(using open-source cfd) surya kiran. peravali, …hani/ofgbg15/peravali_slides.pdfpropeller scaling...
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Propeller scaling effects in the wake of ship hulls(Using Open-Source CFD)
Surya Kiran. Peravali,[email protected]
Chalmers University of Technology, Gothenburg, Sweden
GOTHENBURG REGION OpenFOAM USER GROUP MEETING
November 20, 2015
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 1 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 2 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 3 / 45
ITTC 78 Method and Scaling of Wake
This method is served as a common tool for evaluation ofconventional propellers.
At SSPA self-proplusion model tests are evaluated and scaled to fullscale using this method.
The full scale wake (wTs) is calculated from the model wake (wTm)and the thrust deduction fraction (t) according to:
wTs = (t + 0.04) + (wTm − t − 0.04)(1 + k)CFs + ∆CF
(1 + k)CFm(1)
This was developed in the 70’s for the conventional propellers.
In the last years, this wake scaling formula has been questioned, sinceit sometimes act differently on some unconventional propellerscompared to normal propellers. However it works well for theconventional propeller designs.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 4 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 5 / 45
Objective
The ultimate goal of the project is to investigate the scaling of effectivewake for unconventional propeller using open-source CFD.
Two different propellers (one conventional and one Unconventional)tested at SSPA are being analysed with OpenFOAM CFD in full scaleand model scale in working condition behind same hull.
How the scale effect the flow details and How that is reflected in theITTC wake scaling formula are studied in detail.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 6 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 7 / 45
The Unconventional Propeller
Designed for improving energy efficiency.
Non-planar lifting surface.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 8 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 9 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 10 / 45
Open-Source MeshingBlockMesh and SnappyHexMesh
The mesh is created using BlockMesh and the snappyHexMeshutilities.
checkMesh utility to check the mesh.
Parallel execution
Easy tool to generate mesh, but still lacks some important features.(mainly regarding layer addition)
Time consuming
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 11 / 45
Open-source meshing
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 12 / 45
Open-source meshing
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 13 / 45
Open-Source MeshingOne of the test case
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 14 / 45
Open-Source MeshingArbitrary Mesh Interface - AMI
AMI is a technique that allows simulation across disconnected, butadjacent, mesh domains.
Available for un-matched/non-conformal cyclic patch pairs, slidinginterfaces, mapped patches.
The AMI patches must be conformal to one another. For patches inwhich have low weights, a zero-gradient condition can be applied topatch faces whose weights are below a user-specified threshold usinglowWeightCorrection keyword in the boundary file.
Bugs prevail in this utility for older version (older than 2014)
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 15 / 45
Open-Source MeshingMoving Reference Frame technique
In the MRF approach, the steady state solver simpleFoam computes theflow using the rotating and stationary reference frames. Here theNavier-Stokes equations are modified such that the flux is calculated bythe relative velocity (uR) and an additional source term (corolis force,Ω× uI ) is included in the equations.Rotating zone
5.(uRuI ) + Ω× uI = −5 p +5.(νeff (5uI + (uI )T )) (2)
5.uR = 0
Stationary zone
5.(uIuI ) = −5 p +5.(νeff (5uI + (uI )T )) (3)
5.uI = 0
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 16 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 17 / 45
CFD Model and discretization
k − ω SST along with wall functions.
Implemented through simpleFoam for steady state andpimpleDyMFoam for unsteady simulations.
Time schemes- Euler or backward.
Gradient schemes: Guass
Convection scheme:Gamma,linear upwind, upwind and linear schemes.Guass linear limited for diffusion scheme.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 18 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 19 / 45
Test cases and Mesh studies
Case Scale No. of cells range No. of mesh cases
Bare Hull model 6-16 M 4
Open-water conv. model 2-6 M 3
Open-water unconv. model 2.4-6.2 M 2
Self-propulsion conv. model 12-18 M 3
Self-propulsion unconv. model 12-18 M 2
Bare Hull full scale 67 M 1
Open-water conv. full scale 10-20 M 3
Open-water unconv. full scale 20 M 2
Self-propulsion conv. full scale 70 M 1
Self-propulsion unconv. full scale 73 M 1
total 22
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 20 / 45
ResistanceModel scale
Figure: Ux contour
* OpenFOAM (snappy) Fluent (ICEM) Experiment
Resistance coeff. 0.042165 0.042246 0.044343
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 21 / 45
Wake PlotExperiment
Figure: Normalized values of total wake fraction at propeller disk
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 22 / 45
Wake PlotSimulated
Figure: Normalized values of total wake fraction at propeller disk
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 23 / 45
Openwater TestConventional Propeller
Figure: Iso surface Q plot coloured by Ux magnitude
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 24 / 45
Openwater TestConventional Propeller
Figure: Normalized KT, KQ and ETA vs J
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 25 / 45
Openwater TestUnconventional Propeller
Figure: Iso surface Q plot coloured by Ux magnitude
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 26 / 45
Openwater TestUnconventional Propeller
Figure: Normalized KT, KQ and ETA vs J
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 27 / 45
Unconventional PropellerOther observations
Figure: Iso surface Q
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 28 / 45
Self-propulsionModel scale
Figure: Iso surface Q colored by Ux magnitude
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 29 / 45
Self-PropulsionModel scale
Figure: Difference in propulsive coefficients of unconventional propeller withconventional propeller at test condition.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 30 / 45
Full-scale Openwater
Figure: full scale open-water curves Ittc 78
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 31 / 45
Full-scale Openwater
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 32 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 33 / 45
Full scale OW simulation
Full scale propeller (1:37).
18-20 million cells.
y+ ≈ 90.
Moving reference frame technique
Propulsive coeffcients over predicted when compared with ITTC 78predictions.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 34 / 45
Full scale OW simulation
Figure: Iso surface Q plot coloured by Ux magnitude (conventioanl propeller)
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 35 / 45
Full scale OW simulation
Figure: Iso surface Q plot coloured by Ux magnitude (Unconventional propeller)
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 36 / 45
Full scale OW simulation
Figure: Reynold’s scaling corrections of difference methods of presentunconventional propeller at JTsRANS
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 37 / 45
Outline
1 BackgroundITTC Wake Scaling MethodObjectiveUnconventional propeller concept
2 MethodsOpenFOAM-2.3.0Open-Source MeshingCFD ModelsTest Cases and model scale simulations
3 Results
4 Full scale predictionsFull scale open waterFull scale Self propulsion
5 Summary
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 38 / 45
Full scale Self-propulsion simulation
Figure: Iso surface Q coloured by Ux magnitude
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 39 / 45
Two cases: conventional and unconventional behind same hull
70-73 million cells.
y+ ≈ 150
Sliding mesh. (AMI)
Unsteady simulation with rotating mesh
Same ship speed and propeller rps as full scale design condition
Under propelled. Just comparison between two propellers is studied atthe same design conditions, not at the self-propulsion point.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 40 / 45
Full scale self-propulsion simulation
Figure: Difference in propulsive coefficients of present unconventional propellerwith conventional propeller at the full scale design condition.
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 41 / 45
Other studies
Figure: Axial velocity distribution at x/D =0.18 Full scale
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 42 / 45
Other studies
Figure: Axial velocity distribution at x/D =0.18 model scale
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 43 / 45
Summary
The open-source CFD has an acceptable accuracy in prediction theresistance and different propulsive coefficients. It also showed a goodagreement with commercial CFD tool like Fluent.
In OpenFOAM 2.3.0 bugs prevail in implementing thelowWeightCorrection specifically with the k − ω SST model
There is much scope for developing efficient and high quality mesheswith the open-source tools.
MRF method gave best results similar to AMI for a open-water casesbut for self-propulsion cases AMI is much preferred
Switching between MRF to AMI yield several problems unlike GGI.mapFields utlity can be implemented.
The kkl − ω model stil have to be tested for capturinglaminar-turbulent transition in the flow
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 44 / 45
Other contributions
Function ”RoundSTL”, To round off sharp edges in .stl geometry file.(By Riku Kotiranta,SSPA)
Creating RPM package for compiling OpenFOAM 2.4.x in centOS 6.5(By Henrik Holm, SSPA)
”RefineBL”, utility to refine and project boundary layer mesh to stlsurface ( based on a tutorial by christofer jarpner 2011)
Surya Kiran. Peravali, [email protected] (Chalmers University of Technology)Propeller scaling effects in the wake of ship hulls November 20, 2015 45 / 45