Affiliations: Naval Surface Warfare Center Carderock Division, West Bethesda, MD, USA
Note: [] Corresponding author: Michael J. Hughes, Naval Surface Warfare Center, Carderock Div., 9500 MacArthur Blvd., West Bethesda, MD 20817, USA. Tel.: +1 301 227 4306; Fax: +1 301 227 5442; E-mail: Michael.J.Hughes@Navy.mil
Abstract: A rudder force model is being developed at Naval Surface Warfare Center, Carderock Division (NSWCCD) for use with real time ship maneuvering and seakeeping tools. The goal of this work is to obtain reliable results with acceptable computation time. The rudder of a navy ship is typically designed with a portion of rudder area located outside the propeller slipstream and a portion in the slipstream. The inflow velocities entering the rudder plane vary significantly from the rudder tip to the rudder root due to the ship hull boundary layer. Additionally, with flow acceleration induced by the propeller loading, the portion of the rudder in the slipstream will experience much higher inflow velocities than the portion of rudder outside the slipstream. In this effort, the calculations are performed separately for several spanwise rudder segments, where the segments correspond to the portions of the rudder outside the propeller slipstream and in the upper and lower halves of the propeller slipstream. A method to compute effective inflow velocities entering the rudder plane at each segment is presented in this paper. A separate paper will describe how at each segment, the rudder forces are computed from effective inflow velocity, effective lift curve slope, and effective rudder angles encountered by the rudder. A generalized actuator disk model is applied to obtain the slipstream velocity distributions with a realistic propeller loading. An induction method is adopted to obtain the shape of the contracted slipstream. The theory is extended to calculate the tangential velocity in the slipstream. The present theory is validated against a set of velocity measurements that were conducted in The NSWCCD Large Cavitation Channel.
