Experimental Study of Aerodynamics and Wingtip Vortex of a Rectangular Wing in Flat Ground Effect

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
A. Lu ◽  
V. Tremblay-Dionne ◽  
T. Lee
Keyword(s):  
Vortex Flow ◽  
Ground Surface ◽  
Ground Effect ◽  
Inviscid Flow ◽  
Tip Vortex ◽  
Vortex Strength ◽  
Induced Drag ◽  
Wingtip Vortex ◽  
Ground Distance ◽  
The Impact

The ground effect on the aerodynamics and tip vortex flow of a rectangular wing is investigated experimentally at Re = 2.71 × 105. The results show that there is a large lift increase with reducing ground distance. By contrast, only a small drag increase is observed in ground effect except in close ground proximity for which a great drag increase appears. The tip vortex also moves further outboard and upward with reducing ground distance. Near the ground, there is the presence of a corotating ground vortex (produced by the rolling up of the boundary layer developed on the ground surface), leading to an increased vortex strength. In extreme ground proximity, a counterrotating secondary vortex (SV) (induced by the crossflow of the tip vortex), relative to the tip vortex, appears which causes a reduced vortex strength and a lowered lift-induced drag, as well as a vortex rebound. The impact of ground effect on the vortex flow properties is also discussed. The lift-induced drag, computed based on the crossflow measurements via the Maskell wake integral method, in ground effect is also compared against the inviscid-flow predictions and wind tunnel total drag force measurements.

Effect of Ground Boundary Condition on Near-Field Wingtip Vortex Flow and Lift-Induced Drag

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
A. Lu ◽  
T. Lee
Keyword(s):  
Boundary Condition ◽  
Near Field ◽  
Ground Effect ◽  
Tip Vortex ◽  
Secondary Vortex ◽  
Significant Discrepancy ◽  
Vortex Strength ◽  
Induced Drag ◽  
Wingtip Vortex ◽  
Ground Distance

Abstract The ground proximity is known to induce an outboard movement and suppression of the wingtip vortices, leading to a reduced lift-induced drag. Depending on the ground boundary condition, a large scatter exists in the published lift-induced drag and vortex trajectory. In this experiment, the ground boundary condition-produced disparity in the vortex strength and induced drag were evaluated. No significant discrepancy appeared for a ground distance or clearance larger than 30% chord. As the stationary ground was further approached, there was the appearance of a corotating ground vortex (GV), originated from the downstream progression of a spanwise ground vortex filament, which added vorticity to the tip vortex, leading to a stronger tip vortex and a larger lift-induced drag compared to the moving ground. For the moving ground, the ground vortex was absent. In close ground proximity, the rollup of the high-pressure fluid flow escaped from the wing's tip always caused the formation of a counter-rotating secondary vortex, which dramatically weakened the tip vortex strength and produced a large induced-drag reduction. The moving ground effect, however, induced a stronger secondary vortex, leading to a smaller lift-induced drag and a larger outboard movement of the tip vortex as compared to the stationary ground effect.

Passive Wingtip Vortex Control by Using Tip-Mounted Half Delta Wings in Ground Effect

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Anan Lu ◽  
Tim Lee
Keyword(s):  
Vortex Flow ◽  
Ground Effect ◽  
Tip Vortex ◽  
Secondary Vortex ◽  
Flow Properties ◽  
Delta Wings ◽  
Vortex Control ◽  
Physical Mechanisms ◽  
Induced Drag ◽  
Wingtip Vortex

Abstract The ground effect on the wingtip vortex generated by a rectangular semiwing equipped with tip-mounted regular and reverse half delta wings was investigated experimentally. The passive tip vortex control always led to a reduced lift-induced drag as the ground was approached. In close ground proximity, the presence of the corotating ground vortex (GV) added vorticity to the tip vortex while the counter-rotating secondary vortex (SV) negated its vorticity level. The interaction of the GV and SV with the tip vortex and their impact on the lift-induced drag were discussed. Physical mechanisms responsible for the change in the vortex flow properties in ground effect were also provided.

Experimental Investigation of the Aerodynamics and Flowfield of a NACA 0015 Airfoil Over a Wavy Ground

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
T. Lee ◽  
V. Tremblay-Dionne
Keyword(s):  
Lift Coefficient ◽  
Ground Effect ◽  
Lower Surface ◽  
Moment Coefficient ◽  
Aerodynamic Properties ◽  
Image Velocimetry ◽  
Ground Distance ◽  
Almost All ◽  
Naca 0015 ◽  
The Impact

The aerodynamic properties and flowfield of a NACA 0015 airfoil over a wavy ground were investigated experimentally via surface pressure and particle image velocimetry (PIV) measurements. Flat-surface results were also obtained to be served as a comparison. For the wavy ground, there exhibited a cyclic variation in the sectional lift coefficient Cl over an entire wavelength. The maximum Cl observed at the wave peak (produced by the wavy ground-induced RAM pressure) and minimum Cl occurred at the wave valley (resulting from the unusual suction pressure developed on the airfoil's lower surface due to the converging-diverging flow passage developed underneath it) reduced with increasing ground distance. By contrast, the pitching-moment coefficient showed an opposite trend to the variation in Cl and had an almost all-negative value. Meanwhile, two peak values in the drag coefficient over each wavelength were observed. The wavy ground effect-produced gains in the mean Cl and lift-to-drag ratio were at the expense of longitudinal stability. Additional measurements considering different wavelengths and amplitudes are needed to further quantify the impact of wavy ground on wing-in-ground effect (WIG) airfoils and wings.

Generation Mechanism and Reduction Method of Induced Drag Produced by Interacting Wingtip Vortex System

2017 ◽  
Vol 34 (2) ◽  
pp. 231-241
Author(s):  
M. Zhang ◽  
Y. K. Wang ◽  
S. Fu
Keyword(s):  
Reduction Method ◽  
Tip Vortex ◽  
Detached Eddy Simulation ◽  
Vortex System ◽  
Eddy Simulation ◽  
Induced Drag ◽  
Delayed Detached Eddy Simulation ◽  
Resistance Reduction ◽  
Wingtip Vortex ◽  
Formation And Evolution

AbstractThe formation and evolution of wingtip vortex system generated from three wing configurations are simulated with the improved delayed detached eddy simulation (IDDES) method. Numerical results show that each layout produces an interacting wingtip vortex system. These three corresponding vortical interactions are, respectively, the interaction between wingtip vortex and its counter-rotating vortex, winglet-tip vortex, and winglet four-vortex system. The fluid entrainment of ambient fluid and vortical impulse transport resulted from inductive effect have been founded generally existing in its formation and evolution. These two dominated mechanisms account for induced drag generation. On one hand, the winglet with toed-out angle is considered capable of changing the flow field around the winglet, and decomposing the winglet-tip vortex into four small vortices. Due to quite few fluid entrainment effects, this typical four-vortex system that cannot merge and only dissipate in the near wake scarcely contributes to the induced drag. On the other hand, a potential drag reduction method is also indicated that a lower induced drag can be obtained when the merger of wingtip and winglet-tip vortex is controlled and eliminated. This investigation will offer a novel perspective to guide the design of wingtip device and method of crusing resistance reduction for aircrafts.

scholarly journals Aerodynamic Interaction Studies on Amphibious Vehicle in Forward and Hovering Flight

2019 ◽  
Vol 16 (4) ◽  
pp. 7391-7412 ◽  
Author(s):  
P. Vikram ◽  
E. Balasubramanian ◽  
M. Manova ◽  
G. Surendar
Keyword(s):  
Fluid Dynamic ◽  
Vortex Formation ◽  
Flow Analysis ◽  
Ground Surface ◽  
Ground Effect ◽  
Tip Vortex ◽  
Superior Performance ◽  
Cfd Analysis ◽  
Aerodynamic Interaction ◽  
And Performance

Unmanned aerial vehicles (UAVs) have gained a lot of attention in recent times due to its versatility in deployment for multifaceted operations. The development of amphibious UAVs with inculcating the features of hovercraft and multi-rotor has tremendous impact on military, naval and coastal guard applications. Stability and performance of this kind of vehicle highly depend on aerodynamic interaction of multirotor with respect to various wind conditions. The present study focuses on performing computational fluid dynamic (CFD) analysis on examining the vortex formation, turbulent regimes, wake region, tip vortex formulation and ground effect.Preliminary flow analysis is performed to determine the angle of attack (AoA) and wind speed on which minimal drag is experienced by the amphibious structure. Further, analysis conducted through varying the relative velocity of the vehicle and changing the speed of the propellers. The pressure distribution across the fuselage and rotor surface predicted the stability of the vehicle. The ground effect is examined through varying the clearance between the vehicle and ground surface with respect to a multiplicity of rotor diameter. CFD analysis results suggested that at 5° AoA and 8.3 m/sec the designed amphibious vehicle yielded superior performance characteristics and stability. 

scholarly journals Induced Drag Savings From Ground Effect and Formation Flight in Brown Pelicans

1988 ◽  
Vol 135 (1) ◽  
pp. 431-444 ◽  
Author(s):  
F. REED HAINSWORTH
Keyword(s):  
Ground Effect ◽  
Formation Flight ◽  
Tip Vortex ◽  
Wing Beat ◽  
Vertical Variation ◽  
Induced Drag ◽  
Brown Pelicans ◽  
Vertical Displacements ◽  
Wing Tips ◽  
Wing Tip

Ciné films of brown pelicans flying in formation were used to measure altitudes and wing tip spacing (WTS, distance perpendicular to the flight path between wing tips of adjacent birds at maximum span) for birds flying in ground effect, and vertical displacements and WTS for birds flying out of ground effect. Views were near coplanar with the plane of flight paths, and maximum wing span was used for scale. Induced drag savings in ground effect averaged 49% for gliding. Average WTS varied considerably with no evidence for systematic positioning near an optimum. There were also no differences in average WTS between flapping and gliding in or out of ground effect. Vertical displacements out of ground effect varied less than WTS but more than vertical displacements in ground effect. Few birds had wing beat frequencies similar to the bird ahead as would be needed to track vertical variation in trailing wing tip vortex positions. Imprecision in WTS may be due to unpredictable flow fields in ground effect, and difficulty in maintaining position under windy conditions out of ground effect.

scholarly journals The Effect of LiDAR Sampling Density on DTM Accuracy for Areas with Heavy Forest Cover

Forests ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 265
Author(s):  
Mihnea Cățeanu ◽  
Arcadie Ciubotaru
Keyword(s):  
Forest Cover ◽  
Initial Point ◽  
Ground Surface ◽  
Digital Terrain Model ◽  
Morphological Data ◽  
Sampling Density ◽  
Terrain Model ◽  
Digital Terrain ◽  
Point Density ◽  
The Impact

Laser scanning via LiDAR is a powerful technique for collecting data necessary for Digital Terrain Model (DTM) generation, even in densely forested areas. LiDAR observations located at the ground level can be separated from the initial point cloud and used as input for the generation of a Digital Terrain Model (DTM) via interpolation. This paper proposes a quantitative analysis of the accuracy of DTMs (and derived slope maps) obtained from LiDAR data and is focused on conditions common to most forestry activities (rough, steep terrain with forest cover). Three interpolation algorithms were tested: Inverse Distance Weighted (IDW), Natural Neighbour (NN) and Thin-Plate Spline (TPS). Research was mainly focused on the issue of point data density. To analyze its impact on the quality of ground surface modelling, the density of the filtered data set was artificially lowered (from 0.89 to 0.09 points/m2) by randomly removing point observations in 10% increments. This provides a comprehensive method of evaluating the impact of LiDAR ground point density on DTM accuracy. While the reduction of point density leads to a less accurate DTM in all cases (as expected), the exact pattern varies by algorithm. The accuracy of the LiDAR-derived DTMs is relatively good even when LiDAR sampling density is reduced to 0.40–0.50 points/m2 (50–60 % of the initial point density), as long as a suitable interpolation algorithm is used (as IDW proved to be less resilient to density reductions below approximately 0.60 points/m2). In the case of slope estimation, the pattern is relatively similar, except the difference in accuracy between IDW and the other two algorithms is even more pronounced than in the case of DTM accuracy. Based on this research, we conclude that LiDAR is an adequate method for collecting morphological data necessary for modelling the ground surface, even when the sampling density is significantly reduced.

scholarly journals THE SAFEST REVIEW: THE SHOCK-ABSORBING FLOORING EFFECTIVENESS SYSTEMATIC REVIEW IN CARE SETTINGS

2019 ◽  
Vol 3 (Supplement_1) ◽  
pp. S492-S493
Author(s):  
Amy K Drahota ◽  
Bethany E Keenan ◽  
Chantelle Lachance ◽  
Lambert Felix ◽  
James P Raftery ◽  
...  
Keyword(s):  
Systematic Review ◽  
Injury Prevention ◽  
Ground Surface ◽  
Work Related ◽  
Clinical Trial Registries ◽  
Injurious Falls ◽  
Study Selection ◽  
Health And Social Care ◽  
Implementation Studies ◽  
The Impact

Abstract Falls in hospitals and care homes are a major issue of international concern. Falls cost the US $34 billion a year, with injurious falls being particularly life-limiting and costly. Shock-absorbing flooring decreases the stiffness of the ground surface to reduce the impact of a fall. There is a growing body of evidence on flooring for fall-related injury prevention, however no systematic review exists to inform practice. We systematically reviewed the evidence on the clinical and cost-effectiveness of shock-absorbing flooring use for fall-related injury prevention in care settings. We searched six databases, clinical trial registries, conference proceedings, theses/dissertations, websites, reference lists, conducted forward citation searches, and liaised with experts in the field. We conducted study selection, data collection, and critical appraisal independently in duplicate. We evaluated the influence of shock-absorbing flooring on fall-related injuries, falls, and staff work-related injuries. We adopted a mixed methods approach considering evidence from randomised, non-randomised, economic, qualitative, and implementation studies. We assessed and reported the quality of outcomes using the GRADE approach and Summary of Findings Tables. This review, conducted over the course of 2019, summarises the certainty of the evidence on whether and which shock-absorbing floors influence injuries from falls, the chance of someone falling over, and work-related injuries in staff (e.g. from manoeuvring equipment across softer floors). Our findings are applicable to health and social care professionals, buildings and facilities managers, carers, older adults, architects, and designers. Funded by National Institute for Health Research, Health Technology Assessment (ref 17/148/11); registered in PROSPERO (CRD42019118834).

Effect of Upstream Rotor Vortical Disturbances on the Time-Averaged Performance of Axial Compressor Stators: Part 1—Framework of Technical Approach and Wake–Stator Blade Interactions

1999 ◽  
Vol 121 (3) ◽  
pp. 377-386 ◽  
Author(s):  
T. V. Valkov ◽  
C. S. Tan
Keyword(s):  
Total Pressure ◽  
Axial Compressor ◽  
Tip Vortex ◽  
Technical Approach ◽  
Tip Vortices ◽  
Tip Leakage ◽  
Unsteady Interaction ◽  
Flow Approximation ◽  
Stator Blade ◽  
The Impact

In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stators with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed interrogation of the computed flow field showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically, there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated nontransitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceived by the stator in the same manner as a wake. In Part 1, the focus will be on the framework of technical approach, and the interaction of stator with the moving upstream rotor wakes.

scholarly journals Impact of postglacial warming on borehole reconstructions of last millennium temperatures

2012 ◽  
Vol 8 (3) ◽  
pp. 1059-1066 ◽  
Author(s):  
V. Rath ◽  
J. F. González Rouco ◽  
H. Goosse
Keyword(s):  
Climate Models ◽  
Ground Surface ◽  
Geothermal Gradient ◽  
Temperature Profiles ◽  
Temperature Changes ◽  
Open Questions ◽  
Temperature Signal ◽  
Borehole Temperatures ◽  
Borehole Temperature ◽  
The Impact

Abstract. The investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories. However, there are still many open questions concerning the significance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last Glacial Maximum is still present in borehole temperature profiles. It is shown here that this signal also influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries by producing errors in the determination of the steady state geothermal gradient. However, the impact on estimates of past temperature changes is weaker. For deeper boreholes, the curvature of the long-term signal is significant. A correction based on simple assumptions about glacial–interglacial temperature changes shows promising results, improving the extraction of millennial scale signals. The same procedure may help when comparing observed borehole temperature profiles with the results from numerical climate models.

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