浮式風機跡流行為之數值研究

Abstract

本研究以數值方法探討 Vestas V80 浮式風機之跡流行為，採用 STAR-CCM+ 軟體求解三維暫態連續方程與動量方程，並結合 SST k-ω紊流模型與制動盤模型，模擬風機進行六自由度運動時轉子周圍及下游的流場特性。研究中比較固定式與浮式風機，模擬條件涵蓋風速 9 m/s、15 m/s 及 21 m/s，平移運動振幅為 0.5 至 2.5 公尺，旋轉運動振幅為 1° 至 5°，運動週期則介於 40 至 50 秒。分析結果顯示，根據標準化時間平均風速差異，縱搖與平擺運動會在距離風機下游引發強烈擾動，促進跡流混合並加速風速恢復；而其標準差分析則顯示，橫搖與橫移運動應予以抑制，以減輕下游風機的疲勞損傷。在高風速條件下，流場慣性與穩定性顯著削弱平台運動對跡流的影響。在所分析的各項參數中，風速與運動振幅為影響下游跡流行為的主要因素，而運動週期的影響相對較小。此外，浮式風機的六自由度運動有助於提高跡流的風速恢復效果，進而縮短風機間距、提升單位面積發電效率。雖然平台運動可能降低自身風機的功率輸出，但能改善下游風機的發電性能。浮式風機的運動振幅、下游距離與標準化時間平均風速差異三者之間的關係可以透過二次多項式充分描述。

This study investigates the wake behavior of the Vestas V80 floating offshore wind turbine (FOWT) using numerical methods. The simulations were conducted with STAR-CCM+ by solving the three-dimensional unsteady continuity and momentum equations, coupled with the SST k-ω turbulence model. An actuator disk model was employed to simulate the flow field under six degrees of freedom platform motions. Both fixed-bottom and floating turbine configurations are examined under wind speeds of 9 m/s, 15 m/s, and 21 m/s. The motion amplitudes considered include translational motions ranging from 0.5 m to 2.5 m and rotational motions from 1° to 5°, with motion periods between 40 and 50 s. Based on the analysis of difference in normalized time-average velocity, pitch and yaw motions were found to induce strong downstream disturbances, enhancing wake mixing and wind speed recovery, whereas the analysis of its standard deviation suggests that sway and roll motions should be minimized to mitigate fatigue damage in downstream turbines. At higher wind speeds, the increased flow inertia and stability significantly suppress the wake effects induced by platform motions. Among the parameters examined, wind speed and motion amplitude were identified as the primary factors influencing the downstream wake, whereas the effect of motion period was relatively minor. Furthermore, the motions of the FOWT were found to enhance wake recovery, thereby potentially enabling reduced inter-turbine spacing and improving power generation efficiency per unit area. Although platform motions may decrease the power output of the turbine itself, they can enhance the performance of downstream turbines. Finally, the relationship among motion amplitude, downstream distance, and normalized time-average velocity can be well described by a quadratic polynomial.