The 12th International Conference on Hydrodynamics
18 – 23 september 2016, Egmond aan Zee, The Netherlands
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A NEW PERFORMANCE PREDICTION PROCEDURE FOR PROPELLERS WITH UNCONVENTIONAL TIP SHAPE


Go-down ichd2016 Tracking Number 73

Presentation:
Session: Ship hydromechanics resistance III
Room: Room 1
Session start: 15:30 Mon 19 Sep 2016

Mariano Pérez-Sobrino Pérez-Sobrino   mps@sistemar.com
Affifliation: SISTEMAR

Juan Gonzalez-Adalid   adalid@sistemar.com
Affifliation: SISTEMAR

Ramon Quereda   quereda@cehipar.es
Affifliation: CEHIPAR, El Pardo Model Basin

Amadeo Moran-Guerrero   amadeo.moran@gmail.com
Affifliation: CEHINAV, Universidad Politecnica de Madrid, Spain

Giulio Gennaro   sinm@sinm.it
Affifliation: SINM, Genoa, Italy


Topics: - Ship hydrodynamics resistance, propulsion, powering, seakeeping, manoeuvrability, slamming, sloshing, impact, green water

Abstract:

It is a fact that propellers with unconventional tip shape have proved in many cases at full scale that ship propulsion efficiency can be increased with this type of propellers; however at model scale this improvement is not clearly shown and therefore it is neither shown in the standard predictions of many experimental facilities. For conventional propellers ITTC’78 Performance Prediction Method [1] (ITTC’78-PPM) has been successfully applied, directly or with some variations, in many Institutions, Towing Tanks and specialized companies from 1978 when it was recommended to be used by ITTC. But it has been recognized by ITTC [2] that this method cannot be applied to Unconventional Tip Shape propellers. ITTC’78-PPM includes corrections to Open Water model tests results based on the different Reynolds number of the model tests compared to full scale, meaning that viscous effects in propeller blades are also different, and in consequence propeller open water parameters KT and KQ measured at model scale must be corrected to obtain appropriated values to be used for predictions at full scale. Correction method for conventional propellers implemented in ITTC’78-PPM was based in an extensive work made during several years before, analyzing a lot of correlation data for many types of ships for which model tests and sea trials data were available (for instance see [3]). For new types of unconventional propeller blades this is not the case; there are not so many published data to allow sea trials results to be correlated with model tests results. The lack of a standard procedure to be applicable to this type of propellers is many times an obstacle to the possibility to implement energy saving propellers. For that reason a considerable amount of work has been made in recent years on this question. Three main approaches have been published trying to contribute to solve this problem: Semi-empirical Methods, Strip Methods and CFD based and/or Panel Methods. In this paper a new procedure based in the strip method will be derived applying adequate expressions of the friction line more in accordance with the expected type of flow in each section of the propeller blade, depending of the section Reynolds number. Main conclusions will be the confirmation that ITTC’78-PPM is not useful to predict propulsion characteristics of unconventional tip shape propellers and that present method, going a step deeper in the basic principles of viscous effects, predicts with reasonable accuracy propulsion characteristics of conventional and unconventional propellers, monoblock or CPP type and it is easy to implement. REFERENCES [1] 1978 ITTC Performance Prediction Method. ITTC Recommended Procedures and Guidelines 7.5-02-03-01.4. Revised 2011. [2] 27th ITTC-Copenhagen. Volume II, page 616. 2014. [3] 14th ITTC. Report of the Performance Committee. 1975.