|
4.2 During oblique motion
Flow field calculations were performed for a vessel with rudder (but no propeller) during oblique motion. The example shown in Figure 9 is the wake distribution at the AP section with an oblique motion angle of 10° and a right rudder of 10°. The standing eddies around the main ship hull, generated by oblique motion, affect flow patterns around the rudder behind the ship, as demonstrated by Matsumoto et al [2]. CFD simulations of the complex flow fields at the stern during maneuvering motions can provide valuable information, such as the effects of hull design details and the turning motion of the hull on rudder inflow angle and velocity. The authors intend to continue pursuing research related to rudder force.
Fig.9 |
Computed wake distribution at A.P. section ( β=10deg., δ=10deg., without propeller) |
Next, we used the CFD calculation results for rudder normal force during oblique motion in order to find the rudder angle δR required to make the rudder normal force zero and to investigate the effective rudder inflow characteristics.
Figures 10 and 11 plot the effective rudder inflow angle and velocity results derived from CFD rudder normal force calculations at oblique motion angles of 0°,±10°, ±15°, and ±20°, and rudder angles of 0°,±5°,and ±10°.
Fig.10 |
Effective rudder inflow velocity in oblique motion(Calculated) |
Fig.11 Effective rudder inflow angle in oblique motion
Table.3 |
Comparison of flow-straightening effect coefficient between present calculation and experiment (without propeller) |
| Items |
γ |
| Calculated |
0.393 |
| Exp.(HIROSHIMA UNIV.) |
0.373 |
|
Figure 11 shows both the calculated effective rudder inflow angle characteristics and experimental observations [2].
Similarly, Table 3 compares the calculated values for the coefficient of rectification (which represents the degree of list in Figure 11) with observations from the model trial. Figure 11 and Table 3 demonstrate the consistency of CFD values with the effective rudder inflow characteristics obtained from the scale model tests.
Fig.12 shows the comparison of calculated wake distribution at A.P. section in oblique motion. The wake distribution around the rudder is changed according to oblique motion, and the flow field around rudder bottom particularly changes from β =15.0deg. Such a change of flow field around rudder is correspond to the non-1inear characteristics of effective rudder inflow angle in oblique motion.
We can conclude that CFD simulations represent an effective tool for assessing the effects of interactions between the ship hull and the rudder on the course stability of the ship.
|
