Sani, Reza Maulana (2016) Studi Eksperimen Karakteristik Aliran Melintasi Silinder Sirkular Berpengganggu Prisma Segitiga, Prisma Segiempat Dan Silinder Sirkular “Studi Kasus Variasi Jarak Longitudinal (S/D) = 1,45 - 1,70”. Undergraduate thesis, Institut Teknologi Sepuluh Nopember Surabaya.
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Abstract
Aliran yang melewati silinder sirkular sangat banyak
dijumpai di dunia teknik seperti pada struktur bangunan
pantai, struktur banguan off-shore, bangunan gedung,
struktur jembatan dan sebagainya. Gaya seret (drag force)
merupakan salah satu gaya akibat adanya aliran yang
melewati suatu body. Besarnya gaya drag sebanding
dengan daerah wake yang terjadi, artinya semakin kecil
wake dibelakang silinder utama maka gaya drag yang
terjadi akan semakin kecil. Adanya gaya drag umumnya
tidak diinginkan karena dapat mengurangi efisiensi energi.
Penelitian ini dilakukan secara eksperimen pada
sebuah wind tunnel jenis subsonic dengan benda uji berupa
seilinder sirkular dengan diameter 60 mm dan body
pengganggu berbentuk prisma segitiga, prisma segiempat,
dan silinder sirkular dengan variasi jarak S/D = 1.45; 1.50;
1.55; 1.60; 1.65 dan 1.70; pengujian ini mengunakan
bilangan Reynolds = 5,3 x 104 berdasarkan kecepatan free
stream dan diameter silinder sirkular. Karakteristik aliran
berupa grafik Cp, u/Umax , St dan CD diperoleh dengan
mengukur distribusi tekanan pada kontur silinder utama,
profil kecepatan dibelakang silinder, frekuensi Vortex
shedding dan menghitung gaya drag total.
Hasil yang didapatkan dari penelitian ini
menunjukkan pengganggu yang paling efektif mengurangi
gaya drag ditinjau dari CDp adalah pengganggu tipe D yang
mampu mereduksi gaya drag sebesar 79,04% pada jarak
S/D = 1,45. Ditinjau dari St/St0, maka pengganggu
pengganggu tipe C paling efektif mereduksi gaya drag
dengan St/St0 = 1.006 pada jarak S/D = 1.70. Hal ini
disebabkan penambahan pengganggu mempercepat transisi
lapis batas boundary layer silinder sirkular sehingga
mempercepat transisi boundary layer aliran 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
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Flow around a circular cylinder has been subjected to
extensive research efforts in a wide range of engineering
disciplines. Different studies show that this flow configuration
has many engineering applications and still presents one of the
major challenges in fluid mechanics; for example, bridge piles,
tubes in heat exchangers, and supporting columns for offshore
constructions. 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, some of methods were studied. This study is to present
the reducing of aerodynamics forces on a circular cylinder by
upstream installation of some bluff bodies as passive control or
disturbance, such as square prism, square prism rotate 45o ,
triangle prism rotate 30o, triangle prism rotate 210o, and cylinder
circular.
In order to reduce the drag force on a circular cylinder (D
= 60 mm), five bluff body; 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 = 1.45, 1.50, 1.55, 1.60, 1.65 and 1.70. The experiments
were carried out in a subsonic open circuit wind tunnel. This
facility has a 1780 mm long, with test section 660 mm x 660 mm.
The free stream velocity of wind tunnel could be adjusted
constant to 13.6 m/s, corresponding to Reynolds number Re =
5,3 x 104 (based on diameter D and the free stream velocity).
Seventy-two pressure taps with interval 5◦ were installed on the
wall of the circular cylinder and connected to an inclined
kerosene 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 pitotstatic
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 shedding
behind the cylinder was measured at x/D = 3 and y/D = 1 by hot
wire anemometer.
The experimental result show that there is reduction of
drag coefficient on main cylinder by upstream installation of the
some bluff body as passive control or cylinder disturbance. The
passive control “type D” at S/D = 1.45 gives has the highest drag
reduction on the large circular cylinder situated downstream. It
gives about 0.21 times the drag of a single cylinder
| Item Type: | Thesis (Undergraduate) |
|---|---|
| Additional Information: | RSM 620.106 4 San s |
| Uncontrolled Keywords: | gaya drag, perbandingan jarak S/D, body pengganggu, koefisien drag. |
| Subjects: | Q Science > QC Physics > QC151 Fluid dynamics |
| Divisions: | Faculty of Industrial Technology > Mechanical Engineering > 21201-(S1) Undergraduate Thesis |
| Depositing User: | EKO BUDI RAHARJO |
| Date Deposited: | 05 Jun 2020 00:27 |
| Last Modified: | 05 Jun 2020 00:27 |
| URI: | http://repository.its.ac.id/id/eprint/76104 |
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