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2.3.4. Three Dimensional Model of Culvert Flume with Comparison to Experimental Results The preliminary objective of this study was to develop a computational fluid dynamics (CFD) model to characterize the three-dimentional (3-D) two-phase (air and water) laboratory model associated with three different water depths, two different velocities and three bed elevations. The suitability of the CFD model for fish passage engineering analysis is assessed by comparison with experimental data obtained from TFHRC. In phase 1 of the study, a three-dimentional multi-phase CAD model, as shown in Figure 2.19, was created in Pro-ENGINEER. The CAD model consists of three parts along the flow direction (z axis): the intake, the barrel and the diffuser. Since the two-phase VOF model (water and air) is used for numerical simulation, initially an air layer was included on top of the water domain in the vertical direction (x axis). The culvert model considered in phase 1 of study is the symmetrical half of the culvert pipe having annular corrugations without bed elevation as shown in Figure 2.19. Figure 2.19: Three-dimensional CAD model for multi-phase simulations The experiments in this study were conducted at the FHWA J.Sterling Jones Hydraulics Laboratory, located at the TFHRC. The experiments were conducted in a circulating flume. Figure 2.20 provides the details of the experimental flume dimensions in front and overlook views. The corrugations used are 3 inch by 1 inch annular. Three typical cross sections were monitored in the tests, which were located at the inlet of the barrel (section 1), the middle of the barrel (section 2) and the end of the barrel (section 3), respectively. TRACC/TFHRC Y1Q3 Page 30
Figure 2.20: Dimensional details of the flume (front and top views) The primary purpose of running CFD tests on a three dimensional model of the full TFHRC culvert test flume is to verify that the much smaller domain of a barrel section with cyclic boundary conditions can be used for parametric runs to determine zones for fish passage. A significant difference in the two models is that the small section using a cyclic boundary condition must be run as a single phase flow with a symmetric, free slip boundary condition at the water surface. This requires that the flow be deep enough for the corrugations to have negligible effect on the surface. Truncated CFD models with cyclic boundaries can be utilized as a time-effective tool in completing the large test matrix of the project. 2.3.5. Flow Conditions All the test scenarios in the study involve three different water depths, two velocities, and three bed elevations. Additional design parameters include tilting angle of the flume, open angle of the flap gate, roughness parameters etc.. The flow conditions for the completed multi-phase CFD model tests are listed in Table 2.3. TRACC/TFHRC Y1Q3 Page 31
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Page 39 and 40: Figure 2.25: CFD velocity contour p
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