Rayleigh scattering measurements in supersonic facilities

Abstract

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 a free stream and in a model flow field in the 15-inch, Mach 6 high temperature facility at NASA-Langley. This facility is capable of achieving stagnation temperatures up to 700 K over a range of stagnation pressures from 0.35 to 2.07 MPa. 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. Model flow field measurements were obtained on a 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. Abstract-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.

Rayleigh Scattering Density Measurements, Cluster Theory, and Nucleation Calculations at Mach 10

“…Unfortunately, constituents such as trace amounts of water and naturally occurring carbon dioxide with lower vapor pressures can condense at higher temperatures than nitrogen or oxygen and act as heterogeneous condensation nuclei [13,16,17] for all air constituents. Although modern hypersonic wind tunnels employ all condensation prevention methods, clustering has been observed in all Mach 6 facilities at LARC [9][10][11].…”

“…Mach 6 (15M6) high-temperature tunnel in air using an ArF excimer laser [11]. This facility produces the maximum stagnation enthalpy currently known for any large-scale Mach 6 wind tunnel.…”

“…Later subsonic studies over model wing surfaces increased signal levels using ultraviolet excimer lasers [5]. Two-dimensional images were acquired in air in supersonic flows [6], at Mach 1.5 [7], at Mach 2.5 [8], and in hypersonic flow at Mach 6 [9][10][11]. Most attempts at density measurements were frustrated in supersonic and hypersonic flows by clusters or condensation that overwhelmed molecular LRS signals.…”

NO PLIF Visualizations of the Orion Capsule in LENS-I

“…NO PLIF flow visualization was selected for a variety of reasons. Commonly used flow visualization techniques such as schlieren 25 and Rayleigh scattering 26 would produce poor-quality images in the low pressure, low density region of the vehicle's wake region. Particle Image Velocimetry (PIV) is another option, but the particles could be difficult to seed, could interfere with or not follow the flowfield and perhaps could clog the RCS jet nozzles.…”

Visualization of a Capsule Entry Vehicle Reaction-Control System (RCS) Thruster

“…For example, while the commonly-used schlieren technique provided good visualizations of the forebody shock shape, it is not very sensitive in low pressure wake regions such as that probed in this experiment, as demonstrated below. Similarly, imaging the vehicle wake/jet region with Rayleigh scattering 14 would produce poor-quality images owing to the low density there. Particle-based velocimetry techniques like particle image velocimetry 15 could be used, but the presence of particles could affect the flowfield or could clog the small RCS jet orifice.…”