Abstract
The transition process of the boundary layer develo** over a flat plate with elevated inlet Free Stream Turbulence Intensity (FSTI) has been studied by means of Large Eddy Simulation (LES). To this purpose, four cases with different inflow disturbances have been tested varying the magnitude and the length scale of turbulence. LES has been performed by using the finite-volume ANSYS Fluent code. The computational domain, which was constituted by a rectangular domain with a zero thickness plate, was based on an ERCOFTAC test case in order to provide a validation with a well-known set of data by comparing the boundary layer integral parameters and mean and fluctuating streamwise velocity profiles.
The four cases were discussed within the paper by looking at classical statistical properties as well as advanced post-processing tools. It was shown that the decrease in the free stream turbulence level postpones the transition location, whereas the variation of the integral length scale has a very low influence on the distribution of the time-mean flow properties. Proper Orthogonal Decomposition (POD) has been applied to the instantaneous LES flow fields in order to provide a statistical representation of the structures responsible for transition and their response to free-stream turbulence intensity and length scale. The presence of vortical filaments parallel to the wall, typically referred as boundary layer streaks, is clearly identified; their characteristic dimensions and how they change as a function of FSTI properties were analyzed within the paper.
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Abbreviations
- C :
-
cross correlation matrix
- H 12 :
-
shape factor
- L :
-
domain length
- M :
-
diagonal matrix
- N :
-
number of LES snapshot
- R uu :
-
auto-correlation value
- Re x :
-
Reynolds number based on x coordinate
- U e :
-
external velocity
- U ref :
-
reference velocity
- u :
-
streamwise velocity component
- u′:
-
perturbation streamwise velocity
- V :
-
matrix collecting the LES data
- v :
-
wall-normal velocity component
- w :
-
spanwise velocity component
- X :
-
POD eigenvectors
- x,y,z :
-
coordinate system
- Δx + :
-
non-dimensional wall coordinate in streamwise direction
- Δy + :
-
non-dimensional wall coordinate in wall normal direction
- Δz + :
-
non-dimensional wall coordinate in spanwise direction
- Δz :
-
distance between two observations along spanwise direction
- CFD:
-
Computational Fluid Dynamics
- FSTI:
-
Free Stream Turbulence Intensity
- KH:
-
Kelvin Helmholtz
- LES:
-
Large Eddy Simulation
- POD:
-
Proper Orthogonal Decomposition
- RANS:
-
Reynolds Average Navier Stokes
- RMS:
-
Root Mean Square
- SSTI:
-
Spectral Synthesizer Turbulence Intensity
- URANS:
-
Unsteady Reynolds Average Navier Stokes
- δ*:
-
boundary layer displacement thickness
- λ,Λ :
-
pod eigenvalues
- λ 0 :
-
turbulence length scale at inlet
- λ LE :
-
turbulence length scale at wall leading edge
- σ u :
-
standard deviation of velocity component u
- ϕ :
-
POD modes
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Barsi, D., Costa, C., Lengani, D. et al. Large Eddy Simulation of the By-pass Transition Process under Different Inlet Turbulence Conditions. J. Therm. Sci. 30, 2112–2121 (2021). https://doi.org/10.1007/s11630-021-1389-4
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DOI: https://doi.org/10.1007/s11630-021-1389-4