PhD student, January 2010-December 2013

Transcription

1 Numerical modeling of wave current interactions ata a local scaleand and studyof turbulence closuremodel effects MARIA JOÃO TELES PhD student, January 2010-December 2013 Supervisor: António Pires-Silva, Instituto Superior Técnico (IST)-TULisbon Co-supervisor: Michel Benoit, EDF R&D, LNHE and Saint-Venant Laboratory for Hydraulics Lisboa, 25 th November, 2011

2 1. GENERAL FRAMEWORK 2. CODE_SATURNE 3. DATA AND MODEL SETUP 4. RESULTS AND DISCUSSION 5. CONCLUDING REMARKS 2 2

3 GENERAL FRAMEWORK Coastal waters Waves Tides Wind Problem addressed - The complexity of a combined wave current flow, especially the contrasting time length and velocity scales of the separate components; - The interaction effects from a local scale to a regional scale; - The necessity of a 3D coupled model between waves and currents; 3 3

4 GENERAL FRAMEWORK Purpose: - To evaluate the Code_Saturne model in representing free surface flows; - To access the influence of various schemes to represent turbulence effects; - To improve the predictions of the vertical profile of the flow; - To study the horizontal and vertical velocity changes in the current profile; - To understand the wave current interaction phenomena in nearshore areas; Coupling interface, proposing suitable schemes for combined models of coastal engineering applications at a nearshore scale. 4 4

5 Code Saturne Code_Saturne Mathematic formulation based on RANS equations; Finite volume method; Computational dynamic code for laminar and turbulent flows in three dimensional domains; Code Saturne Kernel RANS equations completed with turbulence closure models Shell Mesh and Post processing Code_Saturne website 5 5

6 Code Saturne Arbitrary Lagrangian Eulerian Method Code_Saturne (ALE module) A new term, the vertical mesh velocity, has to be included in the equations; At each time step the mesh has to be updated. Vertical mesh velocity Given by turbulence closure model 6 6

7 Data Laboratory facility Flow circulation circuit. Klopman (1994), Delft Hydraulics Test section Current characteristics Mean mass transport velocity: U=6 ms -1 ; Discharge: Q=80 ls -1 ; Density: 1000 kgm -3 ; Dynamic viscosity: 1.0*10-3 Ns/m 2 ; Water depth: h=0.5 m; Reynolds number =75000; Bed roughned by coarse sand of 2mm mean diameter 7 7

8 Data Laboratory facility Two computer driven wave boarders; Monochromatic Waves: - Wave Height: 2 m; - Wave Period: 1.44 s; 8 8

9 Model Setup - Geometry and mesh (Prism type) Model Setup x 0. 25m y = 1m 0.005m < z < 0. 02m N x N y N z 215 = 1 23 y=1m z=0.5m x=60m 9

10 Model Setup Model Setup - Wave maker? Second order theory for wave board motion, progressively imposed in time 10 10

11 Model Setup Model Setup - Wave absorber? Wave direction Artificial beach 11 11

12 Model Setup - Boundary conditions? Free Surface Additionally to the defined boundary conditions we also have to impose at the free surface... Model Setup In this way, dissipation increases when approaching the free surface and so both characteristic length and turbulent viscosity are going to decrease. A better description of the turbulence quantities is achieved. Nezu,

13 Model Setup Major assumption in the momentum equation is the Reynolds stress closure hypothesis for the turbulent shear stress. Model Setup - Turbulence closure model? Two equation models: k ε (with linear production) k ω SST Reynolds stress models: R ij ε SSG 13 13

14 Results and Discussion Results and discussion Turbulence part Wave part Steady part Phase averaged 14 14

15 Results and Discussion Only Currents - Vertical profile of the mean horizontal velocity : Data Rij-ε k-ω k-ε E z 0 =0.04 mm U (m/s) U (m/s) 15 15

16 Results and Discussion Only Currents - Vertical profile of the shear stress: Data Rij-ε 0.3 k-ω k-ε

17 Results and Discussion Only Waves - Vertical profile of the mean horizontal velocity : Data Rij-ε k-ω k-ε U (m/s) U (m/s) Wave induced streaming 17 17

18 Results and Discussion Only Waves - Vertical profile of the horizontal velocity amplitude: Data 0.3 Rij-ε k-ω k-ε U (m/s) U (m/s) 18 18

19 Results and Discussion Waves following current - Vertical profile of the mean horizontal velocity : 0.5 Reduction of velocity Data Rij-ε k-ω k-ε z 0 =0.05 mm 0 0 U (m/s)

20 - Vertical profile of the horizontal velocity amplitude: Results and Discussion Waves following current Data 0.3 Rij-ε k-ω k-ε U (m/s) U (m/s) 20 20

21 Results and Discussion Waves opposing current - Vertical profile of the mean horizontal velocity : Increase of velocity Data Rij-ε 0.3 k-ω k-ε z 0 =1.5 mm U (m/s) U (m/s)

22 Results and Discussion Waves opposing current - Vertical profile of the horizontal velocity amplitude: Data Rij-ε 0.3 k-ω k-ε U (m/s) U (m/s) 22 22

23 - Vertical profile of the horizontal velocity amplitude: Results and Discussion Waves and currents interaction Only Currents Waves following currents Waves opposing currents Mass transport due to the waves Wave induced Reynolds stresses U ( m / s ) Apparent bed roughness 23 23

24 - Vertical profile of mean horizontal velocity: Results and Discussion Waves and currents interaction Only Currents Waves following currents Waves opposing currents 0.01 z 0 = mm Mass transport due to the waves Wave induced Reynolds stresses Apparent bed roughness z 0 =0.05 mm U ( m / s ) 24 24

25 Results and Discussion Wave and current interaction ka 1.251e k = s 1.882Uw Uc Waves following currents k k a s = 1.937e 92Uw Uc Waves opposing currents Waves following currents Waves opposing currents Computed ka/ks Present work Christ85 van Rijn84 Computed ka/ks Measured ka/ks Measured ka/ks 25 25

26 Concluding Remarks Concluding remarks Code_Saturne is able to model free surface flows at least at local scale, including progressive waves; Reynolds stress model R ij ε gives more accurate results than the two equation models k ε and k ω; Turbulence effects on the interaction between waves and currents are well reproduced by Code Saturne when the new expression, the free surface boundary condition for the turbulent dissipation, is imposed; The changes of the vertical gradient of mean horizontal velocity and mean amplitude velocity profile caused by a following or an opposing current match qualitatively with the experimental data; The roughness parameter z 0 waves and currents. depends strongly on the combined state of 26 26

27 On going works Coupling interface TOMAWAC with TELEMAC3D Parameterization with the vertical turbulent viscosity profile taken from Code_Saturne; More complex test cases in order to study rip currents? Interaction with structures (e.g. detached breakwaters)? Validation of the coupled code with the 3D version; 27 27

28 Obrigada! Questions? Suggestions? 28 28