Near-Surface Coherent Structures and The Vertical Momentum Flux in a Large-Eddy Simulation of the Neutrally-Stratified Boundary Layer

2006 ◽  
Vol 120 (2) ◽  
pp. 229-255 ◽  
Author(s):  
Ralph C. Foster ◽  
Francois Vianey ◽  
Philippe Drobinski ◽  
Pierre Carlotti
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Coherent Structures ◽  
Momentum Flux ◽  
Near Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Neutrally Stratified

scholarly journals Large-eddy simulation of a neutrally stratified boundary layer: A comparison of four computer codes

1994 ◽  
Vol 120 (520) ◽  
pp. 1457-1484 ◽  
Author(s):  
A. Andren ◽  
A. R. Brown ◽  
P. J. Mason ◽  
J. Graf ◽  
U. Schumann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computer Codes ◽  
Neutrally Stratified

A Framework for Simulating the Tropical-Cyclone Boundary Layer Using Large-Eddy Simulation and Its Use in Evaluating PBL Parameterizations

2021 ◽  
Author(s):  
Xiaomin Chen ◽  
George H. Bryan ◽  
Jun A. Zhang ◽  
Joseph J. Cione ◽  
Frank D. Marks
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Large Eddy Simulation ◽  
Momentum Flux ◽  
Intensity Change ◽  
Length Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbulence Length ◽  
Turbulence Length Scale

AbstractBoundary layer turbulent processes affect tropical cyclone (TC) structure and intensity change. However, uncertainties in the parameterization of the planetary boundary layer (PBL) under high-wind conditions remain challenging, mostly due to limited observations. This study presents and evaluates a framework of numerical simulation that can be used for a small-domain [O(5 km)] large-eddy simulation (LES) and single-column modeling (SCM) to study the TC boundary layer. The framework builds upon a previous study that uses a few input parameters to represent the TC vortex and adds a simple nudging term for temperature and moisture to account for the complex thermodynamic processes in TCs. The reference thermodynamic profiles at different wind speeds are retrieved from a composite analysis of dropsonde observations of mature hurricanes. Results from LES show that most of the turbulence kinetic energy and vertical momentum flux is associated with resolved processes when horizontal grid spacing is O(10 m). Comparison to observations of turbulence variables such as momentum flux, effective eddy viscosity, and turbulence length scale show that LES produces reasonable results but highlight areas where further observations are necessary. LES results also demonstrate that compared to a classic Ekman-type boundary layer, the TC boundary layer is shallower, develops steady conditions much quicker, and exhibits stronger wind speed near the surface. The utility of this framework is further highlighted by evaluating a first-order PBL parameterization, suggesting that an asymptotic turbulence length scale of 40 m produces a good match to LES results.

Effects of incidence angle on a low-pressure turbine blade boundary layer evolution through large eddy simulation

2018 ◽  
Vol 232 (6) ◽  
pp. 722-734 ◽  
Author(s):  
Yunfei Wang ◽  
Xiuming Sui ◽  
Kai Zhang ◽  
Xiaorong Xiang ◽  
Qingjun Zhao
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Coherent Structures ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Leading Edge ◽  
Pressure Side ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

The evolution mechanism of the boundary layer and coherent structures in a low-pressure turbine blade is discussed. Five different incidence angles over the T106A blade for a Mach number Ma = 0.404 and Reynolds number Re = 0.6 × 105 (based on the axial chord and outlet velocity) are performed using large eddy simulation method. The calculation results at +7.8 incidence angle are agreed well with the experimental and direct numerical simulation data. The influence of the incidence angle on the flow field is mainly shown at the front of the suction side and pressure side. As the incidence angle changes from positive to negative, the separation bubble near the leading edge disappears and the blade loading decreases gradually. When the incidence angle reduces to −5°, separation bubble appears near the leading edge of the pressure side. At the case of incidence angle equaling −10°, the length of time-averaged separation bubble on the pressure side grows to 39% axial chord and the evolution process of the coherent structures is extremely complex. The spanwise vortexes roll up near the leading edge and gradually evolve into streamwise vortexes. High-energy fluid in the main flow was driven to near-wall zone by the rotating effect of streamwise vortexes, which increases the fluid momentum inside the boundary layer. The streamwise vortexes are stretched by the strong acceleration of the flow until they transport to the trailing edge.

A scale-dependent dynamic model for large-eddy simulation: application to a neutral atmospheric boundary layer

2000 ◽  
Vol 415 ◽  
pp. 261-284 ◽  
Author(s):  
FERNANDO PORTÉ-AGEL ◽  
CHARLES MENEVEAU ◽  
MARC B. PARLANGE
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Atmospheric Boundary Layer ◽  
Dynamic Model ◽  
Scale Invariance ◽  
Scale Model ◽  
Near Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Dependent Model

A scale-dependent dynamic subgrid-scale model for large-eddy simulation of turbulent flows is proposed. Unlike the traditional dynamic model, it does not rely on the assumption that the model coefficient is scale invariant. The model is based on a second test-filtering operation which allows us to determine from the simulation how the coefficient varies with scale. The scale-dependent model is tested in simulations of a neutral atmospheric boundary layer. In this application, near the ground the grid scale is by necessity comparable to the local integral scale (of the order of the distance to the wall). With the grid scale and/or the test-filter scale being outside the inertial range, scale invariance is broken. The results are compared with those from (a) the traditional Smagorinsky model that requires specification of the coefficient and of a wall damping function, and (b) the standard dynamic model that assumes scale invariance of the coefficient. In the near-surface region the traditional Smagorinsky and standard dynamic models are too dissipative and not dissipative enough, respectively. Simulations with the scale-dependent dynamic model yield the expected trends of the coefficient as a function of scale and give improved predictions of velocity spectra at different heights from the ground. Consistent with the improved dissipation characteristics, the scale-dependent model also yields improved mean velocity profiles.

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