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Interactions of a short-pulsed plane acoustic wave with complex rigid objects: a numerical study
Sangmo Kang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.9
In this paper, we numerically study interactions of a short-pulsed plane acoustic wave with complex rigid objects by solving the linearized Euler equations. For the study, our numerical approach implements an immersed boundary method to satisfy the no-penetration condition on the surface of rigid objects, together with a fully-explicit staggered-grid finitedifference time-domain method having perfectly matched layers. First, we validate our approach for acoustic wave scattering by a circular cylinder, a well-known benchmark problem. Subsequently, we extend our simulations to two representative problems, namely interactions with a circular cylinder and a plano-concave lens which are of paramount interest in terms of acoustic force and acoustic focusing, respectively. Our simulations allow us to better understand the main mechanism of propagation, reflection, and scattering of acoustic waves as a result of interaction with rigid objects. In addition, the effects of pulse width on the interactions are closely investigated.
Electroosmotic Flows in Channel with Two Symmetric Periodic Arrays of Square-Sectioned Ribs
Sangmo Kang,Yong Kweon Suh 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.2
The present study has numerically investigated two-dimensional electroosmotic flows in channel equipped with two symmetric periodic arrays of square-sectioned ribs with one-fifth of the channel half-width in size. For the simulation, the ionic-species and electric-potential equations as well as the continuity and momentum ones are solved using the finite volume method. Instead of assuming the Boltzmann distribution, the Nernst-Plank equation is applied for the ionic species. Results show that the steady electroosmotic flow and ionic distributions depend strongly on the EDL length and streamwise periodic length. For a sufficiently large periodic length, the fluid flows along the wall as in the inviscid flow at a small EDL length compared with the rib size, whereas it flows with involving two recirculation bubbles around the rib as in the pressure-driven flow at a large EDL length. At an intermediate EDL length comparable to the rib size, a very intricate flow pattern is observed around the rib. With decreasing periodic length, on the other hand, the interaction between two adjacent ribs gets stronger and thus the flow pattern significantly changes. This study would contribute to further understanding electroosmotic flows in micro- and nanofluidic devices of complicated geometries.
Unsteady Electroosmotic Channel Flows with the Nonoverlapped and Overlapped Electric Double Layers
Sangmo Kang,Yong Kweon Suh 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.12
In micro- and nanoflows, the Boltzmann distribution is valid only when the electric double layers (EDL's) are not overlapped and the ionic distributions establish an equilibrium state. The present study has numerically investigated unsteady two-dimensional fully-developed electroosmotic flows between two parallel flat plates in the nonoverlapped and overlapped EDL cases, without any assumption of the Boltzmann distribution. For the study, two kinds of unsteady flows are considered ; one is the impulsive application of a constant electric field and the other is the application of a sinusoidally oscillating electric field. For the numerical simulations, the ionic-species and electric-field equations as well as the continuity and momentum ones are solved. Numerical simulations are successful in accurately predicting unsteady electroosmotic flows and ionic distributions. Results show that the nonoverlapped and overlapped cases are totally different in their basic characteristics. This study would contribute to further understanding unsteady electroosmotic flows in micro- and nanofluidic devices.
Approximate Coordinate Transformations for Simulation of Turbulent Flows with Wall Deformation
Sangmo Kang 대한기계학회 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.5
In the present paper, approximate coordinate transformations for simulation of turbulent flows with wall deformation, significantly reducing computational cost with little degradation in numerical accuracy, are presented. The Navier-Stokes equations are coordinate-transformed with an approximation of Taylor-series truncation. The performance is evaluated by performing numerical simulations of a channel flow at Re??=140 with active wall motions of ?? ≤5. The approximate transformations provide flow structures as well as turbulence statistics in good agreement with those from a complete transformation [Phys. Fluids 12,3301 (2000) ] and allow 25- 30% savings in the CPU time as compared to the complete one.