Vibrational relaxation effects in weak shock waves in air and the structure of sonic bangs

Hodgson, J. P.

doi:10.1017/s0022112073002223

Cited by 22 publications

(5 citation statements)

References 5 publications

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“…In steady-state conditions, with the shock overpressure between 30 Pa and 120 Pa, the early portion of the shock rise is dominated by dispersion associated with O 2 relaxation. 12 The fully dispersed shock front has a rise profile that is similar to the hyperbolic tangent form produced by classical ͑thermoviscous͒ damping. The effects of O 2 relaxation can thus be modeled by replacing the classical dissipation coefficient with an effective dissipation coefficient, ␦ eff , 13…”

Section: B Initial Conditionsmentioning

confidence: 89%

Atmospheric turbulence conditions leading to focused and folded sonic boom wave fronts

Piacsek

2002

The Journal of the Acoustical Society of America

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The propagation and subsequent distortion of sonic booms with rippled wave fronts are investigated theoretically using a nonlinear time-domain finite-difference scheme. This work seeks to validate the rippled wave front approach as a method for explaining the significant effects of turbulence on sonic booms [A. S. Pierce and D. J. Maglieri, J. Acoust. Soc. Am. 51, 702-721 (1971)]. A very simple description of turbulence is employed in which velocity perturbations within a shallow layer of the atmosphere form strings of vortices characterized by their size and speed. Passage of a steady-state plane shock front through such a vortex layer produces a periodically rippled wave front which, for the purposes of the present investigation, serves as the initial condition for a finite-difference propagation scheme. Results show that shock strength and ripple curvature determine whether ensuing propagation leads to wave front folding. High resolution images of the computed full wave field provide insights into the spiked and rounded features seen in sonic booms that have propagated through turbulence.

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Section: B Initial Conditionsmentioning

confidence: 89%

Atmospheric turbulence conditions leading to focused and folded sonic boom wave fronts

Piacsek

2002

The Journal of the Acoustical Society of America

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“…We are then led to the conclusion that, though turbulence is the undoubted cause of spike formation, it plays no significant part in thickening the boom structure. Furthermore, we are now aware that the shocks may well be of the fully dispersed type and that the real cause of the anomalous behaviour is to be found, as Hodgson (1972) advocates, in the non-equilibrium behaviour of air, for he has been able to demonstrate that this effect is compatible with the experimental data.…”

Section: J E Ffowcs William and M S Howementioning

confidence: 80%

“…In view of the now known tendency for weak shocks to attain a fully dispersed profile owing to non-equilibrium gas effects, and the demonstration that these effects are consistent with practical measurements (Hodgson 1972)) there seems no remaining mystery regarding the boom's 'anomalous ' structure.…”

Section: Discussionmentioning

confidence: 95%

On the possibility of turbulent thickening of weak shock waves

Williams

Howe

1973

J. Fluid Mech.

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This paper examines the possible thickening of an initially sharp sonic boom by the turbulence it encounters in passing to the ground. Three apparently different viewpoints, all indicating substantial thickening, are shown to be actually identical and to give an irrelevant upper bound on wave thickness. All three approaches describe only the apparent mean diffusion induced by random convection of a sharp wave about its nominal position. Although a wave-front folding mechanism ultimately accounts for an apparent thickening as individual rays are weakened and tangled by turbulence, this process is too slow to be effective in the practical boom situation. The paper then considers what linear thickening of a wave packet results from propagation trough atmospheric turbulence and concludes that, in the relevant limit, a wave may be thickened by a factor of about 2 at the most. The conclusion is therefore reached that atmospheric turbulence cannot be the cause of the thousandfold discrepancy between the measured wave fronts and their Taylor thickness.

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“…In 1971 Hodgson and Johannesen (193) turned aside from the original purpose of this research, namely relaxation phenomena in hypersonic flows, so as to apply their findings to the aircraft sonic bang problem. Their calculations indicated that the weak far field shock waves involved may well be fully dispersed due to the vibrational relaxation of oxygen; a later paper by Hodgson (194) produced the further indication that vibrational relaxation in nitrogen could aid this dispersion. In his survey paper (195) of the same year Hodgson showed a white-light interferogram (Fig.…”

Section: The Department Of the Mechanics Of Fluids And Its Successorsmentioning

confidence: 99%

The Victoria University of Manchester’s contributions to the development of aeronautics

Ackroyd

2007

Aeronaut. j.

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This issue of the Aeronautical Journal celebrates the 50th anniversary of the foundation of the Honours Degree Course in Aeronautical Engineering at the Victoria University of Manchester. The following article therefore describes the aeronautical research and teaching activities of that university up to its recent amalgamation with the University of Manchester Institute of Science and Technology (UMIST) to form the present-day University of Manchester. This juncture provides a further justification for recording the Victoria University’s achievements.Both the Victoria University and UMIST had their roots in the nineteenth century although, apart from the relatively brief period of the First World War, neither of them was particularly involved in aeronautics until after the Second World War. However, as Sections 6.0-10.0 seek to demonstrate, thereafter the Victoria University’s involvement became considerable. The preceding Sections describe the origins of the Victoria University and UMIST and, in the case of the former institution, the subsequent activities of its staff and graduates in engineering and mathematics which, although not always specifically aeronautical in content, nonetheless had a profound influence on the development of the aeronautical sciences.

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Vibrational relaxation effects in weak shock waves in air and the structure of sonic bangs

Cited by 22 publications

References 5 publications

Atmospheric turbulence conditions leading to focused and folded sonic boom wave fronts

Atmospheric turbulence conditions leading to focused and folded sonic boom wave fronts

On the possibility of turbulent thickening of weak shock waves

The Victoria University of Manchester’s contributions to the development of aeronautics

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