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RISS 인기검색어
- 검색키워드
- 저자 : David S.K. Ting (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
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Advancing drag crisis of a sphere via the manipulation of integral length scale
Moradian, Niloofar,Ting, David S.K.,Cheng, Shaohong Techno-Press 2011 Wind and Structures, An International Journal (WAS Vol.14 No.1
Spherical object in wind is a common scenario in daily life and engineering practice. The main challenge in understanding the aerodynamics in turbulent wind lies in the multi-aspect of turbulence. This paper presents a wind tunnel study, which focuses on the role of turbulence integral length scale ${\Lambda}$ on the drag of a sphere. Particular turbulent flow conditions were achieved via the proper combination of wind speed, orifice perforated plate, sphere diameter (D) and distance downstream from the plate. The drag was measured in turbulent flow with $2.2{\times}10^4{\leq}Re{\leq}8{\times}10^4$, $0.043{\leq}{\Lambda}/D{\leq}3.24$, and turbulence intensity Tu up to 6.3%. Our results confirmed the general trends of decreasing drag coefficient and critical Reynolds number with increasing turbulence intensity. More interestingly, the unique role of the relative integral length scale has been revealed. Over the range of conditions studied, an integral length of approximately 65% the sphere diameter is most effective in reducing the drag.
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The subtle effect of integral scale on the drag of a circular cylinder in turbulent cross flow
Younis, Nibras,Ting, David S.K. Techno-Press 2012 Wind and Structures, An International Journal (WAS Vol.15 No.6
The effects of Reynolds number (Re), freestream turbulence intensity (Tu) and integral length scale (${\Lambda}$) on the drag coefficient ($C_d$) of a circular cylinder in cross flow were experimentally studied for $6.45{\times}10^3$ < Re < $1.82{\times}10^4$. With the help of orificed plates, Tu was fixed at approximately 0.5%, 5%, 7% and 9% and the normalized integral length scale (L/D) was varied from 0.35 to 1.05. Our turbulent results confirmed the general trend of decreasing $C_d$ with increasing Tu. The effectiveness of Tu in reducing $C_d$ is found to lessen with increasing ${\Lambda}$/D. Most interestingly, freestream turbulence of low Tu (${\approx}5%$) and large ${\Lambda}$/D (${\approx}1.05$) can increase the $C_d$ above the corresponding smooth flow value.
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The subtle effect of integral scale on the drag of a circular cylinder in turbulent cross flow
Nibras Younis,David S.K. Ting 한국풍공학회 2012 Wind and Structures, An International Journal (WAS Vol.15 No.6
The effects of Reynolds number (Re), freestream turbulence intensity (Tu) and integral length scale (Λ) on the drag coefficient (Cd) of a circular cylinder in cross flow were experimentally studied for 6.45 × 103 < Re < 1.82 × 104. With the help of orificed plates, Tu was fixed at approximately 0.5%, 5%, 7% and 9% and the normalized integral length scale (L/D) was varied from 0.35 to 1.05. Our turbulent results confirmed the general trend of decreasing Cd with increasing Tu. The effectiveness of Tu in reducing Cd is found to lessen with increasing Λ/D. Most interestingly, freestream turbulence of low Tu ( ~5%) and large Λ/D (~1.05 ) can increase the Cd above the corresponding smooth flow value.
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Advancing drag crisis of a sphere via the manipulation of integral length scale
Niloofar Moradian,David S-K. Ting,Shaohong Cheng 한국풍공학회 2011 Wind and Structures, An International Journal (WAS Vol.14 No.1
Spherical object in wind is a common scenario in daily life and engineering practice. The main challenge in understanding the aerodynamics in turbulent wind lies in the multi aspect of turbulence. This paper presents a wind tunnel study, which focuses on the role of turbulence integral length scale Λ on the drag of a sphere. Particular turbulent flow conditions were achieved via the proper combination of wind speed, orifice perforated plate, sphere diameter (D) and distance downstream from the plate. The drag was measured in turbulent flow with 2.2 × 10^4 ≤ Re ≤ 8 × 10^4, 0.043 ≤ ∧/D ≤ 3.24, and turbulence intensity Tu up to 6.3%. Our results confirmed the general trends of decreasing drag coefficient and critical Reynolds number with increasing turbulence intensity. More interestingly, the unique role of the relative integral length scale has been revealed. Over the range of conditions studied, an integral length of approximately 65% the sphere diameter is most effective in reducing the drag.
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Raeesi, Arash,Cheng, Shaohong,Ting, David S.K. Techno-Press 2008 Wind and Structures, An International Journal (WAS Vol.11 No.3
The spanwise flow structure around a rigid smooth circular cylinder model in cross-flow has been investigated based on the experimental data obtained from a series of wind tunnel tests. Surface pressures were collected at five spanwise locations along the cylinder over a Reynolds number range of $1.14{\times}15^5$ to $5.85{\times}10^5$, which covered sub-critical, single-bubble and two-bubble regimes in the critical range. Separation angles were deduced from curve fitted to the surface pressure data. In addition, spanwise correlations and power spectra analyses were employed to study the spatial structure of flow. Results at different spanwise locations show that the transition into single-bubble and two-bubble regimes could occur at marginally different Reynolds numbers which expresses the presence of overlap regions in between the single-bubble regime and its former and later regimes. This indicates the existence of three-dimensional flow around the circular cylinder in cross-flow, which is also supported by the observed cell-like surface pressure patterns. Relatively strong spanwise correlation of the flow characteristics is observed before each transition within the critical regime, or formation of first and second separation-bubbles. It is also noted that these organized flow structures might lead to greater overall aerodynamic forces on a circular cylinder in cross-flow within the critical Reynolds number regime.
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