The formation mechanism and impact of streamwise vortices on NACA 0021 airfoil's performance with undulating leading edge modification (original) (raw)
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The effect of undulating leading-edge modifications on NACA 0021 airfoil characteristics
Physics of Fluids, 2013
In spite of its mammoth physical size, the humpback whale's manoeuvrability in hunting has captured the attention of biologists as well as fluid mechanists. It has now been established that the protrusions on the leading-edges of the humpback's pectoral flippers, known as tubercles, account for this species' agility and manoeuvrability. In the present work, Prandtl's nonlinear lifting-line theory was employed to propose a hypothesis that the favourable traits observed in the performance of tubercled lifting bodies are not exclusive to this form of leading-edge configuration. Accordingly, a novel alternative to tubercles was introduced and incorporated into the design of four airfoils that underwent wind tunnel force and pressure measurement tests in the transitional flow regime. In addition, a Computation Fluid Dynamics study was performed using the Shear Stress Transport transitional model in the context of unsteady Reynolds-Averaged Navier-Stokes at several attack angles. The results from the numerical investigation are in reasonable agreement with those of the experiments, and suggest the presence of features that are also observed in flows over tubercled foils, most notably a distinct pair of streamwise vortices for each wavelength of the tuberclelike feature. C 2013 AIP Publishing LLC. [http://dx.
The effect of leading edge tubercle geometry on the performance of different airfoils
2009
Results are presented of an experimental investigation on the effects of modification to the leading edge geometry of two NACA airfoils with different aerodynamic characteristics. The modification was inspired by the humpback whale flipper, which has rounded tubercles on its leading edge resembling the shape of a sine curve. Force measurements on both modified and unmodified 2-D airfoils show that tubercles are more beneficial for the NACA 65-021 airfoil than the NACA 0021 airfoil. Also, for smaller amplitude tubercles, the modified NACA 65-021 airfoil outperforms its unmodified equivalent for most angles of attack. Hydrogen-bubble visualisation was used to identify characteristic features of the flow for airfoils with tubercles. It appears that the velocity behind the troughs is greater than behind the tubercles themselves at the leading edge. Downstream from the leading edge, the flow from behind the peaks seems to be entrained into this region, giving rise to the formation of stream-wise vortices.
EFFECT OF LEADING EDGE TUBERCLES ON AIRFOIL PERFORMANCE
This thesis provides a detailed account of an experimental investigation into the effects of leading edge sinusoidal protrusions (tubercles) on the performance of airfoils. The leading edge geometry was inspired by the morphology of the Humpback whale flipper, which is a highly acrobatic species. The aim of this study is to investigate the potential advantages and disadvantages of incorporating tubercles into the leading edge of an airfoil. Specific parameters have been varied to identify an optimum tubercle configuration in terms of improved lift performance with minimal drag penalties.
Tubercles Effect on a Wing Performance for NACA 634-421 Aerofoil
International Journal of Science and Engineering Applications, 2020
Humpback whales have a morphological structure on the leading edge of their flippers that provide them with the capability of extreme manoeuvrability. Inspired by nature, tubercle design has been incorporated in wing-like structures such as wind turbines, marine propellers, etc. The idea of tubercles was studied by P Watts and F E Fish to develop their turbine blades and showed that wind farms can produce up to 20% more power with less wind. The purpose of this study was to see how the performance of a finite wing is affected due to the geometrical modification. To understand the effect of tubercles, various parameters are being measured and compared. A Baseline model and model with Tubercles are being tested with a 6 digit NACA 634-421 cambered airfoil, similar to that of the flipper of the Humpback Whale. Tubercles of various wavelength and amplitudes are taken to analyse and study various aerodynamic characteristics. Preliminary analysis was carried out in XFLR for baseline model...
Utilization of Whale-Inspired Tubercles as a Control Technique to Improve Airfoil Performance
This research exploits the Whale-inspired tubercles as a control technique to improve the performance of airfoils. The flow field of NACA0012 airfoil with spherical leading-edge tubercles was computationally simulated. This airfoil section resembles the flipper of the Humpback whale and is used in many engineering applications. Tubercles, with a diameter of 10% of the airfoil chord (C), are arranged such that the span-wise distance between the centerlines of two adjacent tubercles is 20% C. k- turbulence model was used for a wide range of angle of attack (α = 0 o -25 o ) and Reynolds number (Re = 65,000 -1,000,000). Results demonstrated that the presence of tubercles improves the airfoil performance by delaying or even preventing stall in the investigated range of operating conditions (α and Re). Simple active control scheme is proposed to obtain optimum performance (i.e., optimum values of lift and drag coefficients).
Open Engineering, 2024
Using computational models and low-speed wind tunnel tests, the aerodynamic characteristics of the NACA 0012 airfoil with low Re numbers of (8 × 10 4 , 2 × 10 5 , 3 × 10 5 , and 4 × 10 5) and angle of attack (AOA) ranging from 0°t o 18°by two steps are examined. Using the same 3-D wind tunnel dimensions, numerical simulations were run. The software program ANSYS FLUENT was used to solve the mathematical model using the continuity equation, the Navier-Stokes equations, and the k-ω shearstress transport turbulence model. Findings demonstrate that at all AOAs, there is a direct relationship between Reynolds numbers (Re), lift and drag coefficients, kinetic energy, and stall angle. The lift coefficient rises linearly as the AOA increases, peaking at 14°, the stall angle at higher Reynolds number. The lift coefficient was found to decline when the AOA was increased further, reaching its minimal value at an AOA of 18°. With a greater AOA, the airfoil's drag coefficient rises, creating turbulent flow. The eddies produced by the turbulence cause the flow to start separating from the airfoil surface as turbulence increases. As a result, the airfoil lift coefficient drops, and its drag coefficient rises at the same time, leading to poor performance. The validation of the numerical results through wind tunnel experiments provided confidence in the findings of the study.
Performance Variations of Leading-Edge Tubercles for Distinct Airfoil Profiles
AIAA Journal, 2011
An experimental investigation has been undertaken to determine the influence of sinusoidal leading-edge protrusions on the performance of two NACA airfoils with different aerodynamic characteristics. Force measurements on full-span airfoils with various combinations of tubercle amplitude and wavelength reveal that when compared to the unmodified equivalent, tubercles are more beneficial for the NACA 65-021 airfoil than the NACA 0021 airfoil. It was also found that for both airfoil profiles, reducing the tubercle amplitude leads to a higher maximum lift coefficient and larger stall angle. In the poststall regime, however, the performance with largeramplitude tubercles is more favorable. Reducing the wavelength leads to improvements in all aspects of lift performance, including maximum lift coefficient, stall angle, and poststall characteristics. Nevertheless, there is a certain point at which further reduction in wavelength has a negative impact on performance. The results also suggest that tubercles act in a manner similar to conventional vortex generators.
Journal of Fluids and Structures, 2020
Unsteady pressures, forces, and pitching moments generated by foils experiencing vibratory motion in an incompressible, attached flow configuration are studied within this work. Specifically, two-dimensional, unsteady potential flow and unsteady Reynolds-Averaged Navier-Stokes calculations are performed on various Joukowski foils undergoing sinusoidal, variable amplitude, small-scale pitching motion at a chord-based Reynolds number of 10 6 over a range of reduced frequencies between 0.01-100. These calculated results from both approaches are compared directly to predictions from implementing the Theodorsen model, which treats foils as infinitely thin, flat plates that shed a planar sheet of vorticity. The effects of relaxing these seemingly strict conditions are explored, and the particular terms which control the unsteady responses are identified and discussed. For increasing pitch amplitudes and reduced frequencies the shed wake is seen to become quite non-planar and to form coherent vortex structures. Despite this wake behavior, the normalized airfoil responses at the disturbance reduced frequency are seen to be largely unaffected. However, non-negligible responses are generated across a wide range of other frequencies. Potential flow calculations for symmetric Joukowski foils show that there is marginal effect of foil thickness at reduced frequencies less than one. For higher reduced frequency conditions however, the unsteady lift response is seen to experience both an amplification of level and a phase shift relative to the Theodorsen model. A specific augmenting expression is developed for this behavior through analysis within the potential flow framework.
Aerodynamics of a Modified High-Lift Low Reynolds Number Airfoil: Preliminary Analysis
International journal emerging technology and advanced engineering, 2022
Airfoil selection is a crucial phase in the design of a small unmanned fixed-wing aircraft to allow a minimum size and weight of the lifting surfaces. The present study analyzesairfoils to be used in low operating Reynolds number unmanned aerial vehicles (UAV) using XFLR5 software, which was validated against wind tunnel data. Three baseline airfoils were investigated, namely NACA4412, Miley M06-13-128 and Selig S1223. The best performing airfoils are then modified using the inverse airfoil design method to improve their performance in cruising flight. The modified airfoil resulted in larger leading edge radius and slightly thicker chord of the airfoil compared to the baseline airfoil. In general, the modified airfoil showed an improvement in stall characteristic, lift and drag coefficients in the post-stall regime, and a lower magnitude of moment coefficient for almost all investigated angles of attack compared to the baseline airfoil.
Lift Enhancement on Oscillating Airfoils
39th AIAA Fluid Dynamics Conference, 2009
Force and particle image velocimetry measurements were conducted on a NACA 0012 airfoil undergoing sinusoidal plunge oscillations at amplitudes of 2.5% to 20% of chord, a post-stall angle of attack of 15°, and Reynolds number of 10,000. It was shown that airfoil oscillations significantly increase lift and reduce drag. Lift improvement is primarily due to the formation of a strong leading edge vortex on the upper surface. At lower Strouhal numbers this leading edge vortex is shed and convects into the wake, interacting destructively with the trailing edge vortices. Within this regime the lift coefficient increases approximately linearly with plunge velocity. At higher Strouhal numbers the upper surface leading edge vortex remains nearer the leading-edge of the airfoil and is therefore dissipated through the rising motion of the airfoil, whilst on the lower surface a leading edge vortex forms that acts to detract from the lift force. As a result a fall in lift is observed. Local maxima were observed in the lift curves at specific Strouhal numbers for all amplitudes and also for a higher Reynolds number. It was postulated that the peak at a Strouhal number of 0.5 could be due to the vortex convection time scale, however this does not explain the other peaks. A second hypothesis is that all the maxima are due to resonance with the most unstable wake frequency, its subharmonic and harmonics.