On the working principle of pre-swirl stators and on their application benefit and design targets

BACKGROUND: In an early design stage of ship and propeller or in a propeller retrofit case one may consider a pre-swirl stator (PSS) to recover rotational energy. OBJECTIVES: A model for the working principle of a PSS was to be developed and then to be applied for power saving estimates. This model should also support the PSS design procedure. METHODS: The PSS 'working principle model' is based on a very fundamental quantity related to a propellers characteristic, namely the circulation distribution. An extended model addresses hub vortex contraction losses. In specific cases a BEM (Boundary Element Method) based propeller analysis is performed. To confirm actual PSS designs, a RANS/BEM coupling method is invoked. RESULTS: Global parameters as KT and CTH rule the rotational losses of a propeller and determine the energy recovery potential of a PSS accordingly. The potential of a PSS is considerably enlarged, if it works properly against the hub vortex. Estimates for realistic power savings due to a PSS installation are 4-5% when the hub vortex suppression is included. CONCLUSIONS: The simple PSS 'working principle model' delivers very reasonable predictions. RANS results and available full scale trial measurements can be reproduced using this approach. © 2016/2017 - IOS Press and the authors. All rights reserved.