Engineering topics

Hillard, M. E.

Publications and source records attributed to Hillard, M. E..

14 records

NASA NTRS1996

Rayleigh scattering measurements in supersonic facilities

Using a narrow-band, pulsed, ArF excimer laser and a single-intensified CCD camera, planar laser Rayleigh scattering measurements were performed to obtain quantitative density measurements both in the free stream and in a model flow field. These measurements were conducted in the 15-inch, Mach 6 high temperature facility at NASA Langley Research Center. This facility is capable of achieving stagnation temperatures up to 700 K (800 F) over a range of stagnation pressures from 0.35 to 2.07 MPa (50 to 300 psia). The high temperature capability of this facility eliminates the clustering effect observed in earlier Mach 6 studies, and allows quantitative density measurements in the free stream over a range of stagnation pressures from 0.35 to 1.75 MPa (50 to 250 psia). Model flow field measurements were obtained on 38.1 mm diameter cylinder. Measurement locations include the free stream, the region behind the bow shock in front of the model, and the region behind the model including the wake. The densities deduced from the Rayleigh scattering measurements in the model flow field are compared with CFD computations. Measurement uncertainties and the detection limit are discussed.

Shirinzadeh, B.↗

NASA NTRS1992

Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel

Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters.

Shirinzadeh, B.↗

NASA NTRS1991

Study of cluster formation and its effects on Rayleigh and Raman scattering measurements in a Mach 6 wind tunnel

Using a frequency-doubled Nd-YAG pulsed laser and a single-intensified CCD camera, Rayleigh scattering measurements have been performed to study the cluster formation in a Mach 6 wind tunnel at NASA Langley Research Center. These studies were conducted both in the free stream and in a model flow field for various flow conditions to gain an understanding of the dependence of the Rayleigh scattering (by clusters) on the local pressures and temperatures in the facility. Using the same laser system, simultaneous measurements of the local temperature have also been performed using the rotational Raman scattering of molecular nitrogen and determined the densities of molecular oxygen and nitrogen by using the vibrational Raman scattering from these species. Quantitative results are presented in detail with emphasis on the applicability of the Rayleigh scattering for obtaining quantitative measurements of molecular densities both in the free stream and in the model flow field.

Shirinzadeh, B.↗

NASA NTRS1991

Condensation effects on Rayleigh scattering measurements in a supersonic wind tunnel

Rayleigh and Raman scattering measurements have been performed in the 20-in., Mach 6 wind tunnel at the NASA Langley Research Center. Rayleigh results show signal levels much higher than expected for molecular scattering in the tunnel, whereas densities deduced from spontaneous Raman scattering of molecular nitrogen are in good agreement with the expected nitrogen densities in the facility. The apparent discrepancy in the Rayleigh result is attributed to cluster formation as a result of expansion in the tunnel. The dependence of the Rayleigh signal on the stagnation pressure and temperature is also discussed.

Shirinzadeh, B.↗

NASA NTRS1991

Study of Rayleigh scattering for visualization of helium-air mixing at Mach 6

Using an ArF excimer laser, planar Rayleigh scattering measurements were performed to investigate helium mixing into air at supersonic speeds. These experiments were conducted in the Mach 6, high-Reynolds-number facility at NASA Langley Research Center. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment was demonstrated. The qualitative agreement between the averaged Rayleigh results and the reduced mean-mass-densities obtained from probe measurements substantiate that careful application of the technique, even in the presence of clusters, can give very useful results. It was also demonstrated that planar, quantitative measurements can be made in the absence of clusters.

Shirinzadeh, B.↗

NASA NTRS1991

Study of Cluster Formation and its Effects on Rayleigh and Raman Scattering Measurements in a Mach 6 Wind Tunnel

Using a frequency-doubled Nd-YAG pulsed laser and a single-intensified CCD camera, Rayleigh scattering measurements have been performed to study the cluster formation in a Mach 6 wind tunnel at NASA Langley Research Center. These studies were conducted both in the free stream and in a model flow field for various flow conditions to gain an understanding of the dependence of the Rayleigh scattering (by clusters) on the local pressures and temperatures in the facility. Using the same laser system, we have also performed simultaneous measurements of the local temperature using the rotational Raman scattering of molecular nitrogen and determined the densities of molecular oxygen and nitrogen by using the vibrational Raman scattering from these species. Quantitative results will be presented in detail with emphasis on the applicability of the Rayleigh scattering for obtaining quantitative measurements of molecular densities both in the free stream and in the model flow field.

Shirinzadeh, B.↗

NASA NTRS1991

Condensation Effects on Rayleigh Scattering Measurements in a Supersonic Wind Tunnel

Rayleigh and Raman scattering measurements have been performed in the 20-inch, Mach 6 wind tunnel at the NASA Langley Research Center. Rayleigh results show signal levels which are much higher than expected for molecular scattering in the tunnel, while densities deduced from spontaneous Raman scattering of molecular nitrogen are in good agreement with the expected nitrogen densities in the facility. The apparent discrepancy in the Rayleigh result is attributed to cluster formation as a result of expansion in the tunnel. The dependence of the Rayleigh signal on the stagnation pressure and temperature is also discussed.

Shirinzadeh, B.↗

NASA NTRS1991

Planar Rayleigh Scattering Results in Helium/Air Mixing Experiments in a Mach 6 Wind Tunnel

Planar Rayleigh scattering measurements using an ArF-excimer laser have been performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach 6facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross sectional area (5 cm by 10 cm) of the flow field in the absence of clusters.

Shirinzadeh, B.↗

NASA NTRS1987

Half-collision analysis of far-wing diffuse structure in Cs-Xe

Laser excitation in the far red wing of the second principal series doublet of Cs mixed with Xe revealed a diffuse structure associated with the 2P(3/2) component. The structure is thought to originate from a reflection type of spectrum between the weakly bound E 2Sigma(1/2) excited state and the X 2Sigma(1/2) repulsive ground state of CsXe.

Exton, R. J.↗

NASA NTRS1986

Raman Doppler velocimetry - A unified approach for measuring molecular flow velocity, temperature, and pressure

Molecular flow velocity (one component), translational temperature, and static pressure of N2 are measured in a supersonic wind tunnel using inverse Raman spectroscopy. For velocity, the technique employs the large Doppler shift exhibited by the molecules when the pump and probe laser beams are counterpropagating (backward scattering). A retrometer system is employed to yield an optical configuration insensitive to mechanical vibration, which has the additional advantage of simultaneously obtaining both the forward and backward scattered spectra. The forward and backward line breadths and their relative Doppler shift can be used to determine the static pressure, translational temperature, and molecular flow velocity. A demonstration of the technique was performed in a continuous airflow supersonic wind tunnel in which data were obtained under the following conditions: (1) free-stream operation at five set Mach number levels over the 2.50-4.63 range; (2) free-stream operation over a range of Reynolds number (at a fixed Mach number) to vary systematically the static pressure; and (3) operation in the flow field of a simple aerodynamic model to assess beam steering effects in traversing the attached shock layer.

Exton, R. J.↗

NASA NTRS1984

Intensified silicon photodiode array detector linearity Application to coherent anti-Stokes Raman spectroscopy

The linearity of an intensified silicon photodiode array multichannel detector is studied with coherent anti-Stokes Raman and other similar signals. Studies with diffuse and focused (spherically and cylindrically) signals resolved apparent saturation problems which limit the dynamic range of the detector. In addition, it has been shown that there is no short-range wavelength (473-532-nm) dependence on this saturation. Theoretical explanations for these phenomena are also included.

Antcliff, R. R.↗

NASA NTRS1984

Molecular velocimetry using stimulated Raman spectroscopy

Molecular flow velocity of N2 was measured in a supersonic wind tunnel using inverse Raman spectroscopy. This technique employs the large Doppler shift exhibited by the molecules when the pump and probe laser beams are counter-propagating (backward scattering). A retrometer system is employed to yield a vibration-free optical configuration which has the additional advantage of obtaining both the forward and backward scattered spectra simultaneously. The linebreadths and their relative Doppler shift can be used to determine the static pressure, translational temperature, and molecular flow velocity. A demonstration of the concept was performed in a supersonic wind tunnel and included: (1) measurements over the Mach number range 2.50 to 4.63; (2) static pressure measurements (at Mach 2.50) corresponding to a Reynolds number per foot range of 1 to 5 x 10 to the 6th power; and (3) measurements behind the shock wave of a flat plate model.

Exton, R. J.↗

NASA NTRS1978

Laser excited fluorescence in the cesium-xenon excimer and the cesium dimer

Argon ion laser lines are used to excite fluorescence in a mixture of cesium and xenon. Excimer band fluorescence is observed at higher pressures (about 1 atm) while at lower pressures (several torr) a diffuse fluorescence due to the cesium dimer is observed whose character changes with exciting wavelength. The excimer fluorescence is shown to be directly related to the location of the exciting wavelength within previously measured Cs/Xe line shapes. This fact suggests that the excimer systems may be efficiently pumped through these line shapes. Qualitative energy-level schemes are proposed to explain the observations in both the excimer and dimer systems.

Exton, R. J.↗

NASA NTRS1973

Evaluation of Raman scattering as a sensor of temperature and molecular density

The performance of the Raman scattering technique for the remote monitoring of temperature and molecular number density in various wind tunnel and engine testing facilities has been experimentally evaluated. Temperature measurements were made by monitoring the pure rotational spectrum of nitrogen and the rotational branch separations of nu2 of CF4 for temperatures in the range 300 to 1000 K. These measurements yielded an average error of 2.6 and 7.6%, respectively, for temperature measurements at pressures near 1 atm. Molecular number density measurements with 20% error could be made at densities as low as 3.5 times 10 to the 22-nd power per cu m by monitoring the 6 to 8 rotational transition of nitrogen, 3.5 times 10 to the 23-rd power per cu m by monitoring the Q-branch of the fundamental vibrational transition of nitrogen, and 7 times 10 to the 22-nd power per cu m by monitoring the nu1 fundamental vibrational transition of CF4.

Bandy, A. R.↗