Yang, Qiang (2016) Turbulent skin-friction drag reduction control by spanwise motion. PhD thesis, University of Warwick.

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Abstract

Three types of actuators, i.e., oscillating walls, Lorentz force actuators and DBD plasma actuators, were used to actively control turbulent boundary layer for the turbulent skin-friction drag reduction with Direct Numerical Simulations. The main object is to understand drag reduction mechanism in simple spanwise wall oscillation case (Jung et al., 1992), then implement the control using more practical Lorentz force actuators and plasma actuators. A large amount of 40 ± 2%, 30 ± 2% and 20±2% drag reduction was observed at Rer = 200 turbulent channel for oscillating walls, Lorentz force actuators and plasma actuators, respectively. Different configurations for Lorentz force and plasma actuators were intensively studied, with a new configuration proposed for DBD plasma actuators. The present study suggests a good prospective of skin-friction drag reduction by using Lorentz force actuators for ocean transportation, and DBD plasma actuators for land and air transportation. However, no net energy saving was obtained for both actuators considering the fluid power required for flow control, and this situation was even worse if the electric efficiency of the actuators was accounted for. For all three types of actuators, the interaction between the actuators and the near wall turbulent structure is presented using ensemble averaged method. DNS control cases were also performed at moderate Reynolds numbers, i.e, Rer = 800 and 1600, to understand the role of recently discovered very large scale motions (VLSMs). The result suggests that the control of the VLSMs in the outer region is necessary for maximising drag reduction at high Reynolds number turbulent flows

Item Type:	Thesis (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Frictional resistance (Hydrodynamics), Boundary layer control, Actuators, Turbulence
Official Date:	May 2016
Dates:	Date Event May 2016 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Chung, Yongmann M. ; Lockerby, Duncan A.
Format of File:	pdf
Extent:	xvi, 229 pages : illustrations, charts
Language:	eng

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