Two-Dimensional Rotorcraft Downwash Flow Field Measurements by Lidar-Based Wind Scanners with Agile Beam Steering

Abstract A major risk to helicopters is the unexpected encounter of degraded visual environments in close-to-ground operations, where a loss of visibility often is caused by clouds of dust (brownout) or snow (whiteout) stirred up by intense downwash. The understanding of the phenomenon is limited, and there is a need for instruments that can measure flow fields on scales larger than a few meters with good resolution. This paper reports on the use of synchronized continuous-wave Doppler lidars for rotorcraft downwash flow field studies. Built from a modified ZephIR wind lidar and a double-prism arrangement for agile beam steering, a wind scanner—WindScanner—has been developed at the Department of Wind Energy at the Technical University of Denmark (DTU) Risø campus. The WindScanner measures the line-of-sight component of the airflow remotely and by rapid steering, the line-of-sight direction and the focus position; all points in space within a cone with a full opening angle of 120° can be reached from about 8 m out to some hundred meters depending on the range resolution required. The first two-dimensional mean wind fields measured in a horizontal plane and in a vertical plane below a hovering search and rescue helicopter are presented. Since the line-of-sight directions of the two synchronized WindScanners were scanned within the plane of interest, the influence of the wind component perpendicular to the plane was avoided. The results also demonstrate the possibilities within less demanding flows encountered within complex terrain and wind-energy-related research for which the WindScanner technology primarily has been developed.</jats:p

[Academy Lectures 2016.04.20]

1 h, 18 minAcademy Lectures har gleden av å invitere deg til en samtale mellom kunstnere Steinar Haga Kristensen og Kristian Øverland Dahl. Teknikkaliteten og prinsippets viktighet i møte med bildet – fruktbare handlingsrom i møte med malerens nyttige idioti stilt overfor tvilens språklige forfengelighet og omveltningens overdrivelser. Under samtalen vil kunstnerne spille ut sin fascinasjon for maleriets iboende urenhet – konflikten mellom bilde og representasjon, samt hestens strålende anatomi. Steinar er uttalt skeptisk til tvil, mens Kristian er dypt engasjert i ansiktets endeløse uutgrunnelighet, begge forsøker de å håndtere det faktum at de elsker mennesker. Samtalen vil foregå på norsk. Academy Lectures is pleased to invite you to a session where you get to meet the artists Steinar Haga Kristensen and Kristian Øverland Dahl in conversation. Technicalities and the importance of principle – strategies for fruitful engagement when faced with executive government, the temptations of revolutionary excess and the vanities of doubt that derive from lingual structures. During the conversation the artist will play out their fascination with the inherent impurity of painting – the conflict between image and representation, as well as the glorious anatomy of the horse. Steinar is outspokenly skeptical of the concept of doubt, while Kristian is deeply engaged in the endless inscrutability of the human face, and both dealing with the fact that they love people. The conversation will be held in Norwegian