Uncertainty Quantification of Large-Eddy Spray Simulations

2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Noah Van Dam ◽  
Chris Rutland
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Uncertainty Quantification ◽  
Polynomial Chaos ◽  
Screening Method ◽  
Latin Hypercube Sampling ◽  
Experimental Uncertainty ◽  
Large Eddy ◽  
Nested Grids ◽  
Response Variables

Two uncertainty quantification (UQ) techniques, latin-hypercube sampling (LHS) and polynomial chaos expansion (PCE), have been used in an initial UQ study to calculate the effect of boundary condition uncertainty on Large-eddy spray simulations. Liquid and vapor penetration as well as multidimensional liquid and vapor data were used as response variables. The Morris one-at-a-time (MOAT) screening method was used to identify the most important boundary conditions. The LHS and PCE methods both predict the same level of variability in the response variables, which was much larger than the corresponding experimental uncertainty. Nested grids were used in conjunction with the PCE method to examine the effects of subsets of boundary condition variables. Numerical modeling parameters had a much larger effect on the resulting spray predictions; the uncertainty in spray penetration or multidimensional spray contours from physically derived boundary conditions was close to the uncertainty of the measurements.

scholarly journals Experimental study of wall boundary conditions for large-eddy simulation

2001 ◽  
Vol 446 ◽  
pp. 309-320 ◽  
Author(s):  
IVAN MARUSIC ◽  
GARY J. KUNKEL ◽  
FERNANDO PORTÉ-AGEL
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Streamwise Velocity ◽  
New Model ◽  
Eddy Simulation ◽  
Large Eddy

An experimental investigation was conducted to study the wall boundary condition for large-eddy simulation (LES) of a turbulent boundary layer at Rθ = 3500. Most boundary condition formulations for LES require the specification of the instantaneous filtered wall shear stress field based upon the filtered velocity field at the closest grid point above the wall. Three conventional boundary conditions are tested using simultaneously obtained filtered wall shear stress and streamwise and wall-normal velocities, at locations nominally within the log region of the flow. This was done using arrays of hot-film sensors and X-wire probes. The results indicate that models based on streamwise velocity perform better than those using the wall-normal velocity, but overall significant discrepancies were found for all three models. A new model is proposed which gives better agreement with the shear stress measured at the wall. The new model is also based on the streamwise velocity but is formulated so as to be consistent with ‘outer-flow’ scaling similarity of the streamwise velocity spectra. It is therefore expected to be more generally applicable over a larger range of Reynolds numbers at any first-grid position within the log region of the boundary layer.

On Effects of Temperature Boundary Conditions on Heat Transfer in Turbulent Low-Prandtl-Number Flows

2020 ◽  
Author(s):  
Ivan Otic
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Large Eddy ◽  
Heat Flux Boundary Condition ◽  
Effects Of Temperature

Abstract One important issue in understanding and modeling of turbulent heat transfer is the behavior of fluctuating temperature close to the wall. Common engineering computational approach assumes constant heat flux boundary condition on heated walls. In the present paper constant heat flux boundary condition was assumed and effects of temperature fluctuations are investigated using large eddy simulations (LES) approach. A series of large eddy simulations for two geometries is performed: First, forced convection in channels and second, forced convection over a backward facing step. LES simulation data is statistically analyzed and compared with results of direct numerical simulations (DNS) from the literature which apply three cases of heat flux boundary conditions: 1. ideal heat flux boundary condition, 2. non-ideal heat flux boundary condition, 3. conjugate heat transfer boundary condition. For low Prandtl number flows LES results show that, despite very good agreement for velocities and mean temperature, predictions of temperature fluctuations may have strong deficiencies if simplified boundary conditions are applied.

scholarly journals Impact of Surface Flux Formulations and Geostrophic Forcing on Large-Eddy Simulations of Diurnal Atmospheric Boundary Layer Flow

2010 ◽  
Vol 49 (7) ◽  
pp. 1496-1516 ◽  
Author(s):  
Vijayant Kumar ◽  
Gunilla Svensson ◽  
A. A. M. Holtslag ◽  
Charles Meneveau ◽  
Marc B. Parlange
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Boundary Conditions ◽  
Surface Temperature ◽  
Surface Flux ◽  
Large Eddy Simulations ◽  
Surface Boundary ◽  
Temperature Boundary ◽  
Large Eddy ◽  
Temperature Boundary Condition

Abstract The impact of surface flux boundary conditions and geostrophic forcing on multiday evolution of flow in the atmospheric boundary layer (ABL) was assessed using large-eddy simulations (LES). The LES investigations included several combinations of surface boundary conditions (temperature and heat flux) and geostrophic forcing (constant, time varying, time and height varying). The setup was based on ABL characteristics observed during a selected period of the Cooperative Atmosphere–Surface Exchange Study—1999 (CASES-99) campaign. The LES cases driven by a constant geostrophic wind achieved the best agreement with the CASES-99 observations specifically in terms of daytime surface fluxes and daytime and nighttime profiles. However, the nighttime fluxes were significantly overestimated. The LES cases with the surface temperature boundary condition and driven by a time- and height-varying geostrophic forcing showed improved agreement with the observed nighttime fluxes, but there was less agreement with other observations (e.g., daytime profiles). In terms of the surface boundary condition, the LES cases driven by either surface temperature or heat fluxes produced similar trends in terms of the daytime profiles and comparisons with data from soundings. However, in reproducing the fluxes and nighttime profiles, the agreement was better with imposed temperature because of its ability to interact dynamically with the air temperature field. Therefore, it is concluded that surface temperature boundary condition is better suited for simulations of temporally evolving ABL flow as in the diurnal evolution of the ABL.

Testing of logarithmic-law for the slip with friction boundary condition

2022 ◽  
Vol 0 (0) ◽  
Author(s):  
Özgül İlhan ◽  
Niyazi Şahin
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Reynolds Number ◽  
Boundary Conditions ◽  
Turbulent Flows ◽  
Critical Problem ◽  
Slip Conditions ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Logarithmic Law

Abstract Large eddy simulation (LES) seeks to predict the dynamics of the organized structures in the flow, that is, local spatial averages u ̄ $\bar{u}$ of the velocity u of the fluid. Although LES has been extensively used to model turbulent flows, very often, the model has difficulty predicting turbulence generated by interactions of a flow with a boundary. A critical problem in LES is to find appropriate boundary conditions for the flow averages, which depend on the behavior of the unknown flow near the wall. In the light of the works of Navier and Maxwell, we use boundary conditions on the wall. We compute the appropriate friction coefficient β for channel flows and investigate its asymptotic behavior as the averaging radius δ → 0 and as the Reynolds number Re → ∞. No-slip conditions are recovered in the first limit, and free-slip conditions are recovered in the second limit. This study is not intended to develop new theories of the turbulent boundary layer; we use available boundary layer theories to improve numerical boundary conditions for flow averages.

scholarly journals Effect of Wall Boundary Conditions on a Wall-Modeled Large-Eddy Simulation in a Finite-Difference Framework

Fluids ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 112
Author(s):  
H. Jane Bae ◽  
Adrián Lozano-Durán
Keyword(s):  
Boundary Condition ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Eddy Viscosity ◽  
Grid Point ◽  
Eddy Simulation ◽  
Wall Boundary ◽  
Wall Boundary Conditions ◽  
Wide Range ◽  
Large Eddy

We studied the effect of wall boundary conditions on the statistics in a wall-modeled large-eddy simulation (WMLES) of turbulent channel flows. Three different forms of the boundary condition based on the mean stress-balance equations were used to supply the correct mean wall shear stress for a wide range of Reynolds numbers and grid resolutions applicable to WMLES. In addition to the widely used Neumann boundary condition at the wall, we considered a case with a no-slip condition at the wall in which the wall stress was imposed by adjusting the value of the eddy viscosity at the wall. The results showed that the type of boundary condition utilized had an impact on the statistics (e.g., mean velocity profile and turbulence intensities) in the vicinity of the wall, especially at the first off-wall grid point. Augmenting the eddy viscosity at the wall resulted in improved predictions of statistics in the near-wall region, which should allow the use of information from the first off-wall grid point for wall models without additional spatial or temporal filtering. This boundary condition is easy to implement and provides a simple solution to the well-known log-layer mismatch in WMLES.

scholarly journals Uncertainty Quantification of GEKO Model Coefficients on Compressible Flows

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Yeong-Ki Jung ◽  
Kyoungsik Chang ◽  
Jae Hyun Bae
Keyword(s):  
Bayesian Inference ◽  
Uncertainty Quantification ◽  
Compressible Flows ◽  
Polynomial Chaos ◽  
Flow Characteristics ◽  
Latin Hypercube Sampling ◽  
Monte Carlo Sampling ◽  
Ordinary Least Squares ◽  
Equation Model ◽  
Affine Invariant

In the present work, supersonic flows over an axisymmetric base and a 24-deg compression ramp are investigated using the generalized k - ω (GEKO) model implemented in the commercial software, ANSYS FLUENT. GEKO is a two-equation model based on the k - ω formulation, and some specified model coefficients can be tuned depending on the flow characteristics. Uncertainty quantification (UQ) analysis is incorporated to quantify the uncertainty of the model coefficients and to calibrate the coefficients. The Latin hypercube sampling (LHS) method is used for sampling independent input parameters as a uniform distribution. A metamodel is constructed based on general polynomial chaos expansion (gPCE) using ordinary least squares (OLS). The influential coefficient closure is obtained by using Sobol indices. The affine invariant ensemble algorithm (AIES) is selected to characterize the posterior distribution via Markov chain Monte Carlo sampling. Calibrated model coefficients are extracted from posterior distributions obtained through Bayesian inference, which is based on the point-collocation nonintrusive polynomial chaos (NIPC) method. Results obtained through calibrated model coefficients by Bayesian inference show superior prediction with available experimental measurements than those from original model ones.

Sturm-Liouville Problem for Stationary Differential Operator with Nonlocal Two-Point Boundary Conditions

2006 ◽  
Vol 11 (1) ◽  
pp. 47-78 ◽  
Author(s):  
S. Pečiulytė ◽  
A. Štikonas
Keyword(s):  
Boundary Condition ◽  
Differential Operator ◽  
Boundary Conditions ◽  
Nonlocal Boundary Condition ◽  
Nonlocal Boundary ◽  
Liouville Problem ◽  
Complex Case ◽  
Qualitative Behavior ◽  
Point Boundary ◽  
Sturm Liouville

The Sturm-Liouville problem with various types of two-point boundary conditions is considered in this paper. In the first part of the paper, we investigate the Sturm-Liouville problem in three cases of nonlocal two-point boundary conditions. We prove general properties of the eigenfunctions and eigenvalues for such a problem in the complex case. In the second part, we investigate the case of real eigenvalues. It is analyzed how the spectrum of these problems depends on the boundary condition parameters. Qualitative behavior of all eigenvalues subject to the nonlocal boundary condition parameters is described.

Uncertainty Quantification of Transonic Nozzle Flow by Polynomial Chaos Expansion

2017 ◽  
Vol 65 (4) ◽  
pp. 151-156
Author(s):  
Koji MIYAJI ◽  
Tota UENO ◽  
Yasumi KAWAMURA
Keyword(s):  
Uncertainty Quantification ◽  
Polynomial Chaos ◽  
Polynomial Chaos Expansion ◽  
Nozzle Flow ◽  
Chaos Expansion
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