skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Development of a fs/ps CARS system for temperature measurements in supersonic and hypersonic environments
A hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) system was developed for quantitative measurements of temperature in a laboratory-scale supersonic jet facility. Measurements were recorded at low pressures and densities relevant for supersonic and hypersonic environments, with special interest in exploring the feasibility of deploying this technique in the 20-inch Mach 6 and 31-inch Mach 10 wind tunnels located at NASA Langley Research Center. Modifications to the existing supersonic jet facility were made to simulate a test section with a width of 31 inches, so that the size of the test section is relevant for either wind tunnel. The CARS system was designed such that a similar beam geometry can be used in the laboratory to acquire point-based fs/ps CARS measurements along two axes of translation. Rotational Raman transitions of O2 and N2 were targeted.  more » « less
Award ID(s):
2033675
PAR ID:
10533053
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
American Institute of Aeronautics and Astronautics
Date Published:
ISBN:
978-1-62410-711-5
Format(s):
Medium: X
Location:
Orlando, FL
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, American Institute of Aeronautics and Astronautics)
    Hybrid fs/ps coherent anti-Stokes Raman scattering employing coherent control is presented for selective excitation of combustion-relevant species. Femtosecond pulse shaping is accomplished experimentally using a 4-f pulse shaper with a spatial light modulator at the Fourier plane. A feedback-controlled genetic algorithm for adaptive pulse shaping is used to optimize for the selective excitation of CO2 (near 1388 cm−1) and O2 (near 1556 cm−1) rovibrational transitions in a non-reacting flow. 0D fs/ps CARS measurements acquired in a near-adiabatic flame demonstrate the use of coherent control in a combustion environment. 
    more » « less
  2. ; ; ; ; ; (, Optics Letters)
    We report the development of a simple and sensitive two-beam hybrid femtosecond/picosecond pure rotational coherent anti-Stokes Raman scattering (fs/ps CARS) method to simultaneously measure the rotational and vibrational temperatures of diatomic molecules. Rotation–vibration non-equilibrium plays a key role in the chemistry and thermalization in low-temperature plasmas as well as thermal loading of hypersonic vehicles. This approach uses time-domain interferences between ground state and vibrationally excited N2molecules to intentionally induce coherence beating that leads to apparent non-Boltzmann distributions in the pure rotational spectra. These distortions enable simultaneous inference of both the rotational and vibrational temperatures. Coherence beating effects were observed in single-shot fs/ps CARS measurements of a 75 Torr N2DC glow discharge and were successfully modeled for rotational and vibrational temperature extraction. We show that this method can be more sensitive than a pure rotational fs/ps CARS approach using a spectrally narrow probe pulse. Lastly, we experimentally measured the beat frequencies via Fourier transform of the time-domain response and obtained excellent agreement with the model. 
    more » « less
  3. ; ; ; (, AIAA SCITECH 2023 Forum)
    Vibrational and rotational temperatures in various detonation conditions involving diluted hydrogen-oxygen mixtures were studied in a microscale detonation tube using hybrid fem- tosecond/picosecond Coherent anti-Stokes Raman scattering (hybrid fs/ps CARS). Measured temperatures at various locations behind the shockwave were compared to Chapman-Jouguet conditions as predicted by equilibrium calculations. Simultaneous shadowgraphy was also employed to establish timing between the detonation wave and laser beams. Comparison between vibrational nitrogen and oxygen thermometry were made for detonations in the same gas mixture. Oxygen rotational temperature was measured and compared to vibrational temperature measured in a similar gas mixture. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, AIAA Science and Technology Forum and Exposition 2019)
    A new Anechoic Wall Jet Wind Tunnel was built at Virginia Tech. A detailed design based on the old wall jet tunnel was done to improve the quality of the resultant flow. Aerodynamic and acoustic calibrations were performed in order to understand properties and characteristics of the flow generated by this new facility which can be used for various aeroacoustic studies. Far-field acoustics were measured using half-inch B&K microphones in a streamwise array to characterize and reduce the background noise. Sound pressure levels were lower by 10 dB for frequencies up to 700Hz in comparison to the old facility. The turbulent surface pressure fluctuations of the wall-jet flow were studied using Sennheiser microphones placed along streamwise and spanwise locations to record surface pressure fluctuations. Comparison of the autocorrelation plotted for microphones along the same span indicate uniform flow features. A decay in the turbulence levels is observed along the downstream direction as expected. Aerodynamic calibrations included mean velocity measurements along different spanwise locations, wall-jet boundary layer profiles and streamwise cross-sections. Spanwise and cross-sectional velocity profiles show good uniformity of the flow. Detailed boundary layer analyses were performed with the parameters obtained from the experiments. 
    more » « less
  5. ; ; ; ; (, Frontiers in Built Environment)
    Thunderstorm downburst winds are a major cause of severe damage to buildings and other infrastructure. The initiative of the NSF-NHERI Wall of Wind (WOW) Experimental Facility to design and develop a downburst simulator was established to open new horizons for multi-hazard engineering research by extending the current capabilities of the facility to enable the simulation of non-synoptic winds. Five different downburst simulator designs have been tested in the 1:15 small-scale replica of the WOW to identify the optimal design. The design concepts tested herein considered both the 2-D impinging jet and the 2-D wall jet simulation methods. The basic design methodology consists of transforming the available atmospheric boundary layer (ABL) wind simulator into downburst winds by adding an external modification device to the exit of the flow management box. A flow characterization comparison among the five contending downburst simulators, along with comparisons to real downbursts and previous literature findings, has been conducted. The study on the effect of surface roughness length on the height of the peak wind velocity showed that the implementation of a 2-D plane wall jet enables large-scale outflows (higher peak velocity height) with high Reynold numbers, which is advantageous in terms of reducing scaling effects. In general, the current research work showed that four downburst simulation methods were suitable for adoption; however, only one downburst simulator was recommended based on the feasibility of construction in the facility. The chosen downburst simulator consisted of a two louver slat system near the bottom, with a blockage at the top. This configuration enables producing a large rolling vortex passing through the testing section, which would serve adequately in the further study of turbulent flow characterization and testing of larger scale test models. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email