Numerical and laboratory investigation of the hydrodynamic complexity of a river confluence

The paper deals with the hydrodynamic investigation of the junction of two rivers in north-west Hungary in an urban area. The goal of the investigation was to study the flow conditions by means of a 3D k-ε turbulence CFD model and hydraulic scale model. The project gave the opportunity to compare the outcome of the distorted scale model with the ones of the CFD model in field scale, in the distorted hydraulic model scale as well as in undistorted scale, converting all the results to real field scale by assuming Froude similarity. Overall flow patterns, the effect of distortion and the robustness of the k-ε turbulence model in such complex confluence conditions were analysed. Satisfactory agreement was found except for the region straight downstream of the confluence where significant differences between laboratory and numerical results were seen due most probably to the complex swirling and shearing character of the flow. Large scale vortex formation interacting with anisotropic local turbulence would certainly need differential Reynolds stress turbulence closure

THERMOMECHANICAL TESTING OF AN AERATED CONCRETE WALL

A one year old aerated concrete wall still contains a substantial amount of moisture and dries slowly. Full scale tests show that the aerated concrete material, regarded as homogeneous, has a different thermal conductivity through the wall cross section. The relationship between thermal conductivity and moisture content is determined. A 30 cm thick aerated concrete wall with mortars on both sides has a factor of thermal conductivity of 0.59W/m²K in spite of the high moisture content. Testing heat-bridges (corners, slab-wall, wall-floor-footing) shows the standard temperature difference is likely to cause dew on the inner wall surface

Flow Analysis in River Danube by Field Measurement and 3D CFD turbulence modelling

Spatial complexity of turbulent flow conditions has been investigated by means of ADCP measurements and CFD modelling in river Danube. The study area was a meandering river reach, characterized by shallows and strongly influenced by various river training works. High resolution bed survey and freezing plate sampling provided input river bed data for model implementation. The applied k-ε turbulence model could well reproduce velocity distributions measured in nature. Strong spatial variability of the velocity and turbulent kinetic energy fields demonstrated the necessity of 3D model approach under such fluvial conditions

Particle tracking velocimetry (PTV) and its application to analyse free surface flows in laboratory scale models

The methodology and application of particle tracking velocimetry (PTV) for surface flow velocity measurements are presented in a conventional laboratory scale model characterised both by large vortices and turbulence, making use of the fact that PTV allows to take reliable measurements in flows exposed to strong deformations typical in turbulent shear layers. The experimental setup included a river reach with main channel and wide floodplain of different roughness. Surface PTV measurements were carried out by a CCD camera with 30 frames per second frame rate and vertical camera axis. In the evaluation of the recordings an algorithm suitable to be applied in flows with strong strains was needed, capable to find corresponding particles even by highly deformed neighbourhoods. For this aim a modification of the so-called velocity gradient tensor method was used. The reconstructed velocity fields were used first to visualize the mean flow field, then to identify and investigate the various flow structures by means of the swirling strength analysis

On the 2D modelling aspects of wind-induced waves in shallow, fetch-limited lakes

Wind-induced waves play an important role in shallow lake hydro- and sediment dynamics. But most of the field measurement methods can give information about the wave properties only at single point, which calls for wave estimation methods to take the effect of waves into account in multidimensional hydro- and sediment dynamic models. The aim of this study is to improve modelling waves in depth- and fetch-limited lakes generated by the local winds. In the first part of this paper, we describe the calibration and validation of the 2D spectral wave model SWAN (Simulating Waves Nearshore) to the very shallow Lake Neusiedl, Hungary/Austria. The abrupt change of the roughness at the perimeter of the open lake and the gradual change along the fetch due to wave growth result in a systematic, fetch-dependent variation of the wind speed. This spatial inhomogeneity is modelled here by a 1D atmospheric internal boundary layer (IBL) model. It is shown in the second part of this paper that this approach results in a significant effect on wave parameters and, as a consequence, on bottom shear stress

NUMERICAL MODELLING OF FLOW PATTERNS TO ASSIST THE REVITALISATION OF SECONDARY RIVER BRANCHES IN GEIVIENC AREA

Depth-averaged numerical modelling of steady-state horizontal flow patterns carried out in the framework of the revitalisation project of the secondary branches in Gemenc Protected Landscape Area is presented. The feasibility of different variants is investigated in order to increase the water exchange in the secondary branches without creating unfavorable hydraulic and related sediment transport as well as navigation conditions. The applied mathematical model is based on the usual shallow water assumptions. The numerical solution is performed using finite differences and multigrid iteration technique. The model is able to reproduce recirculation zones and the horizontal velocity distribution in an acceptable manner

Távérzékelésen alapuló párolgás-számító algoritmus a turbulens hő és légnedvesség 2-D kapcsolt transzport egyenletéből = Remote-sensing-based areal evaporation algorithm from the coupled 2-D turbulent heat and vapor transport equations

Egy MODIS műholdképeken alapuló térben osztott párolgás-becslési és térképezési eljárást fejlesztettünk ki és teszteltünk a 2000-2009-es időszakra. A módszert egész Magyarország (és más régiókra is) területére nagy sikerrel alkalmaztuk, egészen 0,95-ös r-négyzet értékkel. Korábbi, jelentősen generalizált párolgási térképek így a módszerrel kapott térképekkel lecserélhetők. Jelenleg a módszer adja a legpontosabb és legrészletesebb párolgási térképeket Magyarország területére, ami nagy jelentőségű jövőbeni vízgazdálkodási tervek kidolgozásakor. | A new, evapotranspiration (ET) mapping technique has been worked out for Hungary, using MODIS data. The method was applied over the entire area of Hungary (and other regions as well) with great success for the 2000-2009 period with r-squared values up to 0.95. Earlier, largely generalized ET maps thus can be replaced by the present ET estimates, which therefore provide the most accurate and detailed ET values yet for Hungary. The results may prove invaluable in future water resources management and allocation plans