Aero-Optical Studies of Mixing Flows at Supersonic and Hypersonic Speeds
Abstract
,The performance of image-based sensors aboard hypersonic vehicles can be severely deteriorated by aero-optical distortions caused by, compressible boundary layers and shockwaves but also by atmospheric density fluctuations among other factors. A serious source of a,berrations that has not been studied until now is the effect of cooling flows, which are used to prevent the sensor window from gett,ing damaged by the external high stagnation-temperature flow. We propose to perform a joint experimental and numerical investigation, of the aero-optical and aero-thermal environment for a realistic but generic configuration consisting of a two-dimensional cooling,jet flowing over a flat surface downstream of a backward-facing step. The experimental design will be modular such that different co,oling flow gases and flow parameters can be considered over an external Mach number range between 2 and 6. The cooling flow paramet,ers will include the cooling flow velocity as well as stagnation pressure and temperature. The objective of the research is to isola,te and quantify the different contributors to the aero-optical distortions and aero-thermal loads and to provide much-needed models,and guidelines, sought after by industry and national labs, for designing effective imaging and tracking systems with acceptable aer,o-optical distortions for a variety of hypersonic vehicles. For the proposed experimental research, we will design and manufacture a,idic environment. The set-up will feature a shallow cavity geometry with a backward facing step at the front and a shallow ramp at t,he end. Using the set-up, we will conduct extensive parametric studies of the spatio-temporally-resolved wavefronts, using a high-sp,eed Shack-Hartmann sensor and Schlieren technique. To quantify the density, and temperature fields inside the cavity, we will perfor,m spatially-resolved temperature and density measurements along several spanwise planes, using PLIF and Mie scattering techniques as, well as fast-response pressure, temperature and heat flux sensors, and IR-thermography technique Time permitting, several passive a,nd active flow control techniques will be explored to improve the aero-optical performance without compromising the cooling properti,es.To augment the measurement data and provide guidance/insight into optimizing the experiments, wall-resolved and wall-modeled larg,rimental database. Compared to the experiment, LES provides the entire flow field (velocities, temperature, pressure, mass fraction), with high temporal and spatial resolution. Quantities that are important for the development of aero-optical models, such as the de,nsity correlation length, can readily be computed. Areas of the flow field that cannot easily be accessed by optical diagnostics (e.,g., near-wall regions) or where the diagnostics lack sufficient resolution, will be investigated in all necessary detail based on th,e simulation data. Derived quantities, such as the Q-criterion, dilatation of the velocity field, etc., will aid in the understandin,g of the aero-optical and aero-thermal physics.We will use the collected experimental and simulation database to quantify the spatia,l and temporal characteristics of the aero-optical distortions and related flow properties at supersonic and low hypersonic speeds,,using cross-correlations and spectral and modal (POD, DMD) analyses. More importantly, we will use this database to update existing,and develop new analytical models, capable of predicting the overall time-averaged levels of the aero-optical distortions for differ,ent flow parameters.Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 08, 2022
- Source ID
- N000142212454
Entities
People
- Stanislav Gordeyev
Organizations
- Office of Naval Research
- United States Navy
- University of Notre Dame