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![Comparison of sharp and blunt leading-edge separation. Luckring 7 [2004].](profile/James-Luckring/publication/268290052/figure/fig5/AS:667641622585351@1536189575470/Comparison-of-sharp-and-blunt-leading-edge-separation-Luckring-7-2004.png)
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![Figure 4. Sharp-edged slender wing vortex flow. Hummel 4 [1978].](profile/James-Luckring/publication/268290052/figure/fig3/AS:667641622573060@1536189575201/Sharp-edged-slender-wing-vortex-flow-Hummel-4-1978_Q320.jpg)
![Figure 5. Application of the suction analogy. Polhamus 5 [1966].](profile/James-Luckring/publication/268290052/figure/fig4/AS:667641622564868@1536189575452/Application-of-the-suction-analogy-Polhamus-5-1966_Q320.jpg)
A survey is presented of factors affecting blunt leading-edge separation for swept and semi-slender wings. This class of separation often results in the onset and progression of separation-induced vortical flow over a slender or semi-slender wing. The term semi-slender is used to distinguish wings with moderate sweeps and aspect ratios from the mor...
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... blunt leading edge fundamentally alters this flow, and a sketch contrasting the sharp and blunt leading edge vortical flows is shown in Figure 6. Due to the leading- edge bluntness, the origin of the vortex will be displaced downstream of the apex of the delta wing. ...
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... To understand the specific stall types occurring in the compared scenarios, it is essential to discuss the typical types of stall in correlation with airfoil maximum thickness. According to research conducted by McCullough and Gault [60,61], as elaborated upon by Polhamus [62], Whitford [30], and Luckring [63], stalls can be categorized into three basic groups: leading-edge, trailing-edge, and thin airfoil stall. Furthermore, these stall categories can be linked to airfoil thickness, as indicated by McCullough and Gault [60]. ...
The purpose of this paper is to assess the influence of a novel type of vortex creation device called the leading-edge vortex controller (LEVCON) on the aerodynamic characteristics of a fighter jet. LEVCON has become a trending term in modern military aircraft in recent years and is a continuation of an existing and widely used aerodynamic solution called the leading-edge root extension (LERX). LEVCON is designed to operate on the same principles as LERX, but its aim is to generate lift-augmenting vortices, i.e., vortex lift, at higher angles of attack than LERX. To demonstrate the methodology, a custom delta wing fighter aircraft is introduced, and details about its aerodynamic configuration are provided. The LEVCON geometry is designed and then incorporated into an existing three-dimensional (3D) model of the aircraft in question. The research is conducted using OpenFOAM 8, a high-fidelity computational fluid dynamics (CFD) open-source software. The computational cases are designed to simulate the aircraft’s flight at stall velocities within a high range of angles of attack. The results are assessed and discussed in terms of aerodynamic characteristics. A conclusion is drawn from the analysis regarding the perceived improvements in fighter jet aerodynamics. The analysis reveals that both lift and critical angle of attack can be manipulated positively. With the addition of LEVCON, the average lift gain in the high angle of attack (α) range is between 8.5% and 10%, while the peak gain reaches 19.4%. The critical angle of attack has also increased by 2°, and a flatter stall characteristic has been achieved.
... In the recent studies several wing configurations were introduced such as the diamond configuration, stability and control configuration (SACCON), and multidisciplinary design configuration (MULDICON) in order to obtain optimum aerodynamic characteristics on the UCAV. In addition, the leading-edge profiles of these configurations are designed as sharp leading edge at the apex followed by a blunt leading edge at the midwing section where the bluntness is defined by the radius of the leading edge [1,2]. The flow topology above a blunt leading-edge delta wing is very complicated and unresolved due to that the onset of the primary vortex is not fixed at the apex of the configuration unlike the case of the sharp leading edge where the onset of the primary vortex is fixed at the apex of the configuration primary. ...
... The flow topology above a blunt leading-edge delta wing is very complicated and unresolved due to that the onset of the primary vortex is not fixed at the apex of the configuration unlike the case of the sharp leading edge where the onset of the primary vortex is fixed at the apex of the configuration primary. Therefore, the vortex structure above these delta wing configurations is very complicated which led to several experimental and numerical studies to further understand the flow structure above these delta wing configurations stated above [2]. Furthermore, there are numerous ongoing UCAV programs in the Asia region at present such as in India Autonomous Unmanned Research Aircraft (AURA) and South Korea (K-X) UCAV where the main focus of these UCAV programs is on delta wing configurations with low to medium sweep angle, i.e., 35°to 55°, including different leading-edge profiles such as blunt and sharp leading edges, to improve performance, endurance, and to maximize the lift of the actual flight at a high angles of attack where the flow could be complicated above the configuration due to the multiple flow separations [3]. ...
This paper highlights the results and comparison of the flow topology investigation above the unmanned combat aerial vehicle (UCAV) configuration, namely, multidisciplinary design configuration (MULDICON), with modified leading-edge profile at the apex region from a sharp to a blunt profile to reduce the complexity of the flow structure above the wing. It was found from the flow visualization results that at a low angle of attack, for instance, 10°, the onset of the flow separation took place near the apex region; the onset of a tip vortex at the wing tip was also detected. At a medium angle of attack, for instance, 15°, the onset of the flow separation moved further upstream with the formation of the apex vortex, and the magnitude of the tip vortex increased due to increasing incoming flow with increasing the angle of attack. At higher angle of attack, for instance, 20°, the apex vortex intensity increased and wing tip vortices shedding is observed. Furthermore, at an angle of attack of 25°, the configuration is partially stalled, while a complete stalled occurred at an angle of attack of 30°. The current results obtained from this study have shown that the configuration has a maximum lift coefficient of 0.8 obtained from the K-Omega-SST turbulence model while it is 0.93 calculated from the Spalart-Allmaras turbulence model, while the maximum drag coefficient is 0.31 and 0.35, respectively, when calculated for the K-Omega-SST turbulence model and the Spalart-Allmaras turbulence model at an AOA of 25°. The flow visualization results revealed that there is a single flow separation due to modified leading edge from sharp to blunt, thus flow complexity is reduced.
... Flow can separate from the suction surface of a swept wing at the leading edge or the trailing edge, depending on the airfoil section, wing sweep angle, freestream Reynolds number, and freestream Mach number [4,5]. In cases of trailing-edge separation, the separation is related to spanwise flow development as flow turning causes boundary layer growth over an increased streamtrace length. ...
... The SOFV indicates the formation of a secondary leading-edge vortex outboard of the actuators; an example is highlighted as region (4) in Figure 5. In the case of α = 20°, a secondary detachment region can be observed outboard of the actuators, marked as region (5). Again, the interruption from flow control establishes an outboard state of flow similar to that observed near the wing root. ...
... LEVs are generated when flow separation occurs at the leading-edge region and forms a shear layer that rolls up to generate a vortex structure over the surface [4,5]; a process that commonly occurs at high angles of attack. Various experimental observations over slender delta wings have shown that these vortical structures can preserve their size and magnitude, thus becoming stationary LEVs for a wide range of flow conditions that offer significant lift enhancement [6][7][8][9][10][11]. ...
The leading-edge vortex (LEV) is a common flow structure that forms over wings at high angles of attack. Over the years, LEVs were exploited for augmenting the lift of man-made slender delta wings aircraft. However, recent observations suggested that natural flyers with high-aspect-ratio (high-AR) wings, such as the common swift (Apus apus), can also generate LEVs while gliding. We hypothesize that the planform shape and nonlinear sweep (increasing towards the wingtip) enable the formation and control of such LEVs. In this paper, we investigate whether a stationary LEV can form over a nonlinear swept-back high-AR wing inspired by the swift's wing shape and evaluate its characteristics and potential aerodynamic benefit. Particle image velocimetry (PIV) measurements were performed in a water flume on a high-AR swept-back wing inspired by the swift wing. Experiments were performed at four spanwise sections and a range of angles of attack for a chord-based Reynolds number of 20,000. Stationary LEV structures were identified across the wingspan by utilizing the proper orthogonal decomposition (POD) method for angles of attack of 5-15 degrees. The size and circulation of the stationary LEV were found to grow towards the wingtip in a nonlinear manner due to shear layer feeding and spanwise transport of mass and vorticity within the LEV, thus confirming that nonlinear high-AR swept-back wings can generate stationary LEVs. Our results suggest that the common swift can generate stationary LEVs over its swept-back wings to glide slower and at a higher rate of descent, with the LEVs potentially supporting up to 60% of its weight.
... Furthermore, many studies have been conducted to analyze the vortex flow of delta wings using wind tunnel experiments and CFD [12][13][14][15][16][17][18][19]. These studies investigated the aerodynamic characteristics of wings with constant aspect ratio, LE sweep angles, and varied LE contours. ...
... For the sharp LE slender delta wing (Λ > 55•), the primary flow detachment occurs at the sharp LE, and the detached flow rolls up to form a primary LE vortex [19]. A suction peak is generated due to the spanwise flow over the wing SS which is induced by the primary vortical flow. ...
... Following this suction peak, the unfavorable spanwise pressure gradient detaches the spanwise boundary layer flow, causing a secondary flow detachment and a secondary vortical flow. This secondary vortical flow prompts a suction outboard of the primary vortical flow suction peak [19]. These fundamental studies improved the understanding of delta wing aerodynamics and the recent investigations related to UCAV configurations. ...
View Video Presentation: https://doi.org/10.2514/6.2022-0428.vid At low speeds, the leading-edge sweep angle influences the flight performance of swept wings. The flow behavior of the moderate to highly swept wings is affected by the vortex flow structures, which form at low angles of attack because of leading-edge flow separation. This topic of investigation gained momentum recently due to its application to unmanned combat aerial vehicle (UCAV) configurations that are significantly affected by flow separation at high angles of attack. The present work investigates the flowfield and low-speed aerodynamic characteristics of the generic UCAV models with constant and non-constant leading-edge sweep for a wide range of angles of attack. The open-source computational fluid dynamics (CFD) code OpenFOAM 8.0 was employed for the numerical simulations. The present numerical simulation results matched well with the experimental data in the literature. It was found that the lift and drag characteristics of the UCAV are sensitive to the leading-edge sweep angle, and a non-constant leading-edge sweep angle variant exhibited delayed stall and enhanced aerodynamic performance.
... The separated flow then forms a shear layer, which rolls up to generate a vortex structure [6,7]. Various experimental observations over slender delta wings have shown that these vortical structures can preserve their size and magnitude, thus becoming stationary LEVs for a wide range of flow conditions and offer significant lift enhancement [8][9][10][11][12]. ...
... The LEV rotational core encloses a smaller viscous subcore (with radius R v ), featuring large gradients of velocity (see Fig. 2), through which we assume that the spanwise vorticity and mass transport take place. We assume that the LEV initiates at some spanwise location, aft of the leading-edge location, and progresses toward the wingtip [11,35]. ...
... The wing planform is divided into N discrete quadrangular chordwise segments in the spanwise direction (see Fig. 3a); due to the symmetry condition, the discretization is only depicted for the right half-wing. The LEV is set to initiate at some spanwise location Y s (s > 1), from which it evolves toward the wingtip [11,35]. Because flow separation at the leading-edge region prompts the formation of the vortex, it is plausible to assume that the LEV initiates at the closest wing section to the root that reaches its stalling angle α stall . ...
Enabling a leading-edge vortex (LEV) is a possible mechanism to significantly increase the lift on wings. This is well known for slender delta wings, for which various analytical models were developed and show accurate predictions of the lift enhancement. This paper shows that, when suitably designing the wing planform, LEVs can also exist on high-aspect-ratio (high-AR) wings. In this study, a quasi-three-dimensional flow model is presented for solving the stationary LEV phenomenon over a high-AR swept back wing, with sweep increasing toward the wingtip. Our model captures the three-dimensional phenomenon by satisfying conservation of mass and vorticity within the LEV, and using a combination of strip theory and the lifting-line theory. Our model predictions are compared with flow visualization data on a parabolic swept back wing. Results confirm that suitable sweep wing geometry can fix an LEV steadily over the upper wing surface, resulting in significant lift enhancement of up to 70%.
... Various methods have been used to promote the performance of vortical flows on these wings. Examples are the creation of multiple vortices (e.g., for double delta wings [2] and tandem delta wings known as the chinard configuration [3]), control surfaces [4], passive control with wing flexibility [5], and changing the shape of the leading edge [6]. Controlling the flow on the wings with multiple vortices is also a challenge. ...
{tiThis study examines the effect of nature-inspired leading edge 3D serration on the aerodynamic performance of a 65/35-degree double delta wing. Force measurement experiments were conducted on a smooth-surface model and a model equipped with various combinations of serrated pieces in the leading edge area. Four symmetric different positions were examined in a low-speed wind tunnel. The transitional flow regime was applied with Reynolds numbers of 2×105 and angles of attack (AOA) of 0 to 36 degrees. Compared to the clean model, there is a notable enhancement in the maximum lift coefficient, especially for the pieces located at the apex and kink angle locations. However, when changing the combination of serrated leading edge (SLE) elements, a decline in CL can be seen at some AOAs, and adding more SLE pieces is not always useful. A drag reduction is also achieved by installing these elements, which provided a higher lif}t-to-drag ratio for all AOAs. Finally, the serrated leading edge postponed the stall angle of the double delta wing.
... Advanced numerical analysis of aerodynamics properties due to wing geometry shape and different geometry wing angles that includes different geometry manipulations in order to achieve the optimal aerodynamic flight have been studied over the two decades. For instance, studies concerning swept and semi-slender wings for blunt leading edge shape [5], flap and aileron deflection [6], flapping wings in a hover [7], various leading edge shape [8,9], morphing wings [10] and recently non-slender delta wings [11] have been studied. Finally, classic experimental and theoretical work was performed over the years by [12][13][14][15][16]. ...
This paper presents, aerodynamics coefficients calculation (Lifting & drag coefficients, pressure central location) of Trapeze wing shape configurations for different aspect ratios (ARs) values by using improved vortex lattice method (VLM), compared with finite-wing and slender body theories. The planar wing was divided into panels of the size: 6X6 with trapezoid shape panels. As expected, for high ARs the VLM solution for the lifting coefficient is coincided with the finite wing theory whereas for small ARs (<1) it is coincided with the slender body theory (~1). Afterwards, we obtained that the calculated VLM induced drag becomes closer to the finite-wing theory as the AR value is increased.
... The LEV rotational core encloses a smaller size viscous subcore (with radius R v ), featuring large gradients of velocity (see Fig. A2), through which we assume the spanwise vorticity and mass transport take place. We assume the LEV initiates at some spanwise location, aft of the leading-edge location, and progresses towards the wingtip [18,19]. ...
... The wing planform is divided into N discrete quadrangular chordwise segments in the spanwise direction (see Fig. 3a); due to the symmetry condition, the discretization is only depicted for the right half-wing. The LEV is set to initiate at some spanwise location Y (s) (s > 1), from which it evolves towards the wingtip [18,19]. Since flow separation at the leading-edge region prompts the formation of the vortex, it is plausible to assume that the LEV initiates at the closest wing section to the root that reaches its stalling angle α stall . ...
... The lift values computed are shown to increase with α g in non-linear manner, where the values achieved with the LEV model are higher than the lift coefficients (C L0 ) predicted with Guermond's LLT analysis, as expected. This non-linear lift enhancement ('vortex lift') is attributed to the presence of LEV filament, as also reported for delta wings and swept back wings [5,6,18,42]. The lift coefficients estimated with Guermond's LLT (C L0 ) were subtracted from the values computed with the LEV model, thus yielding the lift enhancement (∆C L ) variation with the geometrical angles for the various wing configurations, as depicted in Fig. 6b. ...
Enabling a leading-edge vortex (LEV) is a possible mechanism to significantly increase the lift on wings. This is well known for slender delta wings, for which various analytical models were developed and shown accurate predictions of the lift enhancement. By suitably designing the wing planform, LEVs can also exist on high aspect ratio (AR) wings. This is a three-dimensional effect and in this study, we present a pseudo-three-dimensional flow model for solving the stationary LEV phenomenon over a high AR swept back wing, with sweep increasing towards the wingtip. Our model captures the phenomenon by satisfying
conservation of mass and vorticity within the LEV, and using a combination of strip theory and the lifting-line theory. An example of a parabolic swept back wing, confirms that wing geometry can have a major role in holding a LEV steadily over the upper wing surface, resulting in significant lift enhancement of up to 70% in certain cases.
... 3 The low pressure regions created by these vortices increase the lift force which is called vortex lift. 4 Therefore, higher lift force in comparison with typical wings with the same conditions improve the maneuverability in higher AOA that reported by some authors. 5,6 Consequently, this type of wing is highly recommended for highmaneuverability airplanes. ...
This research investigates the aerodynamic performance and flow characteristics of a delta wing with 65° sweep angle and with coarse axial riblets, and then compares with that of a smooth-surface delta wing. Particle Image Velocimetry (PIV) were utilized to visualize the flow over the wing at 6 cross-sections upright to the wing surface and parallel to the wing span, as well as 3 longitudinal sections on the leading edge, symmetry plane, and a plane between them at Angles of Attack (AOA) = 20° and 30° and Re = 1.2 × 105, 2.4 × 105, and 3.6 × 105. The effects of the riblets were studied on the vortices diameter, vortex breakdown location, vortices distance from the wing surface, flow lines pattern nearby the wing, circulation distribution, and separation. The results show that the textured model has a positive effect on some of the parameters related to drag reduction and lift increase. The riblets increase the flow momentum near the wing’s upper surface except near the apex. They also increase the flow momentum behind the wing. Keywords: Aerodynamic performance, Coarse riblet, Delta wing, Flow structures, Particle image velocimetry, Vortex
