A Numerical Study of Low-Aspect-Ratio Flapping-Wings in Forward Flight

2019 ◽  
pp. 405-410
Author(s):  
A. Gonzalo ◽  
G. Arranz ◽  
M. Moriche ◽  
O. Flores ◽  
M. García-Villalba
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Flapping Wings ◽  
Forward Flight ◽  
Low Aspect Ratio

Experimental and Numerical Study of Stall Flutter in a Transonic Low-Aspect Ratio Fan Blisk

2003 ◽  
Author(s):  
A. J. Sanders ◽  
K. K. Hassan ◽  
D. C. Rabe
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Strain Gages ◽  
Pressure Transducers ◽  
Low Aspect Ratio ◽  
Benchmark Data

Experiments are performed on a modern design transonic shroudless low-aspect ratio fan blisk that experienced both subsonic/transonic and supersonic stall-side flutter. High-response flush mounted miniature pressure transducers are utilized to measure the unsteady aerodynamic loading distribution in the tip region of the fan for both flutter regimes, with strain gages utilized to measure the vibratory response at incipient and deep flutter operating conditions. Numerical simulations are performed and compared with the benchmark data using an unsteady three-dimensional nonlinear viscous computational fluid dynamic (CFD) analysis, with the effects of tip clearance, vibration amplitude, and the number of time steps-per-cycle investigated. The benchmark data are used to guide the validation of the code and establish best practices that ensure accurate flutter predictions.

Numerical study of the sound generated by two tandem arranged wings in forward flight

2020 ◽  
pp. 095440622092446
Author(s):  
Nathan A Widdup ◽  
Li Wang ◽  
Fang-Bao Tian
Keyword(s):  
Sound Pressure ◽  
Numerical Study ◽  
High Mass ◽  
Flapping Wings ◽  
Sound Generation ◽  
Mass Ratio ◽  
Forward Flight ◽  
Flexible Wings ◽  
Fluid Mass ◽  
Mass Ratios

The sound generated by two tandem arranged flexible wings in forward flight is numerically studied by using an immersed boundary method, at a Reynolds number of 100 and Mach number of 0.1. Three distinct cases are studied, encompassing a single wing and two tandem wings flapping in phase and out of phase. The sound generation of flapping wings is systematically studied by varying the wing flexibility (represented by the frequency ratio [Formula: see text]), structure-to-fluid mass ratio ([Formula: see text]), the phase difference (φ), and the gap ([Formula: see text]) between the two flapping wings. The results show that there is a direct correlation between the wing flexibility and sound generation for all cases considered. Specifically, for wings of low mass ratios ([Formula: see text]), an increase in flexibility resulted in a decrease in sound generation. For wings of high mass ratios ([Formula: see text]), an increase in flexibility resulted in higher sound output. The introduction of a second wing flapping in-phase resulted in an increase in aerodynamic features and sound generation, while the introduction of a second wing flapping out-of-phase experiences a decrease in sound output when compared to the in-phase case. In both cases, the effect of the wing flexibility on the sound production is similar to that of the single wing. An increase in flexibility is also found to have an impact on the plane of maximum sound pressure. For example, increasing flexibility resulted in a rotation of the plane of maximum sound pressure counter-clockwise relative to those at lower frequency ratios. Flexible wings with a structure-to-fluid mass ratio of unity and medium flexibility (i.e. [Formula: see text] and [Formula: see text]) are found to generate lower sound with high aerodynamic performance conserved.

A Numerical Study of Very High Speed Flat Ship Theory

1991 ◽  
Vol 35 (01) ◽  
pp. 63-72
Author(s):  
Todd McComb
Keyword(s):  
Aspect Ratio ◽  
Symbolic Computation ◽  
High Speed ◽  
Numerical Study ◽  
Analytic Solutions ◽  
Low Aspect Ratio ◽  
Lift And Drag ◽  
Very High

This paper uses an asymptotic procedure to generate analytic solutions to the low-aspect-ratio problem of flat ship theory, in the limit for a very fast ship. The first two terms of the solution are worked out for hulls of parabolic planform and with 20 arbitrary constants in the expression for the draft. Optimizations are then performed for lift and drag on a smaller class of hulls. Analytic solutions were found by using symbolic computation, and the results are discussed. Optimal hulls are presented for various values of the ship's speed, optimized with both total lift and static lift held fixed. The optimization solution in the limit as the ship's speed goes to infinity gives independence of some constants in the expression for the hull.

scholarly journals Experimental and Numerical Study of Flow Structures Associated With Low Aspect Ratio Elliptical Cavities

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Taravat Khadivi ◽  
Eric Savory
Keyword(s):  
Aspect Ratio ◽  
Particle Image ◽  
Numerical Study ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Cavity Flows ◽  
Low Aspect Ratio ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

The flow regimes associated with 2:1 aspect ratio elliptical planform cavities of varying depth immersed in a turbulent boundary layer at a Reynolds number of 8.7 × 104, based on the minor axis of the cavity, have been quantified from particle image velocimetry measurements and three-dimensional steady computational fluid dynamics simulations (Reynolds stress model closure). Although these elliptical cavity flows have some similarities with nominally two-dimensional and rectangular cases, three-dimensional effects due to the low aspect ratio and curvature of the walls give rise to features exclusive to low aspect ratio elliptical cavities, including formation of cellular structures at intermediate depths and vortex structures within and downstream of the cavity.

Cross-Wind Influence on Low Aspect Ratio Wings at Low Reynolds Numbers

2013 ◽  
Author(s):  
Amir Karimi Noughabi ◽  
Mehran Tadjfar
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Lift And Drag ◽  
Lift And Drag Coefficient

The aerodynamics of the low aspect ratio (LAR) wings is of outmost importance in the performance of the fixed-wing micro air vehicles (MAVs). The flow around these wings is widely influenced by three dimensional (3D) phenomena: including wing-tip vortices, formation of laminar bubble, flow separation and reattachment, laminar to turbulent transition or any combination of these phenomena. All the recent studies consider the aerodynamic characteristics of the LAR wings under the effect of the direct wind. Here we focus on the numerical study of the influence of cross-wind on flow over the inverse Zimmerman wings with the aspect ratios (AR) between 1 and 2 at Reynolds numbers between 6×104 and 105. We have considered cross-wind’s angles from 0° to 40° and angle of attack from 0° to 12°. The results show that lift and drag coefficient generally decrease when the angle of the cross-wind is increased.

Bio-inspired design of flapping-wing micro air vehicles

2005 ◽  
Vol 109 (1098) ◽  
pp. 385-393 ◽  
Author(s):  
K. D. Jones ◽  
C. J. Bradshaw ◽  
J. Papadopoulos ◽  
M. F. Platzer
Keyword(s):  
Aspect Ratio ◽  
Figure Of Merit ◽  
Ground Effect ◽  
Micro Air Vehicles ◽  
Flapping Wing ◽  
Flapping Wings ◽  
Rechargeable Battery ◽  
Flight Testing ◽  
Low Aspect Ratio ◽  
Air Vehicles

AbstractIn this paper the development and flight testing of flapping-wing propelled, radio-controlled micro air vehicles are described. The unconventional vehicles consist of a low aspect ratio fixed-wing with a trailing pair of higher aspect ratio flapping wings which flap in counterphase. The symmetric flapping-wing pair provides a mechanically and aerodynamically balanced platform, increases efficiency by emulating flight in ground effect, and suppresses stall over the main wing by entraining flow. The models weigh as little as 11g, with a 23cm span and 18cm length and will fly for about 20 minutes on a rechargeable battery. Stable flight at speeds between 2 and 5ms–1has been demonstrated, and the models are essentially stall-proof while under power. The static-thrust figure of merit for the device is 60% higher than propellers with a similar scale and disk loading.

scholarly journals Numerical Study of Multivortex Regulation in Curved Microchannels with Ultra-Low-Aspect-Ratio

Micromachines ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 81
Author(s):  
Shaofei Shen ◽  
Mengqi Gao ◽  
Fangjuan Zhang ◽  
Yanbing Niu
Keyword(s):  
Aspect Ratio ◽  
Chemical Engineering ◽  
Numerical Study ◽  
Channel Height ◽  
Materials Synthesis ◽  
Inertial Microfluidics ◽  
Low Aspect Ratio ◽  
Curved Channels ◽  
Dean Vortex ◽  
Helical Vortex

The field of inertial microfluidics has been significantly advanced in terms of application to fluid manipulation for biological analysis, materials synthesis, and chemical process control. Because of their superior benefits such as high-throughput, simplicity, and accurate manipulation, inertial microfluidics designs incorporating channel geometries generating Dean vortexes and helical vortexes have been studied extensively. However, existing technologies have not been studied by designing low-aspect-ratio microchannels to produce multi-vortexes. In this study, an inertial microfluidic device was developed, allowing the generation and regulation of the Dean vortex and helical vortex through the introduction of micro-obstacles in a semicircular microchannel with ultra-low aspect ratio. Multi-vortex formations in the vertical and horizontal planes of four dimension-confined curved channels were analyzed at different flow rates. Moreover, the regulation mechanisms of the multi-vortex were studied systematically by altering the micro-obstacle length and channel height. Through numerical simulation, the regulation of dimensional confinement in the microchannel is verified to induce the Dean vortex and helical vortex with different magnitudes and distributions. The results provide insights into the geometry-induced secondary flow mechanism, which can inspire simple and easily built planar 2D microchannel systems with low-aspect-ratio design with application in fluid manipulations for chemical engineering and bioengineering.

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