2. Study area

numerical model, for the calculation of turbulent flow in meandering channels. The works provided a hydrodynamic basis for the study of the mechanisms for the formation of river meanders. The authors employed a finite volume numerical method to solve the full Reynoldsaveraged Navier-Stokes (RANS) equations in conjunction with the standard k-ɛ model. The case exhibits some of the features encountered in real rivers, including longitudinal curvature and varying bed topography. Demuren's results were in reasonable overall agreement with the mean velocity measurements of Almquist and Holley [18]. Meselhe focused on proposing a simplified approach for calculating the water surface elevation as a part of the overall solution

All previous studies with both straight and curved channels had adopted a rigid-lid assumption for modeling the free surface. The rigid-lid approximation is a commonly used simplification in the study of density-stratified fluids mainly in oceanography. Assumes, that the displacements of the surface are negligible compared with interface displacements. In a research conducted by Sinha [11], a 3-D model of flow through a 4-km stretch of the Columbia river, downstream of the Wanapum Dam, was developed and validated. Authors succeeded in modeling of flow in rapidly varying bed topography and the presence of islands. In the study three-pronged strategy—composed of the field measurements, the laboratory experiments, and the numerical model—was undertaken. The model solves the (RANS) equations closed

In today's development level of hardware and software, increasingly complex, engineering tasks can be managed, and, thus, three-dimensional hydrodynamic modeling of dam reservoirs became a potential tool for determining more accurate picture of the dependencies, which prevail in the aquatic ecosystem. Whereas in most studies one- and two-dimensional description of flows may be sufficient, in some special cases, three-dimensional approach is needed to determining, for instance, flow patterns in bends or in the vicinity of hydraulic structures (dams and weirs). These issues are evidently three-dimensional, and spatial charac-

Hydrodynamic processes determine the movement of suspended and dissolved matter; heat transfer; intensity of circulation inside the ecosystem; the speed of contaminating processes; and the self-purification of the reservoirs, ultimately provide conditions of the ecosystem function. Kennedy et al. [15] applied a 3-D model to estimate the hydraulic residence time (HRT) for the Thomas Basin (part of the Wachusett Reservoir in central Massachusetts). The basin was modeled using the FLUENT software package with particles used to track travel time in steady-state conditions. A tetrahedral mesh was used with accurate description of basin bathymetry. The model solved the transient Reynolds equations for turbulent flow with standard k-ɛ closure. Modeling was performed to simulate flow pattern during a period when conditions were isothermal and windless. HRT was estimated to 3–4 days which is about half of the HRT that would be expected based on the theoretical mean residence time. The results of the calculations show that the presence of a primary flow path, large-scale eddies, and stagnation zones contributed to the faster travel time. Reductions in inflow rates produce increased residence times and significant changes in flow patterns. However, the authors did not provide

procedure.

40 Dam Engineering

with the standard k-ɛ turbulence model.

ter directly affects pollutant transport processes.

any information about model verification.

Sulejow reservoir is situated on the middle reach of the Pilica river, which is left-hand side tributary of Vistula river, central Poland (Figure 1). One of the biggest artificial reservoirs in

Figure 1. Localization of the Sulejow dam reservoir.

Poland was built by impounding the Pilica river on 138.9 km with a dam in the years 1969– 1973. The reservoir is a shallow water body (mean depth 3.3 m) covering a large area (22 km<sup>2</sup> ).

Sulejow reservoir is a ribbon-type reservoir, which can be divided into two morphological zones each influenced by different forcing agents. The first one (consisting of a riverine zone and a transition zone) is the narrow, shallower part of the reservoir, dominated by the river inflows. The second zone, the wide lacustrine part of the reservoir, is located near the dam. This zone is quite open and behaves like a lake, and the main driving force mechanism causes the movement of water masses wind. The main axis runs from southwest to northeast which is close to the direction of winds that ripple and mix the water. A result is the formation of places with stagnant water on the southern bank of the middle and lower part of the reservoir.

In this study, the "bottom-up" approach was implemented in order to obtain a three-dimensional geometry from the set of separated surfaces. Each measured cross section was defined by the information of the distance between two banks (connection length between probing points in the section was 5 m) and elevation (normal impoundment level in the Sulejow reservoir is 166.6 m amsl). Figure 3 illustrates an example of the cross section built in the Gambit Program. The vertices which determine the reservoir bed were connected to form the edges. Subsequently, edges were combined into faces. The last stage consisted in stitching the faces in order to obtain the volumes. After completion of the segmentation procedure, rendering process was conducted, which facilitated generation of three-dimensional geometry of the reservoir, using the faces obtained from the segmentation. Figure 4 presents the complete geometry that

Three-Dimensional CFD Simulations of Hydrodynamics for the Lowland Dam Reservoir

http://dx.doi.org/10.5772/intechopen.80377

43

Terminal berm of the reservoir consists of earth dam and weir, with integrated hydroelectric power station (Figure 5). The length of the dam with a weir is 1200 m, the maximum height is

middle and left of the weir, drain pipes have been built. Weirs are closed with the oval valves. Cross section of earth dam and weir is shown in Figure 6a and b. Geometry and computational

. The jazz is concrete, in the overflow riffle span,

consists of 36 volumes totally.

Figure 4. Sulejow reservoir geometry.

16 m, and the total volume is 567,000 m3

Figure 3. Example of the cross sections generated with Gambit program.

mesh of the dam are shown in Figure 7.
