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Maestrello, L.

Publications and source records attributed to Maestrello, L..

82 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Sound propagation through a real jet flow field with scattering due to interaction with turbulence

The sound propagation through a nonuniform turbulent jet flow field is studied by means of a system of linearized equations governing the acoustic variables. These equations depend on the fluctuating flow-field variables which are prescribed by experimental results. It is shown that the redistribution of the acoustic energy in the far field depends on space-time correlation of the turbulent velocities and on the mean flow variables and their gradients.

Maestrello, L.↗
NASA NTRS1974

Propagation of sound through a real jet flowfield

The sound propagation of harmonic disturbances through a real jet flowfield, which contains mean flow gradients in pressure and velocities, has been studied. A finite-difference approximation for the equations which govern the acoustic disturbance is obtained for a subsonic axisymmetric jet in terms of acoustic pressure and acoustic energy flux. Experimental results are used to describe the mean flowfield of a model jet. The equations are solved numerically using a Newton-type iterative scheme. The directivity at various distances from a point source located at two jet diameters downstream of the jet exit on its center line compared qualitatively well with the numerical result of Schubert (1972) and with the experimental result of Grande (1966).

Liu, C. H.↗
NASA NTRS1973

On the relationship between acoustic energy density flux near the jet axis and far field acoustic intensity

By measurement and analysis, the relationship between the distribution of the outflow of acoustic energy over the jet boundary and the far-field intensity is considered. The physical quantity used is the gradient of the pressure evaluated on a geometrical plane at the smallest possible radial distance from the jet axis, but outside the vortical region, in the area where the homogeneous wave equation is reasonably well satisfied. The numerical and experimental procedures involved have been checked out by using a known source. Results indicate that the acoustic power output per unit length of the jet, in the region from which the sound emanates, peaks at approximately 9 diameters downstream. The acoustic emission for a jet Strouhal number of about 0.3 exceeds the emission for all other Strouhal numbers nearly everywhere along the measurement plane. However, the far-field peak intensity distribution obtained from the contribution of each station was found to depend on the spatial extent of the region where sound emanates from the jet, which, in turn, depends more on the far-field angle than on the Strouhal number.

Maestrello, L.↗
NASA NTRS1973

On the relationship between acoustic energy density flux near the jet and far field acoustic intensity

The relationship between the distribution of the outflow of acoustic energy over the jet boundary and the far-field directivity and intensity distribution is established by measurement and analysis. The numerical and experimental procedures involved have been checked out by using a known source. The results indicate that the acoustic power output per unit length of the jet, in the region from which the sound emanates, peaks at approximately 9 diameters downstream. The acoustic emission for a jet Strouhal number of about 0.3 exceeds the emission for all other Strouhal numbers nearly everywhere along the measurement plane. However, the far-field peak intensity distribution obtained from the contribution of each station was found to depend on the spatial extent of the region where sound emanates from the jet, which, in turn, depends more on the far-field angle than on the Strouhal number. The implications of these results for sound suppression techniques are discussed.

Maestrello, L.↗
NASA NTRS1972

The estimation of nonstationary spectra from moving acoustic source distributions.

It is shown that the Blackman-Tukey estimation procedure provides a natural estimate of a nonstationary spectrum defined in terms of the acoustic sources. The pressure field from the moving source distribution is discussed together with the estimation procedure. The spectrum can be considered as a time-dependent partition of the variance of the pressure field over a Doppler shifted continuum of frequencies. It is found that the effect of nonstationarity on the bias and variance of the estimate is small in cases of practical interest, provided sources directionality is excluded.

Mcdaid, E.↗
NASA NTRS1970

Acoustic characteristics of a high-subsonic jet

Acoustic characteristics of high subsonic model cold jet using imaging technique and measurements of energy flux of flow, calculating energy flux from flowfield measurements

Maestrello, L.↗