The Effect of Aspect Ratio on Torus Wake Structure

2021 ◽  
pp. 201-226
Author(s):  
Ali Shams ◽  
Rupp Carriveau ◽  
David S.-K. Ting
Keyword(s):  
Aspect Ratio ◽  
Wake Structure

The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders

2019 ◽  
Vol 875 ◽  
pp. 929-960 ◽  
Author(s):  
Yendrew Yauwenas ◽  
Ric Porteous ◽  
Danielle J. Moreau ◽  
Con J. Doolan
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Amplitude Modulation ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Cylinder Wake ◽  
Near Wake ◽  
Wake Structure ◽  
Velocity Amplitude ◽  
Aspect Ratios

This paper presents a combined experimental and large-eddy simulation study to characterise the effect of aspect ratio on the near-wake structure of a square finite wall-mounted cylinder (FWMC). The cylinder aspect ratios (span $L$ to width $W$) investigated in the experiments were $1.4\leqslant L/W\leqslant 21.4$ and the oncoming boundary-layer thicknesses were $1.3W$ and $0.9W$ at a Reynolds number based on cylinder width of $1.4\times 10^{4}$ and $1.1\times 10^{4}$, respectively. In complementary simulations, the cylinder aspect ratios investigated were 1.4, 4.3, 10 and 18.6. The cylinder wake structure was visualised in three-dimensional space using a vortex core detection method and decomposed to its oscillation modes using the spectral proper orthogonal decomposition (SPOD) technique. A parametric diagram is proposed to predict whether the time-averaged wake structure is a dipole or a quadrupole pattern, based on oncoming boundary-layer height and aspect ratio. Cellular shedding occurs when the aspect ratio is high with up to three shedding cells occurring across the span for aspect ratios $L/W>18$. Each of these cells sheds at a distinct frequency, as evidenced by the spectral content of the surface pressure measured on the side face and the near-wake velocity. Amplitude modulation is also observed in the vortex shedding, which explains the amplitude modulation of the acoustic pressure emitted by square FWMCs. SPOD is shown to be a viable method to identify the occurrence of cellular shedding in the wake.

scholarly journals The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel

2008 ◽  
Vol 603 ◽  
pp. 331-365 ◽  
Author(s):  
JAMES H. J. BUCHHOLZ ◽  
ALEXANDER J. SMITS
Keyword(s):  
Aspect Ratio ◽  
Strouhal Number ◽  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Dimensional Structure ◽  
Peak Efficiency ◽  
Thrust Coefficient ◽  
Wake Structure ◽  
Thrust Performance

Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. For ReC = O(104), thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel AR. Propulsive efficiency was sensitive to aspect ratio only for AR less than 0.83; however, the magnitude of the peak efficiency of a given panel with variation in Strouhal number varied inversely with the amplitude to span ratio A/S, while the Strouhal number of optimum efficiency increased with increasing A/S. Peak efficiencies between 9% and 21% were measured. Wake structures corresponding to a subset of the thrust measurements were investigated using dye visualization and digital particle image velocimetry. In general, the wakes divided into two oblique jets; however, when operating at or near peak efficiency, the near wake in many cases represented a Kármán vortex street with the signs of the vortices reversed. The three-dimensional structure of the wakes was investigated in detail for AR = 0.54, A/S = 0.31 and ReC = 640. Three distinct wake structures were observed with variation in Strouhal number. For approximately 0.20 < St < 0.25, the main constituent of the wake was a horseshoe vortex shed by the tips and trailing edge of the panel. Streamwise variation in the circulation of the streamwise horseshoe legs was consistent with a spanwise shear layer bridging them. For St > 0.25, a reorganization of some of the spanwise vorticity yielded a bifurcating wake formed by trains of vortex rings connected to the tips of the horseshoes. For St > 0.5, an additional structure formed from a perturbation of the streamwise leg which caused a spanwise expansion. The wake model paradigm established here is robust with variation in Reynolds number and is consistent with structures observed for a wide variety of unsteady flows. Movies are available with the online version of the paper.

Wake Structure and Performance of Finite Aspect-Ratio Flapping Foils

2005 ◽  
Author(s):  
Haibo Dong ◽  
Rajat Mittal ◽  
Meliha Bozkurttas ◽  
Fady Najjar
Keyword(s):  
Aspect Ratio ◽  
Wake Structure ◽  
And Performance ◽  
Flapping Foils

scholarly journals On the evolution of the wake structure produced by a low-aspect-ratio pitching panel

2005 ◽  
Vol 546 (-1) ◽  
pp. 433 ◽  
Author(s):  
JAMES H. J. BUCHHOLZ ◽  
ALEXANDER J. SMITS
Keyword(s):  
Aspect Ratio ◽  
Wake Structure ◽  
Low Aspect Ratio

The Effect of Pitching Frequency on the Hydrodynamics of Oscillating Foils

2019 ◽  
Vol 86 (10) ◽  
Author(s):  
Arman Hemmati ◽  
Alexander J. Smits
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Strouhal Number ◽  
Vortex Formation ◽  
Free Swimming ◽  
Trailing Edge ◽  
Wake Structure ◽  
Abrupt Transition ◽  
Vortex Streets ◽  
Karman Street

Abstract The effects of two different pitching frequencies (that is, Strouhal number, St) on the wake structure generated by two foils of aspect ratio 1.0 are examined numerically at a Reynolds number of 10,000. Strouhal numbers of 0.5 and 0.2 were studied, the first corresponding approximately to the peak in efficiency and the second corresponding to the point where the thrust is equal to the drag (the free-swimming condition). The two foils have either a square trailing edge or a convex trailing edge that mimics the shape of the caudal fin exhibited by certain species of fish. In previous works, the convex trailing edge panel was found to have higher thrust and efficiency compared with the square panel trailing edge. Here, these differences are related to their characteristic vortex formation and detachment processes leading to differences in wake coherence and extension. The wake of the square panel at St = 0.2 transitions slowly from a reverse von Kármán street (2S) pattern to a paired (2P) system as the wake develops downstream, whereas at St = 0.5, the wake almost immediately takes on a 2P form with an attendant split in the wake structure. For the convex panel, the transition from a 2S to a 2P structure at St = 0.2 is slower than that seen for the square panel, and for St = 0.5, the wake undergoes an abrupt transition leading to two distinct vortex streets that evolve at a considerably slower rate than seen for the square panel.

The Wake Structure of a Stationary and a Rotary Wall-Mounted Low-Aspect-Ratio Cylinder

AIAA Journal ◽  
2021 ◽  
pp. 1-9
Author(s):  
Hisham M. Shehata ◽  
Albert Medina
Keyword(s):  
Aspect Ratio ◽  
Wake Structure ◽  
Low Aspect Ratio

Wake structure of a finite circular cylinder of small aspect ratio

2004 ◽  
Vol 37 (5) ◽  
pp. 720-730 ◽  
Author(s):  
D. Sumner ◽  
J. L. Heseltine ◽  
O. J. P. Dansereau
Keyword(s):  
Aspect Ratio ◽  
Circular Cylinder ◽  
Small Aspect Ratio ◽  
Wake Structure
Sign in / Sign up

Export Citation Format

Share Document