Addition of small amount of cationic surfactant and counter ion causes a drastic drag reduction in a turbulent pipe flow. Function of additives on turbulence control and drag reduction will be discussed.

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This article reviews recent progress in numerical simulation of momentum, heat and mass transfer, and chemical reaction of chemical vapor deposition (CVD). The characteristics of fluid flow and heat transfer in CVD apparatus is very complicated owing to its thermal circumstance. But a 2D-and 3D-simulation model we developed reproduce the transport phenomena including thermal diffusion in CVD reactors. In order to predict film growth rate, it is essential to incorporate the reasonable reaction rate expression to the simulation code. Chemical reaction analysis we developed is believed to be powerful to determine the unknown reaction parameters.

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Three different optimization algorithms, the gradient-based method, Simulated Annealing and Genetic Algorithm, have been discussed for airfoil design using the approximation concept. First, distribution of the objective function for the simplified airfoil shape optimization problem is visualized. The visualization indicates the difficulty of the aerodynamic optimization and the theoretical challenge to fluid dynamics. Then, performance of the three optimization algorithms is directly compared. The results suggest that a global optimization strategy is necessary and Genetic Algorithm is the best for the aerodynamic optimization. Finally, this paper provides a guidance in the selection of design variables before the optimization.

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Turbulent swirling flow in a straight pipe is investigated experimentally. It is extremely different from no-swirl pipe flow. Increasing its strength, the axial velocity decreases in the central domain of the pipe and flow reversal occurs. Although swirl decay and flow reversal mechanism have not been known enough yet, they are applied to the cyclone dust collector, and so on. Especially, earlier flow reversal and higher fluctuating velocity according to swirl strength affect its performance. The swirling angle in the vicinity of the pipe wall, Θ_sw, is employed for representing swirl strength instead of the conventional swirl number. Even on different initial swirl conditions, the flow similarities are ascertained on condition that Θ_sw are same. The displacement radius, R_d, is also proposed by the authors for estimating quantitatively the decrement of axial velocity in the central domain of the pipe according to the swirl motion. The flow reversal are observed on condition that Θ_sw, are greater than 22.5 degrees.

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Fluid flow phenomena of turbulent swirling pipe flow are very complicated not only in the central domain of the pipe but also in the vicinity of the pipe wall. Boundary layer development of such flow are very different from no-swirl pipe flow's. Though on lower swirl strength, their developments are gradual and are enough sustained far downstream. Although their resultant velocity in the vicinity of the pipe wall are several times higher than no-swirl's, turbulence here are also controlled as same as no-swirl's. Turbulent swirling flow in a fully long straight pipe are investigated experimentally using hot-wire anemometer in the wide range of swirl strength up to the swirling angle in the vicinity of the pipe wall, Θ_sw=55 degrees. In this paper, the relationship between boundary layer development and Θ_sw is discussed by means of boundary layer analysis.

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Entrainment coefficients of miscible conservative two-dimensional gravity currents traveling downslope, namely, the front of inclined starting plumes and inclined thermals, are investigated in laboratory. Using a large volume of experimental data, the entrainment coefficients of the front of inclined starting plumes and inclined thermals are quantified as functions of bottom slope angles for the slope angles ranging from 5° to 90°. No significant difference in the amount of entrainment coefficients between the two gravity currents is identified. Consequently, an empirical relationship for the entrainment coefficients for inclined gravity currents is proposed as a linear functions of bottom slope angles.

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