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  • 1
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    Acoustic effects of sprays (1994)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Since the early 1960's, it has been known that realistic combustion models for liquid fuel rocket engines should contain at least a rudimentary treatment of atomization and spray physics. This is of particular importance in transient operations. It has long been recognized that spray characteristics and droplet vaporization physics play a fundamental role in determining the stability behavior of liquid fuel rocket motors. This paper gives an overview of work in progress on design of a numerical algorithm for practical studies of combustion instabilities in liquid rocket motors. For flexibility, the algorithm is composed of semi-independent solution modules, accounting for different physical processes. Current findings are report and future work is indicated. The main emphasis of this research is the development of an efficient treatment to interactions between acoustic fields and liquid fuel/oxidizer sprays.
    Keywords: ACOUSTICS
    Type: Pennsylvania State Univ., NASA Propulsion Engineering Research Center, Volume 2; p 211-215
    Format: application/pdf
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  • 2
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    Numerical simulations of small amplitude acoustic wave propagation in a converging-diverging nozzle (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Numerical simulations of the small amplitude acoustic wave propagation in a converging-diverging nozzle proposed in Category 5 are performed and presented here. The quasi 1-D unsteady flow equations in conservative form are discretized by the DRP scheme with the artificial damping developed by Tam and Webb. Characteristic boundary conditions are used at both the inlet and outlet of the nozzle. The effect of different numerical implementations of the subsonic inflow boundary conditions on the convergence of the solution to the steady state is studied. In the case of a subsonic outflow in which a shock is formed in the nozzle, the interaction between acoustics and the shock is also investigated.
    Keywords: ACOUSTICS
    Type: NASA. Langley Research Center, ICASE(LaRC Workshop on Benchmark Problems in Computational Aeroacoustics (CAA) p 285-290 (SEE N95-30133 10-71); NASA. Langley Resear
    Format: text
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  • 3
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    Jet noise modification by the 'whistler nozzle' (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The farfield noise characteristics of a subsonic whistler nozzle jet are measured as a function of Mach number (0.25, 0.37, and, 0.51), emission angle, and excitation mode. It is shown that a whistler nozzle has greater total and broadband acoustic power than an excited contraction nozzle; and that the intensity of far-field noise is a function of emission angle, Mach number, and whistler excitation stage. The whistler nozzle excitation produces broadband noise amplification with constant spectral shape; the broadband noise amplification (without associated whistler tones and harmonics) increases omnidirectionally with emission angle at all Mach numbers; and the broadband amplification factor decreases as Mach number and emission angle increase. Finally the whistler nozzle is described as a very efficient but inexpensive siren with applications in not only jet excitation but also acoustics.
    Keywords: ACOUSTICS
    Type: AIAA Journal (ISSN 0001-1452); 22; 340-347
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  • 4
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    The whistler nozzle phenomenon (1982)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The whistler nozzle is a simple device which can induce jet self-excitations of controllable amplitudes and frequencies and appears highly promising for many applications involving turbulent transport, combustion and aerodynamic noise. The characteristics of this curious phenomenon are documented for different values of the controlling parameters and attempts to explain the phenomenon. It is shown that the whistler excitation results from the coupling of two independent resonance mechanisms: shear-layer tone resulting from the impingement of the pipe-exit shear layer on the collar lip, and organ-pipe resonance of the pipe-nozzle. The crucial role of the shear-layer tone in driving the organ-pipe resonance is proven by reproducing the event in pipe-ring and pipe-hole configurations in the absence of the collar. It is also shown that this phenomenon is the strongest when the self-excitation frequency matches the preferred mode of the jet.
    Keywords: ACOUSTICS
    Type: NASA-CR-170015 , NAS 1.26:170015 , FM-15
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  • 5
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    Aviation noise overload in the immediate proximity of the Warsaw-Okecie airport (1981)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: The results are presented for investigations on noise overload around the Warszawa-Okecie airport on persons inhabiting the area where it exceeds 100 dB for a single aircraft flight. Of 256 subjects, 91.1 percent complained about aircraft noise overload. In the population studied considerable differences were noted respecting the subjective sensitivity scale. Statistical analysis showed numerous correlations between the individual noise sensitivity threshold and the subject's state of health, age, sex, type of work, etc. At the same time investigations demonstrated various forms and levels of disturbance in the organism for individual subjects and groups. The most frequent complaint was chronic fatigue (68.1 percent), followed by nervousness (36.6 percent), frequent headaches (36.2 percent), hearing disturbances (30.0 percent) and sleep disorders (23.9 percent).
    Keywords: ACOUSTICS
    Type: NASA-TM-75892
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  • 6
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    Interaction of the sonic boom with atmospheric turbulence (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Theoretical research has been carried out to study the effect of free-stream turbulence on sonic boom pressure fields. A new transonic small-disturbance model to analyze the interactions of random disturbances with a weak shock has been developed. The model equation has an extended form of the classic small-disturbance equation for unsteady transonic aerodynamics. An alternative approach shows that the pressure field may be described by an equation that has an extended form of the classic nonlinear acoustics equation that describes the propagation of sound beams with narrow angular spectrum. The model shows that diffraction effects, nonlinear steepening effects, focusing and caustic effects and random induced vorticity fluctuations interact simultaneously to determine the development of the shock wave in space and time and the pressure field behind it. A finite-difference algorithm to solve the mixed-type elliptic-hyperbolic flows around the shock wave has also been developed. Numerical calculations of shock wave interactions with various deterministic and random fluctuations will be presented in a future report.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 93-2943 , ; 12 p.|AIAA, Fluid Dynamics Conference; Jul 06, 1993 - Jul 09, 1993; Orlando, FL; United States
    Format: text
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