SBIR-STTR Award

A comprehensive framework for hypersonic boundary layer transition predictions applicable to wind tunnel and free flight conditions is proposed. The distinguishing feature of this transition prediction framework is that it is developed from the ground up allowing full integration of the important transition regions (receptivity region, linear/secondary/nonlinear stability regimes, etc.) and additional aspects that affect the transition process (e.g. free-stream turbulence and acoustic disturbances). This development does not target incremental improvements in current state-of-the-art prediction tools (e.g LST, PSE/NPSE, etc.) but it addresses the transition process as a whole in a fully integrated way. The important transition regions are coupled through a closed optimization loop that is used to determine the extent of the transition region based on available input free-stream turbulence levels and acoustic power spectra. The predictions for each regime will be validated against existing and newly generated DNS databases and experimental data. A key advantage of this approach is that it is not limited to simple geometries. The approach is applicable to complex geometries relevant for applications of our industry partner Raytheon Missile Systems (Tucson, AZ). This framework will be able to assist product development in early design cycles and bears the potential for enabling innovative designs.

A robust and computationally efficient "Versatile Transition Prediction Methodology" (VTPM) for hypersonic boundary layers is developed, verified and validated. VTPMis based on two approaches: (1) A frequency domain linearized Navier-Stokes solver (VTPM-FD), and (2) an adaptive mesh-refinement wave-packet tracking technique (VTPM-WPT). Both approaches build on the governing equations in their most general form such that all relevant transition mechanisms can be accounted for, e.g. receptivity, convective and absolute instabilities for 3D baseflows, transient growth, crossflow instability, and secondary instability. Both approaches allow for fully three-dimensional flows as encountered for arbitrary complex geometries, and does not require structured grids and pre-defined disturbance marching paths as required for current state-of-the-art PSE based methods. The VTPM framework allows to connect the different transition stages in a consistent fashion, such that the entire transition process can ultimately be predicted solely based on information about the environmental disturbances. Therefore, VTPM will allow a physics-based extrapolation of ground test measurements to free-flight conditions. VTPM can also be directly imported into the transition prediction amplitude method developed by Marineau et al. The software package is developed from the ground up such that the final product will be readily accessible for "non-expert" users.