TITLE:
Comparison of RANS and LES in the Prediction of Airflow Field over Steep Complex Terrain
AUTHORS:
Takanori Uchida, Graham Li
KEYWORDS:
RANS, LES, Isolated Hill, Large-Scale Wind Farm
JOURNAL NAME:
Open Journal of Fluid Dynamics,
Vol.8 No.3,
September
3,
2018
ABSTRACT: The present study compared the prediction accuracy of the three CFD software
packages for simulating airflow around a three-dimensional, isolated hill
with a steep slope: 1) WindSim (turbulence model: RNG k-ε RANS), 2) Meteodyn
WT (turbulence model: k-L RANS), which are the leading commercially
available CFD software packages in the wind power industry and 3)
RIAM-COMPACT (turbulence model: standard Smagorinsky LES), which
has been developed by the lead author of the present paper. Distinct differences
in the airflow patterns were identified in the vicinity of the isolated hill
(especially downstream of the hill) between the RANS results and the LES
results. No reverse flow region (vortex region) characterized by negative wind
velocities was identified downstream of the isolated hill in the result from the
simulation with WindSim (RNG k-ε RANS) and Meteodyn WT (k-L RANS).
In the case of the simulation with RIAM-COMPACT natural terrain version
(standard Smagorinsky LES), a reverse flow region (vortex region) characterized
by negative wind velocities clearly forms. Next, an example of wind risk
(terrain-induced turbulence) diagnostics was presented for a large-scale wind
farm in China. The vertical profiles of the streamwise (x) wind velocity do not
follow the so-called power law wind profile; a large velocity deficit can be
seen between the hub center and the lower end of the swept area in the case of
the LES calculation (RIAM-COMPACT).