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Shear layer characteristics of supersonic free and impinging jets

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Abstract

The initial shear layer characteristics of a jet play an important role in the initiation and development of instabilities and hence radiated noise. Particle image velocimetry has been utilized to study the initial shear layer development of supersonic free and impinging jets. Microjet control employed to reduce flow unsteadiness and jet noise appears to affect the development of the shear layer, particularly near the nozzle exit. Velocity field measurements near the nozzle exit show that the initially thin, uncontrolled shear layer develops at a constant rate while microjet control is characterized by a rapid nonlinear thickening that asymptotes downstream. The shear layer linear growth rate with microjet control, in both the free and the impinging jet, is diminished. In addition, the thickened shear layer with control leads to a reduction in azimuthal vorticity for both free and impinging jets. Linear stability theory is used to compute unstable growth rates and convection velocities of the resultant velocity profiles. The results show that while the convection velocity is largely unaffected, the unstable growth rates are significantly reduced over all frequencies with microjet injection. For the case of the impinging jet, microjet control leads to near elimination of the impingement tones and an appreciable reduction in broadband levels. Similarly, for the free jet, significant reduction in overall sound pressure levels in the peak radiation direction is observed.

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Acknowledgments

The authors would like to acknowledge the support provided by the Florida Center for Advanced Aero-Propulsion (FCAAP). The authors also thank the support of FCAAP staff for their help in conducting experiments.

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  1. Florida State University, 2003 Levy Ave., Tallahassee, FL, 32310, USA

    T. B. Davis & R. Kumar

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  1. T. B. Davis
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  2. R. Kumar
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Correspondence to R. Kumar.

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Communicated by A. Hadjadj.

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Davis, T.B., Kumar, R. Shear layer characteristics of supersonic free and impinging jets. Shock Waves 25, 507–520 (2015). https://doi.org/10.1007/s00193-014-0540-5

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