scholarly journals Development of secondary vortex structures in rotor wakes

2021 ◽  
Vol 63 (1) ◽  
Author(s):  
Clemens Schwarz ◽  
Andrew Bodling ◽  
C. Christian Wolf ◽  
Robert Brinkema ◽  
Mark Potsdam ◽  
...  

AbstractThe blade tip vortex system is a crucial feature in the wake of helicopter rotors, and its correct prediction represents a major challenge in the numerical simulation of rotor flows. A common phenomenon in modern high-fidelity CFD simulations is the breakdown of the primary vortex system in hover due to secondary vortex braids. Since they are strongly influenced by the numerical settings, the degree to which these secondary vortex structures actually physically occur is still discussed and needs experimental validation. In the current work, the development of secondary vortex structures in the wake of a two-bladed rotor in hover conditions was investigated by combining stereoscopic particle image velocimetry measurements in different measurement planes and high-fidelity simulations. Secondary vortex structures were detected and quantified at different axial locations in the wake by applying an identical scheme to the measured and simulated velocity data. In agreement, it was found that the number of secondary vortices is maximum at a distance of $$0.8\,R$$ 0.8 R below the rotor. The more intense secondary vortex structures were quantitatively well captured in the simulation, whereas in the experiment a larger number of weaker vortices were detected. No distinct preferential direction of rotation was found for the secondary vortices, but they tended to develop in vortex pairs with alternating sense of rotation. A clustered occurrence of secondary vortices was observed close to the primary tip vortices, where the rolled-up blade shear layer breaks down into coherent vortex structures. Graphical abstract

2018 ◽  
Vol 84 (6) ◽  
Author(s):  
K. V. Lezhnin ◽  
F. F. Kamenets ◽  
T. Zh. Esirkepov ◽  
S. V. Bulanov

In contrast to hydrodynamic vortices, vortices in a plasma contain an electric current circulating around the centre of the vortex, which generates a magnetic field localized inside. Using computer simulations, we demonstrate that the magnetic field associated with the vortex gives rise to a mechanism of dissipation of the vortex pair in a collisionless plasma, leading to fast annihilation of the magnetic field with its energy transforming into the energy of fast electrons, secondary vortices and plasma waves. Two major contributors to the energy damping of a double vortex system, namely, magnetic field annihilation and secondary vortex formation, are regulated by the size of the vortex with respect to the electron skin depth, which scales with the electron$\unicode[STIX]{x1D6FE}$factor,$\unicode[STIX]{x1D6FE}_{e}$, as$R/d_{e}\propto \unicode[STIX]{x1D6FE}_{e}^{1/2}$. Magnetic field annihilation appears to be dominant in mildly relativistic vortices, while for the ultrarelativistic case, secondary vortex formation is the main channel for damping of the initial double vortex system.


AIAA Journal ◽  
2020 ◽  
Vol 58 (7) ◽  
pp. 2869-2880
Author(s):  
Johannes N. Braukmann ◽  
C. Christian Wolf ◽  
Andreas Goerttler ◽  
Markus Raffel
Keyword(s):  

2019 ◽  
Vol 64 (2) ◽  
pp. 1-14 ◽  
Author(s):  
C. Christian Wolf ◽  
Johannes N. Braukmann ◽  
Wolfgang Stauber ◽  
Till Schwermer ◽  
Markus Raffel

The tip vortex system downstream of a four-bladed instrumented rotor was investigated experimentally through the application of stereoscopic particle image velocimetry (PIV). A dynamic stall test case was facilitated by a high cyclic pitch setting of the swashplate, with additional attached-flow and constant-pitch test cases for comparison reasons. The phase-locked PIV system and a rotation of the swashplate assembly allowed for an acquisition of the tip vortex system over the entire dynamic stall cycle and vortex ages up to at least 235°. The vortex structure and its relation to the blade shear layers were studied by means of both phase-averaged flow fields and the identification of vortex properties such as circulation and swirl velocity distributions. When approaching dynamic stall, a breakdown of the vortex structure started at high vortex ages, accompanied by the entrainment of turbulent structures from the passing blade shear layers into the tip vortices. After the flow over the blade is fully separated and during large parts of the downstroke, the wake of the rotor tips appears as a highly turbulent area with no individual tip vortices traceable, before reestablishing an ordered tip vortex structure shortly before the minimum blade pitch angle.


AIAA Journal ◽  
2004 ◽  
Vol 42 (3) ◽  
pp. 524-535 ◽  
Author(s):  
Yong Oun Han ◽  
J. Gordon Leishman

1987 ◽  
Vol 27 (5) ◽  
pp. 735-739 ◽  
Author(s):  
G. A. Kuz'min ◽  
A. Z. Patashinskii

Author(s):  
Alberto Serena ◽  
Lars E. Bakken

The tip leakage flow affects turbomachines performance generating losses and reducing the effective blading; in addition, unsteady phenomena arise, negatively influencing the machine stability. In this paper, an overview of the existing models is presented. Local measurements of the pressure pulsations, visual flow observations and high quality video recordings from a high speed camera are performed in a novel pump laboratory, which provides the desired visualization of the rotating channels, and allows to study the fluctuating and intermittent nature of this phenomenon, and detect any asymmetry among the channels. A detailed comparison of the vortex tip structure for various tip clearances and with a whole set of numerical simulations finally completes the analysis. The three main focus areas are: tip vortex location, structure and evolution, performance comparison between shrouded and open impeller, at different tip clearance sizes, and study of the rotating instabilities.


1957 ◽  
Vol 1 (03) ◽  
pp. 13-46
Author(s):  
J. D. van Manen

The paper deals with the vortex system of the "screw + nozzle" propeller. The results obtained from systematic experiments with propellers in nozzles in which the length-diameter ratio of the nozzle, the number of blades, and the blade-area ratio of the propeller have been varied are discussed. In addition the results of experiments carried out for determining the optimum diameter of the nozzle system behind the ship are described. Explanatory comments on nozzle design are given, including diagrams for determining the radial inequality of the axial velocities in the nozzle and for making computations with regard to cavitation and strength. The influence of the clearance between blade tip and nozzle wall is discussed.


2019 ◽  
Vol 60 (11) ◽  
Author(s):  
C. Christian Wolf ◽  
Clemens Schwarz ◽  
Kurt Kaufmann ◽  
Anthony D. Gardner ◽  
Dirk Michaelis ◽  
...  

2018 ◽  
Vol 9 (3) ◽  
pp. 373-386 ◽  
Author(s):  
Kurt Kaufmann ◽  
C. Christian Wolf ◽  
Christoph B. Merz ◽  
Anthony D. Gardner

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Anan Lu ◽  
Tim Lee

Abstract The ground effect on the wingtip vortex generated by a rectangular semiwing equipped with tip-mounted regular and reverse half delta wings was investigated experimentally. The passive tip vortex control always led to a reduced lift-induced drag as the ground was approached. In close ground proximity, the presence of the corotating ground vortex (GV) added vorticity to the tip vortex while the counter-rotating secondary vortex (SV) negated its vorticity level. The interaction of the GV and SV with the tip vortex and their impact on the lift-induced drag were discussed. Physical mechanisms responsible for the change in the vortex flow properties in ground effect were also provided.


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