Guilherme Vaz Thomas Lloyd, Douwe Rijpkema
Fifth International Symposium on Marine Propulsors smp’17, 2017.
@conference{Lloyd2017,
title = {Computational fluid dynamics prediction of marine propeller cavitation including solution verification},
author = {Thomas Lloyd, Guilherme Vaz, Douwe Rijpkema, Antoine Reverberi},
url = {http://www.marin.nl/web/Publications/Publication-items/Computational-fluid-dynamics-prediction-of-marine-propeller-cavitation-including-solution-verification.htm},
year = {2017},
date = {2017-06-01},
booktitle = {Fifth International Symposium on Marine Propulsors smp’17},
abstract = {This paper analyses the effect of grid refinement on computational fluid dynamics simulations of cavitating propeller flow. Refinement is made both globally, using geometrically similar grids, and locally, by applying adaptive grid refinement. The test case is the E779A propeller operating in uniform inflow conditions in a cavitation tunnel. This allows more computationally efficient steady simulations to be made, permitting a grid uncertainty analysis not previously seen for cavitating flow computations. Unsteady simulations are also presented in order to compare two turbulence modelling approaches. Differences in the discretisation uncertainty in terms of propeller thrust and torque were found to be small between wetted and cavitating flow conditions, although the order of convergence for the cavitating case is lower. Overall the largest effect of grid refinement is found to be in the tip vortex region, where differences in the predicted cavity extents are significant between grids. The use of adaptive grid refinement allows improved capture of tip vortex cavitation with fewer total grid cells, although the cavity extent is limited by increasing eddy viscosity when using RANS. Application of DDES reduces this influence somewhat, motivating further study into the potential of scale-resolving simulations in combination with adaptive grid refinement for vortex cavitation prediction.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
THOMAS LLOYD CARLO NEGRATO, TOM VAN TERWISGA; BENSOW, RICKARD
NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION Conference
VII International Conference on Computational Methods in Marine Engineering, 2017.
@conference{NEGRATO2017,
title = {NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION},
author = {CARLO NEGRATO, THOMAS LLOYD, TOM VAN TERWISGA, GUILHERME VAZ AND RICKARD BENSOW},
url = {http://www.marin.nl/web/Publications/Publication-items/Numerical-Study-Of-Cavitation-On-A-NACA0015-Hydrofoil-Solution-Verification.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {The present paper analyses a series of Computational Fluid Dynamic simulations of the cavitating flow around a two-dimensional NACA0015 foil. The foil is placed at 6◦ angle of attack and the cavitation number is 1.1. Two mesh designs, namely a block-structured topology and an unstructured topology, are compared; additionally, grid refinements and time step refinements are carried out. Solution Verification is addressed with calculation of the discretization error and the numerical uncertainty. The numerical uncertainty for the average lift coefficient is found to be large, up to 15%. The reason is the difficulty of achieving a grid independent solution: with very fine meshes, the flow shifts from an attached, oscillating sheet cavity pattern to a regime dominated by shedding of cavity clouds. On the other hand, neither the time resolution nor the choice of grid topology influence largely the flow pattern; instead, they only lead to differences in the maximum and minimum cavity size.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Crepier, P.
Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids Conference
VII International Conference on Computational Methods in Marine Engineering (MARINE2017), 2017.
@conference{Crepier2017,
title = {Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids},
author = {Crepier, P.},
url = {http://www.marin.nl/web/Publications/Publication-items/Ship-Resistance-Prediction-Verification-And-Validation-Exercise-On-Unstructured-Grids.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering (MARINE2017)},
abstract = {The prediction of the resistance of a ship is, together with the propeller performance prediction, part of the key aspects during the design process of a ship, as it partly ensures the quality of the power-prediction. Body fitted structured grids for ship simulations can be rather challenging and time consuming to build, especially when dealing with appended ship geometries. For this reason, unstructured hexahedral trimmed grids are more and more used. Such grids can be build by various CFD package such as CD-Adapcos Star CCM+, NUMECAs Hexpress grid generator or OpenFOAMSs SnappyHexMesh. Although their use is increasing or even already adopted, the numerical uncertainty of these simulations seems to be a well-kept secret.
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.
2017
Guilherme Vaz Thomas Lloyd, Douwe Rijpkema
Fifth International Symposium on Marine Propulsors smp’17, 2017.
Abstract | Links | BibTeX | Tags: adaptive grid refinement, cavitation, DDES, RANS, verification
@conference{Lloyd2017,
title = {Computational fluid dynamics prediction of marine propeller cavitation including solution verification},
author = {Thomas Lloyd, Guilherme Vaz, Douwe Rijpkema, Antoine Reverberi},
url = {http://www.marin.nl/web/Publications/Publication-items/Computational-fluid-dynamics-prediction-of-marine-propeller-cavitation-including-solution-verification.htm},
year = {2017},
date = {2017-06-01},
booktitle = {Fifth International Symposium on Marine Propulsors smp’17},
abstract = {This paper analyses the effect of grid refinement on computational fluid dynamics simulations of cavitating propeller flow. Refinement is made both globally, using geometrically similar grids, and locally, by applying adaptive grid refinement. The test case is the E779A propeller operating in uniform inflow conditions in a cavitation tunnel. This allows more computationally efficient steady simulations to be made, permitting a grid uncertainty analysis not previously seen for cavitating flow computations. Unsteady simulations are also presented in order to compare two turbulence modelling approaches. Differences in the discretisation uncertainty in terms of propeller thrust and torque were found to be small between wetted and cavitating flow conditions, although the order of convergence for the cavitating case is lower. Overall the largest effect of grid refinement is found to be in the tip vortex region, where differences in the predicted cavity extents are significant between grids. The use of adaptive grid refinement allows improved capture of tip vortex cavitation with fewer total grid cells, although the cavity extent is limited by increasing eddy viscosity when using RANS. Application of DDES reduces this influence somewhat, motivating further study into the potential of scale-resolving simulations in combination with adaptive grid refinement for vortex cavitation prediction.},
keywords = {adaptive grid refinement, cavitation, DDES, RANS, verification},
pubstate = {published},
tppubtype = {conference}
}
THOMAS LLOYD CARLO NEGRATO, TOM VAN TERWISGA; BENSOW, RICKARD
NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION Conference
VII International Conference on Computational Methods in Marine Engineering, 2017.
Abstract | Links | BibTeX | Tags: cavitation, Discretization Error, NACA0015 foil, RANS, verification
@conference{NEGRATO2017,
title = {NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION},
author = {CARLO NEGRATO, THOMAS LLOYD, TOM VAN TERWISGA, GUILHERME VAZ AND RICKARD BENSOW},
url = {http://www.marin.nl/web/Publications/Publication-items/Numerical-Study-Of-Cavitation-On-A-NACA0015-Hydrofoil-Solution-Verification.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {The present paper analyses a series of Computational Fluid Dynamic simulations of the cavitating flow around a two-dimensional NACA0015 foil. The foil is placed at 6◦ angle of attack and the cavitation number is 1.1. Two mesh designs, namely a block-structured topology and an unstructured topology, are compared; additionally, grid refinements and time step refinements are carried out. Solution Verification is addressed with calculation of the discretization error and the numerical uncertainty. The numerical uncertainty for the average lift coefficient is found to be large, up to 15%. The reason is the difficulty of achieving a grid independent solution: with very fine meshes, the flow shifts from an attached, oscillating sheet cavity pattern to a regime dominated by shedding of cavity clouds. On the other hand, neither the time resolution nor the choice of grid topology influence largely the flow pattern; instead, they only lead to differences in the maximum and minimum cavity size.},
keywords = {cavitation, Discretization Error, NACA0015 foil, RANS, verification},
pubstate = {published},
tppubtype = {conference}
}
Crepier, P.
Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids Conference
VII International Conference on Computational Methods in Marine Engineering (MARINE2017), 2017.
Abstract | Links | BibTeX | Tags: CFD, Double-body, KVLCC2, Unstructured grid, Validation, verification
@conference{Crepier2017,
title = {Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids},
author = {Crepier, P.},
url = {http://www.marin.nl/web/Publications/Publication-items/Ship-Resistance-Prediction-Verification-And-Validation-Exercise-On-Unstructured-Grids.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering (MARINE2017)},
abstract = {The prediction of the resistance of a ship is, together with the propeller performance prediction, part of the key aspects during the design process of a ship, as it partly ensures the quality of the power-prediction. Body fitted structured grids for ship simulations can be rather challenging and time consuming to build, especially when dealing with appended ship geometries. For this reason, unstructured hexahedral trimmed grids are more and more used. Such grids can be build by various CFD package such as CD-Adapcos Star CCM+, NUMECAs Hexpress grid generator or OpenFOAMSs SnappyHexMesh. Although their use is increasing or even already adopted, the numerical uncertainty of these simulations seems to be a well-kept secret.
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.},
keywords = {CFD, Double-body, KVLCC2, Unstructured grid, Validation, verification},
pubstate = {published},
tppubtype = {conference}
}
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.