Flow around two square cylinders is investigated by the measurement of the surface pressure, the flow visualization and the supplementary numerical simulation. Two different types of flow patterns are observed which are characteristic of staggered arrangements. In either case, the gap flow is formed between two cylinders, which is biased towards the upstream cylinder. The biased flow then undergoes two different changes in the subsequent period depending on the relative location of cylinders. In the first case it flows on straightforward and finally builds up a strong vortex behind the upstream cylinder. In the second case it changes the direction and deviates towards the downstream cylinder. A strong vortex is now built up behind the downstream cylinder. However, the second flow is not stable and can not exist by itself. The fluctuation between the first and the second flows always appears in this case. The transition between the two flow regimes is abrupt under the continuous change in the cylinder arrangement.
Studies on the mechanism of ignition and flame-holding by upstream-injection plasma jets were conducted for H2 diffusion flames in high speed air streams. The plasma jets were operated with Ar gas involving active species such as O2, N2 and H2, in the range of relatively low power. It was observed that for ignition and flameholding, the concentration of active species in feedstock is more important than plasma jet power. This fact suggests the effectiveness of active species produced by plasma jets, rather than that of plasma-jet thermal energy, and also the importance of radical concentration supplied to the ignition-point of a fuel jet, compared to the total quantity of radicals produced. It was also found that the effectiveness of additives is in the order, O2≥N2>H2, and the results of numerical simulation on combustion-reaction promotion by the radicals added agreed qualitatively with the experimental ones.
The two-dimensional reacting mixing layer is numerically simulated by the integral of unsteady, incompressible Navier-Stokes equations. The chemical reaction is based on one-step, irreversible model with fast chemical kinetics and the ‘flame sheet’ model is used to describe the location and shape of combustion front. The structure of flame and its evolution are demonstrated. We are aimed to study the processes of formation, evolution and disappearance of flame islands and the effect of diffusion on these processes.
A quick automatic method for computing aerodynamic performance of ducted propellers is presented. The thrust- and power-coefficients and propulsive efficiency are calculated and plotted against the advance ratio. The representative blade section is investigated. It is found that the most suitable section is one at 75% radius as the same as nonducted cases. Thrust coefficient is predicted satisfactorily. But propulsive efficiency is overestimated; the difference seems to be “blower efficiency” defined in a previous paper.