In this study, we investigated the effect of anticyclonic spanwise rotation on the plane Couette flow at the small Reynolds number Re_w = 1300, defined by the moving wall velocity, channel half-width, and kinematic viscosity by direct numerical simulations using the spectral method. We confirmed that at the typical rotation number, the mean velocity distribution became the S-shape, and a negative velocity gradient appeared in the channel centre. At this rotation number, the significant decrease in sweep event, i.e., inrush motion of high-speed fluids toward the wall, and an increase in ejection, i.e., the outward motion away from the wall, were observed in the wall vicinity. In addition, the budget of turbulent kinetic energy showed that the transport of turbulent energy into the wall vicinity was suppressed, and the dissipation rate there was attenuated, which indicated the relaminarization there. Finally, visualization of an instantaneous flow showed that the generated secondary flow swept small-scale vortices near the wall away from the wall.

Research on energy generation characteristics based on pressure retarded osmosis (PRO) using seawater is being widely carried out. However, there are few studies that use polymer solutions. Therefore, the purpose of this study is to evaluate energy generation characteristics when using a polymer solution. We established a PRO model with a constant hydrostatic pressure difference in a semipermeable membrane, through which pure water permeates into the polymer solution side. The concentration of the polymer solution was determined by solving the one-dimensional convection-diffusion equation, and the osmotic pressure difference in the semipermeable membrane was evaluated. The following four dimensionless parameters were derived by making the basic equations dimensionless; the dimensionless second virial coefficient α, the dimensionless hydrostatic pressure difference p*, the Péclet number Pe, and the cross-sectional area reduction ratio of the tube on the solution side β. The generation characteristics of dimensionless power densities were evaluated by changing the α representing the properties of the polymer solution. The value of p* for which the largest dimensionless power density obtained was 0.5 or more, and approached 1 as α increased. When compared with seawater, the power density while using polymer solution was smaller than that while using seawater. However, by preventing the temporal decrease in the concentration of the polymer solution and the generation of a concentration boundary layer, it is possible to significantly improve the power density and obtain a power density close to that of seawater. In addition, when the membrane used for standard PRO is applied to the present model, a commercial-level power density can be obtained.

We propose a method to estimate atomized spray droplet size distribution for multi-hole type nozzles for direct injection gasoline (DIG) engines. In the development of injector nozzles, important factors are spray quality such as spray pattern, penetration, and atomization. Previous studies have already presented methods to predict mean droplet size for a DIG injector by using the relationships among atomization, velocity, and geometric characteristics of its nozzle. However, coarse droplets in spray may cause liquid fuel droplets to remain when ignition starts, which may cause much particulate matter or/and hydrocarbon emissions, even if the spray has the same mean droplet size. To describe characteristics of the spray itself, sometimes not only the mean diameter but also the distribution of droplets must be considered. The difference in droplet size distribution has been considered to be caused by the difference in internal flow characteristics. However, the droplet size distribution is difficult to predict, especially for a DIG injector. As DIG injectors have a narrow fuel passage just upstream of the orifice inlet and short orifice length, the internal flow in an orifice tends to become complex, which affects atomization strongly. This means the droplet size distribution needs to be predicted by using detailed internal flow information. We therefore tried to construct a method to predict the droplet size distribution by using the numerically simulated velocity distribution of the orifice internal flow. This paper discusses a method to extend a previously investigated relationship between velocity and droplet size into a velocity distribution calculated by computational fluid dynamics (CFD). We manufactured sample nozzles with different dimensions to produce a curve converted from simulated velocity into an experimental droplet diameter distribution. As a result, a single conversion curve was observed by using the proposed methodology for differently designed nozzles and different experiment conditions. We concluded that the velocity distribution information from CFD can be used to estimate droplet size distribution from the DIG injector nozzle by the conversion curve.