Dynamics of a wall-mounted cantilever plate under low Reynolds number transverse flow in a two-dimensional channel

Placing bluff bodies in a mixing channel is an important technique to enhance mixing. This paper numerically investigates the effects of transversal spacing and axial spacing of two bluff bodies on the outlet mixing efficiency (Mout), the pressure loss (ΔP), and the combined performance parameter η (the ratio of Mout to dimensionless ΔP) of fluid flow within mixing channels with dual bluff bodies having three cross-sectional shapes of circle, square, and sector with Reynolds numbers based on bluff body dimension Red = 20, 60, and 100. The study reveals that, at Red = 20, altering the spacing between the two bluff bodies in the mixing channel does not improve mixing but instead increases ΔP, leading to a decrease in η. At Red = 60 and 100, changing the transversal spacing and axial spacing in a certain range can effectively enhance mixing and improve the combined performance. There exists an optimal transversal spacing to maximize Mout and η. Furthermore, the mixing channel with sector-shaped dual bluff bodies exhibits the highest Mout and η among the three kinds of cross-sectional shapes. When Red = 60 and 100, η of the mixing channel with sector-shaped dual bluff bodies increases by 212% and 270% by the transversal offsetting compared to the case with zero transversal spacing and increases by 489% and 331% by the axial offsetting compared to the case with an axial spacing of 2 times the bluff body dimension. The present findings hold significant implications for the design optimization and performance improvement of mixers.

Fluid flow and mixing in a channel with dual bluff bodies

Xiao,

Jing

2024

A validated numerical methodology for flow-induced vibration of a semi-spherical end cantilever rod in axial flow

Mao,

Iacovides,

Cioncolini

et al. 2024

This study presents a simulation method for turbulent flow-induced vibrations of cantilever rods with a semi-spherical end exposed to axial flow, a configuration investigated for the first time. This simulation strategy has been developed using solids4Foam, a toolkit for the open-source package OpenFOAM, which uses the finite-volume approach. The fluid and solid domain equations are solved separately. Coupling is achieved with the Interface Quasi-Newton Inverse Least-Squares (IQN-ILS) algorithm. The mean flow is described by the unsteady Reynolds-averaged Navier–Stokes equations. Turbulence is modeled through either the stress-transport model of Launder, Reece, and Rodi or the effective-viscosity k–ω shear stress transport model, both with the wall-function approach accounting for near-wall turbulence. The methodology is validated using experimental data produced during this study. The simulations show good agreement with the measured values of the oscillation amplitude and frequency for both flow directions (toward rod free-end and away from it). Turbulence model comparisons show that (a) Reynolds stress transport models are necessary to reproduce the vibration amplitude and (b) wall functions enable the simulations to be completed in realistic time scales. The significance to the fluid–solid-interaction (FSI) process of a so far overlooked (with the exception of a couple of recent studies) dimensionless number, the ratio of the flow dynamic pressure to the rod's Young's modulus of elasticity, is also explored. Simulations, which decouple the variation of this dimensionless number from that of the Reynolds number, demonstrate this number's strong effect on the vibration amplitude. This finding is important to the contact of further FSI studies and the scaling of FSI data.

Dynamics of a wall-mounted flexible plate in oscillatory flows

Zhang,

Nakamura

2024

The present work numerically studies the dynamics of a two-dimensional wall-mounted flexible plate in an oscillatory flow, aiming to assess the effect of structure bending stiffness and wave orbital excursion on the plate deflection, reconfiguration, and drag reduction. Different modes of dynamic responding behaviors are identified such as quasi-linear, linear, non-linear, and irregular modes with varied studying parameters. The plates of the quasi-linear mode show a fully reconfigured state in oscillatory flow with different wave excursions, of which the tip deflection and effective length for the reconfiguration effect are analyzed and the scaling laws are derived based on force and energy balances. With decreasing elasticity, the plates through linear motion show the limitation of reconfiguration and move passively and rigorously following along oscillatory flow with zero phase lag, wherein the tip deflections saturate to the same order as wave excursions and the effective lengths change slightly where the bending stiffness effect is insignificant. A critical Cauchy number, Cacri, which separates the fully reconfigured state and passive movement state, is proposed using the scaling arguments based on the time scales of flow oscillation frequency and time for plates to reach full reconfiguration for different wave orbital excursions. To account for the non-linear motion effect on drag reduction, we derive a scaling model based on the spatially and temporally averaged relative velocity and the prediction performs well. Furthermore, a rich phenomenology of fluid–structure interaction including phase lag, fluid loading distribution, internal elastic energy, vibration resonance, and vortex structure is presented.