Secondary flows in statistically unstable turbulent boundary layers with spanwise heterogeneous roughness

作     者：Ali Amarloo Pourya Forooghi Mahdi Abkar Ali Amarloo;Pourya Forooghi;Mahdi Abkar

作者机构：Department of Mechanical and Production EngineeringAarhus UniversityAarhus C8000Denmark 

出 版 物：《Theoretical & Applied Mechanics Letters》 (力学快报（英文版）)

年 卷 期：2022年第12卷第2期

页      面：65-71页

核心收录：

学科分类：08[工学] 080103[工学-流体力学] 0801[工学-力学（可授工学、理学学位）] 

基　　金：P.F.thanks the Aarhus University Research Foundation(AUFF)for the financial support.M.A.acknowledges the financial support from the Aarhus University Centre for Digitalisation Big Data and Data Analytics(DIGIT). 

主　　题：Secondary flows Roughness heterogeneity Unstable/convective boundary layer Large-eddy simulation 

摘      要：Large-scale secondary motions are known to occur in turbulent flows over surfaces with spanwise roughness heterogeneity.Numerical studies often use adjacent high-and low-roughness longitudinal strips to investigate these secondary rolls in boundary layers without any thermal stratification.In the present study,the effect of unstable thermal stratification on secondary rolls in a very high-Reynolds-number turbulent flow with spanwise-heterogeneous roughness is investigated by means of large-eddy simulation.The strength of the unstable stratification is systematically changed from L/h=−20 to L/h=−1,where L and h are Monin-Obukhov length and boundary-layer height,respectively.This range covers the transition from neutral stratification to unstable stratification.The results show that the positive buoyancy associated with the unstable thermal stratification acts against the roughness-induced secondary rolls.In the case of unstable stratification,secondary rolls are completely canceled out by buoyancy and replaced by new stronger convection-induced rolls rotating in opposite directions.