8th International PHOENICS User Conference - 8IPUC Luxembourg, May, 2000 THREE-DIMENSIONAL HYDRODYNAMIC MODEL COUPLED WITH DEPTH AVERAGED TWO-DIMENSIONAL MODEL : CASE OF THE MEDJERDA-CAP-BON WATER INTAKE. Zouhaier HAFSIA (1) et Khlifa MAALEL (2) Ecole Nationale dIngénieurs de Tunis. Laboratoire dHydraulique. B.P Le Belvédère, 1002, Tunis, Tunisie. (1) (2) 1 8IPUCENIT - LMHE National Tunisian Engineering School (ENIT)

Geographic location of the Laroussia dam and its waterworks B. LAROUSSIA Bizerte Sidi Salem D. Tebourba Tunis Nabeul Sejnane D. Siliana D. Belli Tunisia Libya Algeria Cap-Bon Sidi El Barrek D. Joumine D. Medjerda Algeria Medjerda M e d i t e r r a n e a n s e a Gulf of Tunis 2 8IPUC Great Channel Medjerda Cap-Bon Channel Fondek Jedid Bejaoua Joumine Medjerda Channel ENIT - LMHE

3 8IPUC Plane view of the three water intakes of the Laroussia dam Nomenclature MCB : Medjerda-Cap-Bon water intake GC : Great-Channel intake C : Hydroelectrical power intake Crest Level (m NGT) /31.50 GC 16 m 3 /s 13 m 3 /s MCB m 3 /s C 87° 68° Medjerda Stream Laroussia dam ENIT - LMHE

4 8IPUC Muds deposits in front of the MCB water intake Deposition zones in front of the MCB and along its junction with the GC intake GC MCB Muds deposited 22/09/95 In 1989, volume of depositis was estimated to : m 3. In 1989, The volume of deposits was estimated to m 3 along the MCB channel and to m 3 along the GC. 28/10/98 Upstream view of the Laroussia dam on the Medjerda Laroussia D. (1956) C 1956 Concave bank in front of the MCB intake GC 1974 MCB /09/95 ENIT - LMHE

5 8IPUC Identification of the essential causes of the muds deposits in front of the MCB water intake. Proposition of solutions to reduce the sedimentation along the MCB channel. Objectives Hydraulic Model with fixed bed Coupled hydrodynamic model (3-D/2-DH ) ENIT - LMHE

6 8IPUC Similitude ratios of the hydraulic model of the Laroussia dam R e =1400 ENIT - LMHE

7 8IPUC Experimental Channel in Hydraulic Laboratary (E.N.I.T.) ENIT - LMHE

8 8IPUC Depth avareged hydrodynamic model (2-DH) Identify the currents structure in the MCB convergent Explain the islet of muds deposits formation in front of the MCB intake To impose more realistic boundary conditions along the MCB intake crest Comparaison criteria between the diffrents studied modifications Objectives of hydrodynamic models Coupled three dimensional hydrodynamic model (3-D/2-DH) ENIT - LMHE

9 8IPUC Mathematical formulation of 3-D Hydrodynamic model = t + ENIT - LMHE

10 8IPUC PHOENICS : Parabolic Hyperbolic Or Elliptic Numerical Integration Code Series Mathematical formulation of 2-DH Hydrodynamic model ENIT - LMHE

11 8IPUC Covariante Derivatives Ordinary Derivatives Covariante formulation in the PHOENICS code Traitement of the pressure-velocity coupling : SIMPLEST Algorithm (SIMPLE ShorTened) ENIT - LMHE

12 8IPUC Multiblocks grid in 2-DH CCM : Collocated Covariant Method NX x NY = 118x20 = 2360 min = 38.5 ° Angle of non orthogonality of BFC grid Block 1 Blocages Block 2 Multiblocks grid in 2-DH of the Laroussia dam and MCB intake ENIT - LMHE

Three dimensional grid of Laroussia dam reservoir (I=20) 13 8IPUC 3-D Grid Staggered Covariante Formulation NX x NY x NZ = 76x20x10=15200 min = 37.3° Free surface blocages Wall Inlet P3 P2 P1 MCB BGE Outlet P4 profile grid on the protype P4 profile grid on the model ENIT - LMHE

14 8IPUC 2-DH grid Vérification. Case of the MCB intake openning : U in = 4.3 mm/s (m 2 /s) Streamlines and equipotential field Direct Method ENIT - LMHE

15 8IPUC 2-DH Hydrodynamic model Visualized bottom currents Q der = 1,3 l/s Simulated currents : D = m 2 /s U in = 4.3 mm/s ENIT - LMHE

16 8IPUC D = m 2 /s (on hydraulic model) V (m/s) U in = 4.3 mm/s Comparaison of the currents structures on hydraulic model scale and prototype scale V (m/s) D = m 2 /s (on prototype scale) U in = 5 * 4.3 mm/s V sim = m/sV mes = m/s ENIT - LMHE

17 8IPUC Principles of modifications * Deposits in front of the MCB intake are inevitable * Reduce the bottom currents ascention * Correction of the MCB intake shape ENIT - LMHE

18 8IPUC Choice criteria between the diffrent alternatives Visualised bottom Currents Q der = 1.3 l/s Simulated Surface currents U in = 4.3 mm/s t = m 2 /s Secondary currents structure in vicinity of the Laroussia dam ENIT - LMHE

2 8IPUC 19 With Approach channel Bottom Currents Q der = 1,3 l/s ENIT - LMHE

20 8IPUC With Approach channel Surface Currents Q der = 1,3 l/s ENIT - LMHE

21 8IPUC Comparaison of secondary currents structures upstream of the MCB intake (before and after approach channel) m/s U in = 21.5 mm/s; t = m 2 /s U in = 4.3 mm/s; t = m 2 /s Before modification m/s After modification m/s ENIT - LMHE

22 8IPUC Another coupled model: Centrifugal pump predimensioning H. Azouz et R. Zgolli Common boundary Volute beak Blade to treat the interactions between rotor flow (rotational) and volute flow : Iterative procedure was needed in MB-FGE ENIT - LMHE

23 8IPUC Another couled model: Centrifugal pump predimensioning H. Azouz et R. Zgolli (Pa) Volute beak (Pa) ENIT - LMHE

24 8IPUC Conclusion Depth Averaged two dimensional hydrodynamic model is sufficient to reproduce the visualised currents structure in the MCB convergent. The currents structure in the convergent are not influenced by the dispersion coefficient. Constant turbulence viscosity model is adopted for the 3-D Hydrodynamic model to overcome the diffuculty of application of the standard k- Model in severe non orthogonal grid An approach channel is proposed to reduce the bottom current ascending toward the MCB intake and allowed the inversion of the secondary currents. In the case of centrifugal pump flow, the interactions between rotational and irrotational flow is treated by iterative coupled 2-D model (H Azouz). ENIT - LMHE