Integrated Measurement and Modeling Characterization of Stratospheric Turbulence

[Under construction]
2017 AFOSR MURI
PO: Dr. Ivett Leyva, High-Speed Aerodynamics
PI: Dr. Brian Argrow, University of Colorado Boulder
MURI Website

Our MURI Team proposes to resolve significant operational issues concerning hypersonic vehicle aerothermodynamics, boundary layer stability, and aero-optical propagation. Turbulence measurements and modeling will quantify spatiotemporal statistics and the dependence of stratospheric turbulence on underlying meteorology to a degree nor previously possible. Particle measurements will characterize concentrations in the middle and upper stratosphere.

Applications of these results for hypersonic boundary layer modeling, aero-optical propagation assessments, and linkages from meteorology to stratospheric turbulence statistics will yield the following expected outcomes addressing US Air Force capabilities:

  • Quantify the roles of atmospheric turbulence and particle concentrations on laminar-turbulent transition for hypersonic flight conditions.
  • Rigorously connect the atmospheric turbulence state to the disturbance forcing amplitude of relevant boundary layer instability mechanisms.
  • Understand how atmospheric particles interact with a hypersonic flow field and promote instability growth and transition to turbulence.
  • Quantify the impacts of stratospheric turbulence spatiotemporal statistics and larger-scale coherent refractive index fluctuations on long-distance aero-optical propagation.
  • Provide a “strawman” stratospheric turbulence forecasting scheme accounting for variable environments and energy inputs from meteorology at lower altitudes.

We have identified four key research questions to be addressed in pursuit of these outcomes:

  • What are the spatiotemporal statistics of small-scale turbulence in the middle and upper stratosphere, and to what extent are they dictated by larger-scale motions, primarily gravity waves (GWs) that arise from meteorological sources at lower altitudes?
  • What are the distributions of particles in the stratosphere, and their dependence on underlying meteorology?
  • What are the relative roles of particles and pre-existing atmospheric turbulence (“freestream turbulence”) for the laminar-turbulent transition at hypersonic speeds in the middle and upper stratosphere?
  • What are the effects of particles, temperature “sheets” and small-scale turbulence in the middle and upper stratosphere on long-range optical propagation, and how can these effects be accurately represented in computational simulations?

These questions will be addressed through three Research Thrusts: 1) Stratospheric Measurements & Analysis with existing and to-be-developed instruments for high-precision, in-situ measurements of turbulent velocity and temperature fluctuations, and particle distributions; 2) Atmospheric Modeling & Forecasting with computational fluid dynamics for multi-scale modeling of gravity waves coupled with high-resolution simulations of instabilities and small-scale turbulence; and 3) Aerothermodynamics & Aero-Optical Modeling with computational aerothermodynamics to study the role of atmospheric turbulence and particles in causing laminar to turbulent transition in hypersonic boundary layers, and computational and theoretical modeling of aero-optical propagation through the stably stratified atmosphere.