Effects of Flow Distortions as They Occur in S-Duct Inlets on the Performance and Stability of a Jet Engine

Abstract

One of the research areas at the Institute of Jet Propulsion focuses on the design and optimization of s-shaped engine inlet configurations. The distortion being evoked within such inlet ducts should be limited to ensure an optimal performance, stability, and durability of the engine’s compression system. Computational Fluid Dynamics (CFD) play a major role in the design process of bent engine inlet ducts. The flow within such ducts can be computed, distortion patterns can be visualized, and related distortion coefficients are easily calculated. The impact of a distortion on flow phenomena within the compressor system can, however, only be computed with major computational efforts and thus the quality of an s-duct design in development is usually assessed by analyzing the evoked distortion with suitable distortion coefficients without a true knowledge of the duct’s influence on the downstream propulsion system. The influence of inlet distortion on both the performance and stability of the Larzac 04 jet engine was parameterized during experimental investigations at the engine test bed of the Institute of Jet Propulsion. Both pressure and swirl distortion patterns as they typically occur in s-duct inlet configurations were reproduced with distortion generators. Pressure distortion patterns were generated using seven types of distortion screens. The intensity of the distortion varies with the mesh size of the screen whereas the extension of the distortion is defined by the dimensions of the screen in radial and circumferential direction. A typical counter rotating twin-swirl was generated with a deltawing installed upstream of the compressor system. First, the development of flow distortion was analyzed for several engine operating points (EOPs). A linear relation between the total pressure loss in the engine inlet and the EOPs was found. Secondly, the flow within the compressor system with an inlet distortion was analyzed and unsteady flow phenomena were detected for severe inlet distortions. Finally, the effect of both pressure and swirl distortion on the performance and stability of the test vehicle was parameterized. A loss in engine performance with increasing inlet distortion is observable. The limiting inlet distortion with respect to engine stability was found and moreover it was shown that pressure distortion has a stronger influence on the stability of the compressor system compared to a counter rotating twin-swirl distortion. The presented parameterization is essential for the s-duct design, which is under development for an experimental set-up with the Larzac 04 jet engine.

Impact of Different Flight Conditions on the Flow in a Highly Curved Intake Duct

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Suction Control of a Boundary Layer Ingestion Inlet

“…Half flush-mounted S-shaped air intake with large boundary layer ingestion (BLI) has been a research hotspot in recent years and has received wide attention thanks to its favorable stealth, small frontal area, and compact structure [1]. As the gas supply apparatus of the future Blended-Wing-Body (BWB) transport aircraft, except for the common benefits mentioned above, numerous studies about it have shown that the boundary layer ingesting propulsor has the potential to improve aircraft fuel efficiency [2][3][4][5][6][7][8]. However, challenges also exist.…”

Fan Stability Enhancement With Partial Casing Treatments

“…This form of separation is exacerbated in future engine designs with larger fan diameters and shorter intake ducts. Nonaxisymmetric inlet distortions are also encountered in tighter airframe-engine integration concepts, such as those found in boundary layer ingestion [2] and low observability military installations [3].…”