Rüzgâr enerjisi uygulamaları ve savonius rüzgar türbini
Wind energy applications and savonius wind turbine
Yazar: MUSTAFA YILMAZ
Danışman: DOÇ. DR. FETHİ HALICI
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Enerji Bilim Dalı
Derece: Yüksek Lisans, 1997
Konu: Mühendislik Bilimleri = Engineering Sciences
Dizin: Dikey eksenli rüzgar türbini = Vertical axis wind turbine

Özet:
Günümüzde kullanılan enerji kaynaklanın büyük bir kısmının tükenebilir nitelikte olması, yeni enerji kaynakları aramaya zorlamıştır. Rüzgâr enerjisi de bu kaynaklardan bir tanesidir. Geniş bir kullanım alanına sahiptir.
Fosil kaynaklı yakıtların kaynağının azalmakta olması üzerine alternatif enerjiler üzerinde yapılan çalışmalar yoğunlaşmıştır. Bu çalışmalardan en büyük payı ise rüzgâr enerjisi almaktadır.
Kaynağının sonsuz olması, mekanik enerjiye kolayca çevrilebilmesi, çevreye zarar vermemesi rüzgâr enerjisinin avantajlarından bir kaçıdır. Bunun yanında rüzgârın düzenli yoğunlukta olmaması başlıca dezavantajıdır. Bundan dolayı enerji depolama yoluna gidilmektedir. Rüzgâr enerjisi; mekanik, kimyasal, ısıl ve elektriksel yöntemlerle depolanabilmektedir.
Yatay eksenli ve düşey eksenli olmak üzere iki çeşit rüzgâr türbini vardır. Yatay eksenli türbinler genellikle büyük uygulamalarda kullanılırken, düşey eksenli türbinler (Darrieus, Filipinni, Savonius) daha düşük güç gerektiren, genellikle kırsal uygulamalarda kullanılırlar.
Savonius türbinini, rüzgârı her yönden alabilme özelliğine sahip olması, yüksek başlama torku ve düşük devir sayısı, aynı zamanda ucuz ve basit konstrüksiyona sahip olması kullanımını cazip kılmaktadır. Daha çok küçük uygulamalarda kullanılan bir türbindir.
Bu çalışmada, M.U. Mühendislik Fakültesi'nde bir Savonius türbini kompozit malzemeden imal edilmiştir.

Abstract:
With increased consciousness about the limited character of the fossil fuel supply, considerable attention has been focused on utilization of wind energy (beside other sources). A wind generator with simple design features and low maintenance is an economic alternative to the high initial investment cost of making electrical energy available at rural regions.
Wind energy use has several attractive features. Typically, high wind regimes occur in areas with low priority land use classification. The energy in the wind can be easily converted to rotary mechanical energy by aero-turbines and to electrical energy by coupling generators. The collection area is perpendicular to the ground surface and except for the small area occupied by the base of the tower and the support structure, the surrounding land can be used for other purposes as long as proper precautions are taken not to interfere with the operations of the aero-turbines. Wind energy is a nonpolluting and abundant renewable resource.
Before 1970, when conventional fuel prices (hydrocarbons, mainly) were low enough. Electric power production by wind energy conversion was not efficient from the economic stand point.
As a result of the oil price high increase in 1970, wind energy was reconsidered as being one of the alternative energies; vast research programs started being organized with in this field.
Even though the oil price decreased temporarily in further periods, the research in this field went on, since the process of wind energy conversion into electric power was not polluting. Meanwhile, the ecological problems have become a priority.
The use of wind energy to produce electric power has also other advantages versus the use of conventional fuels for the same purpose. Therefore, heat is not discharged from wind energy conversion and cooling water is no longer necessary; also, wind energy can be converted in the place and moment when it manifests itself, making unnecessary fuel transportation, as in the hydropower stations case or the accumulation of water supply, as in the hydropower stations case.
Wind energy conversion to electric power has disadvantages, too. Such as:
•	Technical impossibility to carry out high power units, under competitive conditions from the economic view point.
•	Very severe dependence of the produced electric power on the wind energy natural variations.
•	•Large expenses to build wind energy units versus their power and, therefore, a relative high price of the delivered electric power.
Since wind energy availability is very dependent on wind velocity, the collection and representation of wind data has been the subject of extensive research. The data are generally taken at some suitable location and high over one or more years, with the velocity measurement averaged over short period and recorded at least once each hour. This information may be condensed into an average annual velocity, average velocities for each month of the year, or ensemble averaged hourly winds for a typical day. It may also be expressed either as a probability distribution of the hourly velocity for the year or for each month, or as a wind duration curve, which is an integrated or cumulative probability curve. One finds that the use of time series data gives the most reliable results, the use of probability distributions the next best, and the use of averages and ensemble averages the worst. The velocity levels must also be adjusted if the wind turbine will not be located at the same height or at the exact some spot at I which the anemometer data were taken.
Since the power density in moving air (wind) varies as the cube of the wind speed, the power output of a wind energy system will have wide variations in the wind speed. Therefore, to provide a reliable supply (electrical, mechanical or thermal) to consumers, one has to employ some type of energy storage and reconversion system the smooth out the variations and supply energy during calm periods.
Energy can be stored in mechanical, chemical, thermal, or electrical (electromagnetic) form.
A.	Mechanical energy storage
a.	As potential energy,
o	in conjunction with hydroelectric systems (hydroforming)
o	pneumatic storage
o	compressed air storage
b.	As kinetic energy in flywheels
B.	Chemical energy storage
a.	Hydrogen storage
b.	Synthetic fuels and fertilizer
c.	Secondary batteries (electrochemical)
d.	Regenerative systems
C.	Thermal energy storage
a.	As sensible heat
o	in solid media
o	in liquid media
o	Dual (solid and liquid) media
b.	As latent heat.
o	heat of fusion of salt hydrates
o	heat of solid-solid transitions in crystalline structures
c.	Combined sensible and latent heat storage
d.	Thermochemical storage in reversible chemical reactions
D.	Electric or magnetic energy storage
a.	In high-intensity electric fields
b.	In high-intensity (superconducting magnets) magnetic fields
Once reliable cost-effective wind energy systems are developed and tested, the economics of their application within an electrical system is a complex issue. Suppose that we wish to determine the dollar value to a utility of a cluster of wind turbines. The process can be subdivided into the following four steps:
•A representation of the wind at the installation site
•A performance model for the wind energy conversion system, computes the expected power output from the wind velocity
• A representation of the load on the system
•A system model that simulated the technical and economic performance of the system together with the wind power input
There two kinds of wind turbines. These are:
•Horizontal axis wind turbines
•Vertical axis wind turbines.
Horizontal axis wind turbines have two or three blades. Shaft of turbine is parallel to the ground. It is used for high energy producing (wind farms)
Vertical axis wind turbines are used for small project. Darrieus, Filipinni and Savonius rotors are popular rotors of vertical axis wind turbines.
The Savonius rotor concept never become popular until recently, probably because of its low efficiency. However, it has the following advantages over the other conventional wind turbines:
•Simple and cheap construction
•Acceptance of wind from any direction thus eliminating the need for reorientation
•High starting torque
•Relatively low operating speed (rpm)
This advantages may outweigh its low efficiency and make it an ideal economical source to meet small scale power requirements, especially in the rural parts of developing countries.
Savonius used a rotor which was formed by cutting the Flattener cylinder into two halves along the central plane and then moving the two semi cylindrical surfaces sideways along the cutting plane so that the cross section resembled the letter 'S'. According to Savonius the best of his rotors had a maximum efficiency of 31%. Savonius wind generator is especially considered useful for providing the energy demands of small scale agricultural fields for water pumping purposes.
The aerodynamic efficiency of the Savonius rotor is poorer than that of other types of wind turbines. However, it is simple in structure, and has a good starting torque performance with the operating characteristics independent of wind direction. Hence, studies of the Savonius rotor are popular, and some efforts have been made to improve the aerodynamic performance without unduly affecting these characteristic features.
In the past, the performance of the Savonius rotor has been examined by measuring the global characteristics such as the torque and the power performance in order to optimize the geometrical configuration of the rotor for practical design. However, flow visualization experiments have been performed to investigate to flow mechanism around the rotors. Smoke-wire visualization pictures show clear indications of the lift force contributions to the torque mechanism of a rotating rotor, which is different from that of a still rotor.
Further quantitative discussion of the torque mechanism has been conducted by measuring the pressure distributions on the blade surfaces of the rotor with and without rotation (It is worth mentioning that the torque coefficient obtained from the integration of the pressure distributions on both sides of the blades are in close agreement with the direct torque measurement by a torque detector). These experimental investigations explain the mechanism of the torque and the power production of the Savonius rotor angles and tip-speed ratios. However, the experiments are limited to a rotor with fixed overlap ratios.
In this study; by considering the low average of the wind speed in our country (2.5 m/s), the literature research about wind turbines was made in the beginning. Caring on the work; a home kind, changed-Savonius wind turbine whose first motion can be easy in low speed was designed. Manufactured in three-store from composite material in M.U. Engineering Faculty.