Open Access

ARTICLE

Identification of the Flow Structure in Normal and Aggressive S-Shaped Diffusers of the Aeroengine Intake by Flow Visualization Methods

Hussain H. Al-Kayiem^1,*, Ali M. Mohsen², Ajyal A. Hassan Jallout³, Ali M. Tukkee^4,5, Raed A. Jessam⁶
1 College of Engineering Technologies, University of Hilla, Hillah, Babylon, Iraq
2 School of Engineering, Faculty of Innovation and Technology, Taylor’s University, Subang Jaya, Malaysia
3 College of Mechanical Engineering, University of Technology—Iraq, Baghdad, Iraq
4 Department of Petroleum Engineering, University of Kerbala, Karbala, Iraq
5 College of Advanced Technologies, University of Warith Al-Anbiyaa, Karbala, Iraq
6 College of Electromechanical Engineering, University of Technology—Iraq, Baghdad, Iraq
* Corresponding Author: Hussain H. Al-Kayiem. Email: ,

Energy Engineering https://doi.org/10.32604/ee.2026.086266

Received 27 May 2026; Accepted 02 July 2026; Published online 31 July 2026

Abstract

The gas turbine intake, including the S-shaped diffuser must be as short as possible to reduce the aeroengine size and weight. Reducing the length of the bare S-shaped diffuser (BD) results in an aggressive diffuser (AD) with risk of large flow separation and reduced performance. This study aims to investigate and characterize the flow structure, particularly the flow reversal and its separation, in S-shaped diffusers. Flow visualization was achieved using experimental flow visualization with wall-mounted tufts and CFD simulation of the flow field for five models, including BD, AD and AD/VG, fitted with three different types of vortex generators (VGs). The selected VGs are type 1: co-rotating low-profile, type 2: co-rotating streamline sheet, and type 3: trapezoidal. All have been installed at a high-curvature location within the diffusers, designated as plane 5. All experimental tests and computational simulations were performed with an inlet Reynolds number of 40,000. The experimental diffuser models were simulated using ANSYS FLUENT 15, employing the 3D standard k-ε turbulence model to capture flow structures that cannot be visualized by experimental methods. Results revealed the capability of the adopted methods to identify the separation points and the flow structure of each tested case. The separation points were approximately located at dimensionless positions, X_s.p./diffuser length, of 0.4, 0.3, 0.678, and 0.78, experimentally, and 0.406, 0.314, 0.638, and 0.8, numerically, for BD, AD, and AD/VG-1, and AD/VG-3, respectively. The results show increased distortion of the AD compared to the BD by 11.9%, experimentally and 9.6% numerically. Experimentally, the destruction is reduced by 71.8%, 87.8%, and 29.7% by VG-1, VG-2, and VG-3, respectively, and computationally by 44.6%, 88%, and 36.2% by VG-1, VG-2, and VG-3, respectively. The results show that VGs type-2 provides the largest improvement in flow structure by suppressing flow separation to the maximum extent and increasing flow uniformity at the diffuser outlet.

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Keywords

Energy conversion system; flow visualization; gas turbine; S-shaped diffuser; vortex generator

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