Blade Tip Vortex System of a Rotor with Cyclic Pitch

Braukmann, Johannes N.; Wolf, Christian; Goerttler, Andreas; Raffel, Markus

doi:10.2514/1.j058678

Cited by 14 publications

(18 citation statements)

References 26 publications

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“…Fig. 15 Absolute difference between mean vortex locations by PIV and BOS in r r -and z r -direction over the vortex age v for a sample case during upstroke (Blade 4, t∕T = 0.30 -0.13) increases faster during the downstroke motion of the blades ( t∕T > 0.5 ), hinting at an increased sensitivity to perturbations as also found by a previous investigation at the RTG (Braukmann et al 2020). A good agreement between PIV and BOS can be seen during the entire pitch cycle.…”

Section: Phase Dependency Of the Rotor Wakesupporting

confidence: 64%

“…For each bin, the mean swirl velocity of all grid points within the bin is calculated. This approach, which was also used by Wolf et al (2019) and Braukmann et al (2020), assumes rotationally symmetric vortices. Using the swirl velocity of each bin with a certain radius, the circulation can be derived as the line integral of the swirl velocity.…”

Section: Particle Image Velocimetry (Piv)mentioning

confidence: 99%

“…The current study is based on simultaneous BOS and PIV measurements of blade tip vortices of a sub-scale rotor in the rotor test facility Göttingen (RTG) under cyclic pitch conditions. An earlier investigation based on PIV data of a different cyclic test case (Braukmann et al 2020) showed that it is possible to reconstruct the azimuth-dependent downwash of the RTG rotor by means of PIV and also demonstrated the usability of the BOS data to add valuable information to the velocity fields. In addition, the data from computational fluid dynamics (CFD) calculations of the same test case are available, allowing for a comprehensive analysis of the rotor wake and the blade tip vortices .…”

Section: Introductionmentioning

confidence: 99%

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Combining simultaneous density and velocity measurements of rotor blade tip vortices under cyclic pitch conditions

et al. 2021

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An investigation into blade tip vortices of a sub-scale rotor under cyclic pitch conditions is carried out. Background oriented schlieren (BOS), particle image velocimetry (PIV), and computational fluid dynamics (CFD) are applied to the same test cases. This approach allows to combine the velocity data from PIV in a measurement plane, the density related data from BOS in a measurement volume, and the comprehensive set of flow variables provided by unsteady detached eddy simulations. Vortices up to an age of $$\varPsi _{{\text {v}}}= {70}^\circ$$ Ψ v = 70 ∘ in case of PIV and CFD, and up to $$\varPsi _{{\text {v}}}= {200}^\circ$$ Ψ v = 200 ∘ in case of BOS are considered. The vortex locations are obtained through all three techniques. The unsteadiness of the vortices was obtained by the experimental results, whereas CFD provides an average solution. An increased position scatter was observed during the downstroke of the pitch cycle with both experimental methods and was found to be in good agreement. In the second part, the PIV velocity data are compared to common vortex models. An approach to link the density distribution and the swirl velocity is applied to the measured data. Based on the CFD results, it is shown that the assumption of isothermal flow yields better agreement between velocity and density than isentropic flow. Graphic abstract

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Section: Phase Dependency Of the Rotor Wakesupporting

confidence: 64%

Section: Particle Image Velocimetry (Piv)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Combining simultaneous density and velocity measurements of rotor blade tip vortices under cyclic pitch conditions

et al. 2021

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“…The experiment was carried out at the rotor test facility in Göttingen (RTG) [1]. The four-bladed rotor had a radius of R = 0.65 m, a chord length of c = 0.072 m, a DSA-9A airfoil and was arranged horizontally (see Fig.…”

Section: Experimental Setup At the Rtgmentioning

confidence: 99%

“…Over the last years many investigations on rotor blade tip vortices have been carried out in the Institute of Aerodynamics and Flow Technology in Göttingen using optical measurement techniques. In two recent experiments particle image velocimetry (PIV) and the background-oriented schlieren technique (BOS) were combined to investigate the wakes of an isolated rotor on a test stand under cyclic pitch conditions [1] and of a free-flying model helicopter in ground effect [2]. In the present investigation, the BOS data acquired in both experiments are used to reconstruct the corresponding vortex filaments in three-dimensional (3D) space.…”

Section: Introductionmentioning

confidence: 99%

BOS-Based Three-Dimensional Reconstruction of Rotor Blade Tip Vortex Positions

Debernardis

Schwarz

Braukmann

2021

Notes on Numerical Fluid Mechanics and Multidisciplinary Design

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The present work discusses a methodology to reconstruct three-dimensional positions of rotor blade tip vortices based on stereoscopic background-oriented schlieren data. The reconstruction procedure is first applied on a rotor test stand where a comparison with previous PIV measurements is performed to validate the reconstruction scheme. Subsequently, it is adapted for the reconstruction of the vortex system surrounding a model helicopter in free flight during an unsteady takeoff maneuver.

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Quantification of the Influence of Particle Voids on PIV Measurements via Synthetic-PIV

Domogalla

2021

Notes on Numerical Fluid Mechanics and Multidisciplinary Design

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Particle Image Velocimetry (PIV) is an important technique to investigate complex flow fields but limited to the tracking fidelity of the flow tracers and the uncertainties in the evaluation process. To examine these issues this work implements a physic-based motion simulation for small spherical particles, serving as flow tracers in PIV, with existing tools for image generation. Particular focus set on the behavior in vortical structures and the occurrence of "particle voids" due to centrifugal forces. The results show that a realistic particle distribution ideally can be achieved when applying a statistical distribution of the particle size. Furthermore, they suggest a significant error in the velocity prediction if the region of interest has no sufficient particle seeding.

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Blade Tip Vortex System of a Rotor with Cyclic Pitch

Cited by 14 publications

References 26 publications

Combining simultaneous density and velocity measurements of rotor blade tip vortices under cyclic pitch conditions

Combining simultaneous density and velocity measurements of rotor blade tip vortices under cyclic pitch conditions

BOS-Based Three-Dimensional Reconstruction of Rotor Blade Tip Vortex Positions

Quantification of the Influence of Particle Voids on PIV Measurements via Synthetic-PIV

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