Tip vortex effects on oscillating rotor blades in hovering flight

AIAA Journal ◽  
1971 ◽  
Vol 9 (1) ◽  
pp. 106-113 ◽  
Author(s):  
W. P. JONES ◽  
B. M. RAO
Keyword(s):  
Rotor Blades ◽  
Tip Vortex ◽  
Hovering Flight

scholarly journals The Influence of an Upstream Pylon on Open Rotor Aerodynamics at Angle of Attack

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Nishad G. Sohoni ◽  
Cesare A. Hall ◽  
Anthony B. Parry
Keyword(s):  
Potential Field ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Rotor Wake ◽  
Rotor Aerodynamics ◽  
Open Rotor ◽  
Urans Cfd ◽  
Work Done

The aerodynamic impact of installing a horizontal pylon in front of a contra-rotating open rotor engine, at take-off, was studied. The unsteady interactions of the pylon's wake and potential field with the rotor blades were predicted by full-annulus URANS CFD calculations at 0 deg and 12 deg angle of attack (AoA). Two pylon configurations were studied: one where the front rotor blades move down behind the pylon (DBP), and one where they move up behind the pylon (UBP). When operating at 12 deg AoA, the UBP orientation was shown to reduce the rear rotor tip vortex sizes and separated flow regions, whereas the front rotor wake and vortex sizes were increased. In contrast, the DBP orientation was found to reduce the incidence variations onto the front rotor, leading to smaller wakes and vortices. The engine flow was also time-averaged, and the variation in work done on average midspan streamlines was shown to depend strongly on variation in incidence, along with a smaller contribution related to change of radius.

Stability of helical tip vortices in a rotor far wake

2007 ◽  
Vol 576 ◽  
pp. 1-25 ◽  
Author(s):  
V. L. OKULOV ◽  
J. N. SØRENSEN
Keyword(s):  
Rotor Blades ◽  
Tip Vortex ◽  
Tip Vortices ◽  
Radial Extent ◽  
Helical Vortices ◽  
Constant Pitch ◽  
Bladed Rotor ◽  
The Stability ◽  
Further Development ◽  
Far Wake

As a means of analysing the stability of the wake behind a multi-bladed rotor the stability of a multiplicity of helical vortices embedded in an assigned flow field is addressed. In the model the tip vortices in the far wake are approximated by infinitely long helical vortices with constant pitch and radius. The work is a further development of a model developed in Okulov (J. Fluid Mech., vol. 521, p. 319) in which the linear stability of N equally azimuthally spaced helical vortices was considered. In the present work the analysis is extended to include an assigned vorticity field due to root vortices and the hub of the rotor. Thus the tip vortices are assumed to be embedded in an axisymmetric helical vortex field formed from the circulation of the inner part of the rotor blades and the hub. As examples of inner vortex fields we consider three generic axial columnar helical vortices, corresponding to Rankine, Gaussian and Scully vortices, at radial extents ranging from the core radius of a tip vortex to several rotor radii.The analysis shows that the stability of tip vortices largely depends on the radial extent of the hub vorticity as well as on the type of vorticity distribution. As part of the analysis it is shown that a model in which the vortex system is replaced by N tip vortices of strength Γ and a root vortex of strength − N/Γ is unconditionally unstable.

Blade tip vortex measurements on actively twisted rotor blades

2017 ◽  
Vol 58 (5) ◽  
Author(s):  
André Bauknecht ◽  
Benjamin Ewers ◽  
Oliver Schneider ◽  
Markus Raffel
Keyword(s):  
Rotor Blades ◽  
Tip Vortex ◽  
Blade Tip

Experiments on the Weis-Fogh mechanism of lift generation by insects in hovering flight. Part 1. Dynamics of the ‘fling’

1979 ◽  
Vol 93 (1) ◽  
pp. 47-63 ◽  
Author(s):  
T. Maxworthy
Keyword(s):  
Initial Phase ◽  
Angle Of Attack ◽  
Large Angle ◽  
Leading Edge ◽  
Tip Vortex ◽  
Hovering Flight ◽  
Separation Bubbles ◽  
Mechanical Models ◽  
Series Of Experiments ◽  
Edge Separation

From a series of experiments using simplified mechanical models we suggest certain minor modifications to the Weis-Fogh (1973)–Lighthill (1973) explanation of the so-called ‘clap and fling’ mechanism for the generation of large lift coefficients by insects in hovering flight. Of particular importance is the production and motion of a leading edge, separation vortex that accounts for virtually all of the circulation generated during the initial phase of the ‘fling’ process. The magnitude of this circulation is substantially larger than that calculated using inviscid theory. During the motion that subsequently separates the wings, the vorticity over each of them is convected and combined to become a tip vortex of uniform circulation spanning the space between them. This combined vortex moves downwards as a part of a ring, of large impulse, that is then continuously fed from quasi-steady separation bubbles that move with the wings as they continue to open at a large angle of attack. Such effects are able to account for the large lift forces generated by the insect.

scholarly journals Numerical Investigation of a Dynamic Stall on a Single Rotating Blade

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 90
Author(s):  
Yin Ruan ◽  
Manfred Hajek
Keyword(s):  
Numerical Investigation ◽  
Vortex Structure ◽  
Leading Edge ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Dynamic Stall ◽  
Leading Edge Vortex ◽  
Pitching Airfoil ◽  
Edge Vortex ◽  
High Reynolds

Dynamic stall is a phenomenon on the retreating blade of a helicopter which can lead to excessive control loads. In order to understand dynamic stall and fill the gap between the investigations on pitching wings and full helicopter rotor blades, a numerical investigation of a single rotating and pitching blade is carried out. The flow phenomena thereupon including the Ω-shaped dynamic stall vortex, the interaction of the leading edge vortex with the tip vortex, and a newly noticed vortex structure originating inboard are examined; they show similarities to pitching wings, while also possessing their unique features of a rotating system. The leading edge/tip vortex interaction dominates the post-stall stage. A newly noticed swell structure is observed to have a great impact on the load in the post-stall stage. With such a high Reynolds number, the Coriolis force exerted on the leading edge vortex is negligible compared to the pressure force. The force history/vortex structure of the slice r/R = 0.898 is compared with a 2D pitching airfoil with the same harmonic pitch motion, and the current simulation shows the important role played by the swell structure in the recovery stage.

Investigating the Coupled Effects Between Rotor-Blade Aeroelasticity and Tip Vortex Stability

2020 ◽  
Author(s):  
Steven N. Rodriguez ◽  
Athanasios P. Iliopoulos ◽  
John G. Michopoulos ◽  
Justin W. Jaworski
Keyword(s):  
Rotor Blade ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Tip Vortices ◽  
Operational Conditions ◽  
Vortex Stability ◽  
Blade Vortex Interaction ◽  
Wake Interactions ◽  
The Relationship

Abstract The relationship between rotor-blade aeroelasticity and tip-vortex stability is investigated numerically. An aeroelastic framework based on the free-vortex wake and finite element methods is employed to model a subscaled helicopter rotor in hover and forward-tilted conditions. A linear eigenvalue stability analysis is performed on tip vortices to associate the coupled impact of aeroelastic effects and vortex evolution. Prior numerical investigations have shown that highly flexible wind turbine rotor-blades have the potential to decrease levels of the instability of tip vortices. The present work focuses on testing these findings against a subscaled rotor within the range of helicopter operational rotation frequencies. The presented work aims to develop further insight into rotor-wake interactions and blade-vortex interaction to explore the mitigation of adverse rotorcraft operational conditions, such as their effect on aerodynamic-induced airframe vibrations and the associated life-cycle fatigue performance.

Errata: "Compressibility Effects on Oscillating Rotor Blades in Hovering Flight"

AIAA Journal ◽  
1971 ◽  
Vol 9 (8) ◽  
pp. 1664c-1664c
Author(s):  
W. P. JONES ◽  
B. M. RAO
Keyword(s):  
Rotor Blades ◽  
Hovering Flight ◽  
Compressibility Effects

Rotating Instabilities in an Axial Compressor Originating From the Fluctuating Blade Tip Vortex

2000 ◽  
Author(s):  
R. Mailach ◽  
I. Lehmann ◽  
K. Vogeler
Keyword(s):  
Rotor Blade ◽  
Laser Doppler Anemometry ◽  
Stability Limit ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Experimental Investigations ◽  
Flow Phenomenon ◽  
Low Speed ◽  
Blade Tip

Rotating instabilities (RI) have been observed in axial flow fans, centrifugal compressors as well as in low-speed and high-speed axial compressors. They are responsible for the excitation of high amplitude rotor blade vibrations and noise generation. This flow phenomenon moves relative to the rotor blades and causes periodic vortex separations at the blade tips and an axial reversed flow through the tip clearance of the rotor blades. The paper describes experimental investigations of RI in the Dresden Low-Speed Research Compressor (LSRC). The objective is to show that the fluctuation of the blade tip vortex is responsible for the origination of this flow phenomenon. RI have been found at operating points near the stability limit of the compressor with relatively large tip clearance of the rotor blades. The application of time-resolving sensors in both fixed and rotating frame of reference enables a detailed description of the circumferential structure and the spatial development of this unsteady flow phenomenon, which is limited to the blade tip region. Laser-Doppler-Anemometry (LDA) within the rotor blade passages and within the tip clearance as well as unsteady pressure measurements on the rotor blades show the structure of the blade tip vortex. It will be shown that the periodical interaction of the blade tip vortex of one blade with the flow at the adjacent blade is responsible for the generation of a rotating structure with high mode orders, termed as rotating instability (RI).

Rotating Instabilities in an Axial Compressor Originating From the Fluctuating Blade Tip Vortex

2000 ◽  
Vol 123 (3) ◽  
pp. 453-460 ◽  
Author(s):  
R. Mailach ◽  
I. Lehmann ◽  
K. Vogeler
Keyword(s):  
Rotor Blade ◽  
Laser Doppler Anemometry ◽  
Stability Limit ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Experimental Investigations ◽  
Flow Phenomenon ◽  
Low Speed ◽  
Blade Tip

Rotating instabilities (RIs) have been observed in axial flow fans and centrifugal compressors as well as in low-speed and high-speed axial compressors. They are responsible for the excitation of high amplitude rotor blade vibrations and noise generation. This flow phenomenon moves relative to the rotor blades and causes periodic vortex separations at the blade tips and an axial reversed flow through the tip clearance of the rotor blades. The paper describes experimental investigations of RIs in the Dresden Low-Speed Research Compressor (LSRC). The objective is to show that the fluctuation of the blade tip vortex is responsible for the origination of this flow phenomenon. RIs have been found at operating points near the stability limit of the compressor with relatively large tip clearance of the rotor blades. The application of time-resolving sensors in both fixed and rotating frame of reference enables a detailed description of the circumferential structure and the spatial development of this unsteady flow phenomenon, which is limited to the blade tip region. Laser-Doppler-anemometry (LDA) within the rotor blade passages and within the tip clearance as well as unsteady pressure measurements on the rotor blades show the structure of the blade tip vortex. It will be shown that the periodical interaction of the blade tip vortex of one blade with the flow at the adjacent blade is responsible for the generation of a rotating structure with high mode orders, termed a rotating instability.

Cavitation in the Tip Region of the Rotor Blades Within a Waterjet Pump

2008 ◽  
Author(s):  
H. Wu ◽  
F. Soranna ◽  
T. Michael ◽  
J. Katz ◽  
S. Jessup
Keyword(s):  
Measurement Techniques ◽  
Leading Edge ◽  
Suction Side ◽  
Operating Conditions ◽  
Index Of Refraction ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Working Fluid ◽  
Pressure Side ◽  
Cavitation Inception

Recent upgrades to the turbomachinery facility at JHU enable measurements of performance, as well as flow structure, turbulence and cavitation within a water-jet pump. The rotor, stator and pump casing in this optically index-matched facility are made of acrylic that has the same optical index of refraction as the working fluid, a concentrated solution of NaI in water. The essentially “invisible” blades allow unobstructed view and access to optical flow measurement techniques. Initial tests in water focus on observations on occurrence of cavitation in the vicinity of the narrow tip-gap. For the present design and operating conditions, near the leading edge, cavitation in the tip corner of the pressure side causes accumulation of bubbles along the pressure side that extends to mid blade. As rollup of a tip vortex starts, these bubbles cross the tip gap to the suction side, and become primary nuclei for cavitation inception within the tip leakage vortex (TLV). Bursting of this tip vortex as it migrates towards the pressure side of the neighboring blade generates a cloud of bubbles along the aft section of the passage. As the flow in the tip gap increases upstream of the trailing edge, cavitation also develops within the gap, along the pressure side corner.

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