Journal ArticleDOI
Dynamics of an impinging jet. Part 1. The feedback phenomenon
Chih-Ming Ho,N. Nosseir +1 more
TLDR
In this paper, the authors show that a feedback mechanism is responsible for the sudden change observed in the pressure fluctuations at the onset of resonance in a high-speed subsonic jet impinging on a flat plate.Abstract:
In a high-speed subsonic jet impinging on a flat plate, the surface pressure fluctuations have a broad spectrum due to the turbulent nature of the high-Reynolds-number jet. However, these pressure fluctuations dramatically change their pattern into almost periodic waves, if the plate is placed close to the nozzle (x0/d < 7·5). In the present study extensive measurements of the near-field pressure provide solid support for the hypothesis that a feedback mechanism is responsible for the sudden change observed in the pressure fluctuations at the onset of resonance. The feedback loop consists of two elements: the downstream-convected coherent structures and upstream-propagating pressure waves generated by the impingement of the coherent structures on the plate. The upstream-propagating waves and the coherent structures are phase-locked at the nozzle exit. The upstream-propagating waves excite the thin shear layer near the nozzle lip and produce periodic coherent structures. The period is determined by the convection speed of the coherent structures, the speed of the upstream-propagating waves as well as the distance between the nozzle and the plate. An instability process, herein referred to as the ‘collective interaction’, was found to be critical in closing the feedback loop near the nozzle lip.read more
Citations
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Journal ArticleDOI
Boundary conditions for direct simulations of compressible viscous flows
TL;DR: In this article, a boundary condition formulation for the Navier-Stokes equations is proposed, which is compatible with non-disjoint algorithms applicable to direct simulations of turbulent flows.
Journal ArticleDOI
Subharmonics and vortex merging in mixing layers
Chih-Ming Ho,Lein-Saing Huang +1 more
TL;DR: In this paper, it was shown that the spreading rate of a mixing layer can be greatly manipulated at very low forcing level if the mixing layer is perturbed near a subharmonic of the most-amplified frequency.
Journal ArticleDOI
The forced mixing layer between parallel streams
D. Oster,Israel Wygnanski +1 more
TL;DR: The effect of periodic two-dimensional excitation on the development of a turbulent mixing region was studied experimentally in this article, where controlled oscillations of variable ampli- tude and frequency were applied at the initiation of mixing between two parallel air streams.
Journal ArticleDOI
Combustion instability related to vortex shedding in dump combustors and their passive control
Klaus C. Schadow,Ephraim Gutmark +1 more
TL;DR: In this paper, a review summarizes recent research program related to the driving mechanism of dump combustor instability, including experimental research in dump combustors using gaseous fuel, and the emphasis here is on vortex shedding as a driving mechanism.
References
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Journal ArticleDOI
Orderly Structure in Jet Turbulence
S. C. Crow,F. H. Champagne +1 more
TL;DR: In this paper, the authors show that a large-scale orderly pattern may exist in the noiseproducing region of a round subsonic jet by observing the evolution of orderly flow with advancing Reynolds number.
Journal ArticleDOI
Vortex pairing : the mechanism of turbulent mixing-layer growth at moderate Reynolds number
C. D. Winant,F. K. Browand +1 more
TL;DR: A mixing layer is formed by bringing two streams of water, moving at different velocities, together in a lucite-walled channel as mentioned in this paper, where dye is injected between the two streams just before they are brought together, marking the vorticitycarrying fluid.
Journal ArticleDOI
Subharmonics and vortex merging in mixing layers
Chih-Ming Ho,Lein-Saing Huang +1 more
TL;DR: In this paper, it was shown that the spreading rate of a mixing layer can be greatly manipulated at very low forcing level if the mixing layer is perturbed near a subharmonic of the most-amplified frequency.
Journal ArticleDOI
Self-Sustained Oscillations of Impinging Free Shear Layers
Journal ArticleDOI
Large-scale motion in the intermittent region of a turbulent boundary layer
TL;DR: In this paper, the outer intermittent region of a fully developed turbulent boundary layer with zero pressure gradient was extensively explored in the hope of shedding some light on the shape and motion of the interface separating the turbulent and non-turbulent regions as well as on the nature of the related large-scale eddies within the turbulent regime.