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Effect of Pressure Gradients on the Hairpin Structures in Turbulent Boundary Layers
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 Title & Authors
Effect of Pressure Gradients on the Hairpin Structures in Turbulent Boundary Layers
Kim, Gyeong-Cheon; Yun, Hong;
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 Abstract
The effect of pressure gradients on the hairpin structures in three different turbulent boundary layers (ZPG : Re(sub)=910, FPG : Re(sub)=575, APG : Re(sub)=1290) has been examined with instantaneous velocity fields obtained in streamwise-wall-normal planes using PIV (particle image velocimetry) method. In the outer layer hairpin vortices occur in streamwise-aligned packets that propagate with small velocity dispersion. The signature pattern of the hairpin consists of a spanwise vortex core located above a region of strong second quadrant fluctuation (u<0 and v>0 : Q2 event) is clearly observed. The formation of packets explains the occurrence of multiple VITA events in turbulent burst. Noticeable differences are found in the average inclination angles of hairpin vortex packets which are 45, 35.7, and 51.9in the case of ZPG, FPG and APG, respectively. It is found that the large, time-varying, irregularly shaped zones with nearly constant streamwise momentum exist throughout the boundary layer. Within the interior of the envelope the spatial coherence between the velocity fields induced by the individual vortices leads to strongly retarded streamwise momentum, explaining the zones of uniform momentum. The formation of the uniform momentum zone is remarkably different with respect to the pressure gradients especially in the logarithmic layer.
 Keywords
Turbulent Boundary Layer;Hairpin Vortex Structure;Particle Image Velocimetry;Pressure Gradients Effect;Uniform Momentum Zone;
 Language
Korean
 Cited by
1.
장애물 주위의 와구조 형성과정에 관한 수치적 연구,황종연;양경수;

대한기계학회논문집B, 2004. vol.28. 6, pp.672-681 crossref(new window)
 References
1.
Theodorsen, T., 1952, 'Mechanism of Turbulence,' Proceedings from the Second Midwestern Conference of FLuid Mechanics, Ohio State University, Columbus, Ohio, Vol. 123

2.
Head, M. R. and Bandyopadhyay, P., 19*81, 'New Aspects of Turbulent Boundary-Layer Structure,' J. Fluid Mech., Vol. 107, pp. 297-338 crossref(new window)

3.
Smith, C. R., 1984, 'A Synthesized Model of the Near-Wall Behavior in Turbulent Boundary Layers,' In Proc. of 8th Symp. on Turbulence (ed. J. Zakin and G. Patterson), Univ. MissouriRolla, Rolla, Missouri, pp. 299-325

4.
Jeong, J. and Hussain, F., 1995, 'On the Identification of a Vortex,' J. Fluid Mech., Vol. 285, pp. 69-94 crossref(new window)

5.
Adrian, R. J., Meinhart, C. D. and Tomkins, C. D., 1999, 'Vortex Organization in the Outer Region of the Turbulent Boundary Layer,' TAM Report No. 924

6.
Unger, F. and Friedrich, R., 1991, 'Coherent Structures in Favourable and Adverse Pressure Gradient Boundary Layers,' Advances in Turbulentce, Vol. 3, pp. 113-121

7.
Robinson, S. K., 1991, 'Coherent Motion in the Turbulent Boundary Layer,' Ann. Rev. Fluid Mech., Vol. 23, pp. 601-639 crossref(new window)

8.
양준모, 유정열, 최해천, 1997,'난류경계층에서 벽마찰력과 유동방향 속도섭동간의 상관관계 (II) 조건부 검출에 의한 분석,' 대한기계학회논문집, 제21권, 제3호, pp. 427-435

9.
Zhou, J., Adrian, R. J. and Balachandar, S., 1996, 'Autogeneration of Near-Wall Vortical Structures in Channel Flow,' Phys. Fluids, Vol. 8, pp. 288-290 crossref(new window)

10.
Meinhart, C. D. and Adrian, R. J., 1995, 'On the Existence of Uniform Momentum Zones in a Turbulent Boundary Layer,' Phys. Fluids, Vol. 7, pp. 694-696 crossref(new window)

11.
Tomkins, C. D., 1997, 'A Particle Image Velocity Study of Coherent Structures in a Turbulent Boundary Layer,' M.S. Thesis, University of Illinois, Urbana, Illinois, U. S. A.

12.
Zhou, J., Meinhart, C. D., Balachandar, S. and Adrian, R. J., 1997, 'Formation of coherent Hairpin Packets in Wall Turbulence,' In Self-Sustaining Mechanisms of Wall Turbulence(ed. R. L. Panton), Computational Mech. Pubs., Southampton, UK., pp. 109-134