniaturized to 0.84mm, hence probe blockage effects as well as dynamic lift effects are reduced. The shape of the probe head was optimized in view of the manufacturing process as well as aerodynamic considerations. The optimum geometry for pitch sensitivity was found to be a cylindrical surface with the axis perpendicular to the probe shaft. The internal design of the probes led to a sensor cavity eigen frequency of 44 kHz for the yaw sensitive and 34kHz for the pitch sensitive probe. The steady aerodynamic characteristics of the probe were measured using the free jet probe calibration facility of the laboratory. The full set of calibration surfaces is given. Data acquisition is done with a fully automated traversing system, which moves the probe within the test rig and samples the signal with a PC-based A/D-board. An error analysis implemented into the data reduction routines revealed acceptable accuracy for flow angles as well as pressures for many turbomachinery flows. Depending on the dynamic head of the application the yaw angle is accurate within ±0.35° and pitch angle within ±0.7°. Finally, a comparison of time averaged results to five hole probe measurements is discussed.

Design, Numerical and Experimental Investigation of High Swirling Flow in an Annular Combustion Chamber

In this study, an annular combustion chamber of a turbojet engine with a net trust of 1650N is designed. Kerosene is considered as fuel in this study. The design consists of evaluation of the reference quantities, calculation of the required dimensions, estimation of air distribution and pressure drop, estimation of the number and diameter of air admission holes, as well as aerodynamic considerations. The design process is accompanied by Computational Fluid Dynamics (CFD) based on RANS simulation. Three-dimensional simulation of the reacting process within the combustion chamber is carried out based on the finite volume method. The RNG turbulent model and the finite rate/eddy dissipation combustion model are considered in the present study. Finally, the (atmospheric test) AT rig of the combustion chamber is explained. The Turbine Inlet Temperature (TIT) of combustion chamber is measured at different operating conditions. The TIT values in the numerical simulation and experimental measurement are 1191.1K and 1227 K, respectively, in the design point. The SN and the angle of the RZ are equal to 0.9955 and 35.26 degree, respectively. The temperature, velocity and pressure fields of RZ, air-fuel mixture, combustion turbulence are then presented in image outputs and graphs. The results indicate that the temperature distribution at the outlet of combustion chamber is relatively uniform.

Omnidirectional Dual-Polarized Antenna Using Colocated Slots With Wedgy Profile

In this article, an omnidirectional dual-polarized antenna with low windage is presented within a wedge-profiled structure for supersonic onboard systems. Based on aerodynamic analysis, a wedge-profiled cavity is designed with colocated slots for omnidirectional and dual-polarized radiation. For horizontal polarization, two identical half-wavelength slots are etched onto the cavity sidewalls symmetrically. The vertical polarization is achieved by another horizontal slot, with the port isolation higher than 42 dB. A low windage coefficient of 0.11 is obtained within the wedge-profiled cavity with the dimensions of 41.6 ×16 ×30 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ( 0.34λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.13λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.24λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ). The proposed antenna is constructed and tested, with the measured results in agreement with the simulated ones. The operating bandwidths cover the band of 2.40-2.48 GHz, and the gain variations below 3.5 dB are realized in the azimuthal plane for both polarizations. The proposed wedgy antenna is with both electromagnetic and aerodynamic considerations, exhibiting the potentials in supersonic onboard communication systems.

Design and assessment of octocopter drones with improved aerodynamic efficiency and performance

This paper summarizes the development of a hybrid approach that integrates textbook methods, computational fluid dynamics (CFD), and verification experiments to optimize the aerodynamic efficiency and performance of octocopter drones, which can operate in the low-speed subsonic regime. To rectify the drawbacks of conventional octocopters with monolayer and coaxial configurations, a new octocopter configuration is proposed based on a preliminary aerodynamic consideration of theoretical analysis and a summary of experience. To achieve a systematic and accurate aerodynamic analysis, model analytics are conducted with five different octocopter drone models with three different configurations, including a conventional configuration, a coaxial configuration, and a new configuration. A study is conducted with CFD simulations to investigate the effects of rotor blade size, wind and the interference between rotors on the performance and efficiency of multirotor systems. The new configuration is applied to a realistic vehicle to demonstrate its efficiency. An experiment is carried out to verify the feasibility and technical difficulties of the new configuration octocopter with a traditional proportional–integral–derivative (PID) controller. This research proposes a new configuration octocopter drone with a hybrid method that can create 41.5% more thrust than a coaxially configured octocopter drone with the same rotor blade size and 71% more thrust than a conventionally configured octocopter drone with the same fuselage arm length, where the configuration has no higher standard for the flight control system. The developed configuration can serve as a basis for more detailed, aerodynamic, and performance-enhanced studies in the future with regard to multirotor drones.

Classification of tracheal stenosis in children based on computational aerodynamics

Tracheal stenosis is a health condition in which local narrowing of the upper trachea can cause breathing difficulties and increased incidence of infection, among other symptoms. Occurring most commonly due to intubation of infants, tracheal stenosis often requires corrective surgery. It is challenging to determine the most effective surgical strategy for a given patient as current clinical methods used to assess tracheal stenosis are simplistic and subjective, and are not rigorously based on aerodynamic considerations. This paper summarizes a non-invasive approach based on computational fluid dynamics (CFD) and medical imaging to establish relationships between trachea anatomy and inspiration performance. Though patient-specific CFD analysis has gained recent popularity, an objective of this study is to computationally formulate dimensionless analytical correlations between anatomy and performance that are applicable to any member of a class of patients and that can be interpreted within the context of the Myer-Cotton stenotic airway classification system. These correlations can provide aerodynamics-based insight for the development of more robust stenosis evaluation methods and may allow for time-efficient assessment of corrective surgical strategies.

A Robust Roll Stabilization Controller with Aerodynamic Disturbance and Actuator Failure Consideration

A Robust Roll Stabilization Controller with Aerodynamic Disturbance and Actuator Failure Consideration

Anatomy and Flight Performance of the Early Enantiornithine Bird Protopteryx fengningensis: Information from New Specimens of the Early Cretaceous Huajiying Formation of China.

The Early Cretaceous (∼131 Million Years Ago) Protopteryx fengningensis is one of the oldest and most primitive enantiornithine birds; however, knowledge of its anatomy has largely been limited to the succinct description of two specimens (holotype and paratype). This study describes two new specimens of P. fengningensis preserving most of the skeleton and plumage, and it therefore adds significantly to understanding the morphology of this important species and the character evolution of enantiornithine birds. The well-preserved plumage of these specimens also affords a quantitative assessment of the flight performance of P. fengningensis. Our aerodynamic considerations indicate that this early enantiornithine was capable of intermittent flight (bounding or flap-gliding), thus marking the earliest occurrence of such energy-saving aerial strategy. Anat Rec, 303:716-731, 2020. © 2019 American Association for Anatomy.

Estimation of Potential Evapotranspiration by Different Methods in Handan Eastern Plain, China

Potential evapotranspiration estimation is the foundation of water resources assessment. Based on the daily meteorological data during 2000-2005 of Linzhang Meteorological Station in Handan Eastern Plain, temperature-based Hargreaves method, radiation-based Priestley-Taylor method, and FAO Penman-Monteith method with comprehensive consideration of aerodynamics were used to estimate potential evapotranspiration. Correlations between monthly potential evapotranspiration and water surface evaporation were conducted. The results indicated that potential evapotranspiration calculated by Hargreaves method was the largest, while the potential evapotranspiration calculated by Priestley-Taylor method was the smallest. The seasonal potential evapotranspiration values for the three methods were summer > spring > autumn > winter. The correlation between potential evapotranspiration calculated by the FAO Penman-Monteith method and water surface evaporation during the same period was best (r=0.991). In contrast, Penman-Monteith method is more suitable for estimating the potential evapotranspiration in Handan Eastern Plain.

Comparative study of elemental mercury flux measurement techniques over a Fennoscandian boreal peatland

Quantitative estimates of the land-atmosphere exchange of gaseous elemental mercury (GEM) are biased by the measurement technique employed, because no standard method or scale in space and time are agreed upon. Here we present concurrent GEM exchange measurements over a boreal peatland using a novel relaxed eddy accumulation (REA) system, a rectangular Teflon® dynamic flux chamber (DFC) and a DFC designed according to aerodynamic considerations (Aero-DFC). During four consecutive days the DFCs were placed alternately on two measurement plots in every cardinal direction around the REA sampling mast. Spatial heterogeneity in peat surface characteristics (0–34 cm) was identified by measuring total mercury in eight peat cores (57 ± 8 ng g−1, average ± SE), vascular plant coverage (32–52%), water table level (4.5–14.1 cm) and dissolved gaseous elemental mercury concentrations (28–51 pg L−1) in the peat water. The GEM fluxes measured by the DFCs showed a distinct diel pattern, but no spatial difference in the average fluxes was detected (ANOVA, α = 0.05). Even though the correlation between the Teflon® DFC and Aero-DFC was significant (r = 0.76, p < 0.05) the cumulative flux of the Aero-DFC was a factor of three larger. The average flux of the Aero-DFC (1.9 ng m−2 h−1) and REA (2 ng m−2 h−1) were in good agreement. The results indicate that the novel REA design is in agreement for cumulative flux estimates with the Aero-DFC, which incorporates the effect of atmospheric turbulence. The comparison was performed over a fetch with spatially rather homogenous GEM flux dynamics under fairly consistent weather conditions, minimizing the effect of weather influence on the data from the three measurement systems. However, in complex biomes with heterogeneous surface characteristics where there can be large spatial variability in GEM gas exchange, the small footprint of chambers (<0.2 m2) makes for large coefficients of variation. Thus many chamber measurement replications are needed to establish a credible biome GEM flux estimate, even for a single point in time. Dynamic flux chambers will, however, be able to resolve systematic differences between small scale features, such as experimentally manipulated plots or small scale spatial heterogeneity.

Aero-structural optimization of shape memory alloy-based wing morphing via a class/shape transformation approach

Because of the continuous variability of the ambient environment, all aircraft would benefit from an in situ optimized wing. This paper proposes a method for preliminary design of feasible morphing wing configurations that provide benefits under disparate flight conditions but are also each structurally attainable via localized active shape change operations. The controlled reconfiguration is accomplished in a novel manner through the use of shape memory alloy embedded skin components. To address this coupled optimization problem, multiple sub-optimizations are required. In this work, the optimized cruise and landing airfoil configurations are determined in addition to the shape memory alloy actuator configuration required to morph between the two. Thus, three chained optimization problems are addressed via a common genetic algorithm. Each analysis-driven optimization considers the effects of both the deformable structure and the aerodynamic loading experienced by the wing. Aerodynamic considerations are addressed via a two-dimensional panel method and each airfoil shape is generated by the so-called class/shape transformation methodology. It is shown that structurally and aerodynamically feasible morphing of a modern high-performance sailplane wing produces a 22% decrease in weight and significantly increases stall angle of attack and lift at the same landing velocity when compared to a baseline design that employs traditional control surfaces.

Hydro-aerodynamic mathematical model and multi-objective optimization of wing-in-ground effect craft in take-off

Hydro-aerodynamic mathematical model and multi-objective optimization of a popular wing-in-ground effect craft are presented in this research using a hydro-aerodynamic practical method and the genetic algorithm. The primary components of the wing-in-ground effect craft configuration include a compound wing, catamaran hull form and a power-augmented ram platform. The hydro-aerodynamic practical method with low computational time and high accuracy is performed by coupling hydrodynamic and aerodynamic considerations using the potential flow theory in ground effect and the semi-empirical equations proposed for high-speed marine vehicles. The trade-off between hydrodynamic and aerodynamic characteristics makes it difficult to simultaneously satisfy the design requirements of high hydro-aerodynamic performance. In this article, three goals—reduced hump resistance, increased compound wing lift-to-drag ratio and reduced take-off speed—are selected as the objective functions. The longitudinal position of center of gravity, position of outer wing with respect to main wing, power augmented ram platform angle to horizontal and flap angle are also adopted as design variables. Static height stability and the location of the center of gravity with respect to the aerodynamics centers are considered as constraints for the stable flight in ground effect. The optimal solutions of the multi-objective optimization were not unique, rather a set of non-dominated optima, called the Pareto sets, are obtained. As a result of the multi-objective optimization, 25 Pareto individuals are obtained that the naval architects can use in designing wing-in-ground crafts.

Aeroacoustic consequences of tongue troughs in labiodentals

It has long been accepted that the main constriction for fricatives /f, v/ is formed by the lower lip pressing against the upper teeth, thus allowing the tongue to freely coarticulate with preceding and following segments. Here, electromagnetic articulometry data were obtained from 5 subjects in a study of tongue troughs, defined as a discontinuity in anticipatory coarticulation, such as when the tongue drops during a bilabial consonant in /ii/ context. The corpus included /f/ and /v/ in VC(C)V contexts, where V = /i/ for C= /v/, and V = {/i a u/} for C= /f/. The tongue moved down and back for /f/ in all vowel contexts; in /iC(C)i/ context, the troughs were deeper for long (VCCV) than short labial consonants, as predicted, and deeper for /f/ than for /p, b, v, m/, which was unexpected. There seems to be a secondary gesture specifying that the tongue be down during labiodental fricatives. Our hypothesis is that lowering the tongue for /f/ ensures that the airflow resistance will be due only to the labiodental constriction, thus providing an aeroacoustic advantage for the onset of turbulence. This is supported by comparison of asymmetric vowel contexts (e.g., /uffi/-/iffu/ tokens); tongue dorsum and blade sensors show the tongue moving quickly away from /i/ to /f/ position, in contrast to movement from /u/ to /f/. Aerodynamic considerations thus appear to be actively incorporated into the speech motor plan. [Work supported by NIH grant DC-002717.]