Aerodynamics of an Aeroengine Intermediate Compressor Duct: Effects from an Integrated Bleed System
Doctoral thesis, 2020

With the successful development of high-bypass-ratio turbofan engines, major aerodynamic components have been optimized and continuous efficiency improvements are getting harder to maintain. Therefore, to meet the requirements of lower emission of greenhouse gases, auxiliary modules such as intermediate ducts are receiving increasing interest. The Intermediate Compressor Duct (ICD) is an S-shaped duct connecting the engine’s low- and high-pressure compressor systems. Improving the ICD design has the potential to favorably affect the engine’s emission levels by reducing the engine’s length and, therefore, its weight.

In this thesis, a state-of-the-art ICD is simulated using Computation Fluid Dynamics (CFD). The geometry of the ICD represents a test section from an experimental rig. The upstream flow conditions are essential to achieve realistic behavior in the ICD. Therefore, integrated design is considered, including a representative of the last stage from the upstream low-pressure compressor and an upstream rotor off-take bleed system. The bleed

system is an auxiliary module and ensures a stable operation during off-design conditions. Through the bleed system, pressurized air is extracted from the main flow-path and used for different applications. The effect an upstream bleed system has on the ICD is analyzed, where the stability and the flow physics are compared for different bleed ratios. To take advantage of the integrated design and increasing computational resources, higher fidelity CFD simulations, using hybrid RANS/LES turbulence models, are compared to more common industrially applied CFD models and validated using experimental data.

The results show that the stability of the ICD is compromised with high bleed ratios. The flow at the low-pressure compressor’s outlet guide vanes (OGVs) is separated and the separation is more severe at the inner casing. The increased separation is caused by a thicker inner casing boundary layer and the conservation of tangential momentum when extracting axial velocity through the bleed system. As a result, the ICD experiences separated flow at the critical point of diffusion. The separation at the critical point of diffusion increases in magnitude with increased bleed rates.

Comparing the hybrid models to the steady-state RANS models, the hybrid models are capable of predicting the circumferentially averaged total pressure profiles downstream of the ICD. However, the RANS simulations result in over-predicted losses due to over- predicted separation on the OGV blades. The experimental data had a relatively low resolution, and therefore, the hybrid methods need further validations. Furthermore, the hybrid methods are significantly more expensive but represent the transient flow field, whereas the RANS simulations only provide the time-averaged results.






rotor off-take

S-shaped duct

Intermediate Compressor Duct

Bleed system


Opponent: Dr. Sam Grimshaw, Whittle Laboratory, United Kingdom


Elias Siggeirsson

Chalmers, Mechanics and Maritime Sciences, Fluid Dynamics

E. M. V. Siggeirsson, N. Andersson, and M. O. Burak. Numerical and Experimental Aerodynamic Investigation of an S-shaped Intermediate Compressor Duct with Bleed

E. M. V. Siggeirsson, N. Andersson, and M. Lejon. Integrated compressor duct aerodynamics with an integrated rotor off-take bleed

The NASA 2D wall-mounted hump simulated using DDES-SA with the G3D::Flow solver

AIAA Scitech 2019 Forum,; (2019)

Paper in proceedings


Proceedings of ASME Turbo Expo 2018,; (2018)

Paper in proceedings

Air traffic is increasing at an unprecedented rate, with no sign of slowing down, resulting in increased greenhouse gases emission. With stricter emission criteria every year, the aircraft design is subjected to continuous improvements. The development of more efficient aircraft engines plays a central role in lower emission levels.
In this work, simulations are performed using Computational Fluid Dynamic (CFD). The objective is to understand the flow behavior of an Intermediate Compressor Duct (ICD) for different operating conditions. The intermediate compressor duct connects the two main compressor systems of the modern commercial aircraft engine; the low-pressure compressor and the high-pressure compressor. The low-pressure-compressor has a larger radius compared to the high-pressure-compressor to achieve a more efficient engine. To connect the two compressors, a swan neck-shaped annular duct, usually referred to as an S-shaped duct, is used.
It is of great interest to understand the flow physics of the intermediate compressor duct under extreme conditions. A better understanding can result in an improved design. It is critical to the operation of the ICD to achieve an acceptable ratio between the radial offset of the compressors and the length of the S-shaped duct. However, if the radial offset is too large and/or the duct is too short, the engine's performance will suffer increased losses. The increased losses are caused by separated flow in the S-shaped duct. It is highly beneficial to decrease the length of the S-shaped duct, without any separation as it can result in a shorter, and therefore, a lighter engine. A lighter engine will result in a more efficient operation, limiting greenhouse gas emissions.

ELSAA - Effektiv storskalig aerodynamisk analys

VINNOVA, 2017-11-10 -- 2020-06-30.

Intermediate Compressor Case Duct Aerodynamics (IDA)

European Commission (EC), 2018-04-01 -- 2020-09-30.

Areas of Advance



Subject Categories

Aerospace Engineering

Energy Engineering

Fluid Mechanics and Acoustics


C3SE (Chalmers Centre for Computational Science and Engineering)



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4788


Chalmers University of Technology



Opponent: Dr. Sam Grimshaw, Whittle Laboratory, United Kingdom

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