Abstract
In this study, two-dimensional numerical simulation was carried out for an oscillatory flow between parallel flat plates having a suddenly expanded section. Governing equations were discretized with the second-order accuracy by a finite volume method on an unequal interval mesh system resolving finer near walls and corners to obtain the characteristics of the oscillatory flow accurately. Amplitude spectrums of a velocity component were obtained to investigate the periodic characteristics of the oscillatory flow. At low Reynolds numbers, the flow is periodic because the spectrum mostly consists of harmonic components, and then at high Reynolds numbers, it transits to a quasi-periodic flow mixed with non-harmonic components. In conjunction with the periodic oscillation of a main flow, separation vortices that are not uniform in size are generated from the corner of a sudden contraction part and pass through a downstream region coming into contact with the wall. The number of the vortices decreases rapidly after they are generated, but the vortices are generated again in the downstream region. In order to specify where aperiodicity is generated, the turbulent kinetic energy is introduced, and it is decomposed into the harmonic and non-harmonic components. The peaks of the non-harmonic component are generated in the region of the expanded section.
Highlights
Fluid mechanics concern gas and liquid in motion
A fluid flows from left to right between the two parallel flat plates. This geometry is set in in two-dimensional two-dimensional space, space, where the coordinate origin O is set at the center of the suddenly expanded section, the x-coordinate is taken along the parallel flat plates, plates, and and the the y-coordinate y-coordinate is is perpendicular perpendicular to to the the x-coordinate
The sampling position followed that of Mizushima et al [8], and the position was slightly shifted from the channel center in order to handle both symmetric and antisymmetric disturbances at Re = 1200, as shown in Figure 3.2019, 11, x FOR PEER REVIEW
Summary
As the crucial parameter known as the Reynolds number increases, the flow tends to be more complicated because of the characteristic of non-linearity peculiar to fluids. The state of fluid motion can be classified into laminar flow, transition, or turbulent flow. In various industrial applications related to fluid motion as well as the natural phenomena such as atmospheric and oceanic flows, the identification and the control of fluid flow are of great importance. The fluid flow sometimes exhibits the transitional behavior between the laminar and turbulent regimes at a certain range of Reynolds numbers. The transitional flow is considered to be related to the instability of the base laminar flow. The complex mechanism of such flow transition, where the flow characteristic changes from a simple state to another more complicated state, has not been sufficiently understood yet. If one of any disturbance grows, its state is “unstable”
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