Drag and wake structure of a quasi-dandelion pappus model at low and moderate Reynolds numbers: The effects of filament width

2021 ◽  
Vol 33 (12) ◽  
pp. 121904
Author(s):  
Shiqing Li ◽  
Dingyi Pan ◽  
Jun Li ◽  
Xueming Shao
Keyword(s):  
Reynolds Numbers ◽  
Wake Structure

scholarly journals Wake structure and wingbeat kinematics of a house-martin Delichon urbica

2007 ◽  
Vol 4 (15) ◽  
pp. 659-668 ◽  
Author(s):  
M Rosén ◽  
G.R Spedding ◽  
A Hedenström
Keyword(s):  
Reynolds Numbers ◽  
Laminar Flows ◽  
Frequency Model ◽  
Wake Structure ◽  
Global Circulation ◽  
Weight Support ◽  
House Martin ◽  
Lifting Surfaces ◽  
Thrush Nightingale ◽  
Slender Wing

The wingbeat kinematics and wake structure of a trained house martin in free, steady flight in a wind tunnel have been studied over a range of flight speeds, and compared and contrasted with similar measurements for a thrush nightingale and a pair of robins. The house martin has a higher aspect ratio (more slender) wing, and is a more obviously agile and aerobatic flyer, catching insects on the wing. The wingbeat is notable for the presence at higher flight speeds of a characteristic pause in the upstroke. The essential characteristics of the wing motions can be reconstructed with a simple two-frequency model derived from Fourier analysis. At slow speeds, the distribution of wake vorticity is more simple than for the other previously measured birds, and the upstroke does not contribute to weight support. The upstroke becomes gradually more significant as the flight speed increases, and although the vortex wake shows a signature of the pause phase, the global circulation measurements are otherwise in good agreement with surprisingly simple aerodynamic models, and with predictions across the different species, implying quite similar aerodynamic performance of the wing sections. The local Reynolds numbers of the wing sections are sufficiently low that the well-known instabilities of attached laminar flows over lifting surfaces, which are known to occur at two to three times this value, may not develop.

Vortex shedding from circular cylinders at low Reynolds numbers

1971 ◽  
Vol 46 (4) ◽  
pp. 749-756 ◽  
Author(s):  
M. Gaster
Keyword(s):  
Cross Section ◽  
Vortex Shedding ◽  
Circular Cross Section ◽  
Reynolds Numbers ◽  
Similar Type ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Wake Structure ◽  
Low Reynolds Numbers ◽  
Cell Shedding

Experiments on slightly tapered models of circular cross-section have shown that the vortex wake structure exists in a number of discrete cells having different shedding frequencies. Within each cell shedding is regular and periodic, the frequency being somewhat lower than that from a parallel cylinder of the same diameter. A similar type of wake behaviour has also been observed on a parallel model in a non-uniform mean flow. These results suggest that the discontinuities in the shedding law observed by Tritton could arise through non-uniformities in the flow.

Cross-Wire Measurements in the Wake of an Airfoil at Low Reynolds Numbers With and Without Acoustic Excitation

2002 ◽  
Author(s):  
Serhiy Yarusevych ◽  
Pierre E. Sullivan ◽  
John G. Kawall
Keyword(s):  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Surface Flow ◽  
Wake Vortex ◽  
Acoustic Excitation ◽  
Separation Region ◽  
Wind Tunnel Experiments ◽  
Wake Structure ◽  
Low Reynolds Numbers ◽  
Cross Wire

The wake structure and vortex shedding characteristics of a NACA 0025 airfoil were studied experimentally. Wind tunnel experiments were carried out for three Reynolds numbers and three angles of attack by means of cross-wire measurements, spectral analysis and complementary surface flow visualization. Evidence of wake vortex shedding and flow separation was obtained for most of the cases examined, and dependence of these phenomena on Reynolds number and angle of attack was found. External acoustic excitation at a particular frequency was found to eliminate or reduce the separation region and decrease the airfoil wake. Moreover, the results show that the acoustic excitation has a significant effect on vortex shedding and can improve airfoil performance, i.e. produce an increase of the lift and/or decrease of the drag.

scholarly journals Wake structure of a transversely rotating sphere at moderate Reynolds numbers

2009 ◽  
Vol 621 ◽  
pp. 103-130 ◽  
Author(s):  
M. GIACOBELLO ◽  
A. OOI ◽  
S. BALACHANDAR
Keyword(s):  
Vortex Shedding ◽  
Free Stream ◽  
Stokes Equations ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Stream Velocity ◽  
Wake Structure ◽  
Navier Stokes Equations ◽  
Chebyshev Spectral Collocation

The uniform flow past a sphere undergoing steady rotation about an axis transverse to the free stream flow was investigated numerically. The objective was to reveal the effect of sphere rotation on the characteristics of the vortical wake structure and on the forces exerted on the sphere. This was achieved by solving the time-dependent, incompressible Navier–Stokes equations, using an accurate Fourier–Chebyshev spectral collocation method. Reynolds numbers Re of 100, 250 and 300 were considered, which for a stationary sphere cover the axisymmetric steady, non-axisymmetric steady and vortex shedding regimes. The study identified wake transitions that occur over the range of non-dimensional rotational speeds Ω* = 0 to 1.00, where Ω* is the maximum velocity on the sphere surface normalized by the free stream velocity. At Re = 100, sphere rotation triggers a transition to a steady double-threaded structure. At Re = 250, the wake undergoes a transition to vortex shedding for Ω* ≥ 0.08. With an increasing rotation rate, the recirculating region is progressively reduced until a further transition to a steady double-threaded wake structure for Ω* ≥ 0.30. At Re = 300, wake shedding is suppressed for Ω* ≥ 0.50 via the same mechanism found at Re = 250. For Ω* ≥ 0.80, the wake undergoes a further transition to vortex shedding, through what appears to be a shear layer instability of the Kelvin–Helmholtz type.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

TRANSONIC CROSS FLOW (M∞ = 0.8) OVER A CIRCULAR CYLINDER AT HIGH REYNOLDS NUMBERS

2012 ◽  
Vol 43 (5) ◽  
pp. 589-613
Author(s):  
Vyacheslav Antonovich Bashkin ◽  
Ivan Vladimirovich Egorov ◽  
Ivan Valeryevich Ezhov ◽  
Sergey Vladimirovich Utyuzhnikov
Keyword(s):  
Circular Cylinder ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
High Reynolds
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