TY - JOUR AU - Rácz, Norbert AU - Kristóf, Gergely TI - Implementation and validation of a bulk microphysical model of moisture transport in a pressure based CFD solver JF - IDŐJÁRÁS / QUARTERLY JOURNAL OF THE HUNGARIAN METEOROLOGICAL SERVICE J2 - IDŐJÁRÁS VL - 120 PY - 2016 IS - 2 SP - 231 EP - 254 PG - 24 SN - 0324-6329 UR - https://m2.mtmt.hu/api/publication/3121318 ID - 3121318 N1 - Export Date: 4 January 2021 Correspondence Address: Rácz, N.; Department of Fluid Mechanics, Budapest University of Technology and Economics (BME), Bertalan L.u. 4-6, Hungary; email: racz@ara.bme.hu AB - We study wet cooling tower plume formation involving mesoscale meteorological effects (such as stratification or compressibility). This was achieved by incorporating transformations and volume source terms into a pressure based computational fluid dynamics (CFD) solver (ANSYS-FLUENT). Moisture dynamics is taken into account with a bulk microphysical model that was recently implemented into the solver. This model has been validated against known numerical solutions of idealized two-dimensional dry and wet thermals. In particular, the overall thermal profile and the liquid water concentration field indicated good model performance. Model performance has also been compared with measurements for the formation of a large wet cooling tower plume. Simulations are encouraging with regard to the predictability of cumulus like plume structures with complex thermal stratification, the overall liquid water content along the plume axis, and also the turbulent fluctuations caused by the vertical movements in the plume. The advantage of this approach is that a uniform physical description can be used for close- and far-field flow by using a single unstructured mesh with local refinements. This allows for investigating the finely structured microscale flow phenomena around complex orographic features in a single framework. LA - English DB - MTMT ER - TY - THES AU - Rácz, Norbert TI - Micro- and mesoscale modeling of thermal convection, internal waves and cloud formation in the atmosphere (Mikro- és mezoskálájú áramlások, termikus konvekció, gravitációs hullámok és felhőképződés mo PB - Budapesti Műszaki és Gazdaságtudományi Egyetem PY - 2015 SP - 90 UR - https://m2.mtmt.hu/api/publication/3249338 ID - 3249338 LA - English DB - MTMT ER - TY - JOUR AU - Rácz, Norbert AU - Kristóf, Gergely AU - Weidinger, Tamás TI - Evaluation and validation of a CFD solver adapted to atmospheric flows: Simulation of topography-induced waves JF - IDŐJÁRÁS / QUARTERLY JOURNAL OF THE HUNGARIAN METEOROLOGICAL SERVICE J2 - IDŐJÁRÁS VL - 117 PY - 2013 IS - 3 SP - 239 EP - 275 PG - 37 SN - 0324-6329 UR - https://m2.mtmt.hu/api/publication/2695298 ID - 2695298 AB - 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. LA - English DB - MTMT ER - TY - JOUR AU - Kristóf, Gergely AU - Rácz, Norbert AU - Balogh, Miklós TI - Adaptation of Pressure Based CFD Solvers for Mesoscale Atmospheric Problems JF - BOUNDARY-LAYER METEOROLOGY J2 - BOUND-LAY METEOROL VL - 131 PY - 2009 IS - 1 SP - 85 EP - 103 PG - 19 SN - 0006-8314 DO - 10.1007/s10546-008-9325-7 UR - https://m2.mtmt.hu/api/publication/2644657 ID - 2644657 AB - General purpose Computational Fluid Dynamics (CFD) solvers are frequently used in small-scale urban pollution dispersion simulations without a large extent of ver- tical 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. LA - English DB - MTMT ER - TY - JOUR AU - Kristóf, Gergely AU - Rácz, Norbert AU - Balogh, Miklós TI - Atmoszférikus áramlások szimulációja JF - GÉP J2 - GÉP VL - 59 PY - 2008 IS - 5-6 SP - 24 EP - 25 PG - 2 SN - 0016-8572 UR - https://m2.mtmt.hu/api/publication/2687305 ID - 2687305 LA - Hungarian DB - MTMT ER - TY - CONF AU - Kristóf, Gergely AU - Rácz, Norbert AU - Balogh, Miklós TI - Application of ANSYS-FLUENT for Meso-Scale Atmospheric Flow Simulations T2 - ANSYS Conference & 25. CADFEM Users’ Meeting PY - 2007 PG - 8 UR - https://m2.mtmt.hu/api/publication/2645966 ID - 2645966 LA - English DB - MTMT ER - TY - CONF AU - Kristóf, Gergely AU - Rácz, Norbert AU - Balogh, Miklós ED - Sandrine, Aubrun TI - CFD analyses of flow in stratified atmosphere T2 - Proceedings of International Workshop on Physical Modelling of Flow and Dispersion Phenomena C1 - Orléans PY - 2007 SP - 93 EP - 97 PG - 5 UR - https://m2.mtmt.hu/api/publication/2644665 ID - 2644665 LA - English DB - MTMT ER - TY - CONF AU - Rácz, Norbert AU - Kristóf, Gergely AU - Weidinger, Tamás AU - Balogh, Miklós ED - Ranjeet, S Sokhi ED - Maria, Neophytou TI - Simulation of gravity waves and model validation to laboratory experiments T2 - Proceedings of the 6th International Conference on Urban Air Quality C1 - Limassol PY - 2007 SP - 52 EP - 55 PG - 4 UR - https://m2.mtmt.hu/api/publication/2644663 ID - 2644663 LA - English DB - MTMT ER - TY - CONF AU - Kristóf, Gergely AU - Rácz, Norbert AU - Balogh, Miklós ED - Ranjeet, S Sokhi ED - Maria, Neophytou TI - Adaptation of pressure based CFD solvers to urban heat island convection problem T2 - Proceedings of the 6th International Conference on Urban Air Quality C1 - Limassol PY - 2007 SP - 76 EP - 79 PG - 4 UR - https://m2.mtmt.hu/api/publication/2644662 ID - 2644662 LA - English DB - MTMT ER - TY - CHAP AU - Kristóf, Gergely AU - Rácz, Norbert AU - Bányai, T AU - Gál, Tamás Mátyás AU - Unger, János AU - Weidinger, Tamás ED - Weidinger, Tamás ED - Geresdi, I TI - A városi hősziget által generált konvekció modellezése általános célú áramlástani szoftverrel − összehasonlítás kisminta kísérletekkel T2 - Felhőfizika és mikrometeorológia PB - Országos Meteorológiai Szolgálat (OMSZ) CY - Budapest SN - 9789637702976 PY - 2007 SP - 95 EP - 104 PG - 10 UR - https://m2.mtmt.hu/api/publication/1326655 ID - 1326655 LA - Hungarian DB - MTMT ER -