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On the use of microjets to suppress turbulence in a Mach 0.9 axisymmetric jet

Published online by Cambridge University Press:  19 August 2003

V. H. ARAKERI ,
A. KROTHAPALLI ,
V. SIDDAVARAM ,
M. B. ALKISLAR  and
L. M. LOURENCO
V. H. ARAKERI
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street, Florida A&M University and Florida State University, Tallahassee, FL-32310, USA
A. KROTHAPALLI
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street, Florida A&M University and Florida State University, Tallahassee, FL-32310, USA
V. SIDDAVARAM
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street, Florida A&M University and Florida State University, Tallahassee, FL-32310, USA
M. B. ALKISLAR
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street, Florida A&M University and Florida State University, Tallahassee, FL-32310, USA
L. M. LOURENCO
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street, Florida A&M University and Florida State University, Tallahassee, FL-32310, USA
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Abstract

We have experimentally studied the effect of microjets on the flow field of a Mach 0.9 round jet. Planar and three-dimensional velocity field measurements using particle image velocimetry show a significant reduction in the near-field turbulent intensities with the activation of microjets. The axial and normal turbulence intensities are reduced by about 15% and 20%, respectively, and an even larger effect is found on the peak values of the turbulent shear stress with a reduction of up to 40%. The required mass flow rate of the microjets was about 1% of the primary jet mass flux. It appears that the microjets influence the mean velocity profiles such that the peak normalized vorticity in the shear layer is significantly reduced, thus inducing an overall stabilizing effect. Therefore, we seem to have exploited the fact that an alteration in the instability characteristics of the initial shear-layer can influence the whole jet exhaust including its noise field. We have found a reduction of about 2 dB in the near-field overall sound pressure level in the lateral direction with the use of microjets. This observation is qualitatively consistent with the measured reduced turbulence intensities.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 490 , 10 September 2003 , pp. 75 - 98
Copyright
© 2003 Cambridge University Press

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