{"title":"Aeroacoustic Analysis of Asymmetric Lift-Offset Helicopter in Forward Flight","authors":"Paulo Arias, J. Baeder, Y. Jung","doi":"10.4050/f-0077-2021-16690","DOIUrl":null,"url":null,"abstract":"\n In recent years, the University of Maryland has worked on an asymmetric lift-offset compound helicopter. The configuration consists of a single main rotor helicopter with the addition of two key ways to increase the forward speed: a stubbed wing on the retreating fuselage side, and a slowed down rotor. Experiments and simulations have shown that the novel concept provides improved thrust potential and lift-to-drag ratios in high-speed forward flight. This study aims to determine whether the asymmetric lift-offset configuration also provides aeroacoustic benefits in forward flight in addition to its aerodynamic advantages. The aerodynamic results from previous computational and experimental studies are recreated using the Mercury framework, an in-house CFD solver based on Reynolds-Averaged NavierStokes (RANS). The acoustic analysis is performed using an acoustic code based on the Ffowcs William-Hawkings equation to solve for the noise propagating from the surfaces of the aircraft. It was found that for an advance ratio of 0.5 the wing-lift offset configuration can produce 56.8% more thrust at the same collective angle without any penalties in total noise. When the configurations produce equal thrust it was found that the wing-lift offset case has a 4 dB reduction in maximum overall sound pressure level. At an advance ratio of 0.3 with trim for equivalent thrust between configurations, a 3 dB maximum OASPL reduction was obtained with the inclusion of the wing.\n","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"33 1","pages":"0"},"PeriodicalIF":0.0000,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Proceedings of the Vertical Flight Society 77th Annual Forum","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.4050/f-0077-2021-16690","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
In recent years, the University of Maryland has worked on an asymmetric lift-offset compound helicopter. The configuration consists of a single main rotor helicopter with the addition of two key ways to increase the forward speed: a stubbed wing on the retreating fuselage side, and a slowed down rotor. Experiments and simulations have shown that the novel concept provides improved thrust potential and lift-to-drag ratios in high-speed forward flight. This study aims to determine whether the asymmetric lift-offset configuration also provides aeroacoustic benefits in forward flight in addition to its aerodynamic advantages. The aerodynamic results from previous computational and experimental studies are recreated using the Mercury framework, an in-house CFD solver based on Reynolds-Averaged NavierStokes (RANS). The acoustic analysis is performed using an acoustic code based on the Ffowcs William-Hawkings equation to solve for the noise propagating from the surfaces of the aircraft. It was found that for an advance ratio of 0.5 the wing-lift offset configuration can produce 56.8% more thrust at the same collective angle without any penalties in total noise. When the configurations produce equal thrust it was found that the wing-lift offset case has a 4 dB reduction in maximum overall sound pressure level. At an advance ratio of 0.3 with trim for equivalent thrust between configurations, a 3 dB maximum OASPL reduction was obtained with the inclusion of the wing.
近年来,马里兰大学研究了一种不对称升力偏移复合直升机。该结构由一个主旋翼直升机和两个增加前进速度的关键方式组成:后退机身一侧的短翼和减速旋翼。实验和仿真结果表明,这种新型设计在高速前飞中提高了推力潜力和升阻比。本研究旨在确定非对称升力偏移配置是否在前飞中除了气动优势之外还提供气动声学优势。利用基于reynolds - average NavierStokes (RANS)的内部CFD求解器Mercury框架,重新创建了先前计算和实验研究的空气动力学结果。声学分析使用基于Ffowcs william - hawkins方程的声学编码来求解从飞机表面传播的噪声。研究发现,当推进比为0.5时,在相同的总角度下,翼升偏置结构可以产生56.8%的推力,而不会对总噪声产生任何影响。当两种结构产生相同推力时,发现机翼升力偏移的情况下最大总声压级降低了4 dB。在各配置间的等效推力下,在带装饰的推进比为0.3时,在包含机翼的情况下,最大OASPL降低了3 dB。