scholarly journals LES ANALYSIS OF AERODYNAMIC CHARACTERISTICS FOR RECTANGULAR CYLINDERS WITH SMALL SIDE RATIO : Effects of oncoming turbulent flow

2004 ◽  
Vol 69 (581) ◽  
pp. 15-22
Author(s):  
Tetsuro TAMURA ◽  
P.P.N.L. DIAS ◽  
Yoshiyuki ONO
Keyword(s):  
Turbulent Flow ◽  
Aerodynamic Characteristics ◽  
Side Ratio ◽  
Rectangular Cylinders ◽  
Small Side

Transverse Vibration Characteristics of a Rectangular Prism with Small Side Ratio and Flow Field around the Prism

2017 ◽  
Vol 2017 (0) ◽  
pp. S0520506
Author(s):  
Shunichi MIZUKAMI ◽  
Takahiro KIWATA ◽  
Takaaki KONO ◽  
Barata La Ode ◽  
Toshiyuki UENO
Keyword(s):  
Flow Field ◽  
Transverse Vibration ◽  
Vibration Characteristics ◽  
Rectangular Prism ◽  
Side Ratio ◽  
Small Side

Spectral analysis and coherence of aerodynamic lift on rectangular cylinders in turbulent flow

2017 ◽  
Vol 830 ◽  
pp. 408-438 ◽  
Author(s):  
Shaopeng Li ◽  
Mingshui Li
Keyword(s):  
Turbulent Flow ◽  
Closed Form ◽  
Vertical Velocity ◽  
Lift Force ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Velocity Fluctuations ◽  
Dimensional Effects ◽  
Decay Parameters ◽  
Rectangular Cylinders

The goal of the present work is to derive the closed-form expressions of coherence and admittances to describe the spatial distribution of lift on rectangular cylinders in turbulent flow, which can be used to investigate the three-dimensional effects of turbulence. The coherence of the three-dimensional aerodynamic admittance (3D AAF), which takes into full account the spanwise variations in the vertical velocity fluctuations, is introduced to assess the validity of the strip assumption. A theoretical coherence model expressed in a double-exponential form is derived starting from the two-wavenumber spectral tensor of the lift on a thin aerofoil in Fourier space, providing us with explicit insight into the coherence of the lift force. Notably, it is an intrinsic property that the lift force on the structure is more strongly correlated than the oncoming flow and 3D AAF. This coherence model is extended to rectangular cylinders by the introduction of three floating parameters into the decay parameters of the 3D AAF. Based on theoretical and experimental investigations, it is shown that the three-dimensional effects of turbulence grow more prominent as the difference between the decay parameters of the 3D AAF and vertical velocity fluctuations decreases. A generalized approach for rapidly deriving the closed-form expressions of the admittances is proposed to study the unsteady behaviour of the lift force and the distortion of the free stream passing through the rectangular cylinders.

scholarly journals Experimental Study on Aerodynamic Characteristics of a Gurney Flap on a Wind Turbine Airfoil under High Turbulent Flow Condition

2020 ◽  
Vol 10 (20) ◽  
pp. 7258 ◽  
Author(s):  
Junwei Yang ◽  
Hua Yang ◽  
Weijun Zhu ◽  
Nailu Li ◽  
Yiping Yuan
Keyword(s):  
Wind Tunnel ◽  
Turbulent Flow ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Chord Length ◽  
Turbulence Level ◽  
Gurney Flaps ◽  
Gurney Flap ◽  
Delay Phenomenon

The objective of the current work is to experimentally investigate the effect of turbulent flow on an airfoil with a Gurney flap. The wind tunnel experiments were performed for the DTU-LN221 airfoil under different turbulence level (T.I. of 0.2%, 10.5% and 19.0%) and various flap configurations. The height of the Gurney flaps varies from 1% to 2% of the chord length; the thickness of the Gurney flaps varies from 0.25% to 0.75% of the chord length. The Gurney flap was vertical fixed on the pressure side of the airfoil at nearly 100% measured from the leading edge. By replacing the turbulence grille in the wind tunnel, measured data indicated a stall delay phenomenon while increasing the inflow turbulence level. By further changing the height and the thickness of the Gurney flap, it was found that the height of the Gurney flap is a very important parameter whereas the thickness parameter has little influence. Besides, velocity in the near wake zone was measured by hot-wire anemometry, showing the mechanisms of lift enhancement. The results demonstrate that under low turbulent inflow condition, the maximum lift coefficient of the airfoil with flaps increased by 8.47% to 13.50% (i.e., thickness of 0.75%), and the Gurney flap became less effective after stall angle. The Gurney flap with different heights increased the lift-to-drag ratio from 2.74% to 14.35% under 10.5% of turbulence intensity (i.e., thickness of 0.75%). However, under much a larger turbulence environment (19.0%), the benefit to the aerodynamic performance was negligible.

scholarly journals Aerodynamic Differences between New and Used Soccer Balls

2021 ◽  
Vol 11 (16) ◽  
pp. 7204
Author(s):  
Sungchan Hong ◽  
Takeshi Asai
Keyword(s):  
Surface Roughness ◽  
Wind Tunnel ◽  
Turbulent Flow ◽  
Surface Structure ◽  
Reynold Number ◽  
Aerodynamic Characteristics ◽  
Drag Coefficients ◽  
Surface Conditions ◽  
Soccer Ball ◽  
Surface Damages

The surface structure of soccer balls, such as the number and shapes of the ball panels, has recently changed, and research on the aerodynamics and flight trajectories of new soccer balls is actively proceeding. However, these studies are focused on new soccer balls, whereas the used soccer balls were never studied. In this study, the aerodynamic characteristics of soccer balls kicked 1000 times by a robot were investigated through wind tunnel tests. The results were compared with those obtained using new soccer balls. Regarding the aerodynamic characteristics of the soccer balls, it was found that the critical Reynold number, Recrit, changes with usage. This is related to the transition from laminar to turbulent flow of airflow around the ball. The comparison of the drag coefficients of the balls at Recrit showed that the drag coefficients of the new and used Telstar18 balls were 0.15 (Re = 2.5 × 105) and 0.14 (Re = 2.2 × 105), respectively; those of the new and used Merlin were 0.13 (Re = 2.8 × 105) and 0.13 (Re = 2.2 × 105), respectively; and finally, those of the new and used Derbystar were 0.14 (Re = 2.1×105) and 0.14 (Re = 2.1×105), respectively. The surface conditions of a soccer ball, such as the surface roughness and surface damages, are essential factors to determine the aerodynamics of the soccer balls.

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