NDLI: Influence of exit impedance on finite difference solutions of transient acoustic mode propagation in ducts

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Influence of exit impedance on finite difference solutions of transient acoustic mode propagation in ducts

Content Provider	NASA Technical Reports Server (NTRS)
Author	Baumeister, K. J.
Copyright Year	1981
Description	The time-dependent governing acoustic-difference equations and boundary conditions are developed and solved for sound propagation in an axisymmetric (cylindrical) hard-wall duct without flow and with spinning acoustic modes. The analysis begins with a harmonic sound source radiating into a quiescent duct. This explicit iteration method then calculates stepwise in real time to obtain the steady solutions of the acoustic field. The transient method did not converge to the steady-state solution for cutoff acoustic duct modes. This has implications as to its use in a variable-area duct, where modes may become cutoff in the smal-area portion of the duct. For single cutoff mode propagation the steady-state impedance boundary condition produced acoustic reflections during the initial transient that caused finite instabilities in the numerical calculations. The stability problem is resolved by reformulating the exit boundary condition. Example calculations show good agreement with exact analytical and numerical results for forcing frequencies above, below, and nearly at the cutoff frequency.
File Size	1400086
Page Count	16
File Format	PDF
Alternate Webpage(s)	http://archive.org/details/NASA_NTRS_Archive_19810022363
Archival Resource Key	ark:/13960/t4rj98h15
Language	English
Publisher Date	1981-01-01
Access Restriction	Open
Subject Keyword	Acoustics Transient Response Time Dependence Acoustic Ducts Steady State Finite Difference Theory Acoustic Propagation Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science
Content Type	Text
Resource Type	Article

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