The Hypersonic International Flight Research and Experimentation (HIFiRE) 5 flight experiment by Air Force Research Laboratories and Australian Defense Science and Technology Organization is designed to provide in-flight boundary-layer transition data for a canonical 3D configuration at hypersonic Mach numbers. This paper outlines the progress, to date, on boundary layer stability analysis for the HIFiRE-5 flight configuration, as well as for selected test conditions from the wind tunnel experiments supporting the flight test. At flow conditions corresponding to the end of the test window, rather large values of linear amplification factor are predicted for both second mode (N>40) and crossflow (N>20) instabilities, strongly supporting the feasibility of first in-flight measurements of natural transition on a fully three-dimensional hypersonic configuration. Additional results highlight the rich mixture of instability mechanisms relevant to a large segment of the flight trajectory, as well as the effects of angle of attack and yaw angle on the predicted transition fronts for ground facility experiments at Mach 6. Backgroundue to its influence on surface heat transfer, skin-friction drag, and flow-separation characteristics, prediction of boundary layer transition constitutes an important aspect of hypersonic vehicle design. Laminar to turbulent transition over realistic vehicle surfaces is often caused by surface roughness of sufficiently large magnitude. However, when the surface is relatively smooth, the transition process is initiated by linear instabilities of the laminar boundary layer. Typically, the second (or Mack) mode instability dominates transition in 2D and axisymmetric boundary layers with hypersonic edge Mach numbers, although centrifugal (i.e., Gortler) instabilities may also come into play when the surface has concave curvature along the streamwise direction. Three-dimensional boundary layers involve the additional mechanisms of stationary and traveling modes of crossflow instability and, depending on the geometric configuration, may include the attachment line instability as well [1].Regardless of the speed regime, linear stability correlations have been quite successful in predicting the onset of transition when a single instability mechanism dominates the transition process [2]. Mixed mode transition has been more challenging to predict because of possible nonlinear interactions between the relevant modes of instability. To account for the effect of such interactions, an ad hoc composite metric based on the linear amplification factors for the different instability mechanisms has sometimes been used for transition correlation (see, for instance, [3]). Recent work on crossflow instability in low-speed boundary layers [4] has exposed additional shortcomings in applying purely linear predictive models to crossflow dominated transition in 3D boundary layers.The simplest canonical configuration that includes the necessary elements for studying both mixed mode transition and crossflow evolu...
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