Although it is a known fact that there exist coherent motions in a turbulent boundary layer ; the slowly rotating flow in the outer region (turbulent bulge) and the burst in the inner region, the relations between them are not clear yet.
The present experiment was carried out in order to find the dependency between these coherent motions through the simultaneous measurements of the wall pressure and the velocity field because the pressure fluctuations are induced by flow fluctuations throughout the boundery layer. The conclusions are ; (i) the wall pressure fluctuations are composed of low and high frequency components which are responsible to the bulge and the burst respectedly, and (ii) the burst appears in a certain (acceleration) phase in the passage of the bulge, suggesting the close relationship between them.

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The rate of absorption of sound energy by turbulence in a box has been experimentally determined. The box is essentially a reverberant box to eliminate influence of mere scattering of sound. In the box, turbulence is stirred up by a rotating structure and the sound is generated by a loudspeaker with sinusoidal excitation. The data show that the sound absorption by turbulence in general can not exceed 1/1500 m^-1. in terms of the absorption coefficient with 95 % reliability, for the present condition with the typical speed of 35 ms^-1. The absorption is much less efficient than sometimes assumed, and too inefficient to have any significant influence on the jet noise characteristics.

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Exact solutions of some non-linear hydrodynamic equations containing a small parameter are obtained by means of the differential perturbation technique proposed by the authors.
Several important conceptions associated with the differential perturbation technique, such as the degree of non-linearity and the existence condition of exact solutions, are specified in connection with the differential perturbation. The condition that a non-linear equation with a small parameter is transformed into a linear equation with a small parameter is transformed into a linear one by means of this technique is also obtained.
The Cole-Hopf transformation is obtained for the Burgers equation, if the degree of nonlinearity is estimated by examining the equation. Under the similar assumption, an exact solution of the K-dV equation is obtained. This result is parallel with the D-operator procedure proposed by Hirota.
As the last example, a non-linear equation which has a singularity regarding with the small parameter is solved as the parallel application with the PLK method.

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A method for calibrating a hot-wire anemometer is described. To determine directly sensitivities of the system within linear operations to accurately known velocity perturbations, the hot-wire element was sinusoidally shaked at low frequencies in a uniform flow. The direct measurement for sensitivities is unneccessary to strictly linearize the anemometer output against speed. When reciprocals of the sensitivities are integrated with respect to the output voltage of the system, the conventional static calibration curve can be obtained. Accordingly, this method requires no any referred wind speeds and is suitable for calibrating the system at extremely low wind speed. As a example, a constant-temperature hot-wire anemometer with a usual linearizer output was calibrated. A few easy calibrations used this method are described.

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