Due to Intermediate Compressor Ducts (ICDs) potential to reduce overall engine weight and therefore specific fuel consumption, many aerospace industry participants have embarked on programs to develop shorter and more aerodynamically "aggressive" ICD. Unfortunately, most "aggressive" designs have tended to either separate or closely approach their separation limit. As a result, in this paper, the ability of active flow control techniques (boundary layer (BL) blowing and suction) were investigated and novel schemes were designed to suppress the flow separations and thus increase the aerodynamic robustness of such ducts. The test case used in this study is a state-of-the-art, highly aggressive, ICD developed by the Institute of Propulsion Technology, German Aerospace Center (DLR), located aerodynamically close to its separation limit operating at its nominal operating point. Numerical simulations were used to characterize the aerodynamic baseline of the duct as well as the modified design. Analysis of the baseline design results confirmed the strong tendency of the flow to separate at the hub-strut corner (corner separation), mid-strut (passage separation) and in the shroud (near duct exit) regions. Boundary layer energization schemes were then explored at different streamwise locations, to identify its optimum location. The results showed that the application of a BL energization scheme (BL blowing) on the hub resulted in a positive reduction in the passage and hub-strut corner separation while the application of BL suction (at the shroud) assisted in reducing the aerodynamic separations. Finally, when both schemes were employed simultaneously, an aggregated reduction of approximately 21% in the mass-averaged total pressure loss coefficient (compared to the baseline case) was predicted.

The aerospace industry has seen a significant push to develop shorter and more aerodynamically “aggressive” intermediate compressor ducts (ICDs) due to their potential to reduce engine weight and, consequently, overall specific fuel consumption. However, many aggressive designs tend to either experience flow separation or operate close to their separation limit. This study investigates the use of circumferential splitter vanes as a passive flow control device to suppress flow separations and enhance the aerodynamic robustness of these ducts. The test case examined is a state-of-the-art, highly aggressive ICD developed by the Institute of Propulsion Technology at the German Aerospace Center (DLR). This ICD operates near its separation limit at its nominal operating point. Numerical simulations were employed to assess the aerodynamic performance of both the baseline and augmented (splittered) ICD designs. Analysis of the baseline design revealed a strong tendency for flow separation at the hub-strut corner, mid-strut region, and in the shroud region near the duct’s exit plane. The introduction of a double splitter vane in the augmented designs was found to be effective in reducing flow separation in the hub and shroud regions. Nevertheless, the potential benefits must be balanced against the resulting increase in overall total pressure losses, indicating a need for further optimization of the splitter vane design.