Abstract
A new design approach using the concept of a twisted rudder to improve rudder performances has been proposed in the current paper. A correction step was introduced to obtain the accurate inflow angles induced by the propeller. Three twisted rudders were designed with different twist angle distributions and were tested both numerically and experimentally to estimate their hydrodynamic characteristics at a relatively high ship speed. The improvement in the twisted rudders compared to a reference flat rudder was assessed in terms of total cavitation amount, drag and lift forces, and moment for each twin rudder. The total amount of surface cavitation on the final optimized twin twisted rudder at a reference design rudder angle decreased by 43% and 34.4% in the experiment and numerical prediction, respectively. The total drag force slightly increased at zero rudder angle than that for the twin flat rudder but decreased at rudder angles higher than 4° and 6° in the experiment and numerical simulation, respectively. In the experimental measurements, the final designed twin twisted rudder gained a 5.5% increase in the total lift force and a 37% decrease in the maximum rudder moment. Regarding these two performances, the numerical results corresponded to an increase of 3% and a decrease of 66.5%, respectively. In final, the present numerical and experimental results of the estimation of the twisted rudder performances showed a good agreement with each other.
Highlights
Rudders operate in the complex interactive flow between hull, propeller, and rudder, which determines the maneuverability, self-propulsion, and cavitation performances of ships along with hull forms and propellers
The measured and calculated pressure distributions for wetted flow along the twochord lines of the port side (PRT) flat rudder are shown in Figure 4 at the rudder angle of δR = 0◦ and a ship speed of 18 knots
It is seen that the pressures on the inboard and outboard surfaces differ more significantly at the span location of z/s = 0.6 as seen in Figure 4b, which means the inflow angle varies at each spanwise location at a given rudder angle condition
Summary
Rudders operate in the complex interactive flow between hull, propeller, and rudder, which determines the maneuverability, self-propulsion, and cavitation performances of ships along with hull forms and propellers. Kim et al [35] designed three twisted rudders for a large container carrier and verified the speed performances of the ship improved by those twisted rudders through model tests in a towing They analyzed the change in self-propulsion factors by the twisted rudders. Ahn et al [36] developed a twisted rudder to overcome the cavitation problems of large container carriers in the way of the leading edge considering manufacturing productivity They called this rudder the X-Twisted rudder and verified its hydrodynamic performances through various model tests such as resistance, self-propulsion, cavitation, and maneuvering tests. Three twisted rudders with three different twist angle distributions were designed using the results of the CFD simulations and tested both numerically and experimentally to estimate their hydrodynamic performances at a relatively high ship speed. The improvement of the twisted rudders compared with the reference flat rudder is discussed in terms of total cavitation amount, drag, lift, and moment for each twin rudder
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