Tripping
scale corrections for propellers using boundary layer tripping
Running
The aim of this JIP is to develop new propeller scale corrections to be able to predict full scale open water performance and propulsive performance more accurately.
Background
Full scale performance of propellers is still an area of large uncertainty during the propeller design phase, during the extrapolation of model tests for powering predictions and during full scale monitoring. On full scale, propellers usually operate with turbulent flow. On model scale, however, laminar flow, flow transition and more pronounced flow separation are encountered. Model tests and powering predictions suffer from these effects.
Within the Tripping JIP new open-water model tests are performed using turbulators such that the boundary layer is tripped towards a turbulent flow. Turbulators on the leading edge of the model scale propellers are very efficient in tripping the boundary layer. The turbulent flow on the propellers at model scale reduces the scale effect uncertainties.
When making predictions for full scale performance, new scale corrections need to be applied, thereby replacing widely used ITTC-78 corrections. Investigations show that the traditional ITTC corrections often do not even reflect the real model scale effects such that the predicted full-scale performance would also not reflect reality. Using tripping and the corresponding new scale corrections, the uncertainty of the final prediction and the standard deviation to full scale trials would greatly improve.
The Reynolds scale effects for a fully turbulent flow can be computed with CFD. The participants within the Tripping JIP are confident that using RANS computations reliable scale corrections can be obtained for tripped propellers. Using tripping, transition modelling and tuning in RANS is not required anymore. Fully turbulent RANS computations are used, which are mature, reliable and robust.
Also, literature emphasizes that with the tight design margins of modern propulsion units, it is often no longer possible to make designs which can perform well in both model scale experiments and actual full-scale operation. They say that it should be clear that the design focus should be on the full-scale operation and that model tests should more accurately reflect the real full scale situation. It is believed that tripping is the methodology to do so.
Further information on the background of the Tripping JIP can be found in the project plan (Contract and project proposal, version 2.1). This is supported by two recent papers, which are available for download below as well.
Within the Tripping JIP new open-water model tests are performed using turbulators such that the boundary layer is tripped towards a turbulent flow. Turbulators on the leading edge of the model scale propellers are very efficient in tripping the boundary layer. The turbulent flow on the propellers at model scale reduces the scale effect uncertainties.
When making predictions for full scale performance, new scale corrections need to be applied, thereby replacing widely used ITTC-78 corrections. Investigations show that the traditional ITTC corrections often do not even reflect the real model scale effects such that the predicted full-scale performance would also not reflect reality. Using tripping and the corresponding new scale corrections, the uncertainty of the final prediction and the standard deviation to full scale trials would greatly improve.
The Reynolds scale effects for a fully turbulent flow can be computed with CFD. The participants within the Tripping JIP are confident that using RANS computations reliable scale corrections can be obtained for tripped propellers. Using tripping, transition modelling and tuning in RANS is not required anymore. Fully turbulent RANS computations are used, which are mature, reliable and robust.
Also, literature emphasizes that with the tight design margins of modern propulsion units, it is often no longer possible to make designs which can perform well in both model scale experiments and actual full-scale operation. They say that it should be clear that the design focus should be on the full-scale operation and that model tests should more accurately reflect the real full scale situation. It is believed that tripping is the methodology to do so.
Further information on the background of the Tripping JIP can be found in the project plan (Contract and project proposal, version 2.1). This is supported by two recent papers, which are available for download below as well.
Contact
John Huisman
Senior Project Manager
OBJECTIVE
The Tripping JIP aims at reliable full-scale performance predictions for both open-water and propulsive performance. The objective of this JIP is to develop new propeller scale-corrections to more accurately predict full scale open water and propulsive performance.
MOTIVATION
Overall, it is envisaged that this JIP will made a significant step towards a new and widely accepted extrapolation method for propulsion tests, which makes the differences between model institutes less prominent. A broad support on this would also serve as incentive for the ITTC to adapt their guidelines in due course.
SCOPE
The scope of the Tripping JIP project is defined in four work packages:
WP 1
Open water model tests with turbulators – The F-series, FC-series, C-series and B-series are revisited amongst other (public) propellers. About 65 model tests with tripping at 4 different Reynolds numbers will be done.
WP 2
a. Open water RANS computations – The open water performance will be investigated over a large range of Reynolds numbers, up to full scale, also with varying surface roughness. The 65 propellers will be extensively computed.
b. A RANS workshop is being performed by the participants to set the CFD approach.
WP 3
a. Reference tests at other model institutes are performed, to investigate tripping both in open water and in behind conditions.
b. A proposal for a generic scale correction method - Based on the model tests and RANS computations scale corrections and RANS correlation factors are determined. These are to be used with tripped propellers to replace the currently used scale corrections. The corrections will be at least a function of blade number, pitch, blade area ratio, J- value, Reynolds number (both at model scale and full scale) and full scale surface roughness.
WP 4
Development of full scale polynomials for the C-series in design pitch and the 4 to 6 bladed F-series – Combining the open water model tests, the RANS-computations and the generic scale correction methods full scale polynomials can be created. A software package will be provided to use the polynomials.
The C-series (design pitch) will be openly used within the Tripping JIP, while the geometry and dimensionfull results of the F and FC-series will be restricted to the participants of the respective prior JIPs.
FURTHER OPPORTUNITIES
The Tripping JIP provides opportunities for additional work, if the budget increases from the participation of new participants.
A choice for additional work will always be made in mutual agreement by the Participant Steering Group during a JIP meeting. Note that contingency and the double MARIN contribution will be reconsidered first upon the participation of new participants.
PARTICIPANTS AS OF YET
PARTICIPATION FEE
The cost of participation in the JIP is €15k per year for 3 years.
For governmental supported model basin institutes, in-kind contributions are supported.
New participants are welcome to join! Please contact John Huisman (j.huisman@marin.nl).
PLANNING
The project will be carried out by MARIN. Participants are expected to actively contribute to the project meetings.
Two meetings will be arranged each year.
The project is defined as a 3-year project, although it is intended to execute the basic scope of the project earlier.
Due to potential additional work upon the participation of additional participants, the project would probably exceed the timeline of 3 years.
Past meetings
On 30 November 2023 at the VOF in Busan, South Korea, the first version of the proposal was pitched.
The VOF is the Vessel Operator Forum under which the Tripping JIP is hosted: https://www.vesseloperatorforum.com/.
The first work group meeting was organized during The Blue Forum, April 2024 in Venezia, Italy, with 11 participants.
The second work group meeting was held online in May 2024, with 16 participants, including 5 model test institutes.
Next meeting
The next work group meetings on 21 and 22 November 2024, will be organized at MARIN, Wageningen. These days include the meetings for the RANS workshop, about how to create and apply turbulators, as well as a visit to the facilities while model tests with tripping are being conducted.
For more information, please download the Tripping JIP agreement below. This includes the complete project plan.
Follow the Tripping JIP on Tripping JIP on LinkedIn.
The Tripping JIP aims at reliable full-scale performance predictions for both open-water and propulsive performance. The objective of this JIP is to develop new propeller scale-corrections to more accurately predict full scale open water and propulsive performance.
MOTIVATION
- For propeller designers and manufacturers: less surprises during model tests or full scale trials and better control of the propeller design on both model scale and full scale. Rather than optimization for model scale, propellers will be optimized for full scale.
- For yards, ship owners and operators: more reliable full scale predictions and improved propeller designs.
- For R&D: benchmark data for RANS computations on propellers for reference and quality checks.
- For other research institutes, class societies and participants with their own model test facilities: improvement of the extrapolation methodology and more reliable predictions.
Overall, it is envisaged that this JIP will made a significant step towards a new and widely accepted extrapolation method for propulsion tests, which makes the differences between model institutes less prominent. A broad support on this would also serve as incentive for the ITTC to adapt their guidelines in due course.
SCOPE
The scope of the Tripping JIP project is defined in four work packages:
WP 1
Open water model tests with turbulators – The F-series, FC-series, C-series and B-series are revisited amongst other (public) propellers. About 65 model tests with tripping at 4 different Reynolds numbers will be done.
WP 2
a. Open water RANS computations – The open water performance will be investigated over a large range of Reynolds numbers, up to full scale, also with varying surface roughness. The 65 propellers will be extensively computed.
b. A RANS workshop is being performed by the participants to set the CFD approach.
WP 3
a. Reference tests at other model institutes are performed, to investigate tripping both in open water and in behind conditions.
b. A proposal for a generic scale correction method - Based on the model tests and RANS computations scale corrections and RANS correlation factors are determined. These are to be used with tripped propellers to replace the currently used scale corrections. The corrections will be at least a function of blade number, pitch, blade area ratio, J- value, Reynolds number (both at model scale and full scale) and full scale surface roughness.
WP 4
Development of full scale polynomials for the C-series in design pitch and the 4 to 6 bladed F-series – Combining the open water model tests, the RANS-computations and the generic scale correction methods full scale polynomials can be created. A software package will be provided to use the polynomials.
The C-series (design pitch) will be openly used within the Tripping JIP, while the geometry and dimensionfull results of the F and FC-series will be restricted to the participants of the respective prior JIPs.
FURTHER OPPORTUNITIES
The Tripping JIP provides opportunities for additional work, if the budget increases from the participation of new participants.
- Consideration of additional propellers for the F-series, FC-series, C-series or the B-series. For instance, the three and seven bladed F-series may be considered, or the five bladed C-series.
- Model tests and computations for off-design pitch settings for the C-series.
- Consideration of ducted propellers from the Ka-series and D-series. From CFD comparisons, ducted propellers are known to face additional scale effects compared to open propellers. Consideration of the D-series would highly add value to the Tripping JIP. In the absence of any experience concerning this, basic investigations to get the tripping on the duct correct should be included.
- Additional paint tests of specific propellers to visualize the flow phenomena as function of J-value and Reynolds number, on either or both clean blades and blades with turbulators.
- Investigation on the effect of the thickness over chord ratio on scale effects. Ice-class propellers in particular seem to face strong scale effects.
A choice for additional work will always be made in mutual agreement by the Participant Steering Group during a JIP meeting. Note that contingency and the double MARIN contribution will be reconsidered first upon the participation of new participants.
PARTICIPANTS AS OF YET
- MARIN
- Kongsberg
- ABB
- Brunvoll Maritime Group
- Damen Shipyards
- COMMIT (Command Materiel and IT, Ministry of Defence)
- MAN Energy Solutions
- Kawasaki Heavy Industries, Ltd.
- Samsung Heavy Industries Co., Ltd.
- Steerprop Ltd.
- Wartsila
- MARIC
- INTA CEHIPAR
- SINTEF Ocean
- SVA Potsdam
- RISE SSPA
- Qinetiq
- HSVA
PARTICIPATION FEE
The cost of participation in the JIP is €15k per year for 3 years.
For governmental supported model basin institutes, in-kind contributions are supported.
New participants are welcome to join! Please contact John Huisman (j.huisman@marin.nl).
PLANNING
The project will be carried out by MARIN. Participants are expected to actively contribute to the project meetings.
Two meetings will be arranged each year.
The project is defined as a 3-year project, although it is intended to execute the basic scope of the project earlier.
Due to potential additional work upon the participation of additional participants, the project would probably exceed the timeline of 3 years.
Past meetings
On 30 November 2023 at the VOF in Busan, South Korea, the first version of the proposal was pitched.
The VOF is the Vessel Operator Forum under which the Tripping JIP is hosted: https://www.vesseloperatorforum.com/.
The first work group meeting was organized during The Blue Forum, April 2024 in Venezia, Italy, with 11 participants.
The second work group meeting was held online in May 2024, with 16 participants, including 5 model test institutes.
Next meeting
The next work group meetings on 21 and 22 November 2024, will be organized at MARIN, Wageningen. These days include the meetings for the RANS workshop, about how to create and apply turbulators, as well as a visit to the facilities while model tests with tripping are being conducted.
For more information, please download the Tripping JIP agreement below. This includes the complete project plan.
Follow the Tripping JIP on Tripping JIP on LinkedIn.
