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experimental study of natural and forced modes in an axisymmetric jet

Raman, Ganesh Ganapathi
http://rave.ohiolink.edu/etdc/view?acc_num=case1055530276

Abstract Details

1991, Doctor of Philosophy, Case Western Reserve University, Mechanical Engineering.
The present experimental investigation consists of two parts. The first part describes an effort to study naturally occurring instability modes in the axisymmetric shear layer of a high Reynolds number turbulent jet. Untripped (transitional) and tripped (turbulent) nozzle exit conditions, both with 0.1% core turbulence, were studied. For the turbulent nozzle exit boundary layer case, the core turbulence was varied systematically from 0.1% to 5% of the jet exit velocity using various grids located upstream of the nozzle exit. The region up to the end of the potential core was dominated by the axisymmetric mode. The azimuthal modes grew rapidly but dominated only down-stream of the potential core region. For the jet excited by natural disturbances, the energy content of the higher order modes (m > 1) was significantly lower than that of the axisymmetric and m = ±1 modes. The initial boundary layer had a profound effect on the natural jet evolution and consequently on its excitability; the jet decay was faster in the initially transitional case than in the initially turbulent case. The shorter potential core (earlier change in the shape of the velocity profile) allowed the jet in the transitional case to support helical disturbances closer to the nozzle exit than the turbulent case. B ased on the results from these naturally occurring jet instability mode experiments, target modes for efficient excitation of the jet were determined. In the second part of this work an effort to control the axisymmetric shear layer by artificially exciting target modes is described. Under optimum conditions, two-frequency excitation is indeed more effective than single frequency plane wave excitation. It was found that at high amplitudes of fundamental and subharmonic forcing, the subharmonic augmentation and the axial location of the peak are independent of the initial phase difference. However, two-frequency excitation also has its limitations, since axisymmetric waves are damped beyond the potential core. This work concludes with an effort to describe techniques to control an extended region of the jet by forcing combinations of both axisymmetric and helical modes. Higher spreading rates are obtained when multi-modal forcing is applied.
Eli Reshotko (Advisor)
207 p.
experimental study natural forced modes axisymmetric jet

Recommended Citations

Citations

  • Raman, G. G. (1991). experimental study of natural and forced modes in an axisymmetric jet [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1055530276

    APA Style (7th edition)

  • Raman, Ganesh. experimental study of natural and forced modes in an axisymmetric jet. 1991. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1055530276.

    MLA Style (8th edition)

  • Raman, Ganesh. "experimental study of natural and forced modes in an axisymmetric jet." Doctoral dissertation, Case Western Reserve University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1055530276

    Chicago Manual of Style (17th edition)

case1055530276
798
© 1991, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.