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.

A Resonance Tracking Algorithm for the Prediction of Turbine Forced Response With Friction Dampers

2000 ◽  
Author(s):  
C. Bréard ◽  
J. S. Green ◽  
M. Vahdati ◽  
M. Imregun
Keyword(s):  
Rotor Blade ◽  
Turbine Blades ◽  
Turbine Rotor ◽  
Forced Response ◽  
Rotor Blades ◽  
Test Case ◽  
Friction Damper ◽  
Blade Vibration ◽  
Frequency Shifts ◽  
Friction Dampers

This paper presents an iterative method for determining the resonant speed shift when non-linear friction dampers are included in turbine blade roots. Such a need arises when conducting response calculations for turbine blades where the unsteady aerodynamic excitation must be computed at the exact resonant speed of interest. The inclusion of friction dampers is known to raise the resonant frequencies by up to 20% from the standard assembly frequencies. The iterative procedure uses a viscous, time-accurate flow representation for determining the aerodynamic forcing, a look-up table for evaluating the aerodynamic boundary conditions at any speed, and a time-domain friction damping module for resonance tracking. The methodology was applied to an HP turbine rotor test case where the resonances of interest were due to the 1T and 2F blade modes under 40 engine-order excitation. The forced response computations were conducted using a multi-stage approach in order to avoid errors associated with “linking” single stage computations since the spacing between the two bladerows was relatively small. Three friction damper elements were used for each rotor blade. To improve the computational efficiency, the number of rotor blades was decreased by 2 to 90 in order to obtain a stator/rotor blade ratio of 4/9. However, the blade geometry was skewed in order to match the capacity (mass flow rate) of the components and the condition being analysed. Frequency shifts of 3.2% and 20.0% were predicted for the 1T/40EO and 2F/40EO resonances in about 3 iterations. The predicted frequency shifts and the dynamic behaviour of the friction dampers were found to be within the expected range. Furthermore, the measured and predicted blade vibration amplitudes showed a good agreement, indicating that the methodology can be applied to industrial problems.

Tip-Shroud Labyrinth Seal Effect on the Flutter Stability of Turbine Rotor Blades

2019 ◽  
Author(s):  
Roque Corral ◽  
Michele Greco ◽  
Almudena Vega
Keyword(s):  
Rotor Blade ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Stability Prediction ◽  
Labyrinth Seals ◽  
Turbine Rotor Blade ◽  
The Stability ◽  
Shrouded Rotor ◽  
Tip Shroud

Abstract The effect of the tip-shroud seal on the flutter onset of a shrouded turbine rotor blade, representative of a modern gas turbine, is numerically tested and the contribution to the work-per-cycle of the aerofoil and the tip-shroud are clearly identified. The numerical simulations are conducted using a linearised frequency domain solver. The flutter stability of the shrouded rotor blade is evaluated for an edgewise mode and compared with the standard industrial approach of not including the tip-shroud cavity. It turns out that including the tip shroud significantly changes the stability prediction of the rotor blade. This is due to the fact that the amplitude of the unsteady pressure created in the inter-fin cavity, due to the motion of the airfoil, is much greater than that of the airfoil. It is concluded that the combined effect of the seal and its platform tends to stabilise the rotor blade for all the examined nodal diameters and reduced frequencies. Finally, the numerical results are shown to be consistent with those obtained using an analytical simplified model to account for the effect of the labyrinth seals.

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.

scholarly journals Enhancement of Free Vortex Filament Method for Aerodynamic Loads on Rotor Blades

2014 ◽  
Author(s):  
Hamidreza Abedi ◽  
Lars Davidson ◽  
Spyros Voutsinas
Keyword(s):  
Wind Turbine ◽  
Turbine Blades ◽  
Boundary Layer Separation ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Free Vortex ◽  
Irrotational Flow ◽  
Aerodynamic Loads ◽  
Operational Conditions ◽  
Turbine Rotor Blade

The aerodynamics of a wind turbine is governed by the flow around the rotor, where the prediction of air loads on rotor blades in different operational conditions and its relation to rotor structural dynamics is one of the most important challenges in wind turbine rotor blade design. Because of the unsteady flow field around wind turbine blades, prediction of aerodynamic loads with high level of accuracy is difficult and increases the uncertainty of load calculations. A free vortex wake method, based on the potential, inviscid and irrotational flow, is developed to study the aerodynamic loads. Since it is based on the potential, inviscid and irrotational flow, it cannot be used to predict viscous phenomena such as drag and boundary layer separation. Therefore it must be coupled to the tabulated airfoil data to take the viscosity effects into account. The results are compared with the Blade Element Momentum (BEM) [1] method and the GENUVP code [2] (see also the acknowledgments).

3D Measurements of Deterministic Stresses Within a Rotor-Stator Gap at Mid-Span and Tip Regions

Volume 1 ◽  
2004 ◽  
Author(s):  
Oguz Uzol ◽  
Yi-Chih Chow ◽  
Francesco Soranna ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Rotor Blade ◽  
Tip Vortex ◽  
Normal Stresses ◽  
Tip Vortices ◽  
Stress Components ◽  
Stress Levels ◽  
Order Of Magnitude ◽  
Axial Normal Stress

Stereoscopic Particle Image Velocimetry is used for measuring the distributions of the deterministic stresses, in the tip and mid-span regions, within the second stage rotor-stator gap of a two-stage axial turbomachine. This effort extends our previous two-dimensional measurements to study the dynamics of deterministic stresses in a multistage turbomachine using experimental data. All three components of the velocity vector, and all six components of both the turbulent and deterministic stress tensors are obtained at a Reynolds number of 370,000 based on the tip speed and the rotor blade chord, and in an optically unobstructed facility that uses blades and fluid with matched optical indices of refraction. Results at 50% show that although the radial velocity levels are about an order of magnitude smaller than the axial and lateral velocity levels, the flow is not exactly two-dimensional. The wake kinking phenomenon and the presence of chopped-off stator wake segments introduce three-dimensionality to the flow. The radial velocity fluctuations are high around the kink region, and get even higher when the potential field of the stator blade starts to interact with the kink zone. In general, the turbulent normal stresses are higher than the deterministic normal stresses while the turbulent and deterministic shear stress levels are in the same order of magnitude. The flow at 90% span is dominated by the tip vortices, which create high levels of non-uniformities in the distributions of all three velocity components. The tip vortex loses its structure when it gets close to the pressure side of the following rotor blade and undergoes a possible spiral-type vortex breakdown. The meandering and convection of the tip vortices contribute to the elevated levels of average-passage turbulence and deterministic stresses along the tip vortex transport direction. The deterministic axial normal stress is higher than the turbulent axial normal stress; the deterministic lateral normal stress is initially higher, but it quickly drops down to turbulent lateral normal stress levels; and the deterministic radial normal stress is initially close to turbulent radial normal stress levels, but it decays relatively quickly and becomes less than the turbulent radial normal stress levels further downstream. The deterministic shear stress components are 5 to 10 times higher than the turbulent shear stress components.

Effect of Blade Tip Modifications for Unducted Propulsors on Tip Vortex-Rotor Interaction Noise

2014 ◽  
Author(s):  
Florian Danner ◽  
Christofer Kendall-Torry
Keyword(s):  
Rotor Blade ◽  
Stokes Equations ◽  
Acoustic Emissions ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Tip Vortices ◽  
Blade Tip ◽  
Blade Loads ◽  
Blade Tips

Front rotor tip vortices impinging on a downstream blade row of an unducted propulsor induce distinct unsteadiness to blade loads with associated sound emissions. Since the region of unsteadiness is concentrated near the blade tips, reducing the rear rotor tip diameter represents a potential means for minimising interaction noise. A survey on the aeroacoustic effects resulting from a cropped rear rotor in combination with a front rotor blade tip modification is therefore presented. Analyses are based on data from computational fluid dynamics solutions with the Reynolds-averaged Navier-Stokes equations and direct acoustic predictions. The evaluation of polar directivities, blade surface pressure disturbances and details of the unsteady flow field provide insight into the underlying phenomena. Results show that an arbitrary reduction of the rear rotor tip diameter does not necessarily decrease noise radiation and that winglet-like structures applied to the front rotor blade tips are capable of reducing acoustic emissions due to tip vortex-rotor interactions.

A wind-tunnel based study of helicopter tail rotor blade vortex interaction

2004 ◽  
Vol 108 (1083) ◽  
pp. 237-244 ◽  
Author(s):  
F. N. Coton ◽  
R. A. McD. Galbraith ◽  
T. Wang ◽  
S. J. Newman
Keyword(s):  
Wind Tunnel ◽  
Rotor Blade ◽  
Tip Vortex ◽  
Vortex Interaction ◽  
Pressure Transducers ◽  
Control Effectiveness ◽  
Rotating Blade ◽  
Blade Vortex Interaction ◽  
Bladed Rotor ◽  
Development And Validation

AbstractThe interaction of a helicopter tail rotor blade with the tip vortex system from the main rotor is a significant source of noise and, in some flight states, can produce marked reductions in control effectiveness. This paper describes a series of wind-tunnel tests to simulate tail rotor blade vortex interaction with a view to providing data for the development and validation of numerical simulations of the phenomenon. In the experiments, which were carried out in the Argyll wind-tunnel of Glasgow University, a single-bladed rotor located in the tunnel’s contraction was used to generate the tip vortex which travelled downstream into the working section where it interacted with a model tail rotor. The tail rotor was instrumented with miniature pressure transducers that measured the aerodynamic response during the interaction. The results suggest that the rotor blade vortex interaction is similar in form to that measured at much higher spatial resolution on a fixed, non-rotating blade. The combination of the two datasets, therefore, provides a valuable resource for the development and validation of predictive schemes.

scholarly journals Design and analysis of displacement models for modular horizontal wind turbine blade structure

2020 ◽  
Vol 39 (1) ◽  
pp. 121-130
Author(s):  
E.M. Etuk ◽  
A.E. Ikpe ◽  
U.A. Adoh
Keyword(s):  
Wind Turbine ◽  
Rotor Blade ◽  
Structural Damage ◽  
Axial Loading ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Horizontal Wind ◽  
Normal Loading ◽  
Loading Cycle ◽  
Wind Turbine Rotor

This study examined the normal, radial, axial and tangential loading cycles undergone by wind turbine rotor blades and their effects on the  displacement of the blade structure. The rotor blade was modelled using Q Blade finite element sub module, which evaluated the loading cycles in  terms of the forces induced on the blade at various frequencies through several complete revolution cycles (360o each cycle). At frequencies of 5 HZ, 23 Hz, 60 Hz, 124 Hz and 200 Hz, maximum strain deformation of 0.004, 0.04, 0.08, 0.14 and 0.24 were obtained, and geometry of the deformed blades were characterized by twisting and bending configuration. Maximum deflections from tangential loading increased from -0.55-1.2 mm,  -0.39-1.6 mm from axial loading, -0.28-1.8 mmfrom radial loading and -0.01-2.3 mm from normal loading. From these deflection values, normal loading cycle would cause the highest level of structural damage on the rotor blade followed by radial, axial and tangential loading. Moreover, the  strain deformations and deflections of the blade structure increased as the cycles of frequency increased. Keywords: Loading cycle, Wind turbine, Rotor blade, Frequency, Strain deformations, Deflections.

scholarly journals Full scale deformation measurements of a wind turbine rotor in comparison with aeroelastic simulations

2020 ◽  
Author(s):  
Stephanie Lehnhoff ◽  
Alejandro Gómez González ◽  
Jörg R. Seume
Keyword(s):  
Wind Turbine ◽  
Rotor Blade ◽  
Plane Deformation ◽  
Field Measurements ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Strain Gauges ◽  
Aeroelastic Simulations ◽  
Good Agreement ◽  
Wind Turbine Rotor

Abstract. The measurement of deformation and vibration of wind turbine rotor blades becomes highly important as the length of rotor blades increases with the growth in demand for wind power. The requirement for field validation of the aeroelastic behaviour of wind turbines increases with the scale of the deformation, in particular for modern blades with very high flexibility and coupling between different vibration modes. However, performing full-scale field measurements for rotor blade deformation is not trivial and requires high temporal and spatial resolution. A promising deformation measurement technique is based on an optical method called Digital Image Correlation (DIC). A system for the application of DIC for full field measurements of wind turbine rotors has been developed and validated in the past years by ForWind, Institute of Turbomachinery and Fluid Dynamics, Leibniz Universität Hannover. The whole rotor of the wind turbine is monitored with a stereo camera system from the ground during measurement. Recently, DIC measurements on a Siemens Gamesa SWT-4.0-130 test turbine were performed on the tip of all blades with synchronized measurement of the inflow conditions by a ground-based LiDAR. As the turbine was additionally equipped with strain gauges in the blade root of all blades, the DIC results can be directly compared to the actual prevailing loads. In the end, the measured deformations are compared to aeroelastic simulations. The deformation measured with DIC on the rotor blade tips shows the same qualitative behaviour when compared to loads measured with strain gauges in the blade root. This confirms that the DIC measurements correlate with the prevailing loads in reality. The comparison with aeroelastic simulations shows that the amplitude and trend of the in-plane deformation is in very good agreement with the DIC measurements. The out-of-plane deformation shows slight differences, which could be caused by the difference between real wind conditions and the wind statistics on which the simulations are based. The combined rotor blade pitch and torsion angle measured with DIC is in good agreement with the actual pitch value of the turbine. A detailed comparison with aeroelastic simulations shows that the amplitude of torsion measured with DIC is higher which might be caused by an inaccuracy of the experimental setup. This will be focus of future work. All in all, DIC shows very good agreement with comparative measurements and simulations which shows that it is a suitable method for measurements of deformation and torsion of multi-megawatt wind turbine rotor blades.

scholarly journals Numerical and Experimental Vibration Analysis of a Steam Turbine Rotor Blade

2021 ◽  
Vol 15 (4) ◽  
pp. 462-466
Author(s):  
Marko Katinić ◽  
Marko Ljubičić
Keyword(s):  
Numerical Model ◽  
Modal Analysis ◽  
Steam Turbine ◽  
Vibration Analysis ◽  
Rotor Blade ◽  
High Reliability ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Turbine Rotor Blade ◽  
Computer Environment

Damage to the rotor blade of a steam turbine is a relatively common problem and is one of the leading causes of sudden and unplanned shutdowns of a steam turbine. Therefore, the high reliability of the rotor blades is very important for the safe and economical operation of the steam turbine. To ensure high reliability, it is necessary to perform a vibration analysis of the rotor blades experimentally and in a computer environment. In this paper, a modal analysis was performed on the twisted blade of the last stage of the turbine in the Ansys software. The results of the modal analysis of the stationary rotor blade were compared with the results obtained by the bump test, which confirmed the numerical model of the blade. A modal analysis of a rotating rotor blade was performed on the same numerical model, and Campbell diagrams were plotted to determine the critical speed

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