Investigation of Transitional SBLI at Mach 5 using Controlled Forcing: Experiments, Simulations and Theory
Abstract
The interplay between boundary layer transition and separation remains an important topic for basic and applied research relevant to hypersonic systems. These so-called transitional shock/boundary layer interactions (SBLIs) produce unsteadiness and localized regions of elevated surface heat flux that can exceed those found in turbulent flows. In many cases, even predictions of the mean flow behavior (i.e., separation and reattachment locations) are lacking. This is particularly relevant for control surfaces and also impacts the overall survivability of hypersonic vehicles. Despite numerous efforts in recent years, there remains a lack of understandingof the fundamental mechanisms governing transitional SBLIs. This lack of understanding inhibits the development of useful predictive models and ultimately the development of more capable and reliable hypersonic systems.The objective of our proposed research is tounderstand the origin, onset and relationship between mean flow topology, low frequency unsteadiness and localized regions of elevated surface heat flux (i.e., longitudinal hot streaks) for transitional SBLIs. For this research effort, a collaborative approach will be employed encompassing spatially and temporally resolved wind tunnel experiments, high-fidelity numerical simulations, and local & global stability analyses. Research focus will be placed on the axisymmetric geometry of a hollow cylinder flare at Mach 5. Thisbuilds on our previous ONR-funded work and is directly relevant to the NATO AVT-346 task, in collaboration with ONERA. Special attention will initially be placed on a single flare angle (15 deg) that is geometrically equivalent to the ONERA case. This is motivated by mean flow results (reattachment location) that show significant discrepancies between UArizona and ONERA experiments, which arenot yet explained. This discrepancy will be examined by quantifying the impact of unit Reynolds number, boundary-layer development length, leading-edgebluntness, and freestream noise environment, among others.We will also vary the flare angle and other parametersto identify instability mechanisms # cases which are globally stable but convectively unstable versus globally unstable as well as borderline cases. This will be followed by #controlled forcing,# using our newly established capability for producing controlled disturbances (i.e., diagnostic forcing) in both experiments and simulations, to shed light on the relevant physics regarding the interaction between transition and separation for these situations. These tightly coupled efforts employing controlled disturbance inputs are absolutely crucial for extracting the relevant flow physics. In doing so, the fundamental mechanisms that are responsible for generation, sustainment and connection between mean flow topology, low frequency unsteadiness and localized regions of elevated surface heat flux (i.e., longitudinal hot streaks) will be ascertained. The physics-based understanding of transitional SBLIs developed here will provide insight into possible strategies for the prevention and/or mitigation of these detrimental phenomena.This research will provide a fundamental physics-based understanding of the underlying instability mechanisms governing transitional SBLIs which isrequired for reliable and efficient hypersonic flight. The overall outcome of this work will lead to improved capabilities for predictive modeling and control of transitional SBLIs, ultimately reducing design margins and enhancing the capability of hypersonic systems.Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2023
- Source ID
- N000142312645
Entities
People
- Jesse C. Little
Organizations
- Office of Naval Research
- United States Navy
- University of Arizona