7 research outputs found
Spatially resolved mass flux measurements with dual comb spectroscopy
Providing an accurate, representative sample of mass flux across large open
areas for atmospheric studies or the extreme conditions of a hypersonic engine
is challenging for traditional intrusive or point-based sensors. Here, we
demonstrate that laser absorption spectroscopy with frequency combs can
simultaneously measure all of the components of mass flux (velocity,
temperature, pressure, and species concentration) with low uncertainty, spatial
resolution corresponding to the span of the laser line of sight, and no
supplemental sensor readings. The low uncertainty is provided by the broad
spectral bandwidth, high resolution, and extremely well-known and controlled
frequency axis of stabilized, mode-locked frequency combs. We demonstrate these
capabilities in the isolator of a ground-test supersonic propulsion engine at
Wright-Patterson Air Force Base. The mass flux measurements are consistent
within 3.6% of the facility-level engine air supply values. A vertical scan of
the laser beams in the isolator measures the spatially resolved mass flux,
which is compared with computational fluid dynamics simulations. A rigorous
uncertainty analysis demonstrates a DCS instrument uncertainty of ~0.4%, and
total uncertainty (including non-instrument sources) of ~7% for mass flux
measurements. These measurements demonstrate DCS as a low-uncertainty mass flux
sensor for a variety of applications.Comment: Main Text: 15 pages, 7 figure; Supplement: 6 pages, 4 figures;
Submitted to Optic
Hypersonic Combustion Diagnostics with Dual Comb Spectroscopy
Hypersonic engine development requires accurate and detailed measurements of
fluidic and thermodynamic parameters to optimize engine designs and benchmark
computational fluid dynamic (CFD) simulations. Here, we demonstrate that dual
frequency comb spectroscopy (DCS) with mode-locked frequency combs can provide
simultaneous absolute measurements of several flow parameters with low
uncertainty across a range of conditions owing to the broadband and ultrastable
optical frequency output of the lasers. We perform DCS measurements across a
6800-7200 cm^-1 bandwidth covering hundreds of H2O absorption features resolved
with a spectral point spacing of 0.0067 cm^-1 and point spacing precision of
1.68 X 10^-10 cm^-1. We demonstrate 2D profiles of velocity, temperature,
pressure, water mole fraction, and air mass flux in a ground-test dual-mode
ramjet at Wright-Patterson Air Force Base. The narrow angles of the measurement
beams offer sufficient spatial resolution to resolve properties across an
oblique shock train in the isolator and the thermal throat of the combustor. We
determine that the total measurement uncertainties for the various parameters
range from 1% for temperature to 9% for water vapor mole fraction, with the
absorption database/model that is used to interpret the data typically
contributing the most uncertainty (leaving the door open for even lower
uncertainty in the future). CFD at the various measurement locations show good
agreement, largely falling within the DCS measurement uncertainty for most
profiles and parameters