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Comparison between spatial and temporal wall oscillations in turbulent boundary layer flows

หน่วยงาน Nanyang Technological University, Singapore

รายละเอียด

ชื่อเรื่อง : Comparison between spatial and temporal wall oscillations in turbulent boundary layer flows
นักวิจัย : Skote, Martin
คำค้น : -
หน่วยงาน : Nanyang Technological University, Singapore
ผู้ร่วมงาน : -
ปีพิมพ์ : 2556
อ้างอิง : Skote, M. (2013). Comparison between spatial and temporal wall oscillations in turbulent boundary layer flows. Journal of Fluid Mechanics, 730, 273-294. , http://hdl.handle.net/10220/13224 , http://dx.doi.org/10.1017/jfm.2013.344 , 174442
ที่มา : -
ความเชี่ยวชาญ : -
ความสัมพันธ์ : Journal of fluid mechanics
ขอบเขตของเนื้อหา : -
บทคัดย่อ/คำอธิบาย :

Direct numerical simulations have been performed to study the drag reduction resulting from spatial oscillations of a segment of the wall under a turbulent boundary layer. The oscillating motion is imposed by utilizing a streamwise modulated spanwise wall forcing. The results are compared with earlier simulations using temporal oscillations with an identical segment and forcing amplitudes, and with a frequency related to the wavelength through a convective velocity. Two different oscillation amplitudes with equal oscillation wavelength have been used, which allows for a direct comparison between a relatively weak and strong forcing of the flow. The weaker forcing results in 25 % drag reduction while the stronger forcing, with twice the amplitude, yields 41 % drag reduction. Comparison with the temporal cases reveals drastically improved energy savings for the spatial oscillation technique, in accordance with earlier channel flow investigations. The streamwise variation of spanwise shear is shown to follow the analytical solution to the laminar Navier–Stokes equations derived under the assumption of constant friction velocity. Furthermore, the spanwise velocity profiles at various phases are compared with the analytical solution, and show very good agreement. The downstream development of the spatial Stokes layer thickness is theoretically estimated to be ∼x1/15, in general agreement with the simulation data. The spatial variation of the spanwise Reynolds stress is investigated and compared with the variation in time for the temporal wall forcing cases. The controversy regarding a zero or non-zero production of spanwise Reynolds stress in the temporal case is elucidated. In addition, comparison with the spatial case reveals that a second production term originating from the downstream variation of the spanwise wall velocity has a negative contribution to the production, and hence relates to the larger drag reduction in the case of spatial forcing.

บรรณานุกรม :
Skote, Martin . (2556). Comparison between spatial and temporal wall oscillations in turbulent boundary layer flows.
    กรุงเทพมหานคร : Nanyang Technological University, Singapore.
Skote, Martin . 2556. "Comparison between spatial and temporal wall oscillations in turbulent boundary layer flows".
    กรุงเทพมหานคร : Nanyang Technological University, Singapore.
Skote, Martin . "Comparison between spatial and temporal wall oscillations in turbulent boundary layer flows."
    กรุงเทพมหานคร : Nanyang Technological University, Singapore, 2556. Print.
Skote, Martin . Comparison between spatial and temporal wall oscillations in turbulent boundary layer flows. กรุงเทพมหานคร : Nanyang Technological University, Singapore; 2556.