Measurements of the spatial development of disturbance pressure waves in a low-speed axisymmetric turbulent free jet have been carried out. The results show that the wavenumbers of the pressure waves increase monotonically, while the phase velocities decrease as the Strouhal number of the jet increases. The pressure disturbance grows to a maximum at some distance downstream from the nozzle and then decays. The distributions of the amplitude of the pressure waves along the jet are similar if the data are plotted against a normalized distance St x/D. The most amplified mode is at a Strouhal number of 0.5 for the shear layer and 0.35 for the center line. The wave characteristics follow closely the linear stability theory of an inviscid diverged shear flow.

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It is shown theoretically that higher modes of wave-like disturbances can be propagated in the turbulent shear layer of an axisymmetric jet. Both the amplitudes and the extent of the spatially growing waves decrease as the order of the mode increases.

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une Flamme," Czechoslovak J. Phys., Sec. B, B22, No. 5, 394-397 (1972)-1. Acoustic waves have been excited in a flame seeded with potassium. It is shown that the amplitude of the excited wave is proportional to the frequency of a harmonic perturbation imposed on the plasma. This suggests a means of ultrasonic excitation, the limitations of which are analyzed. [Order No. N72-32660.-] Conditions of Coherence in Diffraction Spectra Produced in Liqu.i.ds on Ultrasonic Standing Waves--R. Baer •Translation of "Uber die Koh•irenzverh•iltnisse in den an stehenden Ultraschallwellen in Fltissigkeiten erzeugten Beugungsspektren," Helvetica Phys. Acta 8, No. 7, 591-600 (1935)•. Experiments, ducted to determine which of the different diffraction spectra produced on ultrasonic standing waves in liquids through the diffraction of light are coherent, i.e., can be brought to interfere with each other, are described. The result is the following: any arbitrary pairing of two spectra with even ordinal numbers (including zero order) possesses at least one common component of coherent light; the same is true for any pairing from the group of spectra with odd ordinal numbers. On the other hand, any spectrum of the first group is completely incoherent in combination with any spectrum of the second group. The patterns of ultrasonic standing waves produced by the superposition of several or all of the diffraction spectra may also be explained by such coherence properties. Experimentally determined coherence properties are exactly those obtained from the assumption that higher diffraction spectra originate in multiple diffraction (Brillouin theory). •Order No. N73-11713.• Certain Experiments to Demonstrate the Diffractio..n of Light by Ultrasonic Waves--R. Baer [Translation of "Uber einige Demonstrationsversuche zur Beugung des Lichtes an Ultraschallwellen," Helvetica Phys. Acta 6, No. 8, 570-580 (1933)3. Photographs of diffraction spectra originating in the diffraction of light by ultrasonic waves are reproduced. They show that the intensity at which individual diffraction spectra occur is a function of the ordinal number, ' which exhibits maxima and minima. The position of the r•axima and minima depends on the intensity of the sound beam, the value of the sound wavelength/light wavelength and on the length of the path of the light beam within the sound wave. With an experimental arrangement described by Barand Meyer to record fields of ultrasonic waves in liquids, the diffraction of waves by a wire screen and the refraction and reflection of an ultrasonic beam at the interface of two liquids are examined. [Order No. N73-11714.-] Loudness of Uniform Noises--E. Zwicker and R. Feldtkeller [Translation of "Ueber die Lautstaerke von Gleichfoermigen Geraeuschen," Acustica 5, 303-316 (1955)•. With the aid of equal loudness contours (loudness in zones as a parameter), of the measured width of the frequency groups and reduction of loudness in neighboring frequency groups, the level of sustained noises with given spectra can be calculated. The aur...