Bir Wells Dalga Türbininin Hesaplamalı Akışkanlar Dinamiği Analizi

Year 2016, Volume: 7 Issue: 3, 569 - 576, 01.12.2016

Gökhan Özdamar Mertcan Mut Yeliz Pekbey Aydoğan Özdamar

Abstract

Enerji kaynakları, tükenme durumuna göre dünyanın var olduğu süreç içerisinde tükenen ve tükenmeyen,
kendini devamlı yenileyen yenilenebilir enerji kaynakları olarak iki kısımda incelenebilir. Tükenen enerji
kaynakları, kömür, doğalgaz, petrol gibi fosil kaynaklar ve nükleer enerjiden oluşurken, yenilenebilir enerji
kaynakları ana kaynağa göre üç grupta incelenebilirler: Güneş kaynaklı, Ay kaynaklı ve Dünya kaynaklı.
Ay’ın çekim gücü ile gel git olayı ve Gel-Git Güç Santralleri yardımıyla elektrik enerjisi, Dünya kaynaklı
olarak ise Jeotermal enerji ve Jeotermal enerji santralleri yardımıyla ısı ve elektrik enerjisi üretilmektedir.
Güneşten ise, su, rüzgar, güneş ışınları ve biyokütle enerjileri türemektedir. Güneşin atmosferdeki noktaları
farklı ısıtmasıyla rüzgarlar, rüzgarların deniz serbest su yüzeylerini sürtünme ile hareketlendirmesinden
dalgalar oluşur. Dalgalardaki enerji, dalga türbinleri aracılığı ile elektrik enerjisine dönüştürülürler.
Salınan su sütunu (OWC) tipi dalga türbinleri, bu dönüşümü gerçekleştiren en yaygın türbinlerdendir. OWC
dalga türbinlerinin deneysel olarak elde edilen verimleri ile, hesaplamalı akışkanlar dinamiği yöntemini
kullanan paket programlar yardımıyla hesaplanan verimleri arasında %40’lara varan büyük farklar
bulunmaktadır. Bu çalışmada, literatürde çok sık atıf alan ve deney-nümerik yöntem verimleri arasında
%40’a varan bir çalışmada kullanılan ve özellikleri bilinen bir OWC türbininin sonlu hacimler yöntemini
kullanan ANSYS Fluent paket programında analizi gerçekleştirilmiş ve baz alınan çalışmaya göre, verimde
deney sonuçlarına göre negatif yönde %40’a varan farklara ulaşılmıştır.

Keywords

Dalga Enerjisi, OWC, Wells Türbini, Nümerik Analiz, HAD.

CFD Analysis of a Wells Wave Turbine

Abstract

Sun heats up differently the zones of Atmosphere.
This causes the temperature dependent pressure
gradients between the various regions of air.
Pressure gradients generate the winds. Those winds
can occur at different layers of atmosphere in
different formations. If formations are on the surface
layer of oceans or seas these situations trigger the
creation of the waves. It is clear that, there is an
energy circulation cycle in this period. This cycle
starts from sun lights energy ends at wave stored
energy. This last energy source (wave) becomes
ready for daily usage as an electrical energy after
being processed. The energy that stored in the waves
converted in to the electrical energy by wave
turbines. That conversion is commonly made by
Oscillating water columns (OWC). These systems
are becoming popular while their efficiency values
increase. OWC systems are studied in two main
methods, first one is experimental method, the other
one is CFD. There are important differences
between the test results and CFD analysis results
about efficiency values of OWC’s. These differences
reach up nearly to 40%. At the literature, there is a
big discussion about that gap between the
efficiencies. The strongest hypothesis on this subject
can be described like that Mesh should realize the
real situation of the turbine and at the setup section
of CFD, the turbulence model must be suitable.
These are thought to be the cause.
In this study, the focused point is that the differences
between the efficiencies of numerical and
experimental analysis which are referred commonly
in the international literature. The literature is
described and in those studies one is selected as a
reference. Methods and the turbulence models are
selected from that reference. Generally OWC’s
analysis is a matter of turbine efficiency.
Developments are done especially in the turbine
section. These are special turbines called Wells
turbine. The importance comes from their
bidirectional rotation. It means for the both inlet and
outlet flow of air, they rotates in the same direction.
The properties of the studied Wells turbine are
known from the selected reference study. For
numerical analysis the same Wells turbine was used.
This turbine system consist of 7 NACA 0015
aerofoils with c=74 mm chord length, with Rhub=
101 mm hub radius and diffuser radius Rtip=155
mm. The length of the diffuser is 1000 mm.
To get the data for efficiency of numerical analysis,
ANSYS Fluent software was used. There are big
differences up to 40% between the referred study’s
experimental efficiency values and the Spalart
Allmaras turbulance modeled numerical analysis
studied in this paper.
To describe the methods in details, Ø variable
should be identified as the ratio of rotational
velocity to circumferential speed. Under the different
Ø values, the speed of inlet air is taken constant, 7
m/s in numerical analysis method. Related to that
speed, torque changes and pressure gradients
observed. As it clear in the definition of efficiency,
these are important components. Shortly, the change
of the torque and pressure are effecting efficiency
directly. To get that torque and pressure gradient
values, ANSYS software used for three main parts
first one is modeling, secondly preprocessing called
meshing, and post processing done in setup section.

Keywords

Wave Energy, OWC, Wells Turbine, Numerical Analysis, CFD