Teeter excursions of a two-bladed horizontal-axis wind-turbine rotor in a turbulent velocity field

Anderson, M.; Garrad, A.D.; Hassan, U.

doi:10.1016/0167-6105(84)90035-7

Cited by 13 publications

(16 citation statements)

References 3 publications

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“…Individual pitch control is a promising concept of pitch controlled wind turbines to reduce the aerodynamic imbalances . A common approach to alleviate the hub moments in a two‐bladed wind turbine is the integration of a teeter hinge. The stability of the teeter hinge depends to a large extent on the rotational velocity, because the centrifugal forces act as a restoring moment on the deflected rotor.…”

Section: Introductionmentioning

confidence: 99%

Aero‐structural dynamics of a flexible hub connection for load reduction on two‐bladed wind turbines

Luhmann

Seyedin²,

Cheng

2016

Wind Energy

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In this study, an innovative concept for load reduction on the two-bladed Skywind 3.4 MW prototype is presented. The load reduction system consists of a flexible coupling between the hub mount, carrying the drive train components including the hub assembly, and a nacelle carrier supported by the yaw bearing. This paper intends to assess the impact of introducing a flexible hub connection on the system dynamics and the aero-elastic response to aerodynamic load imbalances. In order to limit the rotational joint motion, a cardanic spring-damper element is introduced between the hub mount and the nacelle carrier flange, which affects the system response and the loads. A parameter variation of the stiffness and damping of the connecting spring-damper element has been performed in the multi-body simulation solver Simpack. A deterministic, vertically sheared wind field is applied to induce a periodic aerodynamic imbalance on the rotor. The aero-structural load reduction mechanisms of the coupled system are thereby identified. It is shown that the fatigue loads on the blades and the turbine support structure are reduced significantly. For a very low structural coupling, however, the corresponding rotational deflections of the hub mount exceed the design limit of operation. The analysis of the interaction between the hub mount motion and the blade aerodynamics in a transient inflow environment indicates a reduction of the angle of attack amplitudes and the corresponding fluctuations of the blade loading. Hence, it can be concluded that load reduction is achieved by a combination of reduced structural coupling and a mitigation of aerodynamic load imbalances.

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Section: Introductionmentioning

confidence: 99%

Aero‐structural dynamics of a flexible hub connection for load reduction on two‐bladed wind turbines

Luhmann

Seyedin²,

Cheng

2016

Wind Energy

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“…al. This equation describes the teeter motion relative to the axis rotating with the main shaft. The centrifugal effect of this rotation is expressed by a d'Alembert force through the centre of mass of each blade, whose moment about the teeter axis is proportional to the teeter displacement.…”

Section: Approachmentioning

confidence: 99%

“…The following formula of the Lock number (according to) uses the rotor moment of inertia ( J ) and is here generalized to a blade of varying chord.

γ = \frac{2 ρ R^{4} C_{l_{α}} c^{*}}{J}

c * here is the nominal blade chord, which can be defined as

c^{*} = \frac{2 true {true\int}_{- R}^{R} c ((), r) true| r true| r^{2} d r}{R^{4}}

…”

Section: Approachmentioning

confidence: 99%

“…Regarding the history of teetered turbines, it becomes obvious that most of the basic work on teeter dynamics has been carried out in the eighties. Garrad and Anderson et al defined the dynamic equations of teeter motion and analysed teeter behaviour in turbulent wind. They mentioned that teeter end impacts may induce high loads into the turbine and that prediction of teeter excursions is essential.…”

Section: Introductionmentioning

confidence: 99%

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Teeter end impacts: analysis and classification of most unfavourable events

2015

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Two-bladed wind turbines are recently being discussed more often as the question arises for the most suitable offshore turbine concept.Regarding this turbine concept, a solution is required for the more challenging dynamics. A teetered hub has often been a load reduction concept of two-bladed turbines. During normal operation, a teetered hub eliminates the hub bending moment coming from unequal blade loading. But looking at extreme load cases, the teeter end impact is a major problem.The teeter end impact is quite often described as the occasion that destroys the load-reducing advantage of the teeter mechanism. The turbine must be designed to withstand the loads from the teeter impacts leading to additional weight, which is actually supposed to be reduced by using the teeter hinge.Although the teeter end impact is often described as a kind of 'killer aspect', a more detailed analysis and quantification of its nature is not given in open literature. This paper will do an analysis and quantification of the loads coming from teeter end impacts using an existing teetered turbine, the Controls Advanced Research Turbine 2 (CART2).First, there will be a look at analytical teeter equations to get an overview of the basic parameters leading to teeter movement.Then, teeter end impact behaviour will be analysed using aeroelastic load simulations of the CART2 according to International Electrotechnical Commission (IEC) 61400-1 edition 3.For each design load case, the most significant teeter response will be examined. A classification of teeter end impacts will be extracted from the simulation data. Results will be compared with a rigid turbine in order to get an evaluation of how severe teeter end impacts are, compared with extreme loads of a rigid turbine.Additionally, these results will be compared with modified teeter parameters of the CART2. These are the introduction of pitch-teeter coupling, a reduced free teeter angle and a different Lock number. It will be shown to what extent these parameters may reduce the intensity of teeter end impacts.Results show that it is worth discussing teetered turbines as an alternative to today's three-bladed turbines. According to this study, teeter end impacts need not be regarded as completely intolerable, and there are several turbine parameters that have a significant influence on them.

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“…The free teeter angle is important for low operational loads and basically the idea behind the teeter hinge at all. 7,[14][15][16] The teeter restraint in the hub must ensure that a certain maximum teeter angle max is not exceeded to prevent the rotor from hitting nacelle or tower. FIGURE 3 Overview of former teetered turbines with a capacity of 500 kW and more, based on Schorbach 1…”

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confidence: 99%

Teeter design for lowest extreme loads during end impacts

2017

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Two bladed wind turbines are discussed as a possible turbine alternative for offshore use as they show a potential to save cost of energy. But compared to three-bladed turbines, their dynamic behavior is much more challenging. A possible solution to handle these larger dynamic loads is the use of a teeter hinge, which can significantly reduce fatigue loads. In contrast to that, extreme loads, coming from teeter end impacts, are often described as a problem for teetered turbines.There are different design parameters of the teeter system of a turbine, which have an influence on extreme loads during teeter end impacts. Despite numerous studies on teeter movement and load reduction potentials of operational loads, scientific literature does not give information about suitable load-reducing combinations of teeter design parameters and their influence on extreme loads. This paper, which is a summary of a PhD thesis, 1 analyses which combination of teeter parameters has the largest load-reducing influence on extreme loads. Aeroelastic load simulations of the teetered turbine CART2 from the NREL test site and one of today's commercial two-bladed turbines, the SCD3MW from aerodyn (both pitch controlled upwind turbines), will be used. KEYWORDSCART2, extreme loads, SCD3MW, teeter, two bladed INTRODUCTIONIn today's literature, teeter end impacts are often described as situations that lead to critical loads. 2-8 Some of these studies even come to the conclusion that teeter end impacts make the load-reducing advantage of the teeter hinge obsolete. However, an overview of turbine design parameters influencing these loads is not given. A summary of research on teeter behaviour and a first approach of influences on teeter extreme loads has been done in Schorbach et al. 9 Closing this research gap is the aim of this study.

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Teeter excursions of a two-bladed horizontal-axis wind-turbine rotor in a turbulent velocity field

Cited by 13 publications

References 3 publications

Aero‐structural dynamics of a flexible hub connection for load reduction on two‐bladed wind turbines

Aero‐structural dynamics of a flexible hub connection for load reduction on two‐bladed wind turbines

Teeter end impacts: analysis and classification of most unfavourable events

Teeter design for lowest extreme loads during end impacts

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