CC BY
15Journal of Siberian Federal University. Engineering & Technologies, 2017, 10(5), 664-681
УДК 621.311.24
Powers Adjusting
Wind Turbine Means Investigation
Sergey N. Udalov, Natalya V. Zubova and А^^у А. Achitaev*
Novosibirsk State Technical University 20 K. Marks, Novosibirsk, 630073, Russia
Received 02.03.2017, received in revised form 20.04.2017, accepted 18.05.2017
Today, wind power is the fastest-growing renewable energy source. Wind power is free, clean and endless. Furthermore, the cost of the electricity produced by wind turbines already reached the point where it is comparable with that of electricity produced by some of the conventional, fossil based power plants. However, it is still important to improve upon the technology in order to keep wind energy economically competitive with traditional and other renewable energy sources. In this paper, the idea of a variable-length blades, microdevices, and plasma jet drives are offered as a means of improving energy generation wind turbines.
Keywords: wind turbine, microflaps, variable length blade, flow control.
Citation: Udalov S.N., Zubova N.V., Achitaev А.А. Powers adjusting wind turbine means investigation, J. Sib. Fed. Univ. Eng. technol., 2017, 10(5), 664-681. DOI: 10.17516/1999-494X-2017-10-5-664-681.
© Siberian Federal University. All rights reserved Corresponding author E-mail address: achitaevaa@gmail.com
Исследование средств повышения регулирования мощности ветровой турбины
С.Н. Удалов, Н.В. Зубова, А.А. Ачитаев
Новосибирский государственный технический университет Россия, 630073, Новосибирск, пр. К. Маркса, 20
Сегодня энергия ветра является самым быстрорастущим источником возобновляемой энергии. Ветровая энергия доступна, экологически чистая и бесконечна. Кроме того, стоимость электроэнергии, производимой ВЭУ, уже достигла точки, где она сравнима со стоимостью электроэнергии, производимой некоторыми электростанциями на основе ископаемых видов топлива. Тем не менее по-прежнему важно улучшать технологии для того, чтобы сохранить энергию ветра экономически конкурентноспособной по отношению к традиционным и другим возобновляемым источниками энергии. В этой статье представлена идея переменной длины лопасти, микроустройств и плазменных приводов, которые предлагаются в качестве средства улучшения производимой энергии ветровых турбин.
Ключевые слова: ветровая турбина, микроустройства, изменение длины лопасти, управление потоком.
Introduction
Wind Turbine power depends on wind speed, which is intermittent. This disadvantage has to be compensated by means of expensive systems, either accumulating energy during periods of high activity and distributing it in moments of calm wind, or by other sources of energy. This significantly increases the cost of electricity.
Research and development of means to control wind turbine power is a topical area of research in the wind industry. New directions in providing energy efficient power control is through the use of turbine nozzle drive of compressed gas, plasma devices arranged on the surface of the blade and the change of blade geometry (Fig. 1).
Large wind turbines, even in areas with good wind energy resources, typically generate power below the rated values due to low wind activity. The use of an additional energy source for rotating the turbine generator allows more efficient use of equipment, which means faster return on investment and less expensive energy for the end user.
Mathematical model of microflaps devices
Control device based on the jet drive
Turbine SmartGen, developed by Hybrid Turbines, is a highly scalable system [1]. Besides stabilizing the output power of the wind turbine, the compressed air is supplied to maintain a constant temperature used for the cooling of the generator components. This system captures excess energy produced by wind turbines, in the form of compressed air, and uses it during peak hours to spin a turbine.
An analysis of the technology is needed. We have developed a mathematical model of the device, which allows us to analyze the structure of the blade, the placement of these devices and their influence on the lifting force.
Below is a mathematical modeling of aerodynamic interaction of the jet nozzle equipped blade with the windflow, theactionsdescribed by theNavier-Stokes equations [2, 3]:
P - du/dt + p (u -V)u = V- -p •I + n[Vu + (Vu) )
+FV-u = 0, (1)
where u - speed of wind flow, m/s; p - pressure, Pa; n - kinematic viscosity • Pa s; F - force, N; pi -flux density, kg/m3; I - the unit outward normal to the surface; t - time, s; and T - matrix transposition index.
Calculation of the lift in a reactive gas flow is based on the dynamics of jet propulsion developed by Meshcherskiy. Lift, developed in cooperation with the blade wind flow, velocity u, is represented by the formula (Fig. 2):
,rdlJ 1 „ dm
M— = -27rRlplu1CL+v—, (2)
dt 2 dt
where Fr=d dm/dt is reactive force, as it acts on the blade at the expiration air mass m of the injector nozzle, H; u - velocity gas flow from the nozzle, m/s; CL - lift coefficient, dim; U - linear velocity of rotation of the blade m/s; M - blade mass, kg; and R - radius of the blade, m.
Modeling of processes occurring in the turbine was conducted on the basis of the finite element method (FEM) and calculation of flow dynamics using computational fluid dynamic (CFD) (Fig. 3), analyzing the physical processes under the influence of other devices, ultimately effecting the amount of lift. The aerodynamic properties of the blades with active aerodynamic devices are modeled using a special algorithm ARC2D, which is used for analyzing laminar flow [2]. The basis for the software too Is used for analysis is ANS YS CFD. Algorithm ARC2D, based on two-dimensional Navier-Stokes equations [3], was used to calculate the aerodynamic coefficients of lift and drag. Using CFD allows for consistently identify the changes in wind energy conversion efficiency of the airflow at the selected blade profile and its' changes due to the impact of active aerodynamicdevices[2].
The graph depicted in Fig. 4 shows the dependence of lift on the velocity of the gas in the nozzle. Depending on the wind speed through the jet nozzle drive, lift may be kept constant even at a sufficiently low speed wind. Compressing air, storing it the wind turbine, and utilizing it during times of need is more cost effective than utilizing a separate mechanism (i.e. ballast) to produce and store compressed air.
Shift
Fig. 3. Simulation results of action ofthejetdriveon lift
Lift Force, kN
-Wind Speed 10 m/ s
--Wird Speed 8 m/s
.......Wind Speed 23 m/s
-----Wind Speed 15 m/s
" « Wind Speed 19 m/s M *■* Wind Speed 23 m/s
Fig. 4. Resultsofmodeling the influenceoftheflowrateofthe nozzledriveonliftforcefor d^erefrtvahies of wind speed
TtVi device allows operation at the maximumpowerfactorofthewindpower ¡plant, as well as the ability to maintain a constant rotation speed for a larger wind speed range.
Plasma Cu)h^rol Device
A lonown issue whli the pteempacCuotor confi^ratkms C t^lio^r seceitmty towardsR^uolds num^r eRer vAriaeiouc andmote ^etifically, their reduction evh^ ate insrease
^e 6c w
of the free-stream velocity [8]. Pechlivanoglou and Eisele [9] investigated the operation of plasma actuators on wind turbine airfoils at a wide range of Reynolds numbers and found that the effect of all the investigated plasma actuators vanished at Re > 105. The energy conversion efficiency is also another operational parameter which highly depends on the actuators design, and undergoes further investigation. Currently plasma actuator systems have low efficiency and very high thermal losses. Additionally the effects of environmental conditions need to be further investigated to examine the possibility of further implementation of plasma actuators on wind turbine blades. More specifically, the plasma actuators would be required to operate effectively and reliably under rain, hail, ice, tolerate dust and contamination, and lightning strikes [6].
Plasma actuators can be used in various types of flow control and flow modification applications depending on their type and positioning. The use of plasma actuators in an intermittent mode allows for the excitation of Tollmien-Schlichting instabilities in laminar flows, and thus triggering transition and achievement of stall delay. Other types of actuators, such as the plasma wall jet actuators, are able to create plasma sheets, vertical or at angle with the wall surface, thus achieving effects similar to vortex generators [7, 8]. Shear flows can also be manipulated by plasma actuators via triggering Kelvin-Helmholz instabilities [10].
The application of these principles in airfoil flow control is currently under extensive investigation. The results for low and medium Reynolds numbers are positive, while the effectiveness of these solutions at high Reynolds numbers is significantly reduced [8]. With respect to wind turbine applications, plasma actuators are under extensive research [9, 11] and their applications in this field seem to be promising. Apart from the apparent application in substitution of the popular passive vortex generator solution, there is also the possibility to utilize them as means of drag and vorticity reduction at the blade root region. Recent experiments by Pechlivanoglou and Eisele have shown that the existence of plasma actuators could reduce the drag due to the Karman vortex shedding behind a bluff body and at the same time generate lift. Such a bluff body is the cylindric root of wind turbines blades where the application of plasma actuators is currently investigated.
The DC surface corona discharge actuator consists of two wire electrodes mounted flush on the surface of a dielectric profile (Fig. 5a). When a high DC voltage (>10 kV) is applied, a corona is formed around the smaller diameter wire (usually the anode) and an electric wind is created tangential to the surface between the two electrodes. The electric wind is capable of modifying the boundary-layer airflow profile. Figure 5b displays a visualization of low velocity airflow along a flat plate. If the actuator is off, the smoke remains horizontal. When the actuator is active, flow above the anode is entrained towards the surface from the outer layer, causing the smoke to be drawn to the surface and then accelerated in the discharge region. The advantage of this device is that it requires a simple power supply; however, the design is limited to use in an electric wind velocity of only a few m/s [12].
Electric field strength produced by a flat plate is determined by the following equation [13]:
where ja is surface density of an anode charge; jk is surface density of a cathode charge, C/m2; s0 is dielectric constant, 8.85^10-12 F/m; E iselectric field strength, V/m.
a)
b)
Fig. 5. a) Schematic view of drive DC corona discharge, b) 2D visualization of controlled air flow along the flat plate [14]
The Finite Element Method (FEM) method in QuickField was used to analyze the electrostatic field [M], Electrostatic problems ¡lire; described by the Pois eon ezuatzon for ehs scalae aleatric potential U. The squatéon is as folfows [14]:
d . d ( dU Id Pvdq) = -—I £x-d- l+—
( dU 1
s
y
(4)
Srly x dx ) dy^ y dy
where U is voltage applied to a plasma actuatuc, V; ex, sl are comjtonf nls of the dielectric tensor; pV is volume denrity of anelectric charg;.
Elcclric felt strength is gsvenby thefollowing expression:
E = -W. (5)
Tl^e electricchai^i^^ ofait ozana porticle in ihe electrostatic field is given by:
q = 4;oer0cn0, (6)
where i^is ^lec;tric charge of an ozone ion, C; r is distance from the particle to the considered point of the space, m;eteis electric cotentisl, V.
In tha plasma, pn ozone particie it certnunded by nihet ohateed particles. Owing to Coulomb (electrostatic) attraction, pl sma particles prevail nearby the considered particle which have an opposite charges related to the charge q. They weaken (or screen) the particle field in the plasma. As is known, a poteitM s olia charga f fl^lcl ns decreagingwgth )he d^tfnce am Ihe p°esmafaster thanin a vacuum.
q =-. (7)
e-/D
A te et>ye icreectcglength D is determined by [16]:
D = <6eJT2l( 2n0e2 ) . (8)
where T2 is absolute temperature of electrons and ions in the plasma, K; k is Boltzmann constant, 1.3807^10-23 J/K; n0 ischargeparticleconcentration, m-3; e ischargeof the electron, C.
Equation (6) allows for the utilization of the calculation of lift force under plasma actuator operations,and its influenceoncomponentsunder examination.
Fig. 6 shows a cross section of the airfoil. When airfoil flows act as an aerodynamic force, they can be divided into two components: the lifting force and resistance. The lifting force acts on the airfoil
- 670 -
a)
b)
Fig. 6. Vector diagram of forces and air flow rate on airfoil cross section: a) with increasing lift force; b) with limited lift force
perpendicular to the direction of flow leakage rate (vr). The resistance force coincides with the direction of the velocity vector free stream flow. Figure 6 depicts the lift (dFL) and drag (dFD) forces are denoted respectively, as well as the plasma actuator action accordingto its locationontheblade surface. The angle OrSwe epthedireclionofflowandspard freeeOreem ira.
Lift (dFL) and drag (dFD) forces are determined by [16]:
Pi
Ch (X yU r (R ) • Cl ■ dX ,
dFL (x) = Ppch (x) • Ur (R1 )2 • CL ■ dx
dFD (x) = P ch (x) Ur (R )2 •CD ■ dx,,
where p1 is air density, 1.223 kg/m3; Ur is relative wind velocity, m/s; CD is drag force coefficient; CL islift forcecoefficient; FD isdragforce, N; FL is lift force, N.
— 671 -
"The resultantrelativevelocity definedthroughits direction rtand its modulus Ur, which is dotormtned h^a^ thenotstianal speed m through:
8 = arctan
v®Ri J
u2 = ®2
( U2 ^
®+R2
V® J
(10)
where at is -^iis^d epaed, mbt; ro is angular speed, rad/s; ig is blade radius , m.
Culculatieg tPe camponent p makes it posgieie tu dotermine th<s umouet of lift. The wind speed given bythtboundarycondttion is constent. loe calculations of mechanicef teesion, wind speed is foreeulatednumerically ahroug^ressure^bsrrit^as [5, 16]:
p = CL P^±Ap,
(11)
to is oir presrure, Pa.
The pressure difference caused by gas ionization depends on temperature and electric field strength.
tp = -=\[ PPRdT = | — --P) Po ■ i e-qE'kT R dT, (12)
where o is ozone molar mass, 48»103 Og/mol; ji2 is mxygen moOar maas, 32»10"3 kg/mol; T, isabsolute temoerrtbre of ram air, K; T2 :1s; absolute temperature of electrons and ions rn t4e piaoma, K; R is onoveosal gns constant, 8.Z145, J/(mo№).
Thepressure differencemay be also given by:
Ap =P=P. 2
wheoe az ieozon denrity, 2.14 kg/m3;
Ceosidrr (ecp and gprive tdr equation for m/
(13)
- p0-\eTElkTRdT.
hfi 1
i =J--
pPiKu p
Am appiladnaa louaicl satino orr a reiird Ourbsne araOo ie eopressed by:
„ n , i c
(14)
F =
p
P
J_
h y
p0 -P C J" eTkTRdT,
(15)
wtere is force of rnfleencr ofaptesma florv on a MbOo, N; o, it platma actuatorarea,m2.
Aocbrdlng do "the WoeOhmann-Franz-Lorehz law, which mskes a aelatiob between the thermal eorrdectioitf, dOeelectricaleonbuetivite aed tie tempcraeere Zod maleculetof ae ionized ozone, the followingoepression isobtained[18]:
5 = 5
Xq2 cm2T2
(16)
where a is electric conductance of an ionized gas, Ohm-1; k isthermal conductivity of ozone molecules, W/(m^K).
Using the similarity method for problems of aerodynamics and mechanical strength, mechanical field calculations are carried out, where pressure increment produced by ionized area of a wind turbine blade is taken as initial data [19].
The software package QuickField was used again, this time to model the influence of the DC surface corona discharge on wind turbine blades [20].
Figure 7 depicts the calculation results of the electrostatic field, on which a visible area of a high concentration of lines of force on the surface is causing a corona discharge. Ionized gas creates extra pressure, and in turn, affects the lifting force.
Figure 8 shows the calculations of mechanical deformations performed by usage QuickField. This software allows solving problems of the theory of elasticity in the terms of plane stresses, plane
The electric field strength E (IC^B/MJ
Fig. 7. Theresult ofthe calculation ofthe distribution ofthe electric field on thesurfaceofthebladeunder the influence of the DC surfac e cotona dischaeee
Fig. 8. The result of the; calculutioo oftlre mechaoical rtress uostributian
it 67C -
deformations ond axially srhmmetrrca1 sfross dolribntioytsfth irotrooic and orthotopic materials. In two-dimensionalformulation,thedisplacement hold ie asrumed to be completely defined by the two componeete oftUo nt^pjl^c^fo^iit-^^^torciat each point [20]:
{S} =
where Sx,Sy are componentsofthe tensor of mechanical displacements, mm. The coiresyonding stress is defined as:
(17)
M=
a
a„
(18)
where ax, ay, Txy are componentsof thetensorofmechanicaldeformations, N/m2. The equationforvolumeforcedensity is given by:
= -f ■ = - fy
+
dx dy
dr =CT
1 y
dx dy
(19)
where /x,/y arecomponents ofthevolume force vector, N/m3.
Calculations ofthe fy componente nableifor debe rmination of the lift force. Windspeed, beina ii^e a onrSant value, lh girtn ba oa boundary eondition. In the terms of stresses, wà nanpenOisformed tboough tfe près sore paermeter acnosdinf to the following equation:
P =
0
PU 0
(20)
Calculations of the mechanical deformations were conducted in QuickField. Figure 8 shows the representation of the flux field calculation result of mechanical deformations that affect the wind turbine blade in contact with wind flow.
Figure 9 shows the calculation results based on the blade lift versus angle of attack, which illustrates the effect of increasing the regulating capacity of the wind turbine blade lifting force using aDCsurfacecoronadischarge on its surface.
The significant advantages of the Plasma Actuators in the field of mechanical structure (e.g. small size and robust construction) lead to easy and effortless integration on wind turbine blade structures. The integration process involves a simple adhesion step where the plasma actuators, in the form of stripes, are glued on the blade surface. The only elements that need to be properly integrated are the actuator power cables. The overall power requirement of such systems is very low [14, 15].
The Concept of Variable Length Blades
The variable length turbine blade was first conceptualized in 1997. In 2002 the first variable length wind turbine was put on a Bonus 120 kW turbine [21]. The blade changed in length from 8 meters to 11 meters, using an existing 9 meter blade as a plug. The proof of concept blades flew
9 8.55 8.1 7.65 Lit Force. N
f
"v.
6.75 6.3 /
/
5.4 4.95 4.5 4.05 3.6 3.15 2.7 2.25
/
/ s
/ \
/ \
■ r \
■—7 ». —
f/
0.9 0.45
Anqle of attack, deq
q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 18 20 -----" plasma actuator ti the lower part of the blade the absence of a plasma actuator plasma actuator at the top part of the blade
Fig. 9. Comparative characteristicsofthewind turbineblade liftversus theangleofattack
for 14 moetha.The Olaees \hfre modeout of Kenetefh 56-101 tipis mountef toslileson 9 meeer bttelei. Ii^notuallr^Ohssp^i^t^S^o^nyp^e Mode s wereefetscerl by proof o5 manufacture blades made during the project [22].
The mathematical model of this device is described by:
PCx^C^A^JW2, (21)
where Cp is power factor of wind turbine.
The basic concept of variable length blades is to increase the swept area of the rotor when there are low -eiedr. As windie ioc rf ase,the rating of the turbine will be achieved, and as the wind continues tb ifarease^th btagarare rtlrattee.This retraction ob bledes ^et^oci^s tie wweet nrea of therolnr, wl^^ctV lowerelvads sit olis tnrbme^wd maintains a ere-dsterminedlurbrns eswer output. In stormy conditions, the blades can be run shorter than the standard length blades they replace.
Calculaeinns have ehown shel powerismcoeased by 3f% by shaygrngnte kngihof tteMadhand these bMet seviss effective a, Sow windspf v dc inZono1! tFig lO^
Expe^^ie^s^fet^l^Wi^bo^g^eni^ato conhwrnsd shffheoreliaat assumpfionsand cntcuiationa.Figurel 1 shown thn nowerpreduneabf Sgs preweoe blefesinshort,mediu m and long positions [22].
In summary, the advantages of variable length blades are: improves power production in low winds; allows turbines to continue running in higher wind speeds than standard bladed turbines; reduces the need for different size blades for different wind regimes; reduces the number of blade molds a manufacturer must make to support a single size of turbine; allows control of peak power output; reduces array losses; lowers the cost of wind energy by improving annual power output; makes shipping and installation easier by shipping in a shortened position; allows blades to be self cleaning for dirt and ice removal; and limits damage in extreme winds because blades can be shortened to less than standard length.
the Aero star (Veriablade)
10 15 20 ¡nil speed, in s
25
30
Fig. 10. Comparison ofthepower curves ofturbines withvariable lrngthblades anc lE^xecllei^jJtht^kdefi
180
tec pa lr0
pe ire
i &H
100 SO 60 40
30
o
10 15 20
Wind speed, tn/s
25
30
—minimum nominal
-maximum
Fig. 11. Experimentalpowercurvesfor variabte lvngShblailes
The develogment oa iuch syit nms is stillenthe rese^i^eh iSage^utiUs Hkefy tgar valhenr£^r^i^1^ure, tl^eywiris^omgSewitli fixad ieisjftUi bnadas, es "ttvoy hnve ohvtvue efficiencx dmneesjis^mei^ie.
^c/e'vo Flow Contarl Dev/ese
One foaetvoaMc ae^e to cyunlvt y^trdssies^^ogtds ie fy su^evtent curvent fu^spam attcts c onlrvl wtih ocahse Siieev cronS^o1 tAFCg devoies. Piichmg cc(rutd siilS be sseed dx oistlit^iztt ^i^anjoe flieiyyaiii cyotrvl aetvbynamic SOTqmz, winc AFc devicee wouib tea dbSi tz veacl fuiiticiir tar redumv ife rtsei^ia.ryeo anU ii^i^]r^ltrehar^i^y1rvnttf cdutf dbc tqrbrfentwinda.The onr^ii^l^^dtdr^Or^the^ (^es'it^ea v1so havc omv pocvntial ivranvfarr' fauefits: eiees]^cpi5 seidy Tseu d^jDte1?^»! fo inett;cos; life af iHif ftqye at ioao winvi ideede, vdowrng the teiine to cut"! eariieiabd capture additional energy; active devices could aid in energy capture end ignU mttiggUo n oo tnh^i^^^ ihai eoperlcnce nigS arimyeiiectb; de\^lres n^Che ueed So peevani towcc sfeikes^Uowing foHae^edrnmeaer rotoroto.c uad^^n^l^ersbaincc^c^t^^n enee^ ccpcm^ and avrocfynanrio pter00 vmance znhancemenO anil nd^ reductkmeopldbpre ^oedtyneamtrnmngkmrnar flow over z tacger accd ef Sde d lsss^s^.
Tnsrsarefiftffn dediceeselathave ehzwn boCentixtfотwiqdtnebinfcontrof future
research. However, several of the techniques have not yet been investigated for wind turbine control. Microflaps are the most promising.
The microflap is a rotating device. It takes the position of the trailing edge and is able to rotate 90° >n °>oeh direcAions. Tgd optimum micvofladienhr isonl^e layerihiokness
(P^e^°/oehued).eOCFe) suoc^^d of a micrvflap iv eAe^ren in Cr^.S2. Rcehringrhoflap ^pdh^^^^t^ienvNgti^vn mlace reduooe tifT and rnhuti ngog Aus^^^i^rArc^p ^i^e;n^rhrv^(2ue^a^^cv>^^ureu^(re Adfo. Ohio oh^u^onpf ie appealing because the trailing-edge location provides more effective lift enhancement and the design dhov noereqdire a bhenitcatimg e^n.LiimOedsAu.kstave.een oenthKnod on this concept, which mlius ml a^i^fincN^l; Oo Nofino afl vf i^O^g Oenefids anf FruwngcPe. Snme antictpaeed hurddev one m^niminfng dir lenuoo anW dos^v^ni^g a eimplo, iffd^i^ivo aoeuation sestemdhatis vfpabloofroratingrhd hi; bi-directionally to an angle of 90° [23].
mendOn gfMoc!eliFg anOCnlculation LtfPForce
This donko Irae deen n^o^id^ieir unr^ rhe sFfewaoe packa.e ElCm aed Comnol anh ehe oevuits vie given above. Profile S830 was selected for investigation (Fig. 13).
Main assumptions and suggestions: Air movement - laminar; neglect transients in aerodynamics blaNe;dpformoiihnls m^edo. in ca!cugatinA the etesOicstoeie; s!enofdlscreeization fdrrolutionhNAio w -edierees.
From modelgngecsnlgs,the characeerietics vrf t/ndretribution of air flow m"esanreactingou!deblaUN (Fig. 14), the distribution of the velocity field of the wind flow in the boundary layer of air surrounding ege Flado(FiglpNand,uaa fina^eou^ nepennenfcogt:hdtif! fo^c^e onrhooNglemlcronhAstotile nradeguogacowgreob!sonnd OFm-K^l-
Fig.l2.Model ofsmisroflapin two positions
positive direction
Fig. 13. Profile of the blade S830
Main stress (N'm*)
Fig. 14. Pressure distribution of the air flow, acting on the blade
Fig. 15. Distribution ofthevelocityfield ofthewind flow intheboundarylayerofair, surrounding the blade
Lift force. kN
]( M 30 « M MJ TO M SO 1« HP 1ÏB J»
— »=0--if3 ......-ipio -----^15 -<i=l;0 microflaps angle,
degree
Fig. 16. The lift force for the blade surface
microflaps rotate m positive direction, filed length blade
—— — microflaps rotate in po sitive direction, length blade increas e from S to 12 m microflaps rotate in negative direction, length blade increas e from â to 12 m *- > i i microflaps rotate in negative direction, feed length blade >—* microflaps rotate in positive direction, length blade decrease from 12 to S m ■ -«■•« microflaps rotate in negative direction, length blade decrease from 12 to S m
Fig. 17. Lift forcechange(windturbineoperating withvariable blade geometry)
After running simulationsofmicrodevices and! -variable length bladesseperately, it was decided to combine thtsetvu mothods andavaluatolhebevefilsvf ve^r^j^l^^iigevmstor. Sitoeldi^oe^s wrre also produced using the ElCut. Blade length varies from 8 to 12 meters, wind speed from 5 to 14 m/s (zone 2), the microflaps rotation angle of ± 40 degrees. The simulation results are presented in Fig. 17.
Conclbsioes
Plaemgyetugtort navu reeetued contidreable attrulionevatlherecebSyeara asa psauttuol flow Ore; Polbeie ydvanraves ever f^s^ts^t^(t^s^slm(^cS^c^ntn^ eOTieeti ghebareanieto directly eorvert electrloseaneegyiptoktueSicensrgy,whichle usedto mvdlaptheasrflowlTbeyhave advantages onas mechamcal dovlces;tУe desPce ss ssmple, linbtwetgbtandslsci nomovmo owns; therefore, it is likely AS beasousee oS o^l^^asson <^r nnite.
Research has also shown that the presence of the electrodes does not interfere with the surrounding airflow when inactive and major modifications to the turbine blade are not required for installation. Another feature is that plasma actuators can be designed to operate in co-flow and counter-flow eon&tkms, wWc1 aUowi for more cgioes w.ee controUingk)caliesdflow.
Amothemrticvlmcdel af DC rurfacoeотonadisevargc was usse! bassdone^rrimentalttudies conduuted indie UlliredSSarer. OnShenntis of tSs mathematlooi mrdct it la sltowo rtsgt tliis DC surfacecoronadtteilaege(moomearisontoo cogyyntlonaS pitch regulrted wiuo trAine, wHi increase ohe onailgVlr repelating rE^nneits' to o^nn^e the angle of attack, which ensures reliable operation of the wind turr>snem0lghwtndloaVcondtrions. WithChywinVlnrbinelnpowoiliimited mode,tha pre s ence of a plasma actuator would minimize the need for low blade angle of attacks. Power corona discharge technology will provide access to the rated power of the wind turbine in less time, as shown in the simulation results.
From these results it is seen that the theoretical assumptions are confirmed. Rotating the microflaps in a negative direction increases the lift force and the converse is true [24]. According to the results, changing of blade geometry through use ofmicroflaps gives 5-10% of regulation, so the wind power
plant can reach rated power more quickly, and in Zone 3the blade will have some reserve regulation to utilize at the angle of attack needed to maintain constant power.
Acknowledgment
The reported study was supported by Russian Foundation for Basic Research, research project No. 31 16-38-60080\15 mol_a_dk and No. 16-38-00147 mol_a.
References
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