Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

20000065633 Institute TNO of Applied Physics, Delft, Netherlands
Modelling Tip Vortex Induced Noise
Geerlings, A. C., Institute TNO of Applied Physics, Netherlands; Dec. 20, 1999; 21p; In English
Contract(s)/Grant(s): A99/KM/150; TNO Proj. 008.00065/01.01
Report No.(s): TD-99-0063; HAG-RPT-990239; Copyright; Avail: Issuing Activity
Sound generated by objects in a flow, such as hydrofoils or propellers, is caused by a number of mechanisms. One mechanism
is due to the tip vortex, a phenomenon caused by the finite length of airfoils and propeller blades. Noise due to the tip vortex can
be considered complementary to other previously studied noise mechanisms such as non-uniform stationary inflow, inflow turbulence
and trailing edge noise. In this literature study a first step is made to come to a design for a parameterized model for tip vortex
noise. The tip vortex induced partial source contribution completes the existing noise emission model for ship propellers. The
proposed model consists of available techniques by which the noise radiation is based on wall pressure fluctuations described by
their temporal and spatial spectra. This requires first the availability of the parameters that describe the turbulent layer. Secondly,
in order to apply these techniques to tip vortex related noise, the time-varying equilibrium position of the tip vortex is required.
For simplified geometries parameter models are available. In case of a complex geometry a numerical solution may be sought
by means of Reynolds-Averaged Navier-Stokes (RANS) calculations.
Author
Vortices; Aeroacoustics; Aerodynamic Noise; Propeller Noise; Propeller Blades; Trailing Edges
20000065657 Georgia Inst. of Tech., Acoustics and Aerospace Technologies Branch, Atlanta, GA USA
High Amplitude Acoustic Behavior of a Slit-Orifice Backed by a Cavity
Ahuja, K. K., Georgia Inst. of Tech., USA; Gaeta, R. J., Jr., Georgia Inst. of Tech., USA; DAgostino, M., Georgia Inst. of Tech.,
USA; 20000331; 53p; In English
Contract(s)/Grant(s): NAG1-1734
Report No.(s): GTRI-A5004/2000-3; No Copyright; Avail: CASI; A04, Hardcopy; A01, Microfiche
The objective of the study reported here was to acquire detailed acoustic data and limited and flow visualization data for
numerical validation a new model of sound absorption by a very narrow rectangular slit backed by a cavity. The sound absorption
model is being developed by Dr. C. K. W. Tam of Florida State University. This report documents normal incidence impedance
measurements of a singular rectangular slit orifice with no mean flow. All impedance measurements are made within a 1.12 inch
(28.5 mm) diameter impedance tube using the two-microphone method for several frequencies in the range 1000-6000Hz and
incident sound pressure levels in the range 130 - 150 dB. In the interest of leaving the analysis of the data to the developers of
more advanced analytical and computational models of sound absorption by narrow slits, we have refrained from giving our own
explanations of the observed results, although many of the observed results can be explained using the classical explanations of
sound absorption by orifices.
Derived from text
Cavities; Orifices; Slits; Amplitudes; Acoustic Attenuation
20000065658 Georgia Inst. of Tech., Acoustics and Aerospace Technologies Branch, Atlanta, GA USA
Sound Absorption of a 2DOF Resonant Liner with Negative Bias Flow
Ahuja, K. K., Georgia Inst. of Tech., USA; Cataldi, P., Georgia Inst. of Tech., USA; Gaeta, R. J., Jr., Georgia Inst. of Tech., USA;
Mar. 31, 2000; 35p; In English
Contract(s)/Grant(s): NAG1-1734
Report No.(s): GTRI-A5004/2000-5; No Copyright; Avail: CASI; A03, Hardcopy; A01, Microfiche
This report describes an experimental study conducted to determine the effect of negative bias flow on the sound absorption
of a two degree-of-freedom liner. The backwall for the liner was designed to act as a double-Helmholtz resonator so as to act as
a hard wall at all frequencies except at its resonant frequencies. All normal incident impedance data presented herein was acquired
in an impedance tube. The effect of bias flow is investigated for a buried septum porosity of 2% and 19.5% for bias flow orifice
mach numbers up to 03 11. As a porous backwall is needed for the flow to pass through, the effect of bias flow on this backwall
all had to be evaluated first. The bias flow appears to modify the resistance and reactance of the backwall alone at lower frequencies
up to about 2 kHz, with marginal effects at higher frequencies. Absorption coefficients close to unity are achieved for a frequency
range of 500-4000 Hz for the overall liner for a septum porosity of 2% and orifice mach number of 0.128. Insertion loss tests performed
in a flow duct facility for grazing flow Mach numbers up to 0.2 and septum mach numbers up to 0.15 showed that negative
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