George Ilhwan Park
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View article: The Evolution of Turbulence Producing Motions in the Neutral ABL Across a Natural Roughness Transition
The Evolution of Turbulence Producing Motions in the Neutral ABL Across a Natural Roughness Transition Open
Landforms such as sand dunes act as roughness elements to Atmospheric Boundary Layer (ABL) flows, triggering the development of new scales of turbulent motions. These turbulent motions, in turn, energize and kick‐up sand particles, influen…
View article: Reference map technique for Lagrangian exploration of coherent structures
Reference map technique for Lagrangian exploration of coherent structures Open
We explore the application of the reference map technique, originally developed for Eulerian simulation of solid mechanics, in Lagrangian kinematics of turbulent flows. Unlike traditional methods based on explicit particle tracking, the re…
View article: An Alternative Scaling for Roughness Transitions in Turbulent Flows: The Role of the Internal Boundary Layer
An Alternative Scaling for Roughness Transitions in Turbulent Flows: The Role of the Internal Boundary Layer Open
When turbulent boundary layer flows encounter abrupt roughness changes, an Internal Boundary Layer (IBL) forms. Equilibrium theory breaks down in the nonequilibrium IBL, which may extend O(10) km for natural atmospheric flows. Here, we fin…
View article: Linear stability analysis of oblique Couette–Poiseuille flows
Linear stability analysis of oblique Couette–Poiseuille flows Open
We perform a detailed numerical study of modal and non-modal stability in oblique Couette–Poiseuille profiles, which are among the simplest examples of three-dimensional boundary layers. Through a comparison with the Orr–Sommerfeld operato…
View article: The Evolution of Turbulence Producing Motions in the ABL Across a Natural Roughness Transition
The Evolution of Turbulence Producing Motions in the ABL Across a Natural Roughness Transition Open
Landforms such as sand dunes act as roughness elements to Atmospheric Boundary Layer (ABL) flows, triggering the development of new scales of turbulent motions. These turbulent motions, in turn, energize and kick-up sand particles, influen…
View article: Revisiting Crossflow-Based Stabilization in Channel Flows
Revisiting Crossflow-Based Stabilization in Channel Flows Open
Stabilization schemes in wall-bounded flows often invoke fluid transpiration through porous boundaries. While these have been extensively validated for external flows, their efficacy in channels, particularly from the standpoint of non-mod…
View article: Mesoscale structure of the atmospheric boundary layer across a natural roughness transition
Mesoscale structure of the atmospheric boundary layer across a natural roughness transition Open
The structure and intensity of turbulence in the atmospheric boundary layer (ABL) drive fluxes of sediment, contaminants, heat, moisture, and CO at the Earth’s surface. Where ABL flows encounter changes in roughness—such as cities, wind…
View article: Physics-based distinction of nonequilibrium effects in near-wall modeling of turbulent separation bubble with and without sweep
Physics-based distinction of nonequilibrium effects in near-wall modeling of turbulent separation bubble with and without sweep Open
Pressure-gradient-induced separation of swept and unswept turbulent boundary layers, based on the DNS studies of Coleman et al. (J. Fluid Mech. 2018 & 2019), have been analyzed for various nonequilibrium effects. The goal is to isolate phy…
View article: Large Eddy Simulation of Separated Flows on Unconventionally Coarse Grids
Large Eddy Simulation of Separated Flows on Unconventionally Coarse Grids Open
We examine and benchmark the emerging idea of applying the large eddy simulation (LES) formalism to unconventionally coarse grids where Reynolds-averaged Navier–Stokes (RANS) would be considered more appropriate at first glance. We disting…
View article: Linear Stability Analysis of Oblique Couette-Poiseuille flows
Linear Stability Analysis of Oblique Couette-Poiseuille flows Open
We perform a detailed numerical study of modal and non-modal stability in oblique Couette-Poiseuille profiles, which are among the simplest examples of three-dimensional boundary layers. Through a comparison with the Orr-Sommerfeld operato…
View article: Reference map technique for Lagrangian exploration of coherent structures
Reference map technique for Lagrangian exploration of coherent structures Open
We explore the application of the reference map technique, originally developed for the Eulerian simulation of solid mechanics, in Lagrangian kinematics of fluid flows. Unlike traditional methods based on explicit particle tracking, the re…
View article: Low-order planar pressure reconstruction of stalled airfoils using particle image velocimetry data
Low-order planar pressure reconstruction of stalled airfoils using particle image velocimetry data Open
We present planar time-resolved particle image velocimetry (PIV) measurements of flow in the streamwise surface-normal plane of a NACA 0012 airfoil at chord-based Reynolds number Rec=7×104. The angles of attack α=13∘ and 15∘ correspond to …
View article: Mesoscale structure of the atmospheric boundary layer across a natural roughness transition
Mesoscale structure of the atmospheric boundary layer across a natural roughness transition Open
The structure and intensity of turbulence in the atmospheric boundary layer (ABL) drives fluxes of sediment, contaminants, heat, moisture and CO$_2$ at the Earth's surface. Where ABL flows encounter changes in roughness -- such as cities, …
View article: Numerical and experimental study on the addition of surface roughness to micro-propellers
Numerical and experimental study on the addition of surface roughness to micro-propellers Open
Micro aerial vehicles are making a large impact in applications such as search-and-rescue, package delivery, and recreation. Unfortunately, these diminutive drones are currently constrained to carrying small payloads, in large part because…
View article: A priori screening of data-enabled turbulence models
A priori screening of data-enabled turbulence models Open
Assessing the compliance of a white-box turbulence model with known turbulent knowledge is straightforward. It enables users to screen conventional turbulence models and identify apparent inadequacies, thereby allowing for a more focused a…
View article: Large-eddy simulation of separated flows on unconventionally coarse grids
Large-eddy simulation of separated flows on unconventionally coarse grids Open
We examine and benchmark the emerging idea of applying the large-eddy simulation (LES) formalism to unconventionally coarse grids where RANS would be considered more appropriate at first glance. We distinguish this idea from very-large-edd…
View article: Wall-modelled large-eddy simulation of three-dimensional turbulent boundary layer in a bent square duct
Wall-modelled large-eddy simulation of three-dimensional turbulent boundary layer in a bent square duct Open
We conduct wall-modelled large-eddy simulation (WMLES) of a pressure-driven three-dimensional turbulent boundary layer developing on the floor of a bent square duct to investigate the predictive capability of three widely used wall models,…
View article: Wall-modeled large-eddy simulation of three-dimensional turbulent boundary layer in a bent square duct
Wall-modeled large-eddy simulation of three-dimensional turbulent boundary layer in a bent square duct Open
We conduct wall-modeled LES (WMLES) of a pressure-driven three-dimensional turbulent boundary layer (3DTBL) developing on the floor of a bent square duct to investigate the predictive capability of three widely used wall models, namely, a …
View article: Numerical implementation of efficient grid-free integral wall models in unstructured-grid LES solvers.
Numerical implementation of efficient grid-free integral wall models in unstructured-grid LES solvers. Open
Two zonal wall-models based on integral form of the boundary layer differential equations, albeit with algebraic complexity, have been implemented in an unstructured-grid cell-centered finite-volume LES solver. The first model is a novel i…
View article: Implementation and performance analysis of efficient grid-free integral wall models in unstructured-grid LES solvers
Implementation and performance analysis of efficient grid-free integral wall models in unstructured-grid LES solvers Open
Two zonal wall models based on integral form of the boundary layer differential equations, albeit with algebraic complexity, have been implemented in an unstructured-grid cell-centered finite-volume LES solver. The first model is a novel i…
View article: Large eddy simulation of aircraft at affordable cost: a milestone in computational fluid dynamics
Large eddy simulation of aircraft at affordable cost: a milestone in computational fluid dynamics Open
While there have been numerous applications of large eddy simulations (LES) to complex flows, their application to practical engineering configurations, such as full aircraft models, have been limited to date. Recently, however, advances i…
View article: Wall-modeled large-eddy simulation of non-equilibrium turbulent boundary layers
Wall-modeled large-eddy simulation of non-equilibrium turbulent boundary layers Open
We conducted WMLES to examine the performance of a simple and widely used ODE-based equilibrium wall model in a spatially-developing 3D TBL inside a bent square duct (Schwarz and Bradshaw 1994) and 3D separated flows behind a skewed bump (…
View article: Wall-Modeled Large-Eddy Simulation for Complex Turbulent Flows
Wall-Modeled Large-Eddy Simulation for Complex Turbulent Flows Open
Large-eddy simulation (LES) has proven to be a computationally tractable approach to simulate unsteady turbulent flows. However, prohibitive resolution requirements induced by near-wall eddies in high–Reynolds number boundary layers necess…
View article: Log-layer mismatch and modeling of the fluctuating wall stress in wall-modeled large-eddy simulations
Log-layer mismatch and modeling of the fluctuating wall stress in wall-modeled large-eddy simulations Open
Log-layer mismatch refers to a chronic problem found in wall-modeled large-eddy simulation (WMLES) or detached-eddy simulation, where the modeled wall-shear stress deviates from the true one by approximately 15%. Many efforts have been mad…
View article: Wall-Modeled Large-Eddy Simulation of a High Reynolds Number Separating and Reattaching Flow
Wall-Modeled Large-Eddy Simulation of a High Reynolds Number Separating and Reattaching Flow Open
The performance of two wall models based on Reynolds-averaged Navier-Stokes is compared in large-eddy simulation of a high Reynolds number separating and reattaching flow over the NASA wall-mounted hump. Wall modeling significantly improve…
View article: A simple dynamic subgrid-scale model for LES of particle-laden turbulence
A simple dynamic subgrid-scale model for LES of particle-laden turbulence Open
In this study, a dynamic model for large-eddy simulations is proposed in order to describe the motion of small inertial particles in turbulent flows. The model is simple, involves no significant computational overhead, contains no adjustab…