Abstract
This study presents the decays of three components of velocity for a ship twin-propeller jet associated with turbulence intensities using the Acoustic Doppler Velocimetry (ADV) measurement and computational fluid dynamics (CFD) methods. Previous research has shown that a single-propeller jet consists of a zone of flow establishment and a zone of established flow. Twin-propeller jets are more complex than single-propeller jets, and can be divided into zones with four peaks, two peaks, and one peak. The axial velocity distribution is the main contributor and can be predicted using the Gaussian normal distribution. The axial velocity decay is described by linear equations using the maximum axial velocity in the efflux plane. The tangential and radial velocity decays show linear and nonlinear distributions in different zones. The turbulence intensity increases locally in the critical position of the noninterference zone and the interference zone. The current research converts the axial momentum theory of a single propeller into twin-propeller jet theory with a series of equations used to predict the overall twin-propeller jet structure.
Highlights
A propeller ejects water backward from the ship in a rotating motion to provide the reacting forces to drive the ship forward
Guo et al [5] investigated the hydrodynamic characteristics of a marine propeller operating in oblique inflow using the computational fluid dynamics (CFD) method
The axial velocity decay of a twin-propeller jet is expressed in Equation (9)
Summary
A propeller ejects water backward from the ship in a rotating motion to provide the reacting forces to drive the ship forward. The initial plain water jet was studied by Albertson et al using the axial momentum theory [1]. This was converted as the theoretical basis for the propeller jet. Hamill [2] measured the internal flow of a single-propeller jet according to the physical model. The two jets developed independently near the propeller, but the two flow fields were mixed as a result of the jet diffusion. The velocity on the seabed induced by a twin-propeller ship without a rudder was investigated and compared with previous theoretical expressions by Mujal-Colilles et al [13]. The prediction equations for ship propeller jet velocity proposed in previous studies and the current study are shown in Appendix A
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