Implicit LES Simulations of a Flapping Wing in Forward Flight

2013 ◽  
Author(s):  
Raymond E. Gordnier ◽  
Luciano Demasi
Keyword(s):  
Reynolds Number ◽  
Angle Of Attack ◽  
Micro Air Vehicles ◽  
Navier Stokes ◽  
Forward Flight ◽  
Freestream Velocity ◽  
Flapping Motion ◽  
Wing Motion ◽  
Low Reynolds Number Flows ◽  
Aerodynamic Angle

Computations of an aspect ratio 3.5 flat plate wing in flapping forward flight are performed. A high-order implicit LES approach is employed to compute the mixed laminar/transitional/turbulent flowfields present for the low Reynolds number flows associated with micro air vehicles. The ILES approach is implemented by exploiting the properties of a well validated, robust, sixth-order Navier-Stokes solver. The analyzed kinematics are a flapping motion described by an anti-clockwise 8 cycle. A Reynolds number based on the freestream velocity of 1250 is prescribed. A detailed description of the dynamic vortex system engendered by the unsteady flapping motion is given and related to the development of lift and thrust during the flapping cycle. Effective angle of attack, which results from the wing motion, and its interplay with the aerodynamic angle of attack play a key role in determining the flow structure and forces produced.

scholarly journals Plunging Airfoil: Reynolds Number and Angle of Attack Effects

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 216
Author(s):  
Emanuel A. R. Camacho ◽  
Fernando M. S. P. Neves ◽  
André R. R. Silva ◽  
Jorge M. M. Barata
Keyword(s):  
Reynolds Number ◽  
High Performance ◽  
Angle Of Attack ◽  
Systems Design ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Low Reynolds Numbers ◽  
Operational Conditions ◽  
Naca0012 Airfoil ◽  
The Mean

Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×103 and 3.4×104, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0∘ to 10∘. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored.

Interactions of Two UAV Rotors at Low Reynolds Number

2020 ◽  
Author(s):  
Yashvardhan Tomar ◽  
Dhwanil Shukla ◽  
Narayanan Komerath
Keyword(s):  
Reynolds Number ◽  
Electric Propulsion ◽  
Low Reynolds Number ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Forward Flight ◽  
Spatial Spread ◽  
Vertical Takeoff And Landing ◽  
Low Reynolds ◽  
Vertical Takeoff

Abstract Vertical takeoff and landing vehicle platforms with many small rotors are becoming increasingly pertinent for small Unmanned Aerial Vehicles (UAVs) as well as distributed electric propulsion for larger vehicles. These rotors operate at low Reynolds number unlike large rotors for which the existing prediction methods were developed. Operating at very low Reynolds number essentially means that viscous effects are more dominant; and their spatial spread is significant with respect to the rotor dimensions. This impacts the nature of inter-rotor aerodynamic interactions which become more difficult to predict and characterize. In the present research, two nominally identical commercial UAV rotors are studied for a range of separations in hover and forward flight, both experimentally and computationally, in parallel with ongoing vehicle flight tests with 4 and 8 rotors. Bi-rotor tests in tandem in-plane configuration were performed in Georgia Tech’s 2.13m × 2.74m test section wind tunnel. Rotor simulations were done using the RotCFD Navier-Stokes solver. In hover, rotor performance is sensitive to the distance between rotors at low rotation speeds, indicating the presence of greater inter-rotor interactions at low Reynolds number. In forward flight, the performance of the downstream rotor gets negatively affected by the upstream rotor wake.

scholarly journals Numerical study of flow across an ellipse and a circle placed in a uniform stream of infinite extent

2020 ◽  
Author(s):  
Adnan Anwar ◽  
Mudassar Razzaq ◽  
Liudmila Rivkind
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Reynolds Number Flow ◽  
Infinite Extent ◽  
Number Flow ◽  
Conforming Finite Element Method ◽  
Drag And Lift

As an example of an aerodynamics prototypical study, we examined a two-dimensional low Reynolds number flow over obstacles immersed in a stream of infinite extent. The Navier Stokes equation is being discretized by non conforming finite element method approach. The resulting discretized nonlinear algebraic system is being solved by using the fixpoint method and the Newton method and multigrid method for the linear sub-problem employed. The magnitude of the uniform upstream velocity under the study of the problem for Reynolds number in the range 1 < Re < 100 and the angle of attack of the upstream velocity at α = -5; 0; 5 degrees performed. Analysis of the resulting drag and lift forces acting on obstacles with respect to the angle of attack of the upstream velocity and the Reynolds number is made. Moreover, the influence of one obstacle on the resulting drag and lift coefficients of other obstacles determined. The results are being presented in a graphical and vector form.

Design of a Bio-Inspired Spherical Four-Bar Mechanism for Flapping-Wing Micro Air-Vehicle Applications

2008 ◽  
Author(s):  
Matt McDonald ◽  
Sunil K. Agrawal
Keyword(s):  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Aerodynamic Performance ◽  
Flapping Wing ◽  
Micro Air Vehicle ◽  
Aerodynamic Forces ◽  
Flapping Motion ◽  
Wing Motion ◽  
Air Vehicle ◽  
Flapping Mechanism

Design of flapping-wing micro air-vehicles presents many engineering challenges. As observed by biologists, insects and birds exhibit complex three-dimensional wing motions. It is believed that these unique patterns of wing motion create favorable aerodynamic forces that enable these species to fly forward, hover, and execute complex motions. From the perspective of micro air-vehicle applications, extremely lightweight designs that accomplish these motions of the wing, using just a single, or a few actuators, are preferable. This paper presents a method to design a spherical four-bar flapping mechanism that approximates a given spatial flapping motion of a wing, considered to have favorable aerodynamics. A spherical flapping mechanism was then constructed and its aerodynamic performance was compared to the original spatially moving wing using an instrumented robotic flapper with force sensors.

scholarly journals Parametric study of a corrugated airfoil in a forward flight at ultra-low Reynolds number

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Mahmoud E. Abd El-Latief ◽  
Khairy Elsayed ◽  
Mohamed M. Abdelrahman
Keyword(s):  
Reynolds Number ◽  
Phase Difference ◽  
Lift Force ◽  
Thrust Force ◽  
Angle Of Attack ◽  
Initial Angle ◽  
Aerodynamic Forces ◽  
Forward Flight ◽  
Propulsive Efficiency ◽  
Stroke Amplitude

AbstractIn the current study, the mid cross section of the dragonfly forewing was simulated at ultra-low Reynolds number. The study aims to understand better the contribution of corrugations found along the wing on the aerodynamic performance during a forward flight. Different flapping parameters were employed. FLUENT solver was used to solve unsteady, two-dimensional, laminar, incompressible Navier–Stokes equations. The results revealed that any stroke amplitude less than 1cm generated no thrust force. The stroke amplitude had to be increased to form the reversed Kármán vortices responsible for generating thrust force. The highest propulsive efficiency was found in the Strouhal number range 0.2 < St < 0.4 with a peak efficiency of 57% at St = 0.39. Changing the phase difference between pitching and plunging motions from advanced to synchronized caused lift force to drop 91% and thrust force to increase by 15%. On the other hand, changing the phase difference from synchronized to delayed caused lift and thrust forces to increase by 89% and 36%, respectively, and propulsive efficiency to deteriorate significantly. In all performed simulations, the airfoil was assumed to start motion from rest with no initial angle of attack. The increase in initial angle of attack generates a very high lift force with a fair loss for both thrust force and propulsive efficiency. The decomposition of flapping motion into its elementary motions revealed that the aerodynamic forces generated are a non-linear superposition from both pure pitching and pure plunging aerodynamic forces. This can be attributed to the non-linear interaction between unsteady vortices generated from these decomposed motions.

Impact of Flexibility on the Aerodynamics of an Aspect Ratio Two Membrane Wing

2012 ◽  
Author(s):  
Raymond E. Gordnier ◽  
Peter J. Attar
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Micro Air Vehicles ◽  
Navier Stokes ◽  
Elastic Membrane ◽  
Pitching Moment ◽  
Flexible Membrane ◽  
Membrane Wing ◽  
The Impact ◽  
Air Vehicles

Development of an aeroelastic solver with application to flexible membrane wings for micro air vehicles is presented. A high-order (up to 6th order) Navier-Stokes solver is coupled with a geometrically nonlinear p-version Reissner-Mindlin finite element plate model to simulate the highly flexible elastic membrane. An implicit LES approach is employed to compute the mixed laminar/transitional/turbulent flowfields present for the low Reynolds number flows associated with micro air vehicles. Computations are performed for an aspect ratio two membrane wing at angles of attack α = 10°, 16° and 23° for a Reynolds number, Re = 24,300. Comparisons of the computational results with experimental PIV and surface deflection measurements demonstrated reasonable agreement. Reduced separation and enhanced lift are obtained due to favorable interactions between the flexible membrane wing and the unsteady flow over the wing. The impact of flexibility on the aerodynamic performance comes primarily from the development of mean camber with some further effects arising from the interaction between the dynamic motion of the membrane and the unsteady flowfield above. At lower angles of attack this lift enhancement comes at the cost of reduced L/D. The nose-down pitching moment increases with flexibility at the lowest angle of attack but is reduced for the higher two angles of attack. These results suggest that membrane flexibility might provide a means to reduce the impact of strong gust encounter by maintaining lift and reducing the effect of the gust on pitching moment.

Computational and experimental investigations of low-Reynolds-number flows past an aerofoil

2007 ◽  
Vol 111 (1115) ◽  
pp. 17-29 ◽  
Author(s):  
W. Yuan ◽  
M. Khalid ◽  
J. Windte ◽  
U. Scholz ◽  
R. Radespiel
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Experimental Investigations ◽  
Eddy Simulation ◽  
Low Reynolds Number Flows ◽  
Low Reynolds ◽  
Reynolds Number Flows

AbstractThis paper presents investigations of low-Reynolds-number flows past an SD7003 aerofoil at Re = 60k, where transition takes place across a laminar separation bubble (LSB). Results of experimental measurements and numerical calculations are analysed and discussed. In particular, reasonably good results were obtained using two different numerical approaches: Large-eddy simulation (LES) that demonstrated vortical structures at different transition stages, and where the transition occurred naturally; unsteady Reynolds-averaged Navier-Stokes (URANS) simulations for several turbulence models based on the ω-length-scale equation, coupled to a linear stability solver to predict the transition position.

Implicit LES Simulations for an Aspect Ratio Two Flexible Membrane Wing

2011 ◽  
Author(s):  
Raymond E. Gordnier ◽  
Peter J. Attar
Keyword(s):  
Vortex Dynamics ◽  
Micro Air Vehicles ◽  
Navier Stokes ◽  
Elastic Membrane ◽  
Geometrically Nonlinear ◽  
Flexible Membrane ◽  
Low Reynolds Number Flows ◽  
Air Vehicle ◽  
Membrane Wing ◽  
Reynolds Number Flows

Development of an aeroelastic solver with application to flexible membrane wings for micro air vehicle applications is presented. A high-order (up to 6th order) Navier-Stokes solver is coupled with a geometrically nonlinear p-version Reissner-Mindlin finite element plate model to simulate the highly flexible elastic membrane. An implicit LES approach is employed to compute the mixed laminar/transitional/turbulent flowfields present for the low Reynolds number flows associated with micro air vehicles. Intitial computations for a baseline rigid membrane wing are presented to understand the complex vortex dynamics associated with these flows before proceeding with the more challenging flexible cases.

An Investigation of the Aerodynamic Performance of a Biomimetic Insect-Sized Wing for Micro Air Vehicles

2016 ◽  
Author(s):  
Jose E. Rubio ◽  
Uttam K. Chakravarty
Keyword(s):  
Reynolds Number ◽  
Structural Integrity ◽  
Angle Of Attack ◽  
Micro Air Vehicles ◽  
Element Model ◽  
Aerodynamic Performance ◽  
Mode Shapes ◽  
Wing Structures ◽  
Artificial Wing ◽  
Air Vehicles

Biologically-inspired micro air vehicles (MAVs) are miniature-scaled autonomous aircrafts which attempt to biomimic the exceptional maneuver control during low-speed flight mastered by insects. Flexible wing structures are critical elements of a nature-inspired MAV as evidence supports that the wings of aerial insects experience highly-elastic deformations that enable insects to proficiently hover and maneuver in different airflow conditions. For this study, a crane fly (family Tipulidae) forewing is selected as the target specimen to replicate both its structural integrity and aerodynamic performance. The artificial insect-sized wing is manufactured using photolithography with negative photoresist SU-8 to fabricate the vein geometry. A Kapton film is attached to the vein pattern for the assembling of the wing. The natural frequencies and mode shapes of the artificial wing are determined to characterize its vibrations. A numerical simulation of the fluid-structure interaction is conducted by coupling a finite element model of the artificial wing with a computational fluid dynamics model of the surrounding airflow. From these simulations, the deformation response and the coefficients of drag and lift of the artificial wing are predicted for different freestream velocities and angles of attack. The deformation along the span of the wing increases nonlinearly with Reynolds number from the root to the tip of the wing. The coefficient of lift increases with angle of attack and Reynolds number. The coefficient of drag decreases with Reynolds number and angle of attack. The aerodynamic efficiency, defined as the ratio of the coefficient of lift to the coefficient of drag, of the artificial wing increases with angle of attack and Reynolds number.

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