Characteristics of recirculation zone structure behind an impulsively started circular cylinder / Chang Lin in Journal of engineering mechanics, Vol. 138 N° 2 (Fevrier 2012)  

Characteristics of recirculation zone structure behind an impulsively started circular cylinder [texte imprimé] / Chang Lin, Auteur ; Shih-Chun Hsieh, Auteur ; Wei-Jung Lin, Auteur . - 2012 . - pp.184198.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 138 N° 2 (Fevrier 2012) . - pp.184198

Mots-clés :	Recirculation Velocity Cylinders Reynolds number
Résumé :	The characteristics of the recirculation zone structure behind an impulsively started circular cylinder for Reynolds number Re ranging from 500 to 2,000 and nondimensional time T ranging from 0.5 to 5.0 are investigated experimentally using particle image velocimetry (PIV) and flow visualization techniques. On the basis of the flow visualization pictures and velocity maps, both obtained by a reference frame with a moving coordinate system, the evolution of the recirculation zone structure is studied with special emphasis on the negative velocity subzone. The negative velocity subzone is enveloped by the boundary consisting of the zero-velocity points inside the recirculation zone, and the streamwise velocity profile inside and near the negative velocity subzone is characterized by a jetlike flow moving toward the cylinder. During the evolution of the recirculation zone, the representative dimensions of the vortical structure both in the streamwise and vertical directions, including the recirculation zone length and the center-to-center distance between two primary vortex cores, are found to increase rapidly with time. Characteristic length and velocity scales are proposed first in the literature not only to demonstrate the similarity profile for streamwise velocity within and near the negative velocity subzone, but also to exhibit the similarity for geometric shape of the negative velocity subzone via the ratio of the width of the negative velocity subzone (i.e., the vertical distance between two zero-velocity points) to the center-to-center distance between two primary vortex cores. The very important observation is that the similarities of velocity profile and geometric shape represent promising self-preservation for the jetlike flow enclosed by the zero-velocity points forming the boundary of the negative velocity subzone. In addition, time variation of the nondimensional circulation of two primary vortices in the recirculation zone is studied and found to increase with an increase in the nondimensional time.
Note de contenu :	Article Outline 1. Introduction 2. Experimental Setup and Procedure 1. Towing Tank and Test Model 2. Flow Visualization Techniques 3. Velocity Measurement Technique 4. Movement of Carriage System and Coordinate System 3. Results and Discussions 1. Test of Two Dimensionality of Flow Field 2. Flow Visualization 3. Velocity Field 4. Characteristic Dimensions of the Recirculation Zone 5. Vorticity of Primary Vortex in Recirculation Zone 4. Conclusions
ISSN :	0733-9399
En ligne :	http://ascelibrary.org/emo/resource/1/jenmdt/v138/i2/p184_s1?isAuthorized=no