Authors: Mahendra J Bhagwat Francis X Caradonna Manikandan Ramasamy
Publish Date: 2015/01/13
Volume: 56, Issue: 1, Pages: 19-
Abstract
This paper focuses on one of the most prominent flow features of the hovering rotor wake the close interaction of the tip vortex with a following blade Such vortex interactions are fundamental determinants of rotor performance loads and noise Yet they are not completely understood largely due to the lack of sufficiently comprehensive experimental data The present study aims to perform such comprehensive measurements not on hovering helicopter rotors which hugely magnifies test complexity but using fixedwing models in controlled wind tunnel tests The experiments were designed to measure in considerable detail the aerodynamic loading resulting from a vortex interacting with a semispan wing as well as the wake resulting from that interaction The goal of the present study is to answer fundamental questions such as a the influence of a vortex passing below a wing on the lift drag tip vortex and the wake of that wing and b the strength of the forming tip vortex and its relation to the wing loading and/or the tip loading This paper presents detailed wing surface pressure measurements that result from the interaction of the wing with an interacting vortex trailing from an upstream wing The data show large lift distribution changes for a range of wing–vortex interactions including the effects of close encounter with the vortex core Significant asymmetry in the vortexinduced lift loading was observed with the increase in wing sectional lift outboard of the interacting vortex closer to the tip being much smaller than the corresponding decrease inboard of the vortexThis test with its unusual test setup and high density instrumentation presented some unique challenges and would not have been possible without the support of our outstanding tunnel crew—Steve Nance Brian Chan Bruce Gesek Gary Buob Hank Schwoob Bill Peneff Perry Kavros and their leader Nili Gold Special thanks to Sam Gunatileka for data acquisition programming that well exceeded our expectations A very special recognition is due to Jim Scott of the NASA Ames model manufacturing branch who conceived the basic wing and instrumentation design and executed the fabrication of this oneofakind model with extraordinary imagination and skill The authors would also like to thank Jon Bader of the NASA Ames Wind Tunnel Support Branch for supporting us in the use of their Task sting balance for this testThe VG trolley was responsible for a noticeable blockage effect An early indication of the presence of this blockage was that the required tunnel power was noticeably reduced with the removal of the trolley Furthermore the flow over the VG trolley also introduced an induced flow angle at the downstream wing Present data must be corrected for this blockage and incidence angle effects However the lift deltas caused by vortex interactions are not a strong function of wing incidence Therefore the behavior of the wing–vortex interaction is not significantly altered by this interference
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