New Method to Harness More Wind Energy

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1 New Metod to Harness More Wind Energy M. Z. I. Sajid, K. Hema Candra Reddy & E. L Nages 1 Quba College of Engineering & Tecnology, Nellore, Andra Prades, India, 2 A & P, JNTU Anantapur, 3 Netaji Institute of Engg.&Tec. Hyderabad, India sajidmi@yaoo.co.in 1, konireddy@gmail.com 2, n2jntu@gmail.com 3 Abstract - A new and novel metod to arness more wind energy as been designed Details of te eperimental results and teoretical eplanation is presented in te paper. Te simplicity and economic viability of te metod is epected to be a boon in converting poor windy sites to usable ones and to arness more energy at te eisting windmill sites. I. INTRODUCTION Wind energy is rapidly emerging as one of te most cost effective and neat form of renewable energy. In te Annual Conference of te World Wind Energy Association, eld on 06t November 2006 at New Deli wit te teme Vision for Wind Energy, His Ecellency, te ten President of India Dr. A P J Abdul Kalam said tat "Energy Independence is te lifeline of a nation". Te main constraint for wider use of windmills for irrigation and wind turbines wind speeds prevailing in any parts of te world. Let is consider te eample of India. Te pattern of wind speeds prevailing in India based on Indian Meteorological Department (IMD) wind data (1,2) are presented in Figure 1. From tis Figure it can be easily seen tat in over alf of te area of India te wind speeds are in te range 5-10 Km/r, most parts of wic are not suitable to tap wind energy (te windmills available in India is around 9 Km/r). If by some means we could increase wind speeds by about 30% we can cover more areas wit windmills and also increase windmill output at te eisting sites. It is a known fact wind speeds above ills are muc larger tan tose at equivalent eigts above flat ground. Moreover power is cube of velocity. Wit tese two facts in mind an attempt is made to design a metod to convert poor windy sites to usable ones. II. EXPERIMENTS Some eperiments were conducted on models simulating dams or escarpments in a slow speed wind runnel. A 60X15 cm and 5 cm ig rectangular model wit longer side perpendicular to te air stream was mounted on te working table of te wind tunnel. Tis enables it to ave an almost two-dimensional wind flow over te central portion of te model. For a 30 0 slope wind velocities were recorded at various eigts in a vertical plane above te centre of te model. Simultaneously, measurements of te velocities was made at equal eigts on plain surface. A micro-mini vane anemometer was used for wind power measurements. Wind velocities at different eigts above te dam were epressed in terms of te corresponding available velocities at equal eigts over a oriontal terrain. Te variation of tis ratio wit eigt epressed as a fraction of te eigt of te model is sown in Figure 2. Te results sow tat wind speed increases over te escarpment starting wit 1.35 times at te top of te dam and increasing gradually upwards. Te maimum increase is noticeable at about alf of te escarpment eigt. Terefore, te windmill if it were to etract te increased wind velocities sould ave its ais at tis eigt. Fig. 1 : Annual Mean Wind Speeds International Journal of Applied Researc In Mecanical Engineering (IJARME), ISSN: , Volume-1, Issue-2,

2 New Metod to Harness More Wind Energy In general, te value of wind speed mentioned in meteorological data is its tis is taken eigt about 12.2 meters and tis is taken into consideration wile calculating te possible wind power tat may be tapped. To know te real gain in field, wind speed as to be found wit respect to te above value. Te calculated values are plotted in Figure 3, along wit a wind profile over a plain terrain. From te grap it can be seen tat te maimum gain is about 1.5 and ence te power (1.5) 3 = Let us take a small village in wic we need about 50 windmills to meet irrigation and drinking water needs and also for small power generation. te above results indicate, if we construct an earten dam of typical 10 meter eigt, 30 0 slope and 10 meter lengt since te power is increased by 3.38 times, we may need only 15 windmills to obtain te same amount of power wit escarpments. Te earten dams are feasible to construct in rural areas in a country like India wic as uge man power. To find an answer for frequent directional canges in wind, furter eperiments were carried out an curved (concave saped) Wind speed at a eigt () above te escarpment Wind speed at te same level on a oriontal terrain Fig. 2 : Wind Speed At Different Heigts Over Te Escarpment 30 0 model and symmetrical triangular 30 0 model. In te curved model wind velocities were measured at te etreme ends and te middle, te increase was found to be almost sane (about 1.5 times) at about alf of te eigt. te triangular model gave an increase in wind speed of about 1.4 times at alf of te eigt. Tese results sow tat in coastal areas were wind direction canges in te day and nigt, symmetrical 30 0 escarpments (10 m eigt) can be utilied. In areas were frequent canges in wind direction occur, curved escarpments will be useful. In furter eperiments a 30 0 slope model wit partial slant portion (equal in scale to 10m) gave an increase in wind speed of about 1.3 times. Te latter eperimental results may be useful to increase wind speed at te eisting windmill sites. In a bid to find a ceap ceap material to make sloping structures and wic are mobile, bamboo as been cosen. Bamboo screens of typical sie (5 X 4m) can be made and te upper portion plastered wit a tin and uniform layer of clay and animal dung. Over te coating a polytene seet is covered. Te polytene covering will elp to give smootness and also prevent it from rain (In open grain storage, large polytene covers are widely used in India wic last for about 2 years). In coosing bamboo for te sloping structure te following advantages were taken into consideration. bamboo is abundantly available in any developing countries. Bamboos as well as blades for windmills in Tailand. Some studies by researcers reveal, bamboo tested ave been found to ave alf te yield strengt of mild steel (3.4). Also some work on bamboo reinforced slabs, bamboo-create wall panels and roofing elements was already carried out. (3,4,5). It was found tat carried reinforced slab can be designed like steel reinforced concrete taking permissible tensile strengt and bond strengt as 24,000 KN/m 2 and 350 KN/ m 2 respectively. Also some studies ave been conducted on bamboo-mortar composite wall panels and roofing elements. Te performance of tese types of structures ave been claimed to be satisfactory under various researcers (4-120 also confirm te versatility of tis low cost construction materials. Te cost of a typical bamboo screen (5 4m) wit clay coating and polytene covering may be about Rs.1000/- (about 25 US). Te bamboo screen can be made locally. Eucalyptus or casuarinas poles can be used in te supporting structure. Te ollow space beneat te bamboo structure can be used for storage. In areas were wind speeds are very ig and were one wants to save ground space, one can install a 10m structure (inclined at 30 0 ) made of asbestos seet before te windmill. Te supporting structure can be wooden or steel. Te Supporting structure can be wooden or steel. Te asbestos witstands rain and eat and as been in wide use as roofing material for a long time. Practical And Economic Feasibility To see te effect of 30 0 slope on wind speed, eperiments were carried out by placing slopes of International Journal of Applied Researc In Mecanical Engineering (IJARME), ISSN: , Volume-1, Issue-2,

3 New Metod to Harness More Wind Energy different rougness before a model windmill and increase in wind speed as been found to be substantial. Toug full scale field tests are yet to be conducted, te results of Bowen and Lindley (13) sow tat tere is good agreement between full scale field measurements and wind tunnel. Bowen and Lindley conducted field tests on a 13 m ig and 26 0 sloping escarpment. Hence, it is felt tat variation in increase in wind speed as was found on a sloping model in wind tunnel. Te earten dams are quite strong. Tere are some earten embankments around water storage tanks in villages in India wic are quite old. III. THEORETICAL EXPLANATION OF FLOW OVER ESCARPMENTS To predict te cange in wind distribution connected wit canges in surface topograpy, a metod as to be evolved wic will elp in te design of structures. Usually te eisting codes of practice suggest rules for modifying te design wind profile above ills, but some measurements ave sown suc ills, but some measurements ave sown suc empirical formula are unreliable (14,15). Hence, te need for simple teoretical solutions to boundary-layer flow over surface obstacles. A teory wic eplains te general features of te effect of a two dimensional surface ump on a turbulent boundary subsequently by Jackson (16) and subsequently by Jackson and Hunt (17). In furter studies (18) Jackson modified te above teories to be applicable to carious escarpment sapes. According to Jackson, as te vorticity in te outer part of te boundary layer is small, one can epect te disturbance to te flow tere to be approimately irrational. Tis implies perturbation caused by a cange in surface topograpy as eactly te same distribution as te perturbation to a uniform, in viscid flow caused by te same surface sape. Ten te surface can be found using ordinary irrotational teory. Near te surface, canges in viscous and Reynolds stresses are also to be taken into account. It can be sown tat te tickness of te layer in wic stress canges are important is muc less tan tat of te boundary layer, so tat close to te boundary layer in wic stress canges are important is muc less tan tat of te boundary layer, so te problem of an inner boundary layer being driven by an inner boundary layer being driven by an eternally generated pressure gradient (19). Metods to deal wit te above problem are available. (20) If te flow field can be divided into two layers as suggested above, te problem can be solved wit eisting tecniques. Before attempting te same, te following points ave to be resolved: i) Te magnitude of te irrotational disturbance in te outer layer must be found, ii) One sould find uniform velocity of te corresponding inviscid flow, iii) How to improve on te initial assumption tat te disturbance is irrotational iv) Te tickness of te inner layer in wic stress canges are important must be found. Te flow field over escarpment is sown in Figure. Here te surface is given as : y = f( L ), Were is te eigt is te eigt of te ill and L is representative lengt. L may be taken as te oriontal distance from te peak in wic te ill falls alf its maimum eigt. Near te ill ~ = = O( 1), L te irrotational layer is assumed as aving tickness of te same order, vi., Y ~ ( y f ) = ( ) =O(1) L we can write an epression for te oriontal velocity wit te limits Y ~ o as: U(Y) = U 0 (Y) +f L Uo 1 (Y)+ L U0 (L) Ũ (1) Here U (Y) is te incident velocity profile, and te first term is cosen to matc te solution in te inner layer near te wall were to lowest order te velocity is assumed to be a simple displacement of U. te second term is cosen for conditions at infinity, we ave U U o (Y) + 2 f 2 U o (Y) + L Uo (L) U U U o (Y) if Ũ o as Y ~ (2) To satisfy te continuity equation, te vertical velocity is written as V = L f 1 () (U- U 0 (Y ~ L)+ L Uo (L) V ~ (3) Were International Journal of Applied Researc In Mecanical Engineering (IJARME), ISSN: , Volume-1, Issue-2,

4 New Metod to Harness More Wind Energy ~ U ~ + ~ V ~ =o Y Equation (1) can be rewritten as U(Y) = U o (Y) +f(/l)u o 1 (Y)+ L Uo (L)Ũ Were Δ U Ũ = (in outer layer) Uo = _ U ( Y ) + /Y~ L U ( Y ) = 1- / Y=L Y ) = 1- = - = - +1 L) L) L) U(Y) = U o (Y) + L Uo (L) - L U(L)+f L Uo 1 (Y) δ = = L U ( Y ) Uo ( Y ) = - L +f L Uo' ( Y) Uo ( Y) Uo ( L) Were δ is increment factor 1 at Y = L, U o (Y) o δ o For te condition Y we ave f L =o o L ΔU ( Y ) 2L L 2L 2L we ave Y = m m = tanθ = 2L 2L tanθ = 2 tanθ L U(Y) can be found by eiter Reed s formula or 1/7 t law. REED S FORMULA Reed (21) using tower observations derived an empirical formula for te wind speed at a eigt ( 2) oter tan te observation eigt ( 1 ), for well eposed sites on flat open ground V( 2 ) = V( 1 ) [ c V( 1 )] a ( 2 / 1) b Were a= l n 1 - (0.0386= l n l n 1 - l n 2 ) b = l n 1/ c = 2.24 (m/s or mp) We ave δ = 2 tanθ [ Uo ( L) - Y ) Te teoretical calculations for finding δ are carried out as follows: 1) Assume U o (10) =1 All velocities ave to be multiplied by U o (10) 2) H, are cosen suc tat = 10m =30 0 tan L is calculated as follows : (a) For te given values of, and L Taking f L = o so long as o L (b) L 2L, Y / tan but For te same values of, and L taking f = L 2L ] International Journal of Applied Researc In Mecanical Engineering (IJARME), ISSN: , Volume-1, Issue-2,

5 New Metod to Harness More Wind Energy (c) 2L for te same values of, and L f L =, y / Te teoretically calculated values of δ at various eigts are plotted in te grap (Figure 3) along wit eperimental values. Tere is fairly good agreement at eigt (between 19 and 22m) and at oter eigts some variation is noticeable. A satisfactory eplanation for te variation in teoretical and eperimental results is difficult for te simple reason tat some factors were left out in te calculations of eperimental results for lack of sopisticated instruments. Neverteless te teory gives a broad picture of te prediction tecnique of wind over escarpments. Tere is still scope prediction,y Horiontal and vertical co-ordinates u Horiontal and vertical velocities, L Heigt and widt of te escarpment f(/l) Sape of escarpment U 0 (y) Incident velocity profile U 0 Δ K Y 0 ا Ũ,Ŭ Geo stropic wind Boundary- layer tickness Von Karman s constant Surface rougness lengt Tickness of inner Reynolds stress layer Perturbation in outer and inner layers Fig. 4 : A sketc of te flow field Tecnique of wind over escarpments. Tere is still scope to improve upon te eisting teory. IV. CONCLUSION Te eperimental and teoretical results sow tat tere is a definite increase in wind speed over a 10m ig, 30 0 sloping escarpment. Te earten dams and bamboo screens are epected to be a boon to cover more areas wit windmills and to arness more energy at te eisting to arness more energy at te eisting windmill sites. Te cost of earten dams, bamboo screens and asbestos seets is epected to be economic in view of te locally available resources and uge man power a available in rural areas in a country like India. Moreover te construction of earten dams and bamboo screens generates employment in rural areas and are a clear case of appropriate tecnology. Fig. 3 : Wind velocities at different elevation (i) Over plain ground (ii) over eart mound REFERENCES [1] IMD climatologically tables of observatories in India ( ), India met. Dept [2] Annamani and S. Rangarajan, solar Radiation over India, Allied Publisers Pvt.Ltd., New deli International Journal of Applied Researc In Mecanical Engineering (IJARME), ISSN: , Volume-1, Issue-2,

6 New Metod to Harness More Wind Energy [3] Datye K.R., Nagaraju S.S. and Pandit C.M., Engineering applications of bamboo, proceedings of te International Conference on materials of Construction for developing Countries, Bangkok, 1978, 1,3-20. [4] Ali and pama R.P., mecanical properties of bamboo reinforced slabe, ibid 1978, 1, [5] Mera S.R. Upal H.L. and Canda L.R., Some preliminary Investigations in te use of Bamboo for Reinforcing Concrete, India concrete Journal 1951, 25,1, [6] Kalita U.C., Kaanci a.c. and Tyagarajan G, Bamboo-create Wall Panels and Roofing Elements for low cost Housing, proceedings of te International conference on materials of Construction for Developing Countries, Bangkok 1978, 1, [7] Men inger R.J. and Plonr [8] idge R.P. Investigation of Treated and Untreated Bamboo as Reinforcing in concrete, Villanova University, Villanova, Pennsylvania [9] Kurien N.P. and Kalan A.K.A. bamboo Reinforced soil cement for Rural use Indian Concrete Journal, 1977,51,12, [10] Broms B.B., Problems and solutions to construction in soft clay, proceedings of te 6 t Asian Regional conference on soil Mecanics and foundation Engineering, Singapore, 1979, 2,3-38. [11] Ai M.A., consolidation of soft compressible clayed soils using split Bamboo filled coconut Coir s, Journal of te Institute of Engineers, Pakistan 1964, 25, [12] M.A. Ai and S.D.Ramaswamy, Appropriate Tecnology in Civil Engineering, Proceedings of te conference eld by te Institution of Civil Engineers, 1980, [13] J.J.A. Janssen, Studies on Mecanical Properties of Bamboo, ibid, [14] Bowen A.J. and Lindley D, Measurements of te Mean wind flow over various escarpment sapes, proceedings of te fift Australasian conference on Hydraulics and Fluid mecanics, Crist curc, new Zealand, 1974, [15] Freest ion D.H., Atmosperic sear flows over Ramps and Escarpments, 5 t Aust.conf.Hyd. and fluid Mec., Crist curc Dec [16] Bowen A.J. and D.Lindley, measurements of te mean wind flow over various escarpment sapes, Crist curc, dec.1974, [17] Jackson P.S., Te flow Round obstacles in Boundary Layers, P.D.tesis, Cambridge University, [18] Jackson P.S. and J.C.R. Hynt, Turbulent wind flow over a low Hill, quarterly T.Roy.Met.Soc. to be publised. [19] Jackson P.S. and A Teory of flow over escarpments, proceedings of te 4 t International conference on wind effects on Buildings and structures, Cambridge university press, 1976, [20] Jackson P.S. and J.C.R.HUNT, Turbulent Wind Flow over a Low Hill Quarterly T.Roy.Met.Soc. to be publised. [21] Launder B.E. and D.B. Spalding, Matematical Models of Turbulence, Academic press, London, [22] Reed J.W., Wind Power Climatology of te united States, Sandia Labs., Sand , June [23] Wind Energy Resource Survey in India-III, 1994,New Deli: Allied Publisers Ltd. [24] Wind Energy Resource Survey in India-IV, 1996,New Deli: Allied Publisers Ltd. [25] Wind Energy Resource Survey in India-V, 1998,New Deli: Allied Publisers Ltd. [26] Ministry of Non-Conventional Energy Sources, Government of India, Annual Report, [27] Meyer, N.I, 1995, Danis Wind Power Development, Energy for Sustainable Development, 2,No.1, [28] Wind Energy Resource Survey in India-VII, 2005 Centre for wind energy tecnology- Cennai. [29] Wind Energy Resource Survey in India-I, 1990,New Deli: Allied Publisers Ltd. [30] Wind Energy Resource Survey in India-II, 1992,New Deli: Allied Publisers Ltd International Journal of Applied Researc In Mecanical Engineering (IJARME), ISSN: , Volume-1, Issue-2,

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