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

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 > (S1) Undergraduate Theses
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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