Adjoint methods for understanding distributed induced transition in hypersonic boundary layers
Abstract
The performance and safety of hypersonic vehicles is crucially dependent upon a profoundunderstanding of the physics and dynamics o"f thin boundary layer flows along their surfaces.In contrast to better-understood low-speed boundary layers, hypersonic boundary la"yerssupport a broader array of different aerothermodynamic effects that can trigger theirtransition to turbulence. Once a hyperson"ic boundary layer becomes turbulent, much moreof its high flow energy is imparted to the vehicle~s surface as intense heat flux, le""ading tovehicle failure. Despite this danger, the weight and expense of current conservative heatshield designs limits their pract""ical applications. Without a conservative heat shield, it isimperative that the boundary layer remains laminar over most of a vehic""le~s surface. Theproposed research will create new understanding of hypersonic boundary layer physics, sothat these hazardous tran""sitions may be avoided. We apply a new, adjoint-basedcomputational approach to this mission-critical problem. In this approach, ins"tabilitiesleading to transition are systematically traced back to their otherwise unobservable origins.This powerful new perspecti"ve will revolutionize understanding of transition physics, andwill guide future experiments and simulations, thus transforming futu""re research.The objective of our proposed research is to understand, analyze, and predict themechanisms by which distributed rough"ness triggers transition in hypersonic boundarylayers. We will address the question ~How rough is rough?~ for hypersonic boundarylayers. Our research differs from standard simulations and experiments that use only a smallnumber of discrete roughness elements. I"n contrast, we use adjoint methods to considerarbitrary distributed roughness fields with millions of degrees of freedom over entir""esurfaces of complex, hypersonic vehicles. These distributed roughness fields are capable ofmodeling the minute details of natural"" surface material roughness more accurately thandiscrete roughness elements allow. For example, DNS of the HIFiRE-5 nose conedemon"strated that wall perturbation levels of only 2 microns reliably produce coherent androbust patterns of crossflow vortices. It is n"ot known, however, which aspects (e.g., location,pattern, wavelength) of the roughness field play the most significant role in the"" transitionprocess. In particular, the interaction of distributed roughness and complex geometry mustbe explored to fully understa""nd all possible transition scenarios. For instance, the HiFIRE-5geometry may be highly sensitive to distributed roughness at its no""se and along its edges, butmay be relatively insensitive to roughness elsewhere. As discussed below, adjoint methodswill quantify" these effects and provide better understanding of hypersonic boundary layertransition.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2017
- Source ID
- N000141712496
Entities
People
- Joseph Nichols
Organizations
- Office of Naval Research
- Regents of the University of Minnesota
- United States Navy