On the tip sharpness of riblets for turbulent drag reduction

作     者：Yiqian Wang Yi Huang Song Fu 王义乾;黄懿;符松

作者机构：School of Mathematical SciencesSoochow UniversitySuzhou 215006China School of Aerospace EngineeringTsinghua UniversityBeijing 100084China 

出 版 物：《Acta Mechanica Sinica》 (力学学报（英文版）)

年 卷 期：2022年第38卷第4期

页      面：39-55,I0001页

核心收录：

学科分类：080704[工学-流体机械及工程] 080103[工学-流体力学] 08[工学] 0807[工学-动力工程及工程热物理] 0801[工学-力学（可授工学、理学学位）] 

基　　金：the National Natural Science Foundation of China(Grant No.11702159) the EU-China Joint Project Drag Reduction via Turbulent Boundary Layer Flow Control(Grant No.690623) 

主　　题：Riblet Turbulent drag reduction Tip sharpness Protrusion height Direct numerical simulation 

摘      要：It is commonly known that riblets with sharper tip generally have better turbulent drag reduction capacity,which,however,poses great challenges for manufacturing and makes the riblets vulnerable to tip *** this study,we show that a scalloped riblet which is not as sharp in the tip as corresponding triangular riblet with same height-width ratio,nevertheless has a larger protrusion height,a quantity solely depending on the riblet shape and calculated through a boundary element algorithm in this study,and thus a higher projected drag reduction *** addition,it is found that,when subjected to tip rounding,this scalloped riblet performs better in terms of protrusion height than corresponding parabolic riblet,which indicates stronger resilience to riblet tip *** the class of scalloped riblets,designed by smoothly connecting two third-order polynomials and thus the tip sharpness and valley curvature can be well defined,it is revealed that two mechanisms,one for the valley curvature at the viscous limit and one for the tip sharpness at infinite deep limit,determine the protrusion height,and thus the projected drag reduction *** numerical simulations are then carried out to investigate controlled boundary layer transition with the scalloped riblet of width s+=20 and 5+=60.A 7.8%drag reduction in the turbulent region is found for the smaller riblet with a preferable transition delay,while for the larger riblet transition is promoted and drag is increased in the turbulent *** is also found that the area fraction of high drag region around the riblet tips is basically the same for the two ***,even higher drag is found around the tip region for the smaller drag-reducing *** the other hand,a much smaller drag coefficient is found in the valley of the smaller riblet,which results in the reduction of turbulent *** is thus inferred that the issue of sharp riblet tip,that hard to manufacture and deteriorate substantially