Finlets, a series of small individual triangular fins located along the dorsal and ventral midlines of the body, are remarkable specializations of tuna and other scombrid fishes capable of high-speed swimming. In this...Finlets, a series of small individual triangular fins located along the dorsal and ventral midlines of the body, are remarkable specializations of tuna and other scombrid fishes capable of high-speed swimming. In this study, a symmetric model containing nine finlets of tuna is proposed to overcome the limitation of measurement without losing authenticity. Hydrodynamic performance along with three-dimensional flow structures obtained by direct numerical simulation are demonstrated to disclose the underlying hydrodynamics mechanism of finlets. Complex interactions of leading-edge vortices(LEVs), trialing-edge vortices(TEVs), tip vortices(TVs) and root vortices(RVs) are observed from the three-dimensional vortical structures around the finlets. Two more cases consisting of the 3rd to 9th(without the first two) and the 3rd to 7th(without the first two and the last two) finlets are also simulated to examine the effects of the first two and the last two finlets.展开更多
Wind tunnel testing and embedded large eddy simulations are employed to study the noise reduction of trailing-edge finlets on an airfoil. Trailing-edge finlets are shown to increase the distance between the highly ene...Wind tunnel testing and embedded large eddy simulations are employed to study the noise reduction of trailing-edge finlets on an airfoil. Trailing-edge finlets are shown to increase the distance between the highly energetic fluid particles and the sharp trailing edge. Experiments were conducted at different angles of attack. Wind tunnel measurements confirm that finlets reduce the broadband noise radiated by the airfoil. Results also reveal that the noise reduction of finlets is dependent on the airfoil angle of attack, and that the highest noise reduction is obtained at the largest angle of attack tested.展开更多
The swimming of a 3Dfish-like bodywith finlets is numerically investigated at Re=1000(the Reynolds number is based on the uniform upstream flow and the length of the fish-like body).The finlets are simply modeled as t...The swimming of a 3Dfish-like bodywith finlets is numerically investigated at Re=1000(the Reynolds number is based on the uniform upstream flow and the length of the fish-like body).The finlets are simply modeled as thin rigid rectangular plates that undulate with the body.The wake structures and the flow around the caudal peduncle are studied.The finlets redirect the local flow across the caudal peduncle but the vortical structures in the wake are almost not affected by the finlets.Improvement of hydrodynamic performance has not been found in the simulation based on this simple model.The present numerical result is in agreement with that of the work of Nauen and Lauder[J.Exp.Biol.,204(2001),pp.2251-2263]and partially supports the hypothesis ofWebb[Bull.Fish.Res.Bd.Can.,190(1975),pp.1-159].展开更多
Noise reduction of different airfoils is important because these sections are used in wind turbines,propellers,and aircraft wings.Several methods are used for passive noise reduction of sections.One of these methods i...Noise reduction of different airfoils is important because these sections are used in wind turbines,propellers,and aircraft wings.Several methods are used for passive noise reduction of sections.One of these methods is the use of surface treatment.In this research,the effect of the typical surface treatment element(finlets)on the vortex structure at different frequencies in the turbulent flow created on the NACA2412 section is investigated.For this purpose,one-dimensional hot wire probe is used.The used surface treatment in this research has a special geometry and the distance between two consecutive finlets is 6 mm(S=6 mm).This study shows that this surface treatment element can be used for noise reduction in high frequencies.Another result of this research is the suggestion of the most suitable position to install this special surface treatment element to reduce vortex energy in all frequency ranges.This installation location is determined based on a dimensionless parameter(X_(aft)/h).展开更多
基金supported by the National Natural Science Foundation of China under grant number 11772172。
文摘Finlets, a series of small individual triangular fins located along the dorsal and ventral midlines of the body, are remarkable specializations of tuna and other scombrid fishes capable of high-speed swimming. In this study, a symmetric model containing nine finlets of tuna is proposed to overcome the limitation of measurement without losing authenticity. Hydrodynamic performance along with three-dimensional flow structures obtained by direct numerical simulation are demonstrated to disclose the underlying hydrodynamics mechanism of finlets. Complex interactions of leading-edge vortices(LEVs), trialing-edge vortices(TEVs), tip vortices(TVs) and root vortices(RVs) are observed from the three-dimensional vortical structures around the finlets. Two more cases consisting of the 3rd to 9th(without the first two) and the 3rd to 7th(without the first two and the last two) finlets are also simulated to examine the effects of the first two and the last two finlets.
文摘Wind tunnel testing and embedded large eddy simulations are employed to study the noise reduction of trailing-edge finlets on an airfoil. Trailing-edge finlets are shown to increase the distance between the highly energetic fluid particles and the sharp trailing edge. Experiments were conducted at different angles of attack. Wind tunnel measurements confirm that finlets reduce the broadband noise radiated by the airfoil. Results also reveal that the noise reduction of finlets is dependent on the airfoil angle of attack, and that the highest noise reduction is obtained at the largest angle of attack tested.
基金This work was supported by Chinese Academy of Sciences under the Innovative Project’Multi-scale modeling and simulation in complex systems’(KJCX-SW-L08),’Mathematical modeling of complex system’(KJCX3-SYW-S01)National Basic Research Program of China(973 Program)under Project No.2007CB814800National Natural Science Foundation of China under Project Nos.10702074 and 10872201.The computations were supported by the Supercomputing Center of ChineseAcademy of Sciences and the Shanghai Supercomputer Center.
文摘The swimming of a 3Dfish-like bodywith finlets is numerically investigated at Re=1000(the Reynolds number is based on the uniform upstream flow and the length of the fish-like body).The finlets are simply modeled as thin rigid rectangular plates that undulate with the body.The wake structures and the flow around the caudal peduncle are studied.The finlets redirect the local flow across the caudal peduncle but the vortical structures in the wake are almost not affected by the finlets.Improvement of hydrodynamic performance has not been found in the simulation based on this simple model.The present numerical result is in agreement with that of the work of Nauen and Lauder[J.Exp.Biol.,204(2001),pp.2251-2263]and partially supports the hypothesis ofWebb[Bull.Fish.Res.Bd.Can.,190(1975),pp.1-159].
文摘Noise reduction of different airfoils is important because these sections are used in wind turbines,propellers,and aircraft wings.Several methods are used for passive noise reduction of sections.One of these methods is the use of surface treatment.In this research,the effect of the typical surface treatment element(finlets)on the vortex structure at different frequencies in the turbulent flow created on the NACA2412 section is investigated.For this purpose,one-dimensional hot wire probe is used.The used surface treatment in this research has a special geometry and the distance between two consecutive finlets is 6 mm(S=6 mm).This study shows that this surface treatment element can be used for noise reduction in high frequencies.Another result of this research is the suggestion of the most suitable position to install this special surface treatment element to reduce vortex energy in all frequency ranges.This installation location is determined based on a dimensionless parameter(X_(aft)/h).