Numerical Investigations of the Nonlinear Transition Stages in Hypersonic Boundary Layers for Navy relevant Mach Numbers and Model Geometrics
Abstract
Our previous research has shown that, due to the stabilizing effects of compressibility,the nonlinear transition regime may cover a very large downstream extent onhypersonic flight vehicles. Associated with the nonlinear regime are localized highskin-friction and heat-transfer rates that can far exceed corresponding turbulent values.This may have profound negative consequences for the structural integrity ofhypersonic vehicles. Therefore, new transition prediction tools are required. Thecurrent ones in use cannot capture the detrimental nonlinear effects because they arebased on linear (small amplitude) stability theory. Therefore, funding is requested forinvestigating the complex flow physics of the nonlinear stages of high-speed boundarylayertransition for Navy relevant Mach numbers and geometries. Two main researchthrusts are proposed: i) Investigation of the relevant flow physics in the linear andnonlinear transition regime for a straight cone at M = 4, and ii) investigation of the flowphysics in the nonlinear transition regime for convex (ogive) cones. Regarding i), M=4 isin the Mach number range that is very relevant for current and future Navy hypersonicapplications. From a physics point-of-view, M=4 is at the crossroads between the first andsecond mode instabilities according to linear theory. Thus nonlinear interactions of firstmode and second mode waves can strongly influence the nonlinear transition physics. It isnecessary to understand which nonlinear breakdown scenario will dominate: Either firstmode (oblique) waves, or second mode waves, or combinations thereof. Regarding ii), inorder to reduce the (shock) wave drag of axisymmetric high-speed projectiles, convexgeometries are often considered for supersonic/hypersonic vehicles. The convex wallgeometry of ogives results in favorable (streamwise) pressure gradients, which have astabilizing effect for linear disturbances. Likewise, the favorable pressure gradient mayalso stabilize the nonlinear regime as well, thus stretching the strongly nonlinear transitionregion even further in the downstream direction - with all its detrimental effects (localizedhigh skin friction and wall heating).Particular emphasis of the proposed research will also include the effects of realisticoperating conditions on the nonlinear transition process, such as the angle of attack, therole of environmental disturbances (free-stream turbulence, noise), nose bluntness,high-enthalpy, etc. We will employ Direct Numerical Simulations (DNS) using ourstate-of-the-art, high-order accurate Navier-Stokes codes that were developed withprevious funding from AFOSR and NASA. The high-accuracy and efficiency of ourcodes allows high-fidelity simulations of the entire transition process, including thenonlinear stages all the way to the fully turbulent flow. In addition, we will employstability theory (both primary and secondary) in order to extract the relevant instabilitymechanism at work at the various transition stages. These investigations will be carriedout in close collaboration with experimental efforts at the University of Arizona (A.Craig), Purdue University (S. Schneider), and Caltech (H. Hornung, J. Shepard). Withthe synergism provided by the collaboration between simulations, theory andexperiments chances are greatly enhanced of understanding the highly complex physicsof boundary-layer transition for Navy relevant Mach numbers and geometries.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 03, 2017
- Source ID
- N000141712338
Entities
People
- Hermann Fasel
Organizations
- Office of Naval Research
- United States Navy
- University of Arizona