Wind Turbines - University Of Exeter
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Wind turbinesSOE3211/2 Fluid Mechanics lecture 10
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Background (A)Much interest in wind power for electricity generation {currently only really competative renewable energy source. UKhas signi cant wind 'reserves'.Several designs investigated over last 20 years { howeverindustry has opted for single design : Horizontal Axis WindTurbine (HAWT). Features : 2-3 airfoil blades (composite construction) Blades connected to hub : axis of rotation horizontal Hub/shaft/generation gear placed on top of support tower
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)AirfoilbladesHub with gearbox,control systems, generatorSupport towerEnergy generation { implies momentum extracted from air owspeed downstream speed upstream{ streamlines expand through rotor disk.Analyse this through Bernoulli.
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)E ciency (A)Edge of slipstreamu1u41234Assume that u2 u3 , soApplying Bernoulli 1 ! 211pa u12 p2 u2222Applying Bernoulli 3 ! 411p3 u32 pa u4222p2 p3 1 ( u 2 u 2 )2 1 2
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Thrust on the turbineF Q (u1 u4 ) A(p2 p3 )Combining these we nd12u2 u3 (u1 u4 )E ciency of turbine loss of k.e. from airstream undisturbedpower through rotor disk area12 Au (uu2) 2 12 1 2 4Au1 u122 (u1 u42)(u3u1 u4 )11 (1 ur ur2 ur3 )2 2with ur u4 u1
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Maximum e ciency { look for turning pointd 1 (1 2ur 3ur2 ) 0dur 2) ur 13for which 1627 59:3%{ the Betz limitInterpretation : Maximum energy extraction when u4 0 { no owthrough turbine, zero power If u4 u1 , ow rate maximised, but no energy extracted Betz represents optimum energy extraction.
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Design issues (A)Various ( uids-related) design issues of importance, includingVibration { air turbulence, vortex shedding, (blade rotation)all generate vibrations at speci c frequencies.This can cause fatigue. Solution : design theinstallation so that its resonant frequencies 6 anylikely driving frequencies.Noise { quite a signi cant NIMBY issue. Designturbines to reduce aerodynamic noise, modelsound propagation to investigate environmentalimpact.System control. Need turbine to point into wind, run atconstant speed : also cut out if wind speed toohigh.
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Yaw, pitch { rotation of assembly to point into prevailing windPitchYaw{ also to reduce e ciency in high winds.Also : control pitch of blades themselves to changeaerodynamic forces or stall the blades when necessary.
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Wind resource modelling (A)Detailed modelling of aerodynamics of blades etc { use CFD.However { also interested in the longer-term average winds {prevailing wind direction, strength etc { particularly whenconsidering wind farm siting.Atmospheric Boundary Layer (ABL) : At heights 1 km, wind hardly a ected by presence ofground At ground level, u 0 { thus there must be a boundarylayer Wind speeds in ABL taken to be logarithmic z u u (z ) logkz0with z0 as roughness parameter { varies from O (mm) forsmooth terrain (ice, water) to o (m) (urban areas).
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B) Sometimes easier to use power law pro le z u (z ) zu (zr )rNon- at terrain { mesoscale modelling (atmospheric processeson spatial scales 1 1000 km) { typically use combination ofABL, simple modi cations for terrain features, and wind atlas.Examples { WAsP, MS3DHJ { extensively used in siting windfarms.
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Larger scale { wind resource information
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Wind statistics (B)Wind is intermittent and uctuating. Characterise uctuationin terms of a probability density function (pdf) :De nitionThe pdf p(u) is the probability that the wind speed liesbetween u and u du.Using this, the probability that the wind speed is between Uaand Ub is given byZUp(Ua u Ub ) p(u )dubUaOf courseZ01p(u )du 1
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Average wind power generated can be calculated if the machinepower curve Pw (u) is known :Z1Pw (u )p(u )duPw 0The actual shape of the pdf for wind is quite complex { oftencharacterised by Rayleigh or Weibull distributions. Curves arenot symmetrical :p(u)uMean wind speedModal wind speed
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Mean wind speed can be evaluated :Z1u up(u )du0not necessarily the same as the modal wind speed (mostfrequent wind speed).Fluctuations around this { turbulence intensity { also importantparameter.Available wind power dependant on u3 . Often use root meancube wind speed as index of 'average' wind speed :p3urmc u 3
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)Blade aerodynamics (B)Individual blades are airfoils with carefully-chosen pro les. Lift(and drag!) forces on the blades create a torque which drivesthe turbine.Blades can turn faster than wind speed (this makes the systemmore e cient). Speed ratios up to 10 can be used. Force on2 , where ublade / urelrel is the relative speed of the blade to theair { a combination of rotation and wind speed.urel increases with distance from the hub (since ub r ).Thus, to calculate the torque, consider small blade element andintegrate.
Wind turbinesBackground(A)E ciency (A)Design issues(A)Wind resourcemodelling (A)Wind statistics(B)Bladeaerodynamics(B)RrdrUbDetermine lift force for small element1 2 b drdF CL urel2and torque1 2 rb drdG CL urel2and integrate. Note that CL may vary with r if necessary.
Wind turbines Background (A) E ciency (A) Design issues (A) Wind resource modelling (A) Wind statistics (B) Blade aerodynamics (B) Wind statistics (B) Wind is intermittent and uctuating. Characterise uctuation in terms of a probability density function (pdf) : De nition The pdf p ( u ) is the probability that the wind speed lies between u and u .
boat wind turbines and make them facing the wind [3]. The number of blades of boat wind turbines is often 3. Three-bladed boat wind turbines can produce power at low wind speed and can be self-started by the wind. This paper is focused on three-bladed boat wind turbines with passive yaw motion.
WIND TURBINES Wind Turbines AP-Power-Wind Turbines-13a Wind power is popular. The market for wind turbines is expanding rapidly and with it is an increasing demand for turbines to be i
Common concerns about wind power, June 2017 1 Contents Introduction page 2 1 Wind turbines and energy payback times page 5 2 Materials consumption and life cycle impacts of wind power page 11 3 Wind power costs and subsidies page 19 4 Efficiency and capacity factors of wind turbines page 27 5 Intermittency of wind turbines page 33 6 Offshore wind turbines page 41
Human chain at Tinos harbor as a form of protest against the wind turbines. [5] Peaceful protest on the mountain that the new wind turbines are planned to be installed. [5] Protest in Athens city center against the wind turbines. [5] Citizens of Tinos blocking the coming of the materials needed for the installation of the new wind turbines. [5] 8
Small Wind Turbines Are Different Utility-Scale Wind Power, 600 - 1,800 kW wind turbines – Professional maintenance crews – 15 mph (7 m/s) average wind speed Small, “Distributed” Wind Power 0.3 - 50 kW wind turbines – Installed at individual homes, farms, busine
Chapter 13: Aerodynamics of Wind Turbines. Chapter 13: Aerodynamics of Wind Turbines. Chapter 13: Aerodynamics of Wind Turbines. Time accurate predictions for a 2-bladed HAWT are shown in the next figure (13.22) At high tip speed ratio (low wind speeds) vortex ring state (part a)
3.Types Of Wind Turbines There are two types of wind turbines. One is Vertical axis wind turbines and the other is horizontal axis wind turbines. We also know that there is sufficient wind to satisfy much of humanity's energy requirements - if it could be gathered effectively and on a large scale.
and hold an annual E-Safety Week. Our Citizenship Award. 4 Through discussion in all our history themes – the rule of law is a key feature. RE and citizenship/PSHEE lessons cover religious laws, commandments and practices. In RE we encourage pupils to debate and discuss the reasons for laws so that all pupils understand the importance of them for their own protection. As part of the .
