1. Diagnostics for Hypersonic Engine Isolator Study Michael S
Diagnostics for Hypersonic Engine Isolator Study Michael S. Brown / Jeffrey M. Donbar (FA D) AFRL/Aerospace Propulsion Division
Implementation of Diagnostics in Isolators of Fueled Engines
Complex Fluid Dynamics
Presently, no comprehensive under-standing of the details of the fluid behavior in isolators of hypersonic engines (in particular, transient behavior).
Transient CFD approaches not yet mature enough for predictive capability.
DNS currently limited to Reynolds numbers well-below those of isolator operation.
Need for Measurements
Measurements of thermodynamic variables during isolator transients needed for:
input to (CFD) modeling efforts
input to reduced order control models
Currently only a few data sets of transient phenomena in hypersonic isolators with fueled combustors exist.
Tandem Measurement Strategy
Simultaneously implement optical diagnostics for in-stream measurements and “surface-mounted” diagnostics.
MAIN ACHIEVEMENTS:
Optical measurements have been executed in the boundary layer of supersonic flows upstream of: a laser spark, a pulse combustion device and a scramjet combustor transient. (Below- shadowgraph of pulse detonation event and corresponding transient optical signal (graph))
Planned Approach
Perform simultaneous optical and non-optical diagnostic measurements in isolators of varying design under varying flow conditions; in particular, transient conditions (along with their corresponding tare conditions).
Perform measurements at data acquisition rates of 1 kHz and higher.
Analyze acquired data to search for variables or correlations thereof that indicate impending fluid behavior changes such as shock-induced boundary-layer separation
Research Goals
Identification of measureable variable(s) whose time-dependent behavior predicts the onset of gross changes in isolator fluid dynamic behavior
Collection of data sets of transient isolator phenomena suitable for CFD study
STATUS QUO
MEASUREMENT STRATEGY
M 2 flow
END-OF-PHASE GOAL
CURRENT APPROACH

2. Boundary Layer Dynamics Reveal Downstream Behavior
Highlight Slide Template
Boundary Layer Dynamics Reveal Downstream
Behavior
Shock associated with cavity flameholder disturbs upstream boundary layer
Dr. Michael Brown
JANNAF Combustion Subcommittee for Diagnostics (organizer)
Associate Fellow, AIAA
Your Pic
Diode laser beams
Density fluctuations in
boundary layer are sensitive
to the downstream behavior
of supersonic flow
Unlit combustor exhibits
simple expansion fan at step
Lit combustor leads to shear
layer and shock wave that
influences the upstream
boundary layer
Laser beam in boundary
layer gets “steered” by
fluctuations
Impacts scramjet engine
control
M 2 flow
expansion fan
combustor
isolator
M 2 flow
oblique shock
shear layer
isolator

3. Keep this space blank, too, same deal as last slide
Boundary layer dynamics lead
to diffraction of laser beams
causing amplitude fluctuations
of transmitted light
These dynamics change ahead
of full combustion as evidenced by
the frequency-weighted power
spectrum of the transition period
(middle spectrum below)
combustion
no combustion
Transmitted Light Amplitude
Time(s)
Brown & Donbar, AFRL