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