Mizue Munekata

Vortex motion in a swirling flow of surfactant solution with drag reduction

Surfactants are well known as additives which induce drag reduction in the straight (nonswirling) pipe flow. However, in industrial applications of the drag-reducing effect, many flow fields besides the straight pipe flow need to be considered. The purpose of this study is to investigate the flow characteristics of the surfactant solution in swirling pipe flow. The drag-reducing effect is estimated from the measurement of wall pressure drop and velocity profiles on various pipe sections by two-dimensional LDV (Laser Doppler Velocimeter). Since the surfactant solution has viscoelasticity, interesting flow characteristics are obtained. The decay of swirl, the vortex type and the turbulence intensity are discussed, compared with the swirling flow of the water. As the results, it is concluded that the change from Rankin s combined vortex to the forced vortex at a more upstream section by suppressing progress of free vortex and stretch of forced vortex introduces considerable drag reduction. Oscillation of the vortex core is also investigated, and it is found that the oscillation is independent of swirl number.

Visualization of Three-Dimensional Flow Structures in the Wake of an Inclined Circular Cylinder

In the previous measurements of the aerodynamic sound generated from an inclined circular cylinder, it is reported that the sound pressure level (SPL) changes with the aspect ratio and the inclined angle. Therefore, we have investigated the changes in the vortex structure of the wake considered as one of the causes of the SPL variation. Using the low-noise wind tunnel, the velocity fluctuation in the wake is measured to obtain the correlation length. Moreover, the flow visualization is performed with a hydrogen bubble method and a numerical analysis method in order to clarify how the wake structure changes by variations of aspect ratio and inclined angle. As a result of this investigation, it is shown that the spanwise structure of Karman’s vortex is highly influenced by the interference of Karman’s vortex with the bottom endplate, and that the influence on the spanwise structure in the wake becomes greater as the aspect ratio decreases and the inclined angle increases.

Uniform ZnO epitaxial films formed at atmospheric pressure by high-speed rotation-type mist chemical vapor deposition

Uniform ZnO epitaxial films were formed on 2-in.-diameter m-plane sapphire substrates by high-speed rotation-type mist chemical vapor deposition at atmospheric pressure, without using any vacuum equipment. The ZnO films were characterized by scanning electron microscopy, X-ray diffraction in θ–2θ and scanning modes, electron backscatter diffraction, and room-temperature photoluminescence measurements. Experimental results show that m-plane ZnO films were epitaxially grown on the m-plane sapphire substrates with high uniformity of not only thickness but also crystallinity and optical properties. These results will promote the progress of ZnO-based devices such as light-emitting diodes.

Direct numerical simulation of gas-particle turbulent swirling flows in an axially rotating pipe

The purpose of this study is to investigate the effect of the turbulent structure of the swirling flows on the particle motions using numerical simulation. In this work, we deal with the swirling turbulent flows in an axially rotating pipe because of focusing on the influence of swirl effect on the particle motions. Direct numerical simulation (DNS) of gas-particle turbulent swirling flows in the axially rotating pipe at the Reynolds number 180, based on the friction velocity and the pipe radius, and the rotating ratios 0.25 and 0.3 based on the bulk velocity was performed. Particle motions were treated by a Lagragian method with inter-particle collisions calculated by a deterministic method. In order to investigate the influence of swirl effect on the particle motions in detail, the one-way method in which fluid motion is not affected by particles is adopted. In particular, the effect of the inter-particle collisions on particle motions was carefully investigated because it is considered that particles accumulate near the wall due to the centrifugal force and local particle concentration is very high in the region.Copyright

Vortex motion in a swirling flow of surfactant solution with drag reduction in a pipe

A surfactant is well known as an additive that brings about drag-reduction in straight (non-swirling) pipe flow. However in industrial applications of the drag-reducing effect, many flow fields exist including the straight pipe flow. The purpose of this study is to investigate the flow characteristics of surfactant solution swirling pipe flow. The drag reducing effect is estimated from the measurement wall pressure loss and the velocity profiles on various pipe sections are measured by 2 dimensional LDV. Since the surfactant solution has viscoelasticity, interesting flow characteristics are shown. The decay of swirl, the vortex type and the turbulence intensity are discussed, compared with the water swirling flow. The oscillating of vortex core is also investigated.© 2003 ASME

A study on numerical analysis method of incompressible flows using high-order accuracy finite difference method

The purpose of this study is to establish finite-difference solutions in use of high-order-accurate upwind scheme. In this paper, numerical analysis method based on a fractional step method was presented. This method used 3rd-order Adams-Bashforth method for convective term and Crank-Nicolson method for viscous term. For spatial derivatives in Navier-Stokes equations, 5th-order-accurate upwind scheme for convective term and 6th-order-accurate centered difference scheme for viscous term are applied. By this method, incompressible viscous flow in three-dimensional cubic cavity is computed at Reynolds numbers of 400, 1000 and 5000, with 41×41×41 grid points. In the analysis of parallel plate flow, the solutions of this investigation are in good agreement with the result of DNS data by Kim et al.. As a result of this analysis, it was made clear that high order numerical analysis for incompressible flows could be carried out by the method suggested in this study.

High-order numerical analysis of two-dimensional square driven cavity flow using vorticity transport equation

In this work, the two-dimensional square driven cavity flow problem is solved by the finite difference method with a uniform mesh. The 3 rd-order upwind scheme and the 5 th-order upwind scheme are applied to the convective term in the vorticity transport equation. It is necessary that the approximation of the convective term is treated carefully. First, therefore, the accuracy of the convective velocity is considered. As a result, it is clarified that accuracy of convective velocity is important in the numerical flow analysis in which vorticity and stream function are unknown quantities. Next, comparison of the 3 rd-order scheme and the 5 th-order scheme is carried out. Finally, by adopting of the highest-order calculation condition, more accurate results than Ghias data for high Reynolds numbers are obtained. The steady solution can be obtained for Reynolds numbers as high as 25000.