유동현 교수

The tip-leakage flow in a turbomachinery cascade is studied using large-eddy simulation with particular emphasis on understanding the underlying mechanisms for viscous losses in the vicinity of the tip gap. Systematic and detailed analysis of the mean flow field and turbulence statistics has been made in a linear cascade with a moving endwall. Gross features of the tip-leakage vortex, tip-separation vortices, and blade wake have been revealed by investigating their revolutionary trajectories and

An improvement of the dynamic procedure of Park et al. [Phys. Fluids 18, 125109 (2006)] for closure of the subgrid-scale eddy-viscosity model developed by Vreman [Phys. Fluids 16, 3670 (2004)] is proposed. The model coefficient which is globally constant in space but varies in time is dynamically determined assuming the “global equilibrium” between the subgrid-scale dissipation and the viscous dissipation of which utilization was proposed by Park et al. Like the Vreman model with a fixed coeffic

The effects of tip-gap size on the tip-leakage vortical structures and velocity and pressure fields are investigated using large-eddy simulation, with the objective of providing guidelines for controlling tip-leakage cavitation and viscous losses associated with the tip-leakage flow. The effects of tip-gap size on the generation and evolution of the end-wall vortical structures are discussed by investigating their evolutionary trajectories and the mean velocity field. The tip-leakage jet and tip

A large-eddy-simulation-based flow solver that combines an immersed-boundary technique with a curvilinear structured grid has been developed to study the temporal and spatial dynamics of an incompressible rotor-tip-clearance flow. The overall objective of these simulations is to determine the underlying mechanisms for low-pressure fluctuations downstream of the rotor near the end wall. Salient features of the numerical methodology, including the mesh topology, the immersed boundary method, the t

Effects of hydrophobic surfaces on the drag and lift of a circular cylinder at Reynolds numbers of 300 and 3900 are investigated using numerical simulations. A cylinder of which the entire surface is no-slip, a cylinder of which the entire surface is hydrophobic, and cylinders with alternating circumferential bands of slip and no-slip conditions are considered. The width of the alternating bands ranges from 0.5λz to 2λz, where λz is a spanwise characteristic wavelength in the near wake. At Reyno

The tip-clearance flow in axial turbomachines is studied using large-eddy simulation with particular emphasis on understanding the unsteady characteristics of the tip-leakage vortical structures and the underlying mechanisms for cavitation-inducing low-pressure fluctuations. A systematic and detailed analysis of the velocity and pressure fields has been made in a linear cascade with a moving end-wall. The generation and evolution of the tip-leakage vortical structures have been investigated thro

An unstructured-grid large-eddy simulation (LES) technique is used to investigate the turbulent flow separation over an airfoil with and without synthetic-jet control. Numerical accuracy and stability on arbitrary shaped mesh elements at high Reynolds numbers are achieved using a finite-volume discretization of the incompressible Navier–Stokes equations based on higher-order conservation principles—i.e., in addition to mass and momentum conservation, kinetic energy conservation in the inviscid l

Microreactors are emerging as an efficient, sustainable synthetic tool compared to conventional batch reactors. Here, we present a new numbering-up metal microreactor by integrating a flow distributor and a copper catalytic module for high productivity of a commercial synthetic drug. A flow distributor and an embedded baffle disc were manufactured by CNC machining and 3D printing of stainless steel (S/S), respectively, whereas a catalytic reaction module was composed of 25 copper coiled capillar

Laminar vortex sheddings behind a circular cylinder with and without splitter plates attached to the cylinder base at the Reynolds numbers of 100 and 160 are simulated by solving the unsteady two-dimensional incompressible Navier-Stokes equations. The Strouhal number, lift, and drag rapidly change with the length of the splitter plate. Acoustic source functions are obtained from the computed near-field velocity and pressure using the Curie's solution of the Lighthill acoustic analogy. I

Large-eddy simulation with a dynamic subgrid-scale model and nondissipative numerics is employed to predict the turbulent flow separation over a wall-mounted hump and its control. Large-eddy simulation results for the baseline (no control), steady suction, and oscillatory-jet control cases are compared with the results of experimental measurements and previous computational predictions using large-eddy simulation with a constant coefficient Smagorinsky model and dissipative numerics, implicit la