Clarifying the mechanisms of movement of a pyroclastic flow is important in studying how to prevent or minimize damage due to pyroclastic flows. Factors presumed to affect the movement of pyroclastic flow include sediment discharge from the flow, the degree of flow liquefaction due to volcanic gas, and topographical conditions such as the flow or sediment gradient.
Basic experiments were conducted to analyze how channel gradients and ascent speed of air affect velocity, sediment length, width, and shape of pyroclastic flows, depending on the degree of liquefaction. Air ascent speed, channel gradient, gradient of the sediment section, and amount of sediment were controlled so that results could be generalized.
The following tendencies can be inferred from our tests.
(1) If the gradient of the flow section was smaller than angle of dynamic friction, the velocities of pyroclastic flows are strongly affected by the channel gradient, the air ascent speed, and the volume of sediment.
(2) If the gradient of the flow section was larger than angle of dynamic friction, the velocities of pyroclastic flows are not affected by the air ascent speed.
(3) If a pyroclastic flow is very liquid and the channel gradient is steep, both the sediment length and width are large and the sediment is thinly dispersed over a large area.
(4) If the channel gradient is steeper than the angle of dynamic friction, the air flow does not greatly affect the sediment length width, and shape of a pyroclastic flow. Instead, these are affected by the channel gradient itself.
(5) If the gradient of the flow section exceeds a certain value with reference to the gradient of the sediment section, the sediment suddenly begins to spread laterally and be deposited. Furthermore, the sediment is likely to be dispersed and deposited for, at least, twice the width of the channel.

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The laminar steady flow of a non-Newtonian fluid through an axisymmetric conical diffuser is studied numerically. In this calculation, Casson model is used as a constitutive equation of fluid. A finite element method is used for the numerical calculation. The calculation conditions are coincided with the venous flow conditions of man and dog. Results are summarized as follows : 1) The non-Newtonian property of Casson fluid has an effect to decrease the separated flow region, and the decrease in the divergent angle increases the difference of the separated flow region between the Newtonian fluid and Casson fluid. 2) At low Reynolds numbers, the pressure recovery of the Casson fluid is lower than that of the Newtonian fluid, but this ineqality becomes reverse with the increase in the Reynolds number. Thus, it is indicated that the non-Newtonian property of the Casson fluid improves the diffuser's efficiency at high Reynolds numbers.

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Zero-mean flow turbulence is formed when a grid is vertically oscillated in a homogeneous fluid. Some characteristic quantities of this turbulence have been investigated by using the k-ε turbulence model analytically. The governing equations and the boundary conditions are non-dimensionalized by using the turbulent energy k₀ and the dissipation rate ε₀ which are given as boundary conditions at the center of the grid oscillation. This non-dimensionalization gives universal vertical profiles of turbulent energy k, energy flux in the vertical direction q, dissipation rate ε, eddy viscosity ν_t and characteristic lengthscale l. Vertical distributions of k, q and ε have been obtained from the velocity measurements. Superposing the experimental data of k and ε on the dimensionless solutions enables us to evaluate k₀ and ε₀. These values have been related to the conditions of the grid oscillation and the kinematic viscosity. If experimental conditions are known, therefore, the five characteristic quantities can be estimated on the basis of their universal vertical profiles and the values of k₀ and ε₀.

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The present paper describes mainly the wall effect on the vortex shedding characteristics of a circular cylinder, which is placed between two walls, and forcedly vibrated in the direction perpendicular to the flow. The investigation is based on a spectral analysis of output signals from a single hot wire located in the cylinder wake. From the measured results, four wake modes, including the locking-in phenomenon, were clarified in terms of the gap ratio and the forcing frequency.

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In this paper, we present the results of an experimental study of the gap flow between coaxial rotating disks. Flow visualization with hydrogen bubble technique, and measurements with a hot-wire anemometer and a laser velocimeter were made. By data reduction, we confirmed that there exists a pair of secondary flow loops at rest.

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