Numerical Study Flow Separation Control in Conical Diffuser Using a Circular Ring Vortex Generator

., Chairunnisa (2015) Numerical Study Flow Separation Control in Conical Diffuser Using a Circular Ring Vortex Generator. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Diffuser is a tool used to convert kinetic energy into pressure energy. Diffuser is a closed channel which cross-sectional area enlarges along the flow. Diffuser is used in industrial field such as heat recovery steam generator (HRSG). The main parameter of diffuser performance is pressure recovery coefficient (Cpr), where the performance of diffuser is considered good if it has a high value Cpr. Cpr with low value is caused by flow separation. Flow separation is caused by large adverse pressure gradient (APG) and excessive friction effect. One of the efforts in controlling the separation is modification of diffuser with addition of vortex generator. Vortex generator contributes to improve flow turbulence to be able against APG and friction effect. Therefore, a research on diffuser modification is needed to determine the changes in the value of Cpr. This study is performed numerically using CFD software. Geometry model used in this research is 3D conical diffuser that has constant divergence angle (2θ) = 30° with variations of area ratio (AR) 2, 6, and 8. Upstream channel length (L1) = 200 mm, diffuser length (N) = 31, 108, and 137 mm, and downstream channel length (L2) = 452.8, 784 and 905.6 mm. The profile vortex generator is a circular ring mounted at a distance x/N of 0.1 from the diffuser inlet which the flow is assumed to be steady. In this study, the variation of Reynolds number (ReD1) = 1.89 x 104 and 4.50 x 104 based on the diameter of the diffuser inlet and the flow velocity at the diffuser inlet. The standard k-ε model and the second order discretization type is used in this study. The results of the study indicate that the addition of vortex generators at AR = 2 for ReD1 = 4.50 x 104 does not cause flow separation. On the other hand, the model of conical diffuser with the others configuration indicate a delay separation for all variations of the AR and ReD1. The delayed separation makes the performances of diffuser increases. It is followed by an increase in Cpr and Cpmax values. At ReD1 = 1.89 x 104 and 4.50 x 104, the value of Cpr decrease 26.3% and 7.8% for AR = 2, but Cpr value increase 6.04% and 16.5% for AR = 6, and AR = 8 Cpr value increase 13.5% and 21.4% based on baseline model. Total pressure loss coefficient (ζ) increases as AR increases. Instead ζ value decreases after adding the vortex generator in the diffuser.

Item Type: Thesis (Masters)
Uncontrolled Keywords: conical diffuser, vortex generator, pressure recovery coefficient, total pressure loss coefficient (ζ), flow separation.
Subjects: Q Science > QA Mathematics > QA911 Fluid dynamics. Hydrodynamics
Divisions: Faculty of Industrial Technology > Mechanical Engineering > (S2) Master Theses
Depositing User: - Davi Wah
Date Deposited: 06 Dec 2019 04:27
Last Modified: 06 Dec 2019 04:27

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