A linear shock cell model for jets of arbitrary exit geometry

Morris, Philip J.; Bhat, Thonse R. S.; Chen, G.

doi:10.1016/0022-460x(89)90592-0

Cited by 49 publications

(18 citation statements)

References 16 publications

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“…Tabulated experimental results for the shock spacings, acoustic wavelengths, screech source locations, and the growth of the null region of a single jet with M j are given in tables 1 and 2. The shock spacings (average of first five shock cells) given in table 1 agree with the predictions of Tam (1988) and Morris, Bhat & Chen (1989). An explicit comparison is not shown since the objective here was not to check shock spacing theories but to explain the mechanism for twin-jet coupling.…”

Section: Coupling Mechanismsupporting

confidence: 66%

Coupling of twin rectangular supersonic jets

Raman

Taghavi

1998

J. Fluid Mech.

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Twin jet plumes on aircraft can couple, producing dynamic pressures significant enough to cause structural fatigue. For closely spaced jets with a moderate aspect ratio (e.g. 5), previous work has established that two coupling modes (antisymmetric and symmetric) are kinematically permissible. However, the dynamics of twin-jet coupling have remained unexplored. In this paper a more fundamental assessment of the steady and unsteady aspects of twin-jet coupling is attempted. While we document and discuss the nozzle spacings and Mach numbers over which phase-locked coupling occurs, our concentration is much more on answering the following questions: (a) What mechanism causes the jets to couple in one mode or the other? (b) Why do the jets switch from one mode to another? (c) Are the two modes mutually exclusive or do they overlap at the transition point? Our results reveal, among many things, the following. (i) For very closely spaced twin jets in the side-by-side configuration phased feedback based on source to nozzle exit distance of adjacent jets does not fully explain the coupling modes. However, the ‘null’ phase regions surrounding the jets where the phase of an acoustic wavefront (arriving from downstream) does not vary appears to correlate well with the existence of the symmetric mode. When the ‘null’ regions of adjacent jets do not overlap antisymmetric coupling occurs and when they do overlap the jets couple symmetrically. We provide a simple correlation using a parameter (α) that can be used as a simple test to determine the mode of coupling. (ii) The switch from the antisymmetric to the symmetric mode of coupling appears to occur because of an abrupt shift in the effective screech source from the third to the fourth shock, which in turn causes the ‘null’ phase region surrounding the jets to grow abruptly and overlap. (iii) The two modes are mutually exclusive. Our results provide considerable insight into the twin-jet coupling problem and offer hope for designing twin-jet configurations that minimize damage to aircraft components.

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Section: Coupling Mechanismsupporting

confidence: 66%

Coupling of twin rectangular supersonic jets

Raman

Taghavi

1998

J. Fluid Mech.

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“…The normalized shock cell-spacing L s /h * is then equal to 2.7, which is in better agreement with the experimental results shown in figure 5.a. This trend is in addition supported by the shock cell model of Morris & Baht,27 which shows in particular that shock spacing of round jets decreases when the mixing layer thickness is increased.…”

Section: Shock-cell Structuresupporting

confidence: 58%

Large Eddy Simulation of Screech Tone Generation in a Planar Underexpanded Jet

Berland

Bogey

Bailly

et al. 2006

12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference)

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The screech tones generated by a three-dimensional planar underexpanded jet are computed directly using compressible large eddy simulation (LES). The jet operates at fully expanded Mach number M j = 1.55, with Reynolds number Re h = 6 × 10 4 . The LES strategy is based on explicit selective filtering with spectral-like resolution, and low dispersion and low dissipation numerical algorithms are implemented to allow direct noise computation of the phenomenon. The investigation of the numerical results shows that the flow development, the shock cell structure and the upstream acoustic field are well reproduced by the computation. Flow visualization of shock/vortex interactions within the third shock-cell provides evidences that screech sound sources can be interpreted using the shock-leakage theory.

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“…In this connection considerable progress has been made in developing simple yet fairly accurate first-order estimates of the gross features of shock-cells and i screech tone frequencies of supersonic jets (Tam, Jackson & Seiner (1985), Tam (1988), Morris (1988), Morris, Bhat & Chen (1989»). The present work provides some clues on the relationship between screech mode changes and the shock-cell structures by intentionally producing spanwise variations in the shock-cells and by studying changes in the span wise screech mode.…”

Section: Objectives Of the Present Workmentioning

confidence: 99%

“…For all nozzles after the Mach disk forms , the screech mode becomes span wise uniform. For rectangular jets with uniform exits, the screech frequency (f) can be predicted if the shock-cell spacing (A) is known (Tam (1988), Morris et al . (1989». In such predictable cases the first four shock-cells are uniform and equally spaced.…”

Section: Characterization Of Span Wise Varying Screech Modesmentioning

confidence: 99%

Screech tones from rectangular jets with spanwise oblique shock-cell structures

Raman

1996

34th Aerospace Sciences Meeting and Exhibit

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Understanding screech is especially important for the design of advanced aircraft because screech can cause sonic fatigue failure of aircraft structures. Although the connection between shock-cell spacing and screech frequency is well understood, the relation between nonuniformities in the shock-cell structures and the resulting amplitude, mode, and steadiness of screech have remained unexplored. This paper addresses the above Issues by intentionally producing spanwise (larger nozzle dimension) variations in the shock-cell structures and studying the resulting spanwise screech mode. The spanwise oblique shock-cell structures were produced using imperfectly expanded convergent-divergent rectangular nozzles (aspect ratio = 5) with nonuniform exit geometries. Three geometries were studied: (a) a nozzle with a spanwise uniform edge, (b) a nozzle with a span wise oblique (single bevelled) edge, and (c) a nozzle that had two spanwise oblique (double bevelled) cuts to form an arrowhead-shaped nozzle.For all nozzles considered, the screech mode was antisymmetric in the transverse (smaller nozzle dimension) direction allowing focus on changes in the spanwise direction. Three types of spanwise modes were observed: symmetric (I), anti symmetric (n), and oblique (Ill). The following significant results emerged: (i) for all cases the screech mode corresponds with the spanwise shock-cell structure, (ii) when multiple screech modes are present, the technique presented here makes it possible to distinguish between coexisting and mutually exclusive modes, (iii) the strength of shocks 3 and 4 influences the screech source amplitude and determines whether screech is unsteady. The results presented here offer hope for a better understanding of screech and for tailoring shock-containing jets to minimize fatigue failure of aircraft components.

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A linear shock cell model for jets of arbitrary exit geometry

Cited by 49 publications

References 16 publications

Coupling of twin rectangular supersonic jets

Coupling of twin rectangular supersonic jets

Large Eddy Simulation of Screech Tone Generation in a Planar Underexpanded Jet

Screech tones from rectangular jets with spanwise oblique shock-cell structures

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