computational modeling of flow over a spillway in vatnsfellsst fla dam in iceland
Download
Skip this Video
Download Presentation
Computational Modeling of Flow over a Spillway In Vatnsfellsstífla Dam in Iceland

Loading in 2 Seconds...

play fullscreen
1 / 57

Computational Modeling of Flow over a Spillway In Vatnsfellsstífla Dam in Iceland - PowerPoint PPT Presentation


  • 110 Views
  • Uploaded on

Computational Modeling of Flow over a Spillway In Vatnsfellsstífla Dam in Iceland. Master’s Thesis Presentation Chalmers University of Technology 2007 – 02 - 02. Presentation Schedule. Introduction and background Method Theory Results Conclusions and future work.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Computational Modeling of Flow over a Spillway In Vatnsfellsstífla Dam in Iceland' - Olivia


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
computational modeling of flow over a spillway in vatnsfellsst fla dam in iceland

Computational Modeling of Flow over a SpillwayIn Vatnsfellsstífla Dam in Iceland

Master’s Thesis Presentation

Chalmers University of Technology

2007 – 02 - 02

presentation schedule
Presentation Schedule
  • Introduction and background
  • Method
  • Theory
  • Results
  • Conclusions and future work
the spillway characteristics
The spillway – characteristics
  • Function: cope with accidental flooding
  • Height above stilling basin bottom: 27.5 m
  • Lenght of spillway crest: 50 m
  • Equipped with a splitter wall and cover to prevent overtopping of the chute sidewalls
  • The velocity of the water is above 20 m/s (=72 km/hour!) where it flows into the stilling basin
the stilling basin characteristics
The stilling basin – characteristics
  • Function: Decrease flow velocity in order to decrease risk for erosion in the river wally downstream the basin
  • Equipped with 28 energy dissipating baffles (height from 1.5 to 2.0 m)
  • Length ca. 33 m and the width increasing from 22 m in the upstream part to 33 m in the downstream part, depth ca. 7 m
  • Downstream the stilling basin is a 35 m long rock rip-rap made of rocks with diameter of

0.4 – 1.2 m

background and goals
Background and goals
  • In 1999 Vattenfall in Sweden did hydraulic experiments for the spillway with a 1:30 model
  • In the experiments flow was investigated over the spillway, through the bottom outlet and in the stilling basin
  • Goals of the present study:
    • investigate flow over the spillway and in the stilling basin with computational methods (CFD)
    • compare CFD-results with experimental results
aspects
Aspects
  • Spillway:
    • water head in the reservoir vs. the discharge capacity of the spillway
    • Water level along the chute sidewalls
    • Pressure acting on the chute bottom
  • Stilling basin:
    • Water level
    • Pressure acting on the baffles and the end sill
    • Flow velocity out of the basin
method
Method
  • Identify the computational domain to be modeled (according to the goals!)
  • Draw the computational domain in 3D in Autodesk INVENTOR
  • Import the geometry into the mesh making software GAMBIT and divide the computational domain into computational cells of different size in GAMBIT
  • Import the mesh into the CFD-solver FLUENT, set up the numerical model, compute and monitor the solution
  • Postprocessing with FLUENT and MATLAB; examine the results and consider revisions to the model
the computational domain
The computational domain
  • Three different domains:
    • One for head vs. flow discharge
    • One for water level and pressure in the spillway chute
    • One for water level, pressure and flow velocity in the stilling basin
  • Why different domains?
    • to spare computational power and get more precise results
slide21
Grids nr. 1 – 7 as seen from above- one grid for each of the seven different cases with flow discharge of 50 – 350 m3/s, ca. 653 000 cells/grid
slide22
Cut through grids nr. 1 and 7 in the downstream end of the reservoir by the spillway crest – different water levels
  • Grid to the left: designed for flow discharge of 50 m3/s
  • Grid to the right: designed for flow discharge of 350 m3/s
grid nr 8 finer in the chute than grids nr 1 7 ca 1393 000 cells
Grid nr. 8: finer in the chute than grids nr. 1 – 7, ca. 1393 000 cells
  • The mesh in the spillway bottom
    • To the left: mesh 7 which is NOT specifically designed to investigate pressure and water level in the spillway chute
    • To the right: mesh 8 which is specifically designed to investigate pressure and water level in the spillway chute
mesh nr 8 finer in the chute than meshes nr 1 7
Mesh nr. 8: finer in the chute than meshes nr. 1 - 7
  • The grid perpendicular to the splitter wall
    • To the left: mesh 7 which is NOT specifically designed to investigate pressure and water level in the spillway chute
    • To the right: mesh 8 which is specifically designed to investigate pressure and water level in the spillway chute
slide25
Grid nr. 9: different types of mesh; consisting of both hexahedron cells and tetrahedron cellsca. 498 000 cells
grid nr 9 includes the stilling basin though coarse in view of the size of the computational domain
Grid nr. 9 includes the stilling basinthough coarse in view of the size of the computational domain
setting up the numerical model
Setting up the numerical model
  • Define
    • Material properties (air, water, concrete)
    • Boundary conditions (inlet, outlet, walls,

air pressure,...)

    • Operating conditions (air pressure, gravity, temperature...)
    • Turbulence model (standard k-ε)
    • Initial solution (nB: steady flow)
    • Convergence criteria
theory equations of motion and the vof method
Theory – equations of motion and the VOF method
  • The continuity equation for incompressible flow:
  • The momentum equation for incompressible flow:
  • VOF method in FLUENT
    • assumes that the two phases (air and water) are not interpenetrating
    • denoting αq as the volume fraction of the q-th phase three possibilities for a given cell can be noted:
    • i) : the cell is empty of the q-th phase,
    • ii) : the cell is full of the q-th phase,
    • iii) : the cell contains the interphase between the q-th phase and one or more phases.
slide31
Water reservoir head vs. flow discharge; Q=CBH3/2where Q= flow discharge, C= discharge coefficient, B = length of crest, H=head
volume fraction of water in the basin longitudinal profile determines the water level
Volume fraction of water in the basin (longitudinal profile) – determines the water level
slide50
Total pressure on the basin end sill- a view under the water surface in the downstream end of the basin
main results summary
Main results - summary
  • Good agreement is reached between the experiments and CFD calculations for the following aspects:
    • head vs. discharge capacity (Q=CBH3/2)
    • pressure in the spillway chute
    • flow velocity above the basin end sill
  • Worse agreement is reached for:
    • pressure on baffles in the upstream end of the basin
    • water depth along chute sidewalls and in the left upstream corner of the basin
    • pressure on the basin end sill
future work what might to be done better or added
Future work – what might to be done better or added?
  • Calculate the flow through the bottom outlet
  • Better resolve the turbulent boundary layers close to walls
  • finer mesh
  • more computational power
  • even parallel processing
ad