FD生成的PMM数据在初步设计阶段进行评估英文文献和中文翻译(11)
Therefore, the final mesh used for the production runs contains app. 3.57 million cells, which is a little finer than the initial medium mesh. It was designed to give a Y+ of maximum 75.5 and an average over the hull of 23.5. After the verification and validation work, all the production runs for the static maneuvers to be used in the simulator model were made. The figures below show comparisons between CFD and EFD for all the computed cases, which cover static drift, static rudder and the combined static drift and rudder conditions. As mentioned earlier only static CFD data will be used as input for the simulator, as the dynamic computations are not finalized at the present time of writing. Figure 8 to Figure 10 show the computed and measured non-dimensionalized forces and moments, X´, Y´and N´ as function of the rudder angle for three different speeds. For X´ it is seen to be close to 0 and negative for the highest speed, whereas it increases to larger positive values as the speed is reduced. This means that the propeller is over-thrusting at the lower speeds. However, based on the applied constant RPM approach, where the propeller RPMs are kept constant at service speed self-propulsion point, the propeller will deliver too much thrust at the lower speeds giving the observed behavior. It is seen that the CFD computations generally predicts X´ fairly well. The slightly larger deviations at large negative rudder angles are probably related to the simplified propeller model not being able to capture the rudder propeller interaction. ‐0.020‐0.0100.0000.0100.0200.0300.0400.0500.060‐40 ‐20 0 20 40X´Rudder angle [deg]CFD, Fr=0.260EFD, Fr=0.260CFD, Fr=0.201EFD, Fr=0.201CFD, Fr=0.156EFD, Fr=0.156Figure 8. Computed and measured non-dim X force for “static rudder”. ‐0.080‐0.060‐0.040‐0.0200.0000.0200.0400.0600.080‐40 ‐20 0 20 40Y´Rudder angle [deg]CFD, Fr=0.260EFD, Fr=0.260CFD, Fr=0.201EFD, Fr=0.201CFD, Fr=0.156EFD, Fr=0.156Figure 9. Computed and measured non-dim Y force for “static rudder”. For Y´ good agreement between EFD and CFD is also observed. Increased rudder angle leads to increased Y-force which makes sense since the rudder lifts more at higher rudder angles. It is seen that the slope of the curves increases as the speed is reduced and the weak non-linearity occurs at the larger rudder angles. N´ also shows increased slope of the curves as the speed is reduced and the weak non-linearity at the larger rudder angles. This behavior is expected as the yaw moment for the static rudder case to a large degree is caused by the rudder lift force. Again good agreement between EFD and CFD is observed. Figure 11 to Figure 13 show the computed and measured non-dimensionalized forces and moments, X´, Y´and N´ as function of the drift angle for three different speeds. Again X´ shows the effect of the constant RPM approach discussed above. Further, it can be noticed that the largest deviations occur at the lowest speed, which presumably is caused by the body-force propeller not being able to model the propeller flow in the case where the propeller loading is increasing. However, in spite of the difference, the CFD code generally predicts the force fairly well compared to the measurement, plus it is able to capture variation in X´ with the drift angle. Figure 12 and Figure 13 show Y´ and N´ for the three speeds. Compared to the static rudder case it is here seen that the non-dimensionalization basically collapses the force and moment curves into one curve, which is often seen for the static drift force and moment. It is also seen that as the drift angle is increased the Y-force becomes non-linear. The yaw moment also shows non-linearity, but not as pronounced as the Y-force. Further, it seems that the non-linearity in N´ is more pronounced for lower speeds. Concerning the comparison between model test and CFD results, it appears the computation agrees well with the measurement. The final set of results to be shown covers the static drift and rudder results. Figure 14 to Figure 16 show the forces and moments as function of the rudder angle for the two negative drift angles β=-4° and β=-12°, while Figure 17 to Figure 19 show the forces and moments as function of the rudder angle for two corresponding positive drift angles β=4° and β=12°.