Effect of Initial Conditions on Aerodynamic and Acoustic Characteristics of High Subsonic Jets from Sharp Edged Circular Orifice

Authors: Murugan, K. N. Sharma, S. D.

Abstract:

The present work involves measurements to examine the effects of initial conditions on aerodynamic and acoustic characteristics of a Jet at M=0.8 by changing the orientation of sharp edged orifice plate. A thick plate with chamfered orifice presented divergent and convergent openings when it was flipped over. The centerline velocity was found to decay more rapidly for divergent orifice and that was consistent with the enhanced mass entrainment suggesting quicker spread of the jet compared with that from the convergent orifice. The mixing layer region elucidated this effect of initial conditions at an early stage – the growth was found to be comparatively more pronounced for the divergent orifice resulting in reduced potential core size. The acoustic measurements, carried out in the near field noise region outside the jet within potential core length, showed the jet from the divergent orifice to be less noisy. The frequency spectra of the noise signal exhibited that in the initial region of comparatively thin mixing layer for the convergent orifice, the peak registered a higher SPL and a higher frequency as well. The noise spectra and the mixing layer development suggested a direct correlation between the coherent structures developing in the initial region of the jet and the noise captured in the surrounding near field.

Keywords: Convergent orifice jet, Divergent orifice jet, Mass entrainment, mixing layer, near field noise, frequency spectrum, SPL, Strouhal number, wave number, reactive pressure field, propagating pressure field.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1086023

References:

[1] K Viswanathan and L T Clark. "Effect of Internal Contour on jet aeroacoustics," in Jet Aeroacoustics, G. Raman, Ed. Essex UK Multi-science Pub 2008, pp. 463-495.
[2] V. H. Arakeri, A.Krothapalli, V. Siddavaram, M B Alkislar and L M . Lourenco. " On the use of microjets to suppress turbulence in a Mach 0.9 axisymmtric jet," Journal of Fluid Mechanics, Vol 490, 2003,pp. 75-98.
[3] K.B. M.Q. Zaman, "Effect of initial condition on subsonic jet noise," AIAA Journal, Vol 23, No. 3, 1985 pp 1370-1373.
[4] L Maesterllo and E McDaid , Acoustic characteristic of high subsonic jet," AIAA Journal , Vol 9, No.6, 1971 pp 1058-1066.
[5] K Vishwanathan, "Noise source mechanism in subsonic jets," AIAA Journal , Vol 46, No.8, 2008 pp 2020-2031
[6] W R Quinn and J. Militzer "Effects of nonparallel exit flow on round turbulent free jets," nt. J. Heat Fluid Flow 10 (2) (1989) 139-145.
[7] R. E. A. Arndt, D. F. Long, and M. N. Glauser, "The proper orthogonal decomposition of pressure fluctuations surrounding a turbulent jet," Journal of Fluid Mechanics. Vol. 340, (1997), pp. 1- 33.
[8] J. Mi, G.J. Nathan, and D Nobes, " Mixing characteristics of axisymmtric free jets issuing from contoured nozzle, an orifice plate and pipe," Journal of Fluids Engineering Vol 123, 2001b, pp 878-883.
[9] W R Quinn, " Upstream nozzle shaping effects on near field flow in round turbulent free jets" European Journal of Mechanics B/Fluids Vol. 25, 2006 pp 279-301.
[10] J. Mi, P. Kalt, G.J. Nathan, and C. Y. Wong, " PIV measurement of a turbulent jet issuing from round sharp-edged plate," Experiments in Fluids, Vol 42, 2007 pp 625-637.
[11] G. L. Brown and A. Roshko, "On density effects and large structure in turbulent mixing layers," Journal of Fluid Mechanics , Vol. 64, 1974, pp 775-816.
[12] H. K Lee and H. S Ribner, " Direct Correlation of Noise and flow field.," Journal of Acoustic Society of America, Vol. 52, No 5(1) 1972 pp 1280-1290.