PENGARUH JARAK ANTAR FIN PADA SILINDER BERSIRIP TERHADAP SEPARASI ALIRAN DI PERMUKAAN SILINDER DAN FIN
DOI:
https://doi.org/10.33752/reaktom.v2i2.203Abstract
Abstrak
Fluida yang mengalir melewati objek akan memberikan pengaruh yang cukup signifikan berupa gaya angkat dan gaya drag pada permukaannya. Besar gaya-gaya ini tergantung pada kecepatan aliran freestream, profil aliran, kondisi permukaan benda, bentuk maupun orientasi benda yang dilintasi. Pada bluff body, gaya drag didominasi oleh pressure drag sedangkan pada streamlined body, didominasi oleh skin friction drag. Efek viskositas memberikan kontribusi terhadap gesekan sehingga fluida pada boundary
layer kehilangan energi selama mengalir. Hal ini dapat menimbulkan separasi aliran di permukaan benda jika dikombinasikan dengan kenaikan tekanan. Semakin cepat separasi aliran terbentuk, maka luas daerah wake semakin besar. Pada penelitian ini, diamati silinder bersirip dengan variasi jarak antar fin untuk mengetahui pengaruh fin pitch tersebut terhadap separasi aliran di permukaan fin.
Benda uji berupa silinder sirkular diameter 25 mm ditambahkan annular fin pada permukaannya dengan tebal fin 2 mm. Pengaruh jarak antar fin dengan variasi 10 mm, 14 mm, dan 18 mm terhadap separasi aliran di permukaan fin diamati dengan metode simulasi numerik menggunakan software Fluent 6.3 dengan bilangan Reynolds 2,5 x 104 berdasarkan diameter silinder dan kecepatan rata-rata inlet.
Hasil pengamatan menunjukkan semakin rapat jarak antar fin, separasi aliran yang terjadi pada ruang antar fin terjadi lebih awal. Ketika jarak antar fin meningkat, posisi separasi aliran dan vorteks di permukaan fin bergerak mendekat ke daerah di belakang silinder. Hal ini menunjukkan bahwa udara tidak mengalir dengan baik pada daerah tersebut untuk fin pitch yang sempit.
Kata Kunci: Silinder bersirip, separasi aliran, jarak antar fin.
Abstract
Fluid flowing through the object will give a significant influence in the form of lift and drag force on the surface. The magnitude of these forces depends on the speed of the free-stream flow, flow profile, surface condition of the object, the shape or orientation of the object being traversed. In bluff body, drag force is dominated by pressure drag while in streamlined body, dominated by skin friction drag. The viscosity effect contributes to friction so that the fluid on the boundary layer loses energy during flow. This can cause flow separation on the surface of the object when combined with the increase in pressure. The faster the flow separation is formed, the larger the wake area. In this study, we observed finned cylinders with variations of the fin distance to determine the effect of the fin pitch on the flow separation at the fin surface.
Test specimens of circular cylinder diameter 25 mm added annular fin on the surface with fin thickness 2 mm. The effect of fin distance between the variations of 10 mm, 14 mm, and 18 mm on the flow separation at the fin surface was observed by numerical simulation method using Fluent 6.3 software with Reynolds number 2.5 x 104 based on cylinder diameter and average speed of inlet. The observations show the closer the distance between fin, the separation of flow that occurs in the space between the fin occurs earlier. As the fin distance increases, the position of the flow separation and the vortex on the fin surface moves closer to the area behind the cylinder. This shows that air does not flow well in the area for a narrow fin pitch.
Keywords: Finned cylinder, flow separation, spacing between fin.
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