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.

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.

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.

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 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.

A Note on the Secondary Vortex Caused by a Thin Foil in a Nonuniform Flow

1988 ◽  
Vol 32 (01) ◽  
pp. 80-81
Author(s):  
B. Yim
Keyword(s):  
Thin Foil ◽  
Uniform Flow ◽  
Secondary Vortex ◽  
Nonuniform Flow ◽  
Vortex Strength ◽  
Finite Span ◽  
Trailing Vortices

WHEN A finite span lifting wing is located in a uniform flow, trailing vortices are generated by the wing. It is well known from the Kelvin theorem that the trailing vortex strength is proportional to the spanwise slope of the bound vortex distribution. When the wing is located in a nonuniform flow, the problem becomes complex. Such flow has been dealt with by Vandry [1], 2 Karman and Tshen [2], Honda [8], and Smith [4]. It has been found that this flow has an extra trailing vortex created by the interaction between the nonuniform flow and the wing. This extra vortex is called the secondary vortex and has been studied extensively in connection with the theory of turbomachinery.

Experimental investigation on the structures and induced drag of wingtip vortices for different wingtip configurations

2020 ◽  
pp. 095441002094791
Author(s):  
Ze-Peng Cheng ◽  
Yang Xiang ◽  
Hong Liu
Keyword(s):  
Growth Rate ◽  
Form Factor ◽  
Drag Coefficient ◽  
Particle Image ◽  
Vortex Center ◽  
Streamwise Location ◽  
Induced Drag ◽  
Wingtip Vortex ◽  
Image Velocimetry ◽  
Drag And Lift

As an effective method to reduce induced drag and the risk of wake encounter, the winglet has been an essential device and developed into diverse configurations. However, the structures and induced drag, as well as wandering features of the wingtip vortices ( WTVs) generated by these diverse winglet configurations are not well understood. Thus, the WTVs generated by four typical wingtip configurations, namely the rectangular wing with blended/raked/split winglet and without winglet (Model BL/ RA/ SP/NO for short), are investigated in this paper using particle image velocimetry technology. Comparing with an isolated primary wingtip vortex generated by Model NO, multiple vortices are twisted coherently after installing the winglets. In addition, the circulation evolution of WTVs demonstrates that the circulation for Model SP is the largest, while Model RA is the smallest. By tracking the instantaneous vortex center, the vortex wandering behavior is observed. The growth rate of wandering amplitude along with the streamwise location from the quickest to the slowest corresponds to Model SP, Model NO, Model BL, Model RA in sequence, implying that the WTVs generated by model SP exhibit the quickest mitigation. Considering that the induced drag scales as the lift to power 2, the induced drag and lift are estimated based on the wake integration method, and then the form factor λ, defined by [Formula: see text], is calculated to evaluate the aerodynamic performance. Comparing with the result of Model NO, the form factor decreases by 7.99%, 4.80%, and 2.60% for Model RA, Model BL, Model SP, respectively. In sum, Model RA and BL have a smaller induced drag coefficient but decay slower; while Model SP has a larger induced drag coefficient but decays quicker. An important implication of these results is that reducing the strength of WTVs and increasing the growth rate of vortex wandering amplitude can be the mutual requirements for designing new winglets.

Wake Analysis of an Aerodynamically Optimized Boxprop High-Speed Propeller

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Alexandre Capitao Patrao ◽  
Tomas Grönstedt ◽  
Anders Lundbladh ◽  
Gonzalo Montero Villar
Keyword(s):  
High Speed ◽  
Tip Vortex ◽  
Lower Amount ◽  
Optimized Design ◽  
Aerodynamic Optimization ◽  
Vortex Strength ◽  
Percentage Point Increase ◽  
Aerodynamic Loading ◽  
Point Increase ◽  
Propeller Blades

The Boxprop is a novel, double-bladed, tip-joined propeller for high-speed flight. The concept draws inspiration from the box wing concept and could potentially decrease tip vortex strength compared with conventional propeller blades. Early Boxprop designs experienced significant amounts of blade interference. By performing a wake analysis and quantifying the various losses of the flow, it could be seen that these Boxprop designs produced 45% more swirl than a conventional reference blade. The reason for this was the proximity of the Boxprop blade halves to each other, which prevented the Boxprop from achieving the required aerodynamic loading on the outer parts of the blade. This paper presents an aerodynamic optimization of a 6-bladed Boxprop aiming at maximizing efficiency and thrust at cruise. A geometric parametrization has been adopted which decreases interference by allowing the blade halves to be swept in opposite directions. Compared with an earlier equal-thrust Boxprop design, the optimized design features a 7% percentage point increase in propeller efficiency and a lower amount of swirl and entropy generation. A vortex-like structure has also appeared downstream of the optimized Boxprop, but with two key differences relative to conventional propellers. (1) Its formation differs from a traditional tip vortex and (2) it is 46% weaker than the tip vortex of an optimized 12-bladed conventional propeller.

Numerical Experiments for Flow Around a Ducted Tip Hydrofoil

2002 ◽  
Author(s):  
Hildur Ingvarsdo´ttir ◽  
Carl Ollivier-Gooch ◽  
Sheldon I. Green
Keyword(s):  
Turbulence Model ◽  
Vortex Core ◽  
Vortex Flow ◽  
Computational Study ◽  
Near Field ◽  
Vortex Formation ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Computational Studies ◽  
Tip Vortices

The performance and cavitation characteristics of marine propellers and hydrofoils are strongly affected by tip vortex behavior. A number of previous computational studies have been done on tip vortices, both in aerodynamic and marine applications. The focus, however, has primarily been on validating methods for prediction and advancing the understanding of tip-vortex formation in general, rather than showing effects of tip modifications on tip vortices. Studies of the most relevance to the current work include computational studies by Dacles-Mariani et al. (1995) and Hsiao and Pauley (1998, 1999). Daeles-Mariani et al. carried out interactively a computational and experimental study of the wingtip vortex in the near field using a full Navier-Stokes simulation, accompanied with the Baldwin-Barth turbulence model. Although they showed improvement over numerical results obtained by previous researchers, the tip vortex strength was underpredicted. Hsiao and Pauley (1998) studied the steady-state tip vortex flow over a finite-span hydrofoil, also using the Baldwin-Barth turbulence model. They were able to achieve good agreement in pressure distribution and oil flow pattern with experimental data and accurately predict vertical and axial velocities of the tip vortex core within the near-field region. Far downstream, however, the computed flow field was overly diffused within the tip vortex core. Hsiao and Pauley (1999) also carried out a computational study of the tip vortex flow generated by a marine propeller. The general characteristics of the flow were well predicted but the vortex core was again overly diffused.

Near-field tip vortex behind a swept wing model

2005 ◽  
Vol 40 (1) ◽  
pp. 141-155 ◽  
Author(s):  
P. Gerontakos ◽  
T. Lee
Keyword(s):  
Near Field ◽  
Tip Vortex ◽  
Swept Wing ◽  
Wing Model
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