Efficiency Improvement in a Two-Dimensional Axial Diffuser by Passive and Active Flow Control Methods

Authors

• Muthana M. Ali, College of Mechanical Engineering, University of Technology-Iraq, Alsinaa street, 10066 Baghdad, IraqFollow
• Qusay Jihad, College of Mechanical Engineering, University of Technology-Iraq, Alsinaa street, 10066 Baghdad, Iraq
• Ali L. Ekaid, College of Mechanical Engineering, University of Technology-Iraq, Alsinaa street, 10066 Baghdad, Iraq

Keywords

Boundary layer control, Separation, Diffuser, Bleeding, Pressure recovery coefficient

Document Type

Article

Abstract

This paper presents a combined numerical and experimental investigation of the effects of boundary-layer bleeding and thermal control on flow behavior and separation within a two-dimensional rectangular diffuser having an inlet cross-section (7 × 25) cm. The experiments were conducted under fully developed flow conditions over a wide range of Reynolds numbers, based on the hydraulic diameter, from (3.4×¹⁰4-1.64×¹⁰5) and for diffuser divergence angles varying from (5^∘ to 20^∘) .To accurately predict the velocity field, pressure distribution, and boundary-layer development, the incompressible Reynolds-Averaged Navier–Stokes (RANS) equations were solved using the finite volume method implemented in ANSYS Fluent 2021 R1 with an appropriate turbulence model. Experimental measurements were performed to evaluate the influence of Reynolds number and divergence angle on flow separation, pressure recovery, and flow stability within the diffuser.

The results demonstrated that increasing the Reynolds number delayed boundary-layer separation and improved pressure recovery performance. Furthermore, the diffuser configuration incorporating an additional secondary wall with a 3 mm bleed slot exhibited superior aerodynamic characteristics by extracting low-momentum near-wall fluid, reducing separation intensity, and enhancing the pressure recovery coefficient (CP_r). In addition, inlet air heating improved flow attachment by increasing near-wall momentum transport and weakening the adverse effects of the pressure gradient. A good agreement was observed between the experimental data and numerical predictions, confirming the reliability of the adopted numerical methodology. Overall, the combined application of boundary-layer bleeding and thermal control significantly enhanced diffuser performance by suppressing flow separation and improving pressure recovery efficiency. The conventional diffuser exhibited pressure recovery coefficient values ranging from 0.18 to 0.32, whereas the heated air with bleed-slot configuration achieved values as high as 0.70, corresponding to an enhancement of approximately 50%. Furthermore, the flow separation point shifted downstream from x/L ≈ 0.15 to x/L ≈ 0.45 demonstrating the effectiveness of the combined boundary-layer bleeding and thermal control strategy in suppressing separation and improving flow attachment. These findings provide valuable insights for the optimization of diffuser performance in aerospace, turbomachinery, and energy-related engineering applications.

Recommended Citation

Ali, Muthana M.; Jihad, Qusay; and Ekaid, Ali L. (2026) "Efficiency Improvement in a Two-Dimensional Axial Diffuser by Passive and Active Flow Control Methods," Engineering and Technology Journal: Vol. 44: Iss. 7, Article 8.
DOI: https://doi.org/10.30684/2412-0758.1578

DOI

10.30684/2412-0758.1578

First Page

187

Last Page

216