WILUJENG, CAHYANINGSIH (2016) STUDI EKSPERIMEN KARAKTERISTIK ALIRAN MELINTASI SILINDER SIRKULAR BERPENGGANGGU PRISMA SEGITGA SAMASISI, PRISMA SEGI EMPAT DAN SILINDER SIRKULAR Studi Kasus Variasi Jarak Longitudinal (S/D) = 1,75÷ 2,00. Undergraduate thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Dalam kehidupan sehari-hari, aplikasi engineering sangat
banyak digunakan dalam berbagai instalasi industri. Aplikasi
engineering tersebut banyak yang berhubungan dengan aliran
eksternal pada mekanika fluida. Salah satu peneletian aliran
eksternal menarik adalah penelitian tentang aliran yang melintasi
body berpengganggu. Pengaruh dari fenomena aliran melintasi
body berpengganggu adalah terbentuknya wake seta drag force
yang disebabkan oleh separasi aliran. Adanya gaya drag
umumnya tidak diinginkan karena dapat mengurangi efisiensi
energy. Salah satu pemanfaatan hasilnya adalah penggunaan
konstruksi bangunan, fondasi bangunan off-shore dan jembatan
agar didapat desain yang maksimum.
Penelitian ini dilakukan secara eksperimen pada sebuah
wind tunnel jenis subsonic dengan benda uji berupa seilinder
utama dengan diameter 60 mm dan body pengganggu berbentuk
prisma segitiga samasisi, prisma segiempat dan silinder dengan
variasi jarak S/D = 1,75, 1,80, 1,85, 1,90, 1,95 dan 2,00.pengujian
ini mengunakan bilangan Reynolds = 5,3 x 104 berdasarkan S/D
dan kecepatan free stream. Karakteristik aliran berupa grafik Cp,
u/Umaz , St dan CD diperoleh dengan mengukur distribusi tekanan
pada kontur silinder utama, profil kecepatan dibelakang silinder
frekuensi vortex shedding. Pengukuran distribusi tekanan
menggunakan wall pressure tap yang dipasang di sekeliling
silinder utama, pengukuran profil kecepatan menggunakan pitot
static tube pada jarak pengukuran x/D= 3. Untuk pengambilan
data untuk perhitungan bilangan Strouhal dilakukan dengan
menempatkan probe HWA padajarak x = 3D dan y = 1D. Metode
Fast Fourier Transform (FFT) digunakan untuk mengubah
domain waktu menjadi domain frekuensi sehingga diperoleh
frekuensi vortex shedding.
Hasil dari penelitian ini menunjukkan pengganggu yang
paling efektif mengurangi gaya drag adalah pengganggu tipe B
yang mampu mereduksi gaya drag sebesar 73,5% pada jarak S/D
= 1.75. Hal ini disebabkan penambahan pengganggu
mempercepat transisi lapis batas boundary layer silinder sirkular
dari laminar menjadi turbulen. Turbulen boundary layer ini lebih
efektif menahan adverse pressure serta gaya gesek yang terjadi
kemudian mengakibatkan titik separasi mundur ke belakang dan
daerah wake menyempit dan menurunkan drag force.
The flow around circular cylinder has been subjected to
intense research efforts in the past, mostly experiment but also by
using numerical simulation. Different studies so that this flow
configuration has many engineering application and still present
one of the challenges in fluid mechanics, such as offshore risers,
bridge piers, periscopes, chimney, towers, masts, stays, cables,
antenne and wires. Therefore, it is still important to continue the
study with circular cylinder as an object, especially on a group
configuration. In order to reduce the drag coefficient of circular
cylinder, same of methods were studied. This study is to present
reducing of aerodynamics forces on a circular cylinder by
upstream installation of some bluff bodies as passive control or
disturbance, such as bodies Type A, Type B, Type C, Type D,
and Type E.
In order to reduce the drag force on a circular cylinder (D
= 60 mm), five bluff bodies; Type A, B, C, D, and E having a
diameter (d) or long side of 7,5 mm were used as a passive
control. The passive control were located in various spacing
positions of S/D = 1.75 ; 1.80 ; 1.85 ; 1.90 ; 1.95 and 2.00. The
experiments were carried out in a subsonic open circuit
windtunnel. This facility has a 1780 mm long, with test section
660mm x 660 mm. the frees stream velocity of wind tunnel could
be adjusted constant to 13,6 m/s, corresponding to Reynolds
number Re = 5,3x104 (base on diameter D and the free stream
velocity). Seventy-two pressure taps with interval 50 were
installed on the wall of the circular cylinder and connected to an
inclined cerosine manometer, which it makes it possible to
measure the pressure distribution around the circular cylinder.
The velocity profile behind the circular cylinder was measured
using a pitot-static tube connected to the inclined manometer. The
pitot-static tube was placed at 18 cm at the rear of the axis of the
cylinder or corresponding to x/d = 3, and finally frequency of
vortex shadding behind the cylinder was measured at x/D = 3 and
y/D = 1 by hot wire anemometer.
The experimental result show that there is redaction of
drag coefficient on main cylinder by upstream installation of the
sum bluff body as passive control or cylinder disturbance. The
passive control “Type B” at S/D = 1.75 gives has the higest drag
reduction on the large circular cylinder situated downstream. It
gives about 0.265 times the drag of a single cylinder.
| Item Type: | Thesis (Undergraduate) |
|---|---|
| Additional Information: | RSM 620.106 4 Wil s |
| Uncontrolled Keywords: | body pengganggu, perbandingan S/D, koefisien drag, vortex shadding, passive flow control, drag, equilateral triangular prism, rectangular prism, and circular cylinder |
| Subjects: | T Technology > TJ Mechanical engineering and machinery |
| Divisions: | Faculty of Industrial Technology > Mechanical Engineering > 21201-(S1) Undergraduate Thesis |
| Depositing User: | Users 13 not found. |
| Date Deposited: | 30 Dec 2016 07:37 |
| Last Modified: | 27 Dec 2018 08:36 |
| URI: | http://repository.its.ac.id/id/eprint/1236 |
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