Vortical Flow Development in Round Ducts Across Scales for Engine Inlet Applications

TL;DR

This study investigates the development of vortical flow in round ducts across different scales, demonstrating that vortex behavior is largely Reynolds number independent, which simplifies experimental analysis for engine inlet applications.

Contribution

The paper provides experimental evidence that vortex development in ducts is similar across scales, enabling cost-effective small-scale studies for engine inlet flow analysis.

Findings

Vortex development is Reynolds number independent within tested range.

Secondary flow driven by 2D vortex dynamics is consistent across scales.

Small-scale turbulence shows vortex-related instabilities.

Abstract

Turbofan engine performance depends highly on the characteristics and conditions of the inlet flow. Swirl distortions, caused by non-uniformities in flows arising from boundary layer or ground/fuselage vortex ingestion are of concern and need to be fully understood to guarantee efficiency and safety of propulsion systems. To investigate a fundamental single-vortex distortion development in a duct at different Reynolds numbers, a StreamVane distortion generating device was designed and experimentally analyzed in a small-scale low-speed wind tunnel (ReD 500,000) and in a full-scale engine testing rig (ReD 3 million). Stereoscopic particle image velocimetry was used to measure the three-component velocity fields at discrete measurement planes downstream of the distortion device. Results show that the secondary flow is generated and develops very similarly in both scales, and is mostly driven by two-dimensional (2D) vortex dynamics. Induced velocities arising from the proximity of the vortex to the duct wall causes the vortex center to convect circumferentially around the duct, in the same sense as the vortex rotation, as it travels downstream. Small-scale turbulence results show small-scale instabilities related to the development of the vortex. This work shows that the development of this vane-generated, vortex-dominated flow is largely Reynolds number independent for the covered range, so that details of similar duct-bounded flows can be analyzed in depth in small-scale experiments, decreasing development efforts and cost.