Nurmuyassar, Fayyadh Muhammad (2026) Studi Numerik Pengaruh Penambahan Forward Facing Step pada Pelat Datar terhadap Karakteristik Aliran dengan Variasi Ketinggian Facing Step dan Bilangan Reynolds. Other thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Sektor penerbangan modern menghadapi tantangan besar terkait efisiensi konsumsi bahan bakar akibat krisis energi global dan tuntutan dekarbonisasi. Salah satu penyumbang utama pemborosan energi pada pesawat adalah gaya hambat aerodinamis (drag) yang dipicu oleh fenomena pemisahan aliran (flow separation) pada lapisan batas (boundary layer). Untuk mengatasi masalah ini, teknologi manipulasi aliran pasif seperti boundary layer control (BLC) terus dikembangkan guna menunda titik separasi. Secara teoritis, penempatan rintangan geometris pada pelat datar akan memicu perubahan gradien tekanan lokal (pressure gradient). Keberadaan forward facing step berfungsi menginduksi pusaran kecil atau daerah separasi lokal (separation bubble) yang secara aktif menyuntikkan momentum ke dalam lapisan batas yang mulai melemah. Karakteristik dari manipulasi aliran ini sangat bergantung pada parameter ketinggian step (h) dan bilangan Reynolds (Re). Semakin besar ketinggian step diperkirakan akan memperbesar area resirkulasi fluida akibat perubahan tekanan yang mendadak. Sementara itu, bilangan Reynolds bertindak sebagai pengontrol tingkat turbulensi aliran yang menentukan stabilitas serta jangkauan pemulihan aliran (reattachment) di area hilir setelah melewati rintangan tersebut. Investigasi ini dilakukan melalui pendekatan komputasi dinamika fluida (Computational Fluid Dynamics - CFD) menggunakan perangkat lunak ANSYS Fluent 2024 R1. Tahapan awal dimulai dengan pemodelan geometri dua dimensi (2D) di ANSYS Space Claim yang mengintegrasikan pelat datar dengan forward facing step. Pada tahap pre-processing, dilakukan pembuatan jaringan elemen (meshing) yang rapat di dekat dinding pelat beserta penentuan kondisi batas (boundary conditions). Simulasi dijalankan pada kondisi aliran tunak (steady state) dengan memvariasikan ketinggian step sebesar 15 mm, 20 mm, dan 25 mm dan menguji dua kondisi bilangan Reynolds yang berbeda, yaitu 6.750 dan 19.000 Pemodelan fenomena turbulensi di dekat dinding dihitung menggunakan model viskositas k-ω SST (Shear Stress Transport) demi menjamin akurasi prediksi separasi. Hasil simulasi komputasi menunjukkan bahwa penambahan forward facing step (FFS) secara signifikan mengubah karakteristik lapisan batas dan tingkat hambatan aerodinamis pelat datar. Pada Re = 6.750, peningkatan ketinggian step dari h=15" mm" , 20" mm" , hingga 25" mm" memperbesar dimensi separation bubble di hilir undakan secara bertahap, dengan panjang gelembung (l_b/L) meningkat dari 0,0512 menjadi 0,0821, serta ketebalan gelembung (h_b/L) meningkat dari 0,0058 menjadi 0,0112. Peningkatan bilangan Reynolds ke Re = 19.000 terbukti mempercepat proses reattachment akibat tingginya momentum aliran, yang ditunjukkan oleh perpendekan panjang bubble hingga rentang l_b/L=0,0485-0,0789. Nilai koefisien drag (C_d) total mengalami kenaikan drastis akibat dominasi pressure drag lokal di sekitar FFS, pada Re = 19.000, C_d meningkat dari 0,00441 (pelat datar tanpa facing step) menjadi 0,45881 (h=15" mm" ), 0,63533 (h=20" mm" ), dan mencapai nilai tertinggi sebesar 1,19942 (h=25" mm" ). Meskipun secara keseluruhan penambahan FFS meningkatkan total gaya hambat (C_d), energi turbulensi dan pasokan momentum yang diinduksi di hilir step mampu menekan nilai shape factor (H) pada area hilir (x/L=0,9) dari 1,66 menjadi rentang 1,39-1,59, yang menandakan terjadinya transisi aliran menuju turbulen penuh yang lebih stabil dan lebih tahan terhadap separasi utama di sepanjang permukaan pelat. Secara keseluruhan, penambahan forward facing step pada pelat datar terbukti efektif berfungsi sebagai turbulent manipulator yang mempercepat transisi aliran menuju turbulen dan meningkatkan ketahanan terhadap separasi utama di hilir, meskipun konsekuensinya terjadi peningkatan total gaya hambat (drag force) akibat dominasi pressure drag lokal.
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The modern aviation sector faces major challenges related to fuel consumption efficiency due to the global energy crisis and decarbonization demands. One of the main contributors to energy waste in aircraft is aerodynamic drag caused by flow separation phenomena in the boundary layer. To address this issue, passive flow manipulation technologies such as boundary layer control (BLC) continue to be developed to delay separation points. Theoretically, placing geometric obstacles on a flat plate will trigger changes in the local pressure gradient. The presence of a forward-facing step functions to induce small vortices or local separation regions (separation bubbles) that actively inject momentum into the weakening boundary layer. The characteristics of this flow manipulation heavily depend on the step height parameter (h) and the Reynolds number (Re). It is expected that the larger the step height, the greater the fluid recirculation area due to the sudden pressure change. Meanwhile, the Reynolds number acts as a controller of the flow turbulence level, which determines the stability and the extent of flow reattachment in the downstream area after passing the obstacle. This investigation was carried out through a computational fluid dynamics (CFD) approach using ANSYS Fluent 2024 R1 software. The initial stage began with two-dimensional (2D) geometry modeling in ANSYS Space Claim, integrating a flat plate with a forward-facing step. In the pre-processing stage, a dense element mesh near the plate wall was created along with the determination of boundary conditions. The simulation was run under steady-state flow conditions by varying the step height at 15 mm, 20 mm, and 25 mm, and testing two different Reynolds numbers, namely 6.750 and 19.000. The modeling of turbulence phenomena near the wall was calculated using the k-ω SST (Shear Stress Transport) viscosity model to ensure the accuracy of separation predictions. Computational simulation results demonstrate that the addition of a forward-facing step (FFS) significantly alters the boundary layer characteristics and aerodynamic drag of the flat plate. At Re = 6.750, increasing the step height from h=15" mm" , 20" mm" , to 25" mm" progressively enlarges the downstream separation bubble, with the non-dimensional bubble length (l_b/L) increasing from 0.0512 to 0.0821, and the bubble thickness (h_b/L) expanding from 0.0058 to 0.0112. Increasing the Reynolds number to Re = 19.000 accelerates the reattachment process due to higher fluid momentum, effectively shortening the bubble length to a range of l_b/L=0.0485-0.0789. The total drag coefficient (C_d) experiences a sharp increase dominated by local pressure drag around the FFS, at Re = 19.000, C_d rises from 0.00441 (flat plate) to 0.45881 (h=15" mm" ), 0.63533 (h=20" mm" ), and peaks at 1,19942 (h=25" mm" ). Although the FFS modification increases overall drag (C_d), the turbulence energy and momentum injection downstream of the step successfully reduce the shape factor (H) at the downstream region (x/L=0.9) from 1.66 to a range of 1.39-1.59, indicating a transition to a fully turbulent boundary layer that exhibits greater resistance against main flow separation along the plate surface. Overall, the addition of a forward-facing step on the flat plate is proven to effectively act as a turbulent manipulator that accelerates boundary layer transition and enhances resistance against main flow separation downstream, despite the trade-off of an increased total drag force dominated by local pressure drag.
| Item Type: | Thesis (Other) |
|---|---|
| Uncontrolled Keywords: | Facing Step, Pelat Datar, Studi Numerik, Turbulent Boundary Layer, Turbulent Flow Facing Step, Flat Plate, Numerical Study, Turbulent Boundary Layer, Turbulent Flow |
| Subjects: | Q Science > QC Physics > QC151 Fluid dynamics |
| Divisions: | Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21201-(S1) Undergraduate Thesis |
| Depositing User: | Fayyadh Muhammad Nurmuyassar |
| Date Deposited: | 01 Aug 2026 03:42 |
| Last Modified: | 01 Aug 2026 03:42 |
| URI: | http://repository.its.ac.id/id/eprint/141418 |
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