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Mean-flow and acoustic characteristics of cold-air jets issuing from a rectangular hypersonic nozzle were investigated experimentally. The final goal of this study is (even though qualitative to some extent) to establish a method capable of predicting the acoustic characteristics of the high-temperature and high-velocity jets issuing from a hypersonic engine. As the first step, a high-enthalpy wind-tunnel plant without anechoic treatment was used for the cold-air jet experiments, and the acoustic data obtained were compared with those obtained in a small anechoic chamber. It is shown that, while it is necessary to pay attention to some noted exceptions, the directivity patterns and spectral shapes agree well at a wide range of radiation angles by taking into account the correction of −2.5 dB. The mean-flow measurements revealed that, due to the complicated geometry of the nozzle, the jet has a highly asymmetric velocity profile at the ramp end and that the development of the jet plume is also inclined and asymmetric, which resulted in the complicated patterns of the acoustic radiation. By fitting the sound spectra for the large turbulence structure noise and fine-scale turbulence noise, the contributions of the two noise sources in the hypersonic nozzle were investigated. Nomenclature

Dispersed rheology of lipophilized-smectite (SAN)/toluene (TOL) suspensions with various concentrations φ of (0.03-3.77) × 10 -2 vol fraction was examined by a stress-controlled rheometer and Ubbelohde type viscometer. Under the quiescent state of the SAN/TOL suspensions, the original laminate structure in the solid state of SAN was lost and exfoliation of the silicate layers took place as revealed by X-ray diffraction analysis. In the dilute SAN/TOL suspension with 10 2 φ e 0.2, the value of ηsp/φ (ηsp being specific viscosity) is independent of concentration up to φ ∼ 2 × 10 -3 and exhibits abrupt increasing beyond φ ∼ 2 × 10 -3 . The dense concentration region exhibits elastic gel-like properties, and rheopexy behavior imposed by shear stress was observed. The limiting value of the dynamic storage modulus G′ was given by G′(ωf0) ∼ φ 4 , whereas the loss tangent δ exhibited independence of φ and remains at a constant value of about 0.1.

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