Papers by Gergely KristÓf
Application and assessment of a GPU-based LES method for predicting dynamic wind loads on buildings
Journal of Wind Engineering and Industrial Aerodynamics
Estimation of local tracer gas concentration probability from minimum input data
Journal of Wind Engineering and Industrial Aerodynamics
Investigation of the flow and dispersion characteristics of repeated orographic structures by assuming transient wind forcing
Journal of Wind Engineering and Industrial Aerodynamics
Áramlások Numerikus Modellezése
Junction Losses for Arbitrary Flow Directions
Journal of Fluids Engineering
Two hydraulic losses take effect at the junction point of three cylindrical conduits. These two q... more Two hydraulic losses take effect at the junction point of three cylindrical conduits. These two quantities are considered to be functions of the three signed flow rates and two geometrical parameters: the cross-sectional area ratio and the angle between the main conduit and branch tube. A new design of experiment is developed for exploring the parameter space with continuous response surfaces, which cover both dividing and combining flow regimes with a general trigonometric formula. The loss coefficients are determined by using a steady-state, single-phase, three-dimensional (3D) computational fluid dynamics (CFD) model. To help the analytical treatment, a new reference velocity formulation is introduced. The new loss coefficient formula is validated against known empirical correlations for different junction types and flow directions. The obtained continuous solution promotes the applicability of the resistance model in hydraulic network models.
Atmosphere
While large eddy simulation has several advantages in microscale air pollutant dispersion modelli... more While large eddy simulation has several advantages in microscale air pollutant dispersion modelling, the parametric investigation of geometries is not yet feasible because of its relatively high computational cost. By assuming an analogy between heat and mass transport processes, we utilize a Graphics Processing Unit based software—originally developed for mechanical engineering applications—to model urban dispersion. The software allows for the modification of the geometry as well as the visualization of the transient flow and concentration fields during the simulation, thus supporting the analysis and comparison of different design concepts. By placing passive turbulence generators near the inlet, a numerical wind tunnel was created, capable of producing the characteristic velocity and turbulence intensity profiles of the urban boundary layer. The model results show a satisfactory agreement with wind tunnel experiments examining single street canyons. The effect of low boundary wa...
Optimization of urban building patterns for pollution removal efficiency by assuming periodic dispersion
Journal of Wind Engineering and Industrial Aerodynamics
Periodica Polytechnica Mechanical Engineering
A simplified model of gearbox lubrication flow is investigated. A metric gear with module size 4 ... more A simplified model of gearbox lubrication flow is investigated. A metric gear with module size 4 mm, tooth number 38, tip radius 80.25 mm and width 40 mm, is partially immersed and rotated between 0-12 1/s frequencies in room temperature distilled water. Flash and laser sheet visualizations of the global flow field and the boundary layer are presented. Resolved mass flow distributions in the fluid sheet above the water surface are obtained with in-situ liquid trapping (bucketing). The relation between the circumferential velocity and integrated mass flux of the fluid sheet is found to be linear above a critical speed, for which an analytical formula is given. Using dimensional analysis, we show that the relation between the mass flux and gear speed signifies a Reynolds-number independent behavior of the boundary layer around the immersed part of the gear.
Long-Term Abrasion Test for Seabed Mining Hose Liners
Offshore Technology Conference, 2017
Hydraulic Loss of Finite Length Dividing Junctions
Journal of Fluids Engineering, 2016
A general hydraulic loss coefficient correlation for perpendicular, cylindrical, finite length di... more A general hydraulic loss coefficient correlation for perpendicular, cylindrical, finite length dividing pipe junctions is developed and implemented in a discrete dividing-flow manifold model. Dividing-flow manifolds are used in several technical appliances, e.g., in water and wastewater treatment, swimming pool technology, air engineering, and polymer processing. Ensuring uniform flow distribution is a major goal of a flow manifold system design, whose accuracy is usually determined by the accuracies of applied flow coefficients. Coefficient of turning losses is calculated by a computational fluid dynamics (CFD)-based approach applying a nonlinear fit. In the case of a single-phase flow, the loss coefficient depends on four dimensionless parameters: the Reynolds number, the ratio of port and header flow velocities, the diameter ratio, and the ratio of the port length and the diameter of the pipe. Instead of experimentally covering this four-dimensional parameter space, more than 100...
Advanced flutter simulation of flexible bridge decks
Coupled Systems Mechanics, 2012
ABSTRACT In this paper a bridge flutter prediction is performed by using advanced numerical simul... more ABSTRACT In this paper a bridge flutter prediction is performed by using advanced numerical simulation. Two novel approaches were developed simultaneously by utilizing the ANSYS v12.1 commercial software package. The first one is a fluid-structure interaction simulation involving the three-dimensional elastic motion of a bridge deck and the fluid flow around it. The second one is an updated forced oscillation technique based on the dynamic mode shapes of the bridge. An aeroelastic wind tunnel model was constructed in order to validate the numerical results. Good agreement between the numerical results and the measurements proves the applicability of the novel methods in bridge flutter assessment.
Atmospheric Chemistry and Physics Discussions, 2016
Budapest platform for Aerosol Research and Training (BpART) was created for advancing long-term o... more Budapest platform for Aerosol Research and Training (BpART) was created for advancing long-term on-line atmospheric measurements and intensive aerosol sample collection campaigns in Budapest. A joint study including atmospheric chemistry/physics, meteorology and fluid dynamics on several-year long data sets obtained at the platform confirmed that the location represents a well-mixed, average atmospheric environment for the city centre. The air streamlines indicated that the host and neighbouring buildings together with the natural orography play an important role in the near field dispersion processes. Details and features of the air flow structure were derived, and they can be readily utilised for further interpretations. An experimental method to determine particle diffusion losses in the DMPS system of the BpART facility was proposed. It is based on CPC/CPC and DMPS/CPC comparisons. Growth types of nucleated particles observed in 4 years of measurements were presented and discuss...
Periodica Polytechnica Mechanical Engineering, 2016
A novel discrete model with variable flow coefficients is developed for dividing-flow manifold de... more A novel discrete model with variable flow coefficients is developed for dividing-flow manifold design. The applicability and accuracy of the new model is also investigated, and a validation procedure is performed. Dimensionless volume flow rate distributions along a simple dividing-flow manifold are calculated with two different approaches: the discrete model and a three-dimensional CFD model are applied. In order to validate the calculated results, laboratory experiments are carried out. Results of the discrete model compare favourably with high resolution CFD results and also with experimental data, which underlines the applicability of the new loss coefficient parametrisation used in the discrete model.
A new approach to modelling conventional and special core analyses has been studied and identifie... more A new approach to modelling conventional and special core analyses has been studied and identified as feasible for answering the challenges arising from certain aspects of data acquisition processes in this field. the present phase of development comprises studying the current trends in modelling and identifying those areas where new approaches should be applied that are tailored to our specific requirements. Here, were construct particle models of depositional rocks in a slightly modified way, analysing and applying geostatistical methods for pattern generation of clastic rocks, studying the lattice-Boltzmann method for modelling one-phase flow through porous rocks and characterising porous systems, including pore size distribution. the first results of project i-core are inspiring and prove that there is considerable potential in developing and applying such models for both technical and economic reasons.
In this paper a numerical flutter simulation with the ANSYS software is presented. A fully aeroel... more In this paper a numerical flutter simulation with the ANSYS software is presented. A fully aeroelastic wind tunnel model was constructed in order to make a validation possible. First the dynamic properties of the bridge were determined. Second the critical wind speed for the flutter instability was captured. Taking into account the dynamic properties and the contour of the bridge, the CSD and the CFD models of that were built. By using the fluid-structure interaction solver of the ANSYS, the three-dimensional coupled simulation was performed. The critical wind speed was calculated by monitoring the structural motion at different inlet velocities. Comparing the measured and calculated critical wind speeds, good agreement was found considering the complexity of the problem. Alternatively the critical wind speed was evaluated by using the flutter derivatives extracted from a two-dimensional CFD simulation made with the FLUENT software.
Simulation of compressed air injection module
Large eddy simulation of flow in internally grooved heat exchanger tubes
Geometries of internally grooved tubes play a big role in the performance of heat exchangers. Alt... more Geometries of internally grooved tubes play a big role in the performance of heat exchangers. Although there are great databases of measurement data for some groove geometries, the empirical correlations based on these databases are often inaccurate for new groove patterns. While it is usually too expensive to manufacture a new groove geometry for optimization of heat exchangers, an accurate prediction model for the performance of non-existing groove geometries is of great importance. A model based on large eddy simulation (LES) of turbulent pipe flow is proposed. Three-dimensional unsteady Navier-Stokes and mass continuity equations are solved in OpenFOAM, [1]. Equations are solved for streamwise periodic variables in order to investigate fully developed turbulence. Simulations are carried out for a smooth pipe and a helically grooved tube. Accuracy of different mesh resolutions and different sub-grid scale models are investigated. Great effort is done in minimizing computational c...
Modelling of flow past a building in urban heat island-induced flow
Effects of Blade Skew in an Axial Flow Rotor of Controlled Vortex Design
Turbulens áramlások szimulációja = Simulation of turbulent flows
A gépészeti gyakorlatban aktuális műszaki problémák megoldására elvégeztük a háromdimenziós turbu... more A gépészeti gyakorlatban aktuális műszaki problémák megoldására elvégeztük a háromdimenziós turbulens áramlási tér szimulációját FLUENT szimulációs rendszerben létező Reynolds-átlagolt turbulencia modellekkel. A modellek pontosságát és megbízhatóságát szélcsatornás és egyéb laboratóriumi kisminta mérésekkel való összehasonlítás alapján értékeltük. Új módszereket dolgoztunk ki az áramlások numerikus szimulációjának számos területén: - Az állandósult áramkép megjelenítésére; - Mozgó koherens struktúrák azonosítására turbulens áramlásban; - Atmoszférikus áramlások esetében a turbulencia modellek belépő peremfeltételeinek meghatározására; - Nagy méretű érdességi elemek - például atmoszférikus áramlásban a növényzet és épületek - hatásának figyelembevételére; - A szabad aktív klór koncentrációjának ivóvíz vagy fürdővíz medencékben történő meghatározására; - Tűz és füst terjedés modellezésére. Szélcsatornás mérésekkel validáltuk a FLUENT szimulációs rendszerben rendelkezésre álló turbulen...
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Papers by Gergely KristÓf