US EPA

3259238 

Journal Article 

Evaluation and validation of a CFD solver adapted to atmospheric flows: Simulation of topography-induced waves 

Racz, N; Kristof, G; Weidinger, T 

2013 

Yes 

Idojaras (Budapest, 1905)
ISSN: 0324-6329 

117 

3 

239-275 

WOS:000324776800001 

Mountain wave phenomena have been simulated by using a
well-known general purpose computational fluid dynamic (CFD) simulation system adapted to
atmospheric flow modeling. Mesoscale effects have been taken into account with a novel approach
based on a system of transformations and customized volume sources acting in the conservation and
governing equations. Simulations of linear hydrostatic wave fields generated by a two-dimensional
obstacle were carried out, and the resulting vertical velocity fields were compared against the
corresponding analytic solution. Validation with laboratory experiments and full-scale
atmospheric flows is a very important step toward the practical application of the method.
Performance measures showed good correspondence with measured data concerning flow structures and
wave pattern characteristics of non-hydrostatic and nonlinear mountain waves in low Reynolds
number flows. For highly nonlinear atmospheric scale conditions, we reproduced the well-
documented downslope windstorm at Boulder in January 1972, during which extreme weather
conditions, with a wind speed of approximately 60 m s(-1), were measured close to the ground. The
existence of the hydraulic jump, the strong descent of the stratospheric air, wave breaking
regions, and the highly accelerated downslope wind were well reproduced by the model. Evaluation
based on normalized mean square error (NMSE), fractional bias (FB), and predictions within a
factor of two of observations (FAC2) show good model performance, however, due to the horizontal
shift in the flow pattern, a less satisfactory hit rate and correlation value can be observed. 

complex terrain; gravity waves; CFD simulation; model validation; numerical weather prediction