Draft Tube calculations using OpenFOAM-1.5dev and validation with FLINDT data

6th OpenFOAM Workshop, June 13-16 2011, PennState University, USA Draft Tube calculations using OpenFOAM-1.5dev and validation with FLINDT data C. Devals, Y. Zhang and F.Guibault École Polytechnique de Montréal, Canada T. Vu and B. Nennemann Andritz Hydro, Pointe-Claire, Canada 1

Context Viscous flow simulations for hydraulic turbo-machinery design Distributor Spiral casing Runner Draft-tube 2

Context Previous work: 25 th IAHR Symposium on Hydraulic Machinery and Systems September 20-24, 2010, Timisoara, Romania Steady and unsteady flow computation in an elbow draft tube with experimental validation T.C. Vu, C. Devals, Y. Zhang, B. Nennemann and F. Guibault International Journal of Fluid Machinery and Systems Vol 4, No 1, January-March 2011 Lt=1%D th Lt=0.5%D th Lt=0.25%D th 3

Objectives Understand why the recovery coefficient for Phi=0.368 shows an important decrease for Lt=0.5%D th. Validate OpenFOAM RANS simulations for draft tube on hexahedral meshes Compare recovery coefficient χ prediction with experimental data 4

Test Case Description Model draft tube test: FLINDT FLINDT is for FLow INvestigation in Draft Tubes Project (LMH-EPFL Switzerland) Throat diameter: D th = 0.4 m Rotational speed: N=1000 RPM Angular velocity: ϖ=104.66 Hz Flow coefficient ϕ: 0.340, 0.360, 0.368, 0.380, 0.390 and 0.410 corresponding swirl: 0.332, 0.242, 0.214, 0.198, 0.149 and 0.076 Recovery coefficient pstat static pressure difference between inlet and outlet χ = A ref reference section area A ref =0.17538m 2 1 2 P ρ stat Q A ref 2 ϕ = Q πϖr 3 th 5

Physical Properties and Models Steady state Reynolds averaged Navier-Stokes equations Newtonian fluid r r ( U U) r U = 0 ν = ν ρ = ν ν lam lam + ν turb 997kg.m µ = = ρ µ ρ turb turb = = p r r T = ( I + ν ( U + U )) ρ 1 0.89257.10 C mu k ρ 2 ε µ = 6 rel m 2 s µ µ turb lam 1 k ε turbulence model 6

Boundary Conditions Inlet pressure type zerogradient U, k type profile1dfixedvalue filename "profil-rr.csv" epsilon type turbulentmixinglengthdissipationrateinlet mixinglength 0.0003285 U profile k profile 7

Boundary Conditions Outlet pressure type fixedmeanvalue meanvalue 0 value uniform 0 U, k and epsilon type zerogradient 8

Boundary Conditions pier U type fixedvalue value uniform (0 0 0) p, k and epsilon type zerogradient No slip Wall condition 9

Boundary Conditions main U type fixedvalue value uniform (0 0 0) p, k and epsilon type zerogradient No slip Wall condition 10

Boundary Conditions ext U type fixedvalue value uniform (0 0 0) p, k and epsilon type zerogradient No slip Wall condition 11

Numerical Model Steady state (RANS) calculations (10000 iterations) Solver: SimpleFOAM Convection term discretization: normalized variable diagram (NVD) scheme GammaV (between 0 and 1) Linear solver: PBiCG for all variables except P, GAMG for P Turbulence model: k-epsilon Velocity inlet BC : axi-symmetrically averaged velocity measures Turbulence inlet BC: axi-symmetrically averaged k measures 4 turbulence length scales tested (epsilon) Convergence: tolerance of 1.e-6, reltol of 0.01 for all variables Monitoring variable: pressure recovery factor Pstat χ = 1 Q ρ 2 Aref 2 12

Test Cases Mesh investigation # nodes # elements CRS 288744 276560 STD 782283 757968 FINE 1875470 1830884 Scheme GammaV investigation: ψ=0, ψ=0.5 and ψ=1 GammaV is the improved version of the NVD gamma scheme (ψ=0 best accuracy and ψ=1 more robust) Mixing length investigation: Lt=0.25%D th, 0.5%D th, 1.0%D th and 5%D th Initial conditions investigation 13

Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 14

Mesh investigation GammaV 1 Coarse mesh Standard mesh Fine mesh 15

Mesh investigation GammaV 1 Coarse mesh Standard mesh Fine mesh Phi=0.368 Phi=0.380 X=-0.25 16

Mesh investigation GammaV 1 Phi=0.380 203 207 209 213 ct2 ct1 202 205 208 211 214 CFD Experimental Data Steady probe Coarse mesh CFD Experimental Data Steady probe Fine mesh Static Pressure Axial Component Radial Component Tangential Component Energy 17

Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 18

Scheme investigation GammaV Coarse mesh GAMMAV 0.0 GAMMAV 0.5 GAMMAV 1.0 19

Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 20

Mixing length investigation Standard mesh GammaV 1 Lt=0.25%Dth Lt=0.50%Dth Lt=1.00%Dth Lt=5.00%Dth 21

Mixing length investigation Standard mesh GammaV 1 Relative Viscosity Lt=0.50%Dth Relative Viscosity Lt=5.00%Dth X=0.20 X=0.20 X=0.25 X=0.25 X=0.00 X=0.00 X=-0.25 X=-0.25 X=-0.20 X=-0.20 22

Test Cases Mesh investigation Scheme GammaV investigation Mixing length investigation Initial conditions investigation 23

Initial condition investigation Std mesh GammaV 1 Lt=0.25%Dth Initial conditions from no previous calculation Initial conditions from previous calculation 24

Conclusions and Perspectives Conclusions Results are quite good compared to experimental data Results are not so sensitive to mesh resolution except for Phi=0.368 Results are sensitive to scheme Results are sensitive to initialization Perspectives Validation and comparison with OpenFOAM-1.6ext Runner and Draft-Tube calculations Unsteady cases Wall function investigation 25

Thank you for your listening Any questions? 26