Skip to main content
    • Aa
    • Aa

Axis switching and spreading of an asymmetric jet: the role of coherent structure dynamics

  • K. B. M. Q. Zaman (a1)

The effects of vortex generators and periodic excitation on vorticity dynamics and the phenomenon of axis switching in a free asymmetric jet are studied experimentally. Most of the data reported are for a 3:1 rectangular jet at a Reynolds number of 450 000 and a Mach number of 0.31. The vortex generators are in the form of ‘delta tabs’, triangular-shaped protrusions into the flow, placed at the nozzle exit. With suitable placement of the tabs, axis switching could be either stopped or augmented. Two mechanisms are identified governing the phenomenon. One, as described by previous researchers, is due to the difference in induced velocities for different segments of a rolled-up azimuthal vortical structure. The other is due to the induced velocities of streamwise vortex pairs in the flow. While the former mechanism, referred to here as the ωθ-dynamics, is responsible for a rapid axis switching in periodically forced jets, e.g. screeching supersonic jets, the effect of the tabs is governed mainly by the latter mechanism, referred to as the ωx-dynamics. Both dynamics can be active in a natural asymmetric jet; the tendency for axis switching caused by the ωθ-dynamics may be, depending on the streamwise vorticity distribution, either resisted or enhanced by the ωx-dynamics. While this simple framework qualitatively explains the various observations made on axis switching, mechanisms actually in play may be much more complex. The two dynamics are not independent as the flow field is replete with both azimuthal and streamwise vortical structures which continually interact. Phase-averaged measurements for a periodically forced case, over a volume of the flow field, are carried out in an effort to gain insight into the dynamics of these vortical structures. The results are used to examine such processes as the reorientation of the azimuthal vortices, the resultant evolution of streamwise vortex pairs, as well as the redistribution of streamwise vortices originating from secondary flow within the nozzle.

Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

Ahuja, K. K. & Brown, W. H.1989Shear flow control by mechanical tabs. AIAA Paper 89-0994.

Bell, J. H. & Mehta, R. D. 1992 Measurements of the streamwise vortical structures in a plane mixing layer. J. Fluid Mech. 239, 213248.

Bradshaw, P.1987Turbulent secondary flows. Ann. Rev. Fluid Mech.19, 5372.

Crow, S. C. & Champagne, F. H. 1971 Orderly structures in jet turbulence. J. Fluid Mech. 48, 547591.

Davis, D. O. & Gessner, F. B.1992Experimental investigation of turbulent flow through a circular-to-rectangular transition duct. AIAA J.30, 367375.

Dhanak, M. R. & Bernardinis, B. D. 1981 The evolution of an elliptic vortex ring. J. Fluid Mech. 109, 189216.

Grinstein, F. F.1993Vorticity dynamics in spatially-developing rectangular jets. AIAA Paper 93-3286.

Grinstein, F. F., Gutmark, E. & Parr, T.1994Numerical and experimental study of the near field of subsonic, free square jets. AIAA Paper 94-0660.

Gutmark, E. & Schadow, K. C.1987Flow characteristics of orifice and tapered jets. Phys. Fluids30, 34483454.

Hertzberg, J. R. & Ho, C.-M.1992Time-averaged, three-dimensional flow in a rectangular sudden expansion. AIAA J.30, 24202425.

Hussain, F. & Husain, H. S. 1989 Elliptic jets. Part 1. Characteristics of unexcited and excited jets. J. Fluid Mech. 208, 257320.

Hussain, A. K. M. F. & Zaman, K. B. M. Q. 1980 Vortex pairing in a circular jet under controlled excitation. Part 2. Coherent structure dynamics. J. Fluid Mech. 101, 493544.

LeBoeuf, R. L. & Mehta, R. D.1995On using Taylor's hypothesis for three-dimensional mixing layers, Phys. Fluids7, 15161518.

Liepmann, D. & Gharib, M. 1992 The role of streamwise vorticity in the near-field entrainment of round jets. J. Fluid Mech. 245, 643668.

Kambe, T. & Takao, T.1971Motion of distorted vortex rings. J. Phys. Soc. Japan31, 591599.

Koshigoe, S., Tubis, A. & Ho, C.-M.1988Vortex deformation in elliptic-core jets from the perspective of linear instability analysis. Phys. Fluids31, 25042517.

Krothapalli, A., Baganoff, D. & Karamcheti, K. 1981 On the mixing of rectangular jet. J. Fluid Mech. 107, 201220.

Miau, J. J., Leu, T. S., Chou, J. H., Lin, S. A. & Lin, C. K.1990Flow distortion in a circular-to-rectangular transition duct. AIAA J.28, 14471456.

Quinn, W. R.1992Streamwise evolution of a square jet cross section. AIAA J.30, 28522857.

Raman, G., Zaman, K. B. M. Q. & Rice, E. J.1989Initial turbulence effect on jet evolution with and without tonal excitation. Phys. Fluids A 1, 12401248.

Sforz, M. P., Steiger, H. M. & Trentacoste, N.1966Studies on three-dimensional viscous jets. AIAA J.4, 800806.

Tsuchiya, Y., Horikoshi, C. & Sato, T.1986On the spread of rectangular jets. Exps. Fluids4, 197204.

Viets, H. & Sforza, P. M.1972Dynamics of bilaterally symmetric vortex rings. Phys. Fluid15, 230240.

Zaman, K. B. M. Q.1994Effect of ‘delta tabs’ on mixing and axis switching in jets from asymmetric nozzles. AIAA Paper 94-0186.

Zaman, K. B. M. Q. & Hussain, A. K. M. F. 1980 Vortex pairing in a circular jet under controlled excitation. Part 1. General jet response. J. Fluid Mech. 101, 449491.

Zaman, K. B. M. W. & Hussain, A. K. M. F. 1981 Taylor hypothesis and large-scale coherent structures. J. Fluid Mech. 112, 379396.

Zaman, K. B. M. Q., Reeder, M. F. & Samimy, M.1994Control of an axisymmetric jet using vortex generators. Phys. Fluid A 6, 778793.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Full text views

Total number of HTML views: 0
Total number of PDF views: 75 *
Loading metrics...

Abstract views

Total abstract views: 164 *
Loading metrics...

* Views captured on Cambridge Core between September 2016 - 22nd September 2017. This data will be updated every 24 hours.