The role of effective angle of attack in hovering pitching-flapping-perturbed revolving wings at low Reynolds number

2020 ◽  
Vol 32 (1) ◽  
pp. 011906
Author(s):  
Long Chen ◽  
Chao Zhou ◽  
Jianghao Wu
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Angle Of Attack ◽  
Effective Angle ◽  
Low Reynolds

scholarly journals Determine Aerodynamic Characteristics for FX63-137 Aerofoil by Using Subsonic Wind Tunnel

2014 ◽  
Vol 695 ◽  
pp. 651-654 ◽  
Author(s):  
Magedi Moh M. Saad ◽  
Norzelawati Asmuin
Keyword(s):  
Reynolds Number ◽  
Aluminum Alloy ◽  
Wind Tunnel ◽  
Low Reynolds Number ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
Cnc Machine ◽  
Subsonic Wind Tunnel ◽  
Low Reynolds

This paper is primarily concentrated with determining aerodynamic characteristics and choosing the best angle of attack at a maximum lift and low drag for the FX 63-137 aerofoil at a low Reynolds number and a speed of 20m/s and 30m/s, by using subsonic wind tunnel through manufacturing the aerofoil by aluminum alloy using a CNC machine. The proposed methodology is divided into several stages. Firstly, manufacturing the aerofoil using an aluminum alloy. Secondly, the testing process is carried out using subsonic wind tunnel. Thirdly, the results are displayed and compared with results produced from related works, in order to find out the best angle of attack at a maximum lift.

Unsteady swimming of small organisms

2012 ◽  
Vol 702 ◽  
pp. 286-297 ◽  
Author(s):  
S. Wang ◽  
A. M. Ardekani
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Fundamental Equation ◽  
Added Mass ◽  
Natural Environments ◽  
Mean Velocity ◽  
Unsteady Forces ◽  
Uniform Background ◽  
Low Reynolds

AbstractSmall planktonic organisms ubiquitously display unsteady or impulsive motion to attack a prey or escape a predator in natural environments. Despite this, the role of unsteady forces such as history and added mass forces on the low-Reynolds-number propulsion of small organisms, e.g. Paramecium, is poorly understood. In this paper, we derive the fundamental equation of motion for an organism swimming by means of the surface distortion in a non-uniform background flow field at a low-Reynolds-number regime. We show that the history and added mass forces are important as the product of Reynolds number and Strouhal number increases above unity. Our results for an unsteady squirmer show that unsteady inertial effects can lead to a non-zero mean velocity for the cases with zero streaming parameters, which have zero mean velocity in the absence of inertia.

Vertical Migration of the Small Organisms in a Stratified Fluid

2012 ◽  
Author(s):  
Amin Doostmohammadi ◽  
Arezoo M. Ardekani
Keyword(s):  
Reynolds Number ◽  
Vertical Migration ◽  
Low Reynolds Number ◽  
Nonlinear Effects ◽  
Stratified Fluid ◽  
Salinity Gradients ◽  
Density Interfaces ◽  
Low Reynolds ◽  
Made In

Significant progress has been made in analyzing low-Reynolds number locomotion in homogeneous fluids. Even though density interfaces due to temperature or salinity gradients (pycnoclines), ubiquitously occur in oceans and lakes, the effects of stratification on the hydrodynamics of swimming of small organisms, their interaction with each other and their migration are very poorly understood. In this article, we implement a direct numerical simulation of the migration of swimmers at pycnoclines and illustrate the role of the diffusivity of the stratified agent on the swimming of small organisms. We demonstrate that for an archetypal swimmer model, squirmer, the migration at density stratified fluid can be largely influenced by buoyancy effects. We also show that the effects of density stratification are increased as the diffusivitty of the stratified agent is reduced. The results demonstrate that the stratification suppresses the vertical migration and consequently affects the life of low Reynolds number swimmers across pycnoclines. Our recent computational results reveal the full nonlinear effects of stratification on the locomotion of small organisms.

scholarly journals Numerical Investigation on Aerodynamic Performance of Bird’s Airfoils

2020 ◽  
Author(s):  
Ashraf Omar ◽  
Rania Rahuma ◽  
Abdulhaq Emhemmed
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Angle Of Attack ◽  
Aerodynamic Performance ◽  
Airfoil Surface ◽  
Aerodynamic Efficiency ◽  
Gliding Flight ◽  
Surface Permeability ◽  
Low Reynolds ◽  
Better Than

In this work, the aerodynamic performance of four types of bird’s airfoils (eagle, stork, hawk, and albatross) at low Reynolds number and a range of angles of attack during fixed (unflapping) gliding flight was numerically investigated utilizing open-source computational fluid dynamics (CFD) code Stanford University unstructured (SU2) and K-ω Shear Stress Transport (K-ω SST) turbulence model. The flow of the simulated cases was assumed to be incompressible, viscous, and steady. For verification and comparison, a low Reynolds number man-made Eppler 193’s airfoil was simulated. The results revealed that stork has the greatest aerodynamic efficiency followed by albatross and eagle. However, at zero angle of attack, the albatross aerodynamic efficiency exceeded all the other birds by a significant amount. In terms of aerodynamics efficiency, stork’s and albatross’s airfoils performed better than Eppler 193 at angles of attack less than 8°, while at a higher angle of attack all studied birds’ airfoils performed better than Eppler 193. The effect of surface permeability was also investigated for the eagle’s airfoil where the permeable surface occupied one-third of the total airfoil surface. Permeability increased the generated lift and the aerodynamic efficiency of the eagle’s airfoil for angles of attack less than 10°. The increase reached 58% for the lift at zero angle of attack. After the specified angle, the permeability had an adverse effect on the flow which may be due to the transition to turbulent ahead of the permeable section.

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