Multiple laser excitation for enhancement of large scale structures

J. B. Crawford, G. S. Elliott

Research output: Contribution to conferencePaper

Abstract

A creative method of forcing and controlling supersonic mixing layers has been demonstrated. A laser beam from a frequency-doubled pulsed Nd:YAG laser is focused at the nozzle exit of an axisymmetric jet. Pulsing the laser causes a sudden thermal peak at the nozzle surface, forcing the shear layer of the jet where it is initiated. Experiments show that this is an effective means to enhance and control the large-scale structures formed at the exit of perfectly expanded jets with Mach numbers of 1.36, 1.5 and 2.0. The convective Mach numbers of these jets are 0.63, 0.68, and 0.85, respectively. Two laser pulses are used: the first excites the flow, and the second, delayed in time and formed into a sheet, interrogates the flow for visualization. The convective velocity of the large-scale structures was found to be slightly higher than predicted theoretically. Since the formation of the large-scale structures can be controlled, high frequency pressure measurements were made simultaneously with each instantaneous image. The pressure trace indicates, the lower and higher pressures associated with the vortex core and braid regions of the large-scale structures, respectively. Multiple excitation pulses were also used to force the shear layer. Not only did the use of two excitation pulses force the shear layer, but the forced structures were found to interact with one another as they convect downstream, although this interaction is suppressed at the higher Mach number. Laser excitation was found to provide excellent forcing and control of the shear layer and promote interaction between forced structures.

Original languageEnglish (US)
StatePublished - Jan 1 1999
Externally publishedYes
Event37th Aerospace Sciences Meeting and Exhibit, 1999 - Reno, United States
Duration: Jan 11 1999Jan 14 1999

Other

Other37th Aerospace Sciences Meeting and Exhibit, 1999
CountryUnited States
CityReno
Period1/11/991/14/99

ASJC Scopus subject areas

  • Space and Planetary Science
  • Aerospace Engineering

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    Crawford, J. B., & Elliott, G. S. (1999). Multiple laser excitation for enhancement of large scale structures. Paper presented at 37th Aerospace Sciences Meeting and Exhibit, 1999, Reno, United States.