The Development and Implementation of a Cryogenic Pressure Sensitive Paint System in the National Transonic Facility

55th AIAA Aerospace Sciences Meeting

2017

Femtosecond laser electronic excitation tagging (FLEET) velocimetry was used to study the flowfield around a symmetric, transonic airfoil in the NASA Langley 0.3-m TCT facility. A nominal Mach number of 0.85 was investigated with a total pressure of 125 kPa and total temperature of 280 K. Two-components of velocity were measured along vertical profiles at different locations above, below, and aft of the airfoil at angles of attack of 0°, 3.5°, and 7°. Measurements were assessed for their accuracy, precision, dynamic range, spatial resolution, and overall measurement uncertainty in the context of the applied flowfield. Measurement precisions as low as 1 m/s were observed, while overall uncertainties ranged from 4 to 5 percent. Velocity profiles within the wake showed sufficient accuracy, precision, and sensitivity to resolve both the mean and fluctuating velocities and general flow physics such as shear layer growth. Evidence of flow separation is found at high angles of attack.

Section: Introductionmentioning

confidence: 99%

FLEET Velocimetry Measurements on a Transonic Airfoil

Burns

55th AIAA Aerospace Sciences Meeting

2017

“…10 , 11 Pressure sensitive paint (PSP) has also found success in its application to cryogenic facilities. A number of different researchers have been able to implement pressure-sensitive paint (PSP) for measuring the surface pressure on different types of models including a delta-wing airfoil at Japan's NAL 0.1-m Transonic Cryogenic Wind Tunnel 13 , a super-critical airfoil in NASA Langley's 0.3-m Transonic Cryogenic Tunnel (0.3-m TCT) 14 , and a blended-wing body 15 and sub-scale commercial transport in NASA Langley's National Transonic Facility (NTF) 16 .…”

Section: Introductionmentioning

confidence: 99%

Application of FLEET Velocimetry in the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel

Reese

31st AIAA Aerodynamic Measurement Technology and Ground Testing Conference

Jiang

et al. 2015

Femtosecond laser electronic excitation and tagging (FLEET) velocimetry is demonstrated in a large-scale transonic cryogenic wind tunnel. Test conditions include total pressures, total temperatures, and Mach numbers ranging from 15 to 58 psia, 200 to 295 K, and 0.2 to 0.75, respectively. Freestream velocity measurements exhibit accuracies within 1 percent and precisions better than 1 m/s. The measured velocities adhere closely to isentropic flow theory over the domain of temperatures and pressures that were tested. Additional velocity measurements are made within the tunnel boundary layer; virtual trajectories traced out by the FLEET signal are indicative of the characteristic turbulent behavior in this region of the flow, where the unsteadiness increases demonstrably as the wall is approached. Mean velocities taken within the boundary layer are in agreement with theoretical velocity profiles, though the fluctuating velocities exhibit a greater deviation from theoretical predictions.

“…A. 3 Equations A.3 and A.4 rely on the wavenumber ( ̅ [cm -1 ]) rather than the wavelength. Additionally, the index of refraction has a density dependence, which is referenced in Eq.…”

Section: Appendix I Theoretical Rayleigh Scattering Intensity Estimamentioning

confidence: 99%

“…Temperature sensitive paints have been used prominently for the study of laminar-to-turbulent transition in transonic cryogenic tunnels (TCTs). 1,2 Reliable cryogenic versions of pressure sensitive paints to measure surface pressure distributions are still in development, 3 though modern, lifetime-based variants have shown significantly improved sensitivity than older formulations. 4 Velocity measurements have proven challenging in high-pressure, cryogenic wind tunnels due to the particle seeding requirements of many common techniques such as particle image velocimetry (PIV) and laser Doppler velocimetry (LDV), which have the potential to cause significant contamination of flow circuits.…”

Section: Introductionmentioning

confidence: 99%

Rayleigh Scattering Density Measurements from Ultrafast Lasers in High-Pressure, Cryogenic Wind Tunnels

Burns

2018 AIAA Aerospace Sciences Meeting

2018

The Rayleigh scattering signal from femtosecond laser pulses is examined for its utility at making instantaneous density measurements in the NASA Langley 0.3-m Transonic Cryogenic Tunnel. An electron-multiplying CCD camera is used to visualize Rayleigh scattering signal taken concurrently with velocity measurements utilizing the femtosecond laser tagging velocimetry technique (FLEET). The results indicate a strong potential for making instantaneous measurements. Viable single-shot images are obtained over the full operational envelope of the facility, and shot-to-shot variations are found to be on average 6 percent (at 95 percent confidence level) and tend to decrease as the facility density is increased. The Rayleigh scattering signals observed before the optical focus exhibit a characteristically linear dependence on the mass-density of the gas, while signals after the focus exhibit a nonlinear (sublinear) density dependence, indicative of stronger absorption at higher densities. The measured Rayleigh scattering signals compare favorably to theoretical assessments made at the tunnel operating conditions.