下洗流場對直升機懸停海域結構物影響之數值模擬

NUMERICAL SIMULATION OF THE DOWNWASH FLOW EFFECT ON A HELICOPTER HOVERING ABOVE OFFSHORE STRUCTURES

Since the information of the downwash flow field, which affects the take-off and landing of a helicopter, as well as the data of the surface effect, is not easily measured during experiments, this study proposes combining the computational fluid dynamics (CFD) and the sliding mesh method (SMM) to simulate the flow field of the offshore structure during the hovering situation of a shipboard helicopter. This study focuses on the downwash flow dynamics that affect the helicopter and marine structures. As shown in the simulation results, when the hovering height is more than twice the rotor radius, the ground effect can be negligible. Additionally, when a helicopter is hovering above the deck of a ship containing an aircraft shelter at a height at which the ground effect is present, the main rotor thrust is larger than when the helicopter is hovering above ground. That is, the effect of the ground effect on a ship is more significant than on land. The simulation results can be used to examine the effect of the geometry of the offshore structure on the downwash flow field of the helicopter, thus facilitating the design of the helipad. 由於直升機在起飛和降落過程中，深受旋翼下洗流場與地面效應之影響，若要藉由實驗方式量測其相關資訊並不容易，因此本研究結合計算流體力學（CFD）與滑移網格技術（SMM）模擬船載直升機懸停於船舶與海域結構物，並探討其下洗流場對直升機和海域結構物之影響。由本研究之模擬結果可知，當直升機懸停高度大於旋翼半徑兩倍時，可以忽略地面效應之影響。此外，當直升機在配備直升機庫船舶之甲板懸停時，若其懸停在具有地面效應影響之高度，則此時相較於懸停在相同高度之地面上，直升機主旋翼將有更大的升力，由此可知地面效應在船舶上之影響遠大於在地面上之影響。本文所獲得之研究成果，將可深入探討直升機下洗流場對不同構型海域結構物之影響，進而在直升機停機坪之設計工作上提供實質效益。