A Study on the Far Wake of Elliptic Cylinders

作     者：Subhankar Sen Sanjay Mittal 

作者机构：Department of Mechanical EngineeringIndian Institute of Technology KanpurIndia Department of Aerospace EngineeringIndian Institute of Technology KanpurIndia 

出 版 物：《Computer Modeling in Engineering & Sciences》 (工程与科学中的计算机建模（英文）)

年 卷 期：2017年第113卷第1期

页      面：35-55页

核心收录：

学科分类：08[工学] 080103[工学-流体力学] 0835[工学-软件工程] 0811[工学-控制科学与工程] 0701[理学-数学] 0801[工学-力学（可授工学、理学学位）] 0812[工学-计算机科学与技术（可授工学、理学学位）] 

主　　题：Elliptic cylinder stabilized finite-element far wake angle of attack blockage 

摘      要：The evolution of far wake of stationary elliptic cylinders with angle of attack is investigated for the unsteady flow at Re=200 using a stabilized finite-element method.The Reynolds number,Re,is based on the major axis of cylinder and free-stream speed.Cylinder aspect ratios,AR considered are 0.2,0.5 and 0.8 while the angle of attack,αvaries from 0° to 90°.With increasingα,the Karman or primary shedding frequency of each cylinder decreases monotonically while the primary wavelength and time-averaged as well as r.***.s.drag increase monotonically.The time-averaged lift and moment coefficients initially increase withαand then decrease.The power spectrum analysis of unsteady transverse velocity signal at various stations along the wake centerline is used to study the associated frequencies.The Karman or primary shedding frequency exists for eachα.For the AR=0.2 cylinder,the secondary and subsequently,low magnitude tertiary frequencies appear in the wake asαcontinues to increase from 30°.In contrast to the decaying nature of primary frequency withα,secondary frequency exhibits a nonmonotonic variation.The secondary frequency in general is not a sub-harmonic of the primary.This suggests that the secondary structures do not form due to merging of primary vortices.With increasingα,the location of formation of secondary structures advances upstream.For a given orientation,the upstream advancement is more dominant with decreasing AR.Power spectrum analysis indicates that the wake state for confined flow is characterized by the primary frequency alone,i.***.the imposition of blockage suppresses the formation of secondary structures.