探討計算流體力學中船舶興波阻力的尺度效應

INVESTIGATION OF SCALE EFFECT ON NUMERICAL SHIP WAVE-MAKING RESISTANCE

國際船模試驗水槽會議（ITTC）建議之估算實船總阻力方法建基於興波阻力僅為福勞德數的函數，亦即無尺度效應。本研究使用公開貨櫃船型進行相同福勞德數但相異雷諾數的數值模擬，以釐清尺度效應對興波阻力的影響。數值模擬軟體為商用軟體Star-CCM+，求解不可壓縮黏性流非穩態雷諾平均方程（RANS），並使用體積分量法捕捉自由液面波形。比較模船和實船雷諾數的計算結果，隨著雷諾數提高，興波阻力係數有微幅上升的趨勢，摩擦阻力係數則明顯下降，總阻力係數因後者顯著尺度效應而下降。對於興波與黏性的交互作用，黏性效應衰減波浪能量傳遞，艏波未受影響，而船艉波高衰減顯著且伴隨相位偏移。波形上的差異推測是源自較強的黏性效應對船尾流場影響，從而間接改變波源位置。

The standard procedure of extrapolating full-scale ship resistance is recommended by the International Towing Tank Conference (ITTC) guidelines, which assume wave-making resistance coefficient is independent of Reynold's number. This study uses computational fluid dynamics to simulate a containership under various Reynold's numbers at the same Froude number. Commercial software Star-CCM+ solves Reynolds-averaged Navier-Stokes equation (RANS) for unsteady, incompressible, and viscous flow. The results show that wave-making resistance coefficient has slight positive Reynold's effect. The causes are investigated via comparing the flow field and we found that strong viscous effect around the stern altered the transverse and divergent wave profiles, while the bow wave is almost identical. The tangential flow on the propeller plane is also faster in full scale, thus loses more energy in the stern waves.