Recent developments in background oriented Schlieren methods for rotor blade tip vortex measurements

Kindler, Kolja; Goldhahn, Erik; Leopold, Friedrich; Raffel, Markus

doi:10.1007/s00348-007-0328-9

Cited by 67 publications

(41 citation statements)

References 9 publications

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“…The conditionally averaged vortex radius at w v ¼ 3 is found to be in agreement with corresponding results from Background Oriented Schlieren (BOS) measurements based on the same experimental configuration (r c =c ¼ 5:5 and 6% also at w v ¼ 3 ) (Kindler et al 2007). The conformity of the full-scale PIV and BOS results is attributed to the fact that the Schlieren measurements are equally effected by smearing due to aperiodicity.…”

Section: Effective Vortex Parameterssupporting

confidence: 85%

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Aperiodicity in the near field of full-scale rotor blade tip vortices

et al. 2010

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Blade tip vortices are the dominant vortical structures of the helicopter flow field. The inherent complexity of the vortex dynamics has led to an increasing interest in full-scale in situ experiments, where the near field, closely behind the blade, is of particular interest, since measures of vortex control mostly target this initial stage of development. To examine the near field, threecomponent particle image velocimetry (PIV) measurements of blade tip vortices of a full-scale helicopter in simulated hover flight in ground effect were conducted. A feasible and robust evaluation procedure was developed to minimise the shortcomings of full-scale PIV applications, such as a moderate spatial resolution and an elevated measurement noise level. At vortex ages ranging from w v ¼ 1 to 30°, a pronounced aperiodicity and asymmetry of the vortex were observed in -sections perpendicular to the vortex axes. At w v ¼ 1 , a preferential orientation of the vortex was observed. For increasing wake age, vortex wandering increased while the asymmetry of the vortex cores decreased. The high level of aperiodicity and core asymmetry must be taken into account when considering phase-averaged vortex characteristics in the near wake region. List of symbols

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Section: Effective Vortex Parameterssupporting

confidence: 85%

“…Thereafter, vortex wandering increased while the asymmetry of the vortex cores decreased. When considering phase averages to deduce effective vortex parameters in the near field (Kindler et al 2007;Valla et al 2009), both asymmetry and aperiodicity effects must be taken into account. yielding a blade tip Mach number of Ma ¼ 0:64.…”

Section: List Of Symbolsmentioning

confidence: 99%

Aperiodicity in the near field of full-scale rotor blade tip vortices

et al. 2010

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“…This has been shown, for example, by Venkatakrishnan (2005), Venkatakrishnan and Suriyanarayanan (2009) and Sourgen et al (2004Sourgen et al ( , 2012. Kindler et al 2007 applied the tomographic reference-free BOS method for the study of rotor blade tip vortices. Ota et al (2011) demonstrated that the Algebraic Reconstruction Technique (ART) can also be used in order to derive density distributions.…”

Section: Density Determination Of 2d Flowsmentioning

confidence: 99%

Background-oriented schlieren (BOS) techniques

2015

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“…Diagnostics of flows in supersonic and hypersonic facilities by BOS has been carried out in references [22][23][24][25][26], while in references [27][28][29] BOS has been used in the outdoors, with a large field of view. Several improvements of the technique are proposed, mainly in obtaining 3D measurements by tomographic imaging, [30][31][32], or by increasing the accuracy through colored backgrounds, [33].…”

Section: Principles Of Bosmentioning

confidence: 99%

Review of background oriented schlieren and development for ballistic range applications

Gojani

Kamishi

Obayashi

2013

EPJ Web of Conferences

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Abstract. Quantitative measurements of fluid flow can be achieved by flow visualization techniques, and this paper reviews and outlines background oriented schlieren, with emphasis on its performance: measurement sensitivity and uncertainty. Since the technique depends on cross-correlation, an assessment of image evaluation is also conducted. Background oriented schlieren is applied to two flows: shock reflection from a wedge in a shock tube, and natural cooling by convection. It is estimated that the technique can be applied to ballistic facilities.

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Recent developments in background oriented Schlieren methods for rotor blade tip vortex measurements

Cited by 67 publications

References 9 publications

Aperiodicity in the near field of full-scale rotor blade tip vortices

Aperiodicity in the near field of full-scale rotor blade tip vortices

Background-oriented schlieren (BOS) techniques

Review of background oriented schlieren and development for ballistic range applications

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