Headwind Conditions Research Articles

Numerical study on aerodynamic performance of an intake duct affected by ground effect

Abstract This paper numerically studied the aerodynamic performance of an intake duct affected by the ground effect on a mobile test bench. The simulations were conducted under no wind and headwind conditions. The time evolution of the ground effect indicates that the coherent structure of the vortex system is mainly composed of the ground vortex, the horse-shoe vortex, and the creeping vortex under no wind condition. And it is mainly composed of the ground vortex, the trailing vortex, and the creeping vortex under headwind condition. Compared to the results under no wind condition, the integral vorticity of the ground vortex is larger than that under the headwind condition. The difference of the total pressure recovery coefficient is small, and the total pressure distortion index is large. The results show that with the decrease of the velocity at the intake duct outlet, the intensity of the ground vortex decreases, and the total pressure recovery coefficient at the intake duct outlet increases.

Departure, routing and landing decisions of long-distance migratory songbirds in relation to weather.

Migrating birds flexibly adjust their individual migratory decisions, i.e. departing, routing and landing, based on intrinsic (e.g. energy stores) and extrinsic (e.g. landscape features and weather) factors modulating the endogenous stimuli. So far, these decisions have mostly been studied separately. Notably, we lack information on which factors landing decisions during active flight are based on. Therefore, we simultaneously recorded all three decisions in free-flying long-distance migratory songbirds in a coastal stopover area via regional-scale radio-telemetry and related them to the prevailing weather. Birds departed under favourable weather conditions resulting in specific nights with increased departure probability. Once departed, birds could either fly offshore or take a route along the coast, which was predicted by wind support. Radio-tracking revealed that departed individuals more likely interrupted their migratory endurance flight under overcast or headwind conditions. Studying departure, routing and landing decisions in concert, we highlight the importance of weather as a common driver across all migratory decisions. By radio-tracking individuals between stopovers, we provide evidence that avoidance of adverse weather conditions is an important function of stopover. Understanding how birds adjust migratory decisions and how they affect the timing of migration and survival is key to link migration performance to individual fitness.

Black-tailed gulls alter their flight height and airspeed according to wind conditions during their coastal commuting trips

Seabirds are expected to increase their flight height in tailwind and to increase their airspeed in headwind during goal-oriented flight to minimize their cost of transport. To understand how flapping birds respond to variability in wind speed and direction experienced during their commuting flights between their breeding colony and foraging areas, we measured the flight height and speed of black-tailed gullsLarus crassirostrisusing GPS loggers. We analyzed the relationships between these flight parameters and local wind speed and direction. Over the course of the 2016 to 2018 breeding seasons, we tagged 105 birds at 2 colonies in northern Hokkaido, Japan. A total of 90 flight track-lines within a 500 m radius of 5 coastal meteorological stations were analyzed. The median flight height ranged from 0 to 153.8 m, and the median ground speed and airspeed were between 18.6-82.1 and 19.5-93.0 km h-1, respectively. Gulls flew higher with greater tailwind speed, supporting the hypothesis that birds utilize greater wind assistance at higher altitudes. Furthermore, gulls increased their airspeed under strong headwind conditions, suggesting they adjust airspeed to achieve the most cost-effective speed to reach their destination. Better understanding the drivers of seabird flight height is key to assessing the potential for collisions with wind turbines in coastal and offshore wind farms. These findings provide useful information to reduce collisions with coastal and offshore wind facilities.

Do Seabirds Control Wind Drift during Their Migration across the Strait of Gibraltar? A Study Using Remote Tracking by Radar

This study presents data on the directional flying behaviour of the five most abundant seabird species migrating across the Strait of Gibraltar in relation to the wind, as observed from the north coast, based on radar tracking, and identified to species level by visual observations. A total of 318 seabird trajectories were analysed, illustrating the expected east–west or west–east movements in spring and autumn. We hypothesised that the seabirds that cross the Strait channel during their migrations would behave differently with respect to compensation for wind direction, depending on their flight styles, the migratory period, and the prevailing winds. In this regard, our results showed that flapping birds (Razorbill, Puffin, Northern Gannet, and Balearic shearwater) compensated for wind drift independently of the season and the predominant wind direction. This agrees with the theory that suggests that under moderate winds and whenever visual contact with the coastline is present (as in the case of our study), migrants should compensate for wind drift to avoid being drifted towards the coast, off their main direction of flight. However, Cory’s shearwater, an active gliding seabird with long, slender wings, showed an adaptive directional response to wind, allowing it to be drifted in spring when westerly tailwinds were prevalent, but compensated for wind in autumn, when both easterly and westerly winds were similarly frequent. This adaptive flight behaviour allows it to take advantage of the prevailing tailwinds in spring, gaining ground speed and saving energy during its passage through the Strait, while in autumn, more frequent headwind conditions and a more directional migration to the south may favour compensating for wind drift. Our results support the usefulness of bird radar as a remote tool for describing the pattern of animal movements in the marine environment, as well as their behavioural response to atmospheric conditions. These studies are particularly relevant in the current framework of climate change.

Investigation on effects of time-frequency characteristics of ship airwake on helicopter flight characteristics

A conventional helicopter flight dynamics model, which can be coupled with ship airwake date, is developed in this study. In the method, the ship airwake data is obtained by the high-accuracy DES model, and a strategy which can transmit CFD data to the flight dynamics model is established based on the "one-way" coupling idea. Then, the SFS2 ship model and UH-60A helicopter are chosen as a combination to investigate the influences of the spatial and temporal characteristics of ship airwake from the aspects of control margins and unsteady level. The time-averaged simulation results show that for the counterclockwise-rotor helicopter, although pilot could have more collective pitch margin under crosswind condition compared to the headwind condition, he might possess much less pedal margin due to the sidewash in the airflow. The unsteady results indicate that the unsteady loading level of the helicopter would increase significantly under the crosswind condition compared to the headwind condition due to the increase of turbulent density in the airwake. Furthermore, for the conventional helicopter, the disturbances on the forces and moments which along the rotor hub (i.e., thrust and yaw moment) are the critical factors that increasing the pilot workload during the landing procedure.

Calculation and Analysis of Aircraft Pollutant Emission Based on Time Wake Separation Mode under Coastal Airport and Headwind Conditions

During the final approach, the headwind leads to a reduction of landing rate, which affects the achieved capacity and the predictability of operation, time, fuel efficiency, and environmental pollution. Under headwind conditions, ground speed decrease results in increased flight time. Time-based separation (TBS) changes the separation rule of the final approach, which changes the distance separation between two aircrafts into a time separation. This paper introduces the time-based separation (TBS) based on the distance-based separation (DBS). According to the aircraft landing schedule of each airport, the ICAO (International Civil Aviation Organization) aircraft engine emission database, Boeing Fuel Flow Method 2 (BFFM2), and meteorological data of Pu-dong airport, this study uses the modified P3-T3 aviation pollutant emission model to calculate, respectively, the fuel consumption and pollutant emissions based on distance separation mode and time separation mode. According to the calculation results, TBS operation mode can save 32.52%, 19.12%, and 30.41% fuel, reduce 28.93%, 17.9%, and 29.29% CO, 31.02%, 19.36%, and 33.78% HC, 30.85%, 16.42%, and 28.67% NOx, respectively, compared with the DBS operation mode at three stages of the day. It ends that TBS has an obvious optimization effect on fuel consumption and pollutant emission compared with DBS from data.

Experimental and numerical simulations of simple frigate with suction flow control over the deck

The air wake generated behind a frigate superstructure is a very complex and unsteady three-dimensional flow characterized by highly turbulent flow structures with great velocity gradients that result in flow separation over the flight deck where helicopter operations take a significant role. Naturally, this turbulent flow should be removed or, at least, reduced as maximum as possible to avoid accidents during the interaction between frigates and helicopters. This paper involves experimental and numerical analysis on a simple frigate model (SFS2) to understand and simulate the adverse effect of the turbulent flow of the air wake over the deck and tries to minimize it as with active flow control. The experimental study has been performed in the Low Speed Wind Tunnel nº1 of Instituto Nacional de Técnica Aeroespacial ‘‘Esteban Terradas'’ (INTA) with Particle Image Velocimetry (PIV) to obtain the velocity field over the flight deck. The frigate has been tested for the headwind condition of 0° (wind aligned with the flight deck) with a velocity of 10 m/s. The active flow control consists on generating suction on the flight deck by a mesh of holes. Several configurations of this suction mesh have been studied according to the diameter and location of holes and suction intensity. The suction mesh configuration with the highest diameter and flow rate presents the greatest aerodynamic improvement. The low-speed area over the deck is reduced from 36% to a minimum of 3%.

Migrating curlews on schedule: departure and arrival patterns of a long-distance migrant depend on time and breeding location rather than on wind conditions

BackgroundDeparture decisions in long-distance migratory bird species may depend on favourable weather conditions and beneficial resources at the destination location, overarched by genetic triggers. However, few studies have tried to validate the significance of these three concepts simultaneously, and long-term, high-resolution tagging datasets recording individual movements across consecutive years are scarce. We used such a dataset to explore intraspecific and intra-individual variabilities in departure and arrival decisions from/to wintering grounds in relation to these three different concepts in bird migration.MethodsWe equipped 23 curlews (Numenius arquata) wintering in the Wadden Sea with Global Positioning System data loggers to record their spatio-temporal patterns of departure from and arrival at their wintering site, and the first part of their spring migration. We obtained data for 42 migrations over 6 years, with 12 individuals performing repeat migrations in consecutive years. Day of year of departure and arrival was related to 38 meteorological and bird-related predictors using the least absolute shrinkage and selection operator (LASSO) to identify drivers of departure and arrival decisions.ResultsCurlews migrated almost exclusively to Arctic and sub-Arctic Russia for breeding. They left their wintering site mainly during the evening from mid- to late April and returned between the end of June and mid-July. There was no difference in departure times between the sexes. Weather parameters did not impact departure decisions; if departure days coincided with headwind conditions, the birds accounted for this by flying at higher altitudes of up to several kilometres. Curlews breeding further away in areas with late snowmelt departed later. Departures dates varied by only < 4 days in individual curlews tagged over consecutive years.ConclusionsThese results suggest that the trigger for migration in this long-distance migrant is largely independent of weather conditions but is subject to resource availability in breeding areas. The high intra-individual repeatability of departure days among subsequent years and the lack of relationship to weather parameters suggest the importance of genetic triggers in prompting the start of migration. Further insights into the timing of migration in immatures and closely related birds might help to further unravel the genetic mechanisms triggering migration patterns.

Breathing resistance in heat and moisture exchanging devices

The purpose of this study was to investigate the resistance to breathing (RES) in heat and moisture exchanging devices (HME) intended for use during physical activity in the cold. RES was investigated for seventeen HMEs, including different types of filters. In addition, the influence of headwind on RES was tested using four representative HMEs. HMEs were mounted to the face of an artificial head manufactured from ABS plastic. The HMEs were connected to a mechanical lung simulator, which delivered standardised inspiratory and expiratory air flow rates ([Formula: see text], L/s). The delta pressure (Δ p, Pa) between ambient air and the air inside the HME was measured, whereupon RES was calculated. The results showed significant ( p &lt; 0.05) differences in RES between HMEs from different manufacturers, while the difference was smaller, and in some cases not significant ( p &gt; 0.05), between different models/filters within the same brand. The results also showed that RES was highly influenced by different ventilations and headwind conditions. RES increased with increased [Formula: see text] and, when a headwind was introduced, RES decreased during inspiration and increased during expiration. Calculations showed that the oxygen and energy cost for breathing through an HME was very small for most of the tested models. The effect of HME dead space on pulmonary gas fractions depends on the tidal volume. At large tidal volumes and ventilations, the effect of HMEs on pulmonary gas fractions becomes relatively small.

Numerical investigation on the ship/multi-helicopter dynamic interface

The issue of single helicopter shipboard landing has been widely studied. This paper focuses on the helicopters/ship dynamic interaction for simultaneous landing of two helicopters. A numerical method combining the Detached Eddy Simulation, momentum source model and flight mechanics model via a one-way coupling strategy is developed. With this method, the coupling ship/helicopter flow-field and its effect on unsteady loading and handling behaviors of downwind shipborne helicopter at different conditions are investigated. The results show that in the headwind condition, the super vortex, formed by the upwind rotor wake merging into the deck-edge and superstructure vortex, is a principal factor affecting the downwind helicopter landing operation. Influenced by super vortex, high level of turbulence intensity is evident in the coupling ship airwake, giving rise to a sharp increase in unsteady loading levels and perturbations in control inputs and attitudes, compared with the baseline case (without upwind rotor), and pedal control margin is reduced accordingly. While increasing the translation height can effectively weaken the effect of super vortex, thereby reducing unsteady loading levels and alleviating control margin limits. When wind-over-deck (WOD) angle increases, despite no super vortex formed, the inclined upwind rotor wake interacting with the shear layer in ship airwake results in a higher level of turbulence intensity in the area over the deck. Perturbations in unsteady loading levels, controls and attitudes are more pronounced and complicated than the headwind case, causing great pilot workload.

Develop of a fuel consumption model for hybrid vehicles

Despite extensive work on the fuel consumption of vehicles, the evaluation of hybrid electric vehicles (HEVs) requires a model that can predict fuel consumption second by second. In this paper, a fuel consumption model for hybrid vehicles is developed based on the operation of internal combustion engine (ICE), electric machine (EM) and battery. The fuel consumption model for engine is based on steady-state fuel mapping with a transient correction. EM and battery module (EBM) is introduced to estimate the fuel consumption for different modes of hybrid vehicle. The Argonne National Laboratory (ANL) measurements of different driving cycles including the steady-state cycle, the Urban Dynamometer Driving Schedule (UDDS) cycle, the Highway cycle and the United States 06 (US06) cycle are used to verified the model. With cellular automaton simulation, we study the fuel consumption in traffic flow and show that the fuel consumption can be significantly reduced by hybrid mode. The mean fuel saving is approximately 30% in the traffic flow on a horizontal road. The fuel consumption of traffic flow under uphill, downhill, tailwind and headwind conditions also showes considerable fuel saving. The model can be used to evaluate the fuel economy of HEVs, and provide eco-driving route-choice suggestions for drivers.

Aerodynamic Forces Acting on Ahmed-Type Vehicles under Fluctuating Headwind Conditions

Aerodynamic Forces Acting on Ahmed-Type Vehicles under Fluctuating Headwind Conditions

Optimization of the flight technique in ski jumping: The influence of wind

Ski jumping performance is strongly affected by wind. Flight technique optimization for maximizing jump length is a highly complex motor-control task that also depends on the wind. Pontryagin's minimum principle was used in this study to gain a better understanding on how wind influences flight technique optimization. Optimum time courses of the angle of attack α of the skis and of the body-to-ski angle β were computed for seven realistic wind scenarios on the large hill and on the flying hill. The optimum values of α were smaller at headwind, and larger at tailwind when compared to the optimum time course at calm wind. The optimum values of β were the smallest possible ones at the given flight technique constraints, except for the last part of the flight. Optimum adjustments of α increased the jump lengths between 0 and 1.8 m on the large hill, and between 0 and 6.4 m on the flying hill. Maximum jump length increases were achieved at the highest headwind speed. Even larger jump length effects can be achieved by using smaller β-angles, which might be possible in headwind conditions, but this is associated with increased problems to keep the flight stable.

Entropy-based detached-eddy simulation of the airwake over a simple frigate shape

The wind past the ship superstructure produces an unsteady turbulent airwake which has a significant effect on aircraft performance and consequently pilot workload during ship landing process. Computational fluid dynamics simulations of a generic simple frigate shape ship airwake have been performed using the entropy-based detached-eddy simulation method. The results were compared with the steady-state Reynolds-averaged Navier–Stokes calculations and the wind tunnel data, indicating the capability of entropy-based detached-eddy simulation to resolve the unsteady large-scale turbulent features. An analysis of the airwake flow topology at headwind condition highlights the vortex pairing process which dominates the flowfield above the deck. Additionally, the influence of hangar-door state (open, closed or half-open) on the airwake was also investigated in detail. Determination of this complex flow can assist in the definition of safe ship–helicopter operating limits and future ship design.

Inlet ground vortex aerodynamics under headwind conditions

Quantitative velocity flow field measurements of the vortex system for a small scale model intake have been taken using a three component PIV system along with fan face total pressure distortion measurements. The effect of velocity ratio, non-dimensional height and approaching boundary layer thickness have been assessed under quiescent and headwind conditions. A range of inlet vortex flow modes are identified which depend on the intake velocity ratio and are characterised by the primary vorticity source. As the headwind velocity increases, and the velocity ratio reduces, the vortex strength initially increases until a local maximum is reached. Further reductions in the velocity ratio leads to a strong reduction in the vortex strength until a ‘blow-away’ condition is achieved at which the vortex no longer forms. A clear link is established between the external vortical flow-field and the intake internal flow-field. Consequently, these characteristics are also observed for the total pressure distortion coefficient within the intake. As the ground clearance is increased the peak vortex strength reduces and the corresponding velocity ratio increases. At intermediate velocity ratios, the vortex strength is greater at higher ground clearances. At the selected external vortex measurement plane, the vortex strength is generally insensitive to the approaching boundary layer thickness. The intake total pressure distortion increases with boundary layer thickness due to increased total pressure loss for a given ingested mass-flow. The vortex strength and distortion distributions are shown to be self-similar when non-dimensionalised by the peak values and associated velocity ratio. This dataset establishes a quantitative map for headwind ground vortices which presents a new formation criterion as well as a measure of the vortex strength as a function of ground clearance and intake velocity ratio.

Computational and experimental study of intake ground vortices

AbstractThe ground vortices generated by an intake under both headwind and crosswind configurations have been investigated using computational and experimental approaches. The flow field of a scale-model intake was experimentally studied using stereoscopic particle image velocimetry to measure the ground vortex in conjunction with induct total pressure measurements for the internal flow. The computational predictions were performed using an unsteady Reynolds averaged Navier-Stokes approach. The experimental results show that under crosswind conditions a single ground vortex forms which becomes stronger as the crossflow velocity is increased. Under headwind conditions the measured ground vortex strength initially increases with freestream velocity before it reaches a local maximum and then reduces thereafter. The computations also exhibit the same characteristics and show good agreement with the measurements for some configurations. Based on the predictions, the complex flow field topology is investigated and a detailed flow model of the vortex flow field under crosswind conditions is proposed.

Experimental Investigation of Intake Ground Vortices During Takeoff

A quantitative experimental investigation has been conducted to simulate intake ground vortex formation during aircraft takeoff under headwind conditions. The experiments were performed using a small-scale intake model in conjunction with a rolling ground plane in a low-speed wind tunnel. The Reynolds number was fixed at 1.26 x 10 6 based on the inner diameter and average intake velocity. Stereoscopic particle image velocimetry was used to measure the ground vortex velocity field, and in-duct total pressure measurements have been performed to assess the internal flow. Measurements were taken for an extensive range of configurations, including a static and simulated moving intake under a variety of headwind conditions. A moving intake was simulated in the wind tunnel by synchronizing the ground and tunnel wind velocities and using extensive suction to remove the approaching boundary layer. The results show that at high velocity ratios there are no substantial differences due to the moving ground plane. At low velocity ratios, the simulated moving intake results in a significantly different flowfield in which the ground vortex is weaker, steadier in space, and more symmetric relative to the static ground case. These results indicate the relative importance of the ground vortex vorticity sources and highlight the importance of including the effects of a moving ground when simulating an aircraft takeoff.

Modelling of efficiency of aerodynamic devices on a tractor-trailer

While trucking accounts for 60% of freight energy use in the US, aerodynamic drag is responsible for 65% of the total energy expenditure for a heavy truck at 70 miles per hour. Reducing the aerodynamic resistance of a heavy truck can significantly improve its fuel economy. While multiple aerodynamic devices have been proposed for heavy trucks, they do not always promote the most efficient operation, as they may hinder manoeuvring and docking. This limited acceptance by the industry can be summarised as a contradiction: aerodynamic devices are useful at cruising speed, but during docking or manoeuvring, they may be an obstacle to efficient operations. This contradiction can be resolved if the devices are only deployed or interact with the incoming flow at high speed. Examples are dynamic (foldable) side fairings and vortex generators (VGs). Computational fluid dynamics (CFD) modelling of the VGs under head and side wind conditions has shown that they are more efficient for side winds than for head winds.

Optic flow based autopilot: From insects to rotorcraft and back

When insects are flying forwards, the image of the ground sweeps backwards across their ventral viewfield, forming an flow, which depends on both the groundspeed and the height of flight. To explain how these animals manage to avoid the ground using this image motion cue, we suggest that insect navigation hinges on a visual feedback loop we have called the optic flow regulator, which controls the vertical lift. To test this idea, we built a micro-helicopter equipped with a fly-inspired optic flow sensor and an optic flow regulator. We showed that this fly-by-sight microrobot can perform exacting tasks such as takeoff , level flight and landing. Our control scheme accounts for many hitherto unexplained findings published during the last 70 years on insects' visually guided performances, including the facts that honeybees descend under headwind conditions, land with a constant slope and drown when travelling over mirror-smooth water. Our control scheme explains how insects manage to fly safely without any of the instruments used onboard aircraft to measure the height of flight, the airspeed, the groundspeed, and the descent speed. An optic flow regulator could be easily implemented neurally. It is just as appropriate for insects (1) as it would be for aircraft (2,3).

The effects of temperature, humidity, and barometric pressure on short-sprint race times

A numerical model of 100 m and 200 m world class sprinting performances is modified using standard hydrodynamic principles to include effects of air temperature, pressure, and humidity levels on aerodynamic drag. The magnitude of the effects are found to be dependent on wind speed. This implies that differing atmospheric conditions can yield slightly different corrections for the same wind-gauge reading. In the absence of wind, temperature is found to induce the largest variation in times (0.01 s per 10°C increment in the 100 m), while relative humidity contributes the least (under 0.01 s for all realistic conditions for 100 m). Barometric pressure variations at a particular venue can also introduce fluctuations in performance times on the order of a 0.01 s for this race. The combination of all three variables is essentially additive, and is more important for head-wind conditions that for tail-winds. As expected, calculated corrections in the 200 m are magnified due to the longer duration of the race. The overall effects of these factors on sprint times can be considered a ``second order'' adjustment to previous methods that rely strictly on a venue's physical elevation, but can become important in extreme conditions.PACS Nos.: 01.80, 02.60L