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Shock structures and instabilities formed in an underexpanded jet impinging on to cylindrical sections

Abstract

Schlieren visualisations are used to investigate the influence of cylindrical surface curvature on both the time-invariant and oscillatory behaviour of the shock structures within underexpanded jets impinging on to a surface. At moderate standoff distances \(\left( \frac{h}{d} < 5\right) \), the impingement surface curvature affects the temporal behaviour of the flow significantly, but with only slight variations in the time-invariant structure. A convex surface curvature constrains flapping oscillations to a single plane, the normal of which is parallel to the cylinder axis; the oscillation frequency is largely unaffected. For the standoff distances and nozzle pressure ratios studied, concave surface curvature suppresses the formation of impingement tones. A mechanism is proposed whereby entrainment of the recirculated wall jet flow alters the shear layer receptivity to acoustic disturbances, breaking the acoustic feedback loop that drives the jet oscillations.

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Acknowledgments

The authors gratefully acknowledge the support given to the project by the Australian Research Council.

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Correspondence to N. Mason-Smith.

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Communicated by F. Seiler.

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Mason-Smith, N., Edgington-Mitchell, D., Buchmann, N.A. et al. Shock structures and instabilities formed in an underexpanded jet impinging on to cylindrical sections. Shock Waves 25, 611–622 (2015). https://doi.org/10.1007/s00193-015-0561-8

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  • DOI: https://doi.org/10.1007/s00193-015-0561-8

Keywords

  • Aeroacoustics
  • Schlieren
  • Impinging jet