What is it about?
This paper shares insights, CFD simulation best practices, and lessons learned from revisiting a challenging benchmark case study for simulating unsteady and steady-state aerodynamics of a complex serpentine inlet of interest to the propulsion community. In an earlier workshop where this same test case was investigated, participant contributions resulted into a non-trivial amount of scatter despite participants using a common set of workshop-supplied meshes. Employing a number of methods and suggestions developed from the earlier workshop demonstrated a significant reduction in variation of reported results in this latest validation study.
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Why is it important?
Increasing demands on aircraft range and efficiency require engineers to understand the various mechanisms at work across the entire aerodynamic envelope, including the propulsion system. The desire for compact propulsion systems has led to inlets and diffusers of low length to diameter ratios, which often have flow turning to circumvent such internal features as cockpits, weapon bays, and/or landing gear. With flow turning in at least one plane, and often in two planes, undesirable secondary flows are generated flow separation is common. Additionally, cross-sectional shape changes from the highlight of the inlet to the diffuser and finally to the engine face present opportunities for secondary flows and losses in total pressure. These adverse effects serve to reduce the available total pressure at the engine face which decreases engine performance. Even more problematic are the large variations (both radial and circumferential) in total pressure seen at the AIP, leading to various types of total pressure distortion. Other factors, such as swirl distortion, also arise from these serpentine duct systems. The prediction of separated flows, secondary flows, and dynamic unsteady content has been problematic in past studies in diffusers and ducts with flow turning. While not a new subject, there is a lack of comprehensive data on the subject. To help address this issue, the Inlets, Nozzles, and Propulsion Systems Integration Technical Committee has sponsored the 4th Propulsion Aerodynamics Workshop to further explore the influence of turbulence modeling, grid resolution, and solver accuracy on predicting such complex aerodynamic flows of interest to the propulsion community.
Perspectives
Desires for more rapid design times, reduced wind tunnel testing, and increased performance all require higher fidelity CFD techniques for inlets, as well as faster geometry-to-solution time on both research and production programs. While there is no denying the importance of the prediction of turbulent flow in S-Ducts, there has been little success or consensus on this class of problem. The addition of flow control adds complexity which is not fully understood in a modeling sense. The goal of replacing, or reducing wind tunnel testing with high fidelity CFD cannot be realized until CFD validation studies, like this one, have been performed for this class of diffuser problem.
Zach Davis
Kratos Defense & Rocket Support Services
Read the Original
This page is a summary of: Summary of the 4th Propulsion Aerodynamics Workshop: S-duct Results, August 2019, American Institute of Aeronautics and Astronautics (AIAA),
DOI: 10.2514/6.2019-3845.
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