Industrial clean rooms have become indispensable equipments for various kinds of industries recently. Most typical ones are those used in the production lines of semiconductors. The air flow in a clean room is very complex. It consists of various types of recirculating flow and the direction of mean air flow is changed locally. In order to keep the air to be clean in a clean room, it is necessary to control the movement of dispersed particles effectively. Therefore the design of air velocity distribution is most important for cleanness control because the movement of particles may be assumed to be passive. In this report, the characteristics of air flow in various types of clean rooms are analysed by the methods of numerical simulation, measurement and visualization. The diffusion of airborne particles are also described.

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Many kinds of dendritic structures in nature, such as rivers, blood vessels, electric breakdown patterns, cracks, viscous fingers and aggregates of fine particles, are reviewed based upon their mathematical models, with an interest in a common origin of these structures. It is stressed that the role of their formation is played essentially by an ensemble of conservative flows, and that the ensemble forms a dendritic structure if the flows have a tendency to aggregete each other.

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With the aid of the development of supercomputers, flow Field simulations using the compressible Navier-Stokes equations have become feasible. It is recently reported that a numerical solution of viscous transonic flow field over a practical wing model is obtained about one hour using 200, 000 grid points on a supercomputer. Such progress of Computational Fluid Dynamics is also owing to the development of numerical methods.
In this paper, the recent development of finite-difference methods for solving the compressible Navier-Stokes equations is discussed. First, the concept of the generalized coordinater is described, which is important to apply computational techniques to arbitrary geometries. Next, the contemporary upwind difference techniques are introduced to obtain high-resolution oscillation-free schemes which give the sharp profiles of shock waves. Finally, the implicit procedures for the finite-difference equations are reviewed. The AF (Approximate Factorization) schemes and the 'unfactored' schemes using relaxation algorithms are considered.
The development of Computational Fluid Dynamics will make it possible to simulate the three-dimensional complicated and unsteady phenomena. Numerical simulation will take the place of wind-tunnel test in part.

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Turbulent rectangular-duct flow is studied numerically by using an anisotropic k-ε model. A prominent feature of this model lies in an expression for the Reynolds stress, where the deviation of the Reynolds stress from its isotropic eddy-viscosity representation is taken into account. A wall damping function and a corner function are introduced to impose the no slip boundary condition on solid walls and to properly take the corner effect into account. The results obtained show that calculated turbulence characteristics of rectangular-duct flow are in good agreement with experimental data. Especially, the anisotropy of turbulent intensities as well as secondary flows normal to the mainstream, which the usual k-ε model cannot predict, are well reproduced.

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Pressure-flow relationships are derived for the steady flow through an eccentric circular tube, whose cross section takes the form of annulus bounded by two circles, not concentric in general. The velocity distribution can be obtained by solving a two-dimensional Poisson equation by use of the conformal mapping. In case when the two circles are touched each other, a mapping function of different type is required to solve the equation. The relationships thus derived are reduced to the well-known formula in the limit of concentric circles. It is found that when the region between touched circles becomes sufficiently thin, the tube conductance behaves like cube of the difference of radii of the two circles.

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