Adaptation of Pressure Based CFD Solvers for Mesoscale Atmospheric Problems

Abstract

General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations without a large extent of vertical flow. Vertical flow, however, plays an important role in the formation of local breezes, such as urban heat island induced breezes that have great significance in the ventilation of large cities. The effects of atmospheric stratification, anelasticity and Coriolis force must be taken into account in such simulations. We introduce a general method for adapting pressure based CFD solvers to atmospheric flow simulations in order to take advantage of their high flexibility in geometrical modelling and meshing. Compressibility and thermal stratification effects are taken into account by utilizing a novel system of transformations of the field variables and by adding consequential source terms to the model equations of incompressible flow. Phenomena involving mesoscale to microscale coupled effects can be analyzed without model nesting, applying only local grid refinement of an arbitrary level. Elements of the method are validated against an analytical solution, results of a reference calculation, and a laboratory scale urban heat island circulation experiment. The new approach can be applied with benefits to several areas of application. Inclusion of the moisture transport phenomena and the surface energy balance are important further steps towards the practical application of the method.

CFD investigation of the atmospheric boundary layer under different thermal stability conditions

“…Therefore, even under neutral atmospheric conditions, the CFD code activates the heat conduction terms as it sees a vertical temperature gradient over the computational element. A correction heat source must therefore be added to the energy equation (Equation 3-3) (Kristóf et al 2009). We have seen that potential temperature has the property of being conserved with height (thus its use in exchange theory for heat (Blackadar 1997)), and therefore we can transform the temperature gradient in the energy equation to potential temperature gradient, so that zero heat transfer will prevail under neutral conditions.…”

“…We have seen that potential temperature has the property of being conserved with height (thus its use in exchange theory for heat (Blackadar 1997)), and therefore we can transform the temperature gradient in the energy equation to potential temperature gradient, so that zero heat transfer will prevail under neutral conditions. The same is true for the buoyant production of turbulence, which should be zero under neutral conditions, and therefore this term in the turbulent transport equations must also be transformed to potential temperature gradient (Kristóf et al 2009). …”

Urban Air Quality, Long Term Trends and Road Traffic Air Pollution Modeling of Szeged

“…Several models of industrial accident risk assessment have been run. Input data for these models are yielded by the prediction system of the Hungarian Meteorological Service from the ALADIN and MM5 model outputs and the forecast datasets of the ECMWF centre (Hanna et al, 2001;Havasi & Zlatev, 2002;Moussiopoulos et al, 2003;Mensink et al, 2008;Kristóf et al, 2009;Mészáros et al, 2010). WRF, earlier the ETA numerical weather prediction model systems are also used for air pollution modelling purposes (Weidinger et al, 2006).…”

Numerical Study of the Neutral Atmospheric Boundary Layer Over Complex Terrain

“…However, the use of mesoscale atmospheric simulation codes is generally limited to highly complex terrains in which near-surface characteristics are needed (Kristóf et al 2009). …”