Booth 7120

Booth 7120

Hydraulic Yaw System for Wind Turbines with New Compact Hydraulic Motor Principle

EWEA 2011, 14-17 March, Brussels

Rasmus M. Sørensen*, Liftra & Department of Mechanical and Manufacturing Engineering, Aalborg University, Denmark

Ole Ø. Mouritsen, Department of Mechanical and Manufacturing Engineering, Aalborg University, Denmark

Michael R. Hansen, Department of Engineering, University of Agder, NorwayPer E. Fenger, Liftra, Denmark

Funded by:Liftra

Danish Agency for Science Technology and Innovation

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Agenda• Introduction• Motor principle• Simulation• Prototype tests• Compare simulation and prototype results• Conclusion

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Introduction• The main goal is to develop a new hydraulic motor principle

that is suited for the yaw system with a view to avoid the fundamental disadvantages associated with the gear wheel connections used today.

• The volumetric efficiency is critical for large low speed high torque motors, whereas the leakage flow of the new hydraulic motor principle is highlighted in this presentation.

• The aim of this work is to develop a fluid structural simulation model that is capable of predicting the critical structural deflections of the motor.

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Motor Principle• The vanes are hydraulic actuated.• The leakage flow to the drain is the focus of the work.

Vane

Stop

Rotor

High pressure

Low pressure

Stator

Housing

Housing

Housing

Housing

Section A-AA

A

R

H

θ

S

Stator

Drain

Shaft

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Characteristics of the Motor Principle• The specific displacement, i.e. the displacement per outer

motor volume is favourable when comparing with existing hydraulic motors. Potentially, this allows for very compact motors used for direct drive applications with high torque requirements. It has a specific displacement substantially higher than that of commercially available motors.

• Specific displacement for the prototype is around 3 times higher than that for the world ‘s largest radial piston motors from Hagglunds.

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The Hydraulic Motor in a Wind Turbine• Small hydraulic motors in

mesh with the yaw gear rim. The high reduction gearboxes are saved.

• Large hydraulic motor shaped as a ring in the same size as the existing yaw gear rim. The motor has e.g. 40 chambers located in a radius equal to that of the tower.

Nacelle

Gear rimMotor Nacelle Motor

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Fluid Structural Simulation• The aim is to calculate the

structural deflections of the housing.

• Solving Reynolds equation for the pressure distribution across the end faces of the rotor.

• Applying the pressure distribution as the load input to the structural FEM deflection calculations on the housings.

h

rp

hrr

prh

r6=

1+ 33

r

θ

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Simulation Results• The pressure distribution

across the end faces of the rotor.

• The pressures are the load input to the structural FEM calculations.

• The input and the boundary conditions is measured pressures.

Pressure [Pa]

3.90e6

3.63e6

3.36e6

3.09e6

2.81e6

2.54e6

2.27e6

2.00e6

1.73e6

1.46e6

1.19e6

9.14e5

6.43e5

3.71e5

1.00e5

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Simulation Results• Deflections of the

housing.• The calculated node

deflections are input to next fluid calculation.

Deflection [mm]

0.034

0.031

0.029

0.026

0.024

0.022

0.019

0.017

0.014

0.012

0.010

0.007

0.005

0.002

0.000

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Prototype• 6 chambers.• Outer diameter of the

prototype is 340mm.• Displacement is D = 1.75

l/rev.• Theoretically T = 2240Nm,

when Δp = 80 bar.• Compensation volumes.• Moving coil actuator with

a 0.1 μm resolution encoder.

Compensation volumes

Stop pressusre

Drain

MCAMCA

mounting

Housing

Housing

Stop

Shaft

Rotor

Stator

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Test Results• The volumetric efficiency is decreased with the

structural deflections of the housing.

580 590 600 610 620 630 6400

50

100

Time [s]

Def

lec.

[m

]

580 590 600 610 620 630 6400

0.5

1

Time [s]

Vol

. Eff.

[]

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Deflection Comparison• It is considered inexact to validate

the FSI simulation by comparing absolute dimensions in the μm range.

• The theoretical deflection difference is 26 μm and the measured deflection difference is 40 μm.

• The percentage deviation is a concern.

Condition 1 Condition 2

p1 12.5 bar 6.5 bar

P2 55 bar 39 bar

Pcomp 35 bar 35 bar

hTheo 57 μm 31 μm

hMeas 50 μm 10 μm

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Conclusion• The FSI simulation is reflecting the behaviour and the

volumetric efficiency trends of the prototype motor, but the boundary conditions in the FEM model must be calibrated by examining a wider range of tests.

• The test results show that the volumetric efficiency can be kept at an acceptable level by the use of compensation pressure volumes.

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Hydraulic Yaw System Perspectives

• Designing the motor to withstand a maximum working pressure far beyond the nominal working pressure.

• Active damping by regulating the pressures in the stop volumes.

• Include the yaw bearing in the motor.