Transonic Cryogenic Wind Tunnel Research Articles

A Review on the Precise Control of the Liquid Nitrogen Supplying System in Transonic Cryogenic Wind Tunnel

A Review on the Precise Control of the Liquid Nitrogen Supplying System in Transonic Cryogenic Wind Tunnel

Mechanisms of trace water vapor desublimation over airfoil in transonic cryogenic wind tunnels

Cryogenic wind tunnels can provide a larger operating Reynolds number compared to conventional ones. However, the internationally known “moisture contamination problem” resulting from the residual trace water vapor desublimation in the cryogenic wind tunnel may affect the accuracy of the aerodynamic data. Due to extreme difficulties in experiments, the detailed trace water desublimation characteristics remain unrevealed. An Euler–Euler two-phase flow model based on classical nucleation theory and a droplet growth model were established to predict the trace water vapor spontaneous desublimation in the nitrogen flow over airfoil in a transonic cryogenic wind tunnel. The proposed model was validated by experimental data obtained from the literature and showed good agreements. The verified model was applied to 0.152-m National Advisory Committee for Aeronautics 0012 airfoil in a Langley 0.3-m transonic cryogenic wind tunnel under a series of operating conditions. The simulated results reveal that the water vapor desublimation process in a transonic cryogenic wind tunnel can be divided into two patterns by a critical region. In pattern I, over the upper critical total temperature, the water vapor desublimates quickly during the rapid expansion of gas flow over the airfoil surface. In pattern II, below the lower critical total temperature, the water vapor is sufficiently supercooled and desublimates completely into small ice particles in the free-stream flow. For pattern I, the desublimation characteristics were analyzed in detail, and the influences of the desublimation process on the aerodynamic data were quantitatively evaluated, which can provide theoretical guidance for the practical operation of transonic cryogenic wind tunnels.

Application of femtosecond-laser tagging for unseeded velocimetry in a large-scale transonic cryogenic wind tunnel

Femtosecond laser electronic excitation tagging (FLEET) velocimetry was applied in the National Transonic Facility and assessed for its use in providing quantitative velocity measurements in a large-scale cryogenic wind tunnel. Comparisons of freestream results with theory and existing tunnel measurements indicate that FLEET velocity measurements agree within 1% of the tunnel reference, while the largest error among all conditions remained within 2.5%. For single-shot velocity measurements, binning of the FLEET intensity data improved the signal-to-noise ratio sufficiently to provide measurement precisions on the order of 1% of the freestream velocity. After confirmation of system performance, spatially resolved velocity profile measurements were obtained in the wake downstream of the Common Research Model wing. Effects of the model angle-of-attack on velocity deficit profiles were explored, and a two-dimensional, one-component velocity map resolving the wake region was constructed by scanning the laser’s position within the test section. The experimental campaign described herein represents the first non-intrusive, quantitative measurements of velocity made in this facility since its inception in 1984.

A109 流体計測のための担持型TSPの開発とPSPへの応用

In this paper, current status of the development of luminophore-pendant temperature-sensitive paint of poly[l-(trimetylsilyl)phenyl-2-phenylacetylene] (PTMST) is discussed. PTMST uses poly(l-trimethylsilyl-l-propyne) (PTMSP) based polymer, which is known as one of the highest gas permeable polymers. Because of its high gas permeability and single luminescent compound, we can expect fast response of PTMST to the change in temperature and pressure of the test gas. We can also create PTMST-based two-color PSP for temperature-compensated pressure sensor by simply mixing pressure-sensitive luminophore in PTMST. In this paper, we mix platinum tetrakis (pentafluorophenyl) porphyrin (PtTFPP) as a pressure-sensitive luminophore to create PTMST-based two-color PSP (PtTFPP-PTMST). Spectral analysis shows that PtTFPP-PTMST provides temperature sensitive peak of PTMST (around 540 nm) and pressure sensitive peak of PtTFPP (around 650 nm), which can be separated by band-pass filters. We have calibrated PTMST from 100 K to 373 K as well as PtTFPP-PTMST from 120 K to 333 K to study the static characteristics of these sensors. PTMST provides the temperature sensitivity over the calibrated range, giving the maximum value of 2.72%/K at 100 K. PTMST itself is almost pressure independent. Pressure sensitivity of PtTFPP-PTMST is 0.26%/kPa at 293 K. PtTFPP-PTMST shows pressure sensitivity of 0.66%/kPa even at cryogenic temperature of 120 K. The unsteady characteristic of PtTFPP-PTMST is determined using a step response to a pressure change caused by a shock tube. The response time of PtTFPP-PTMST is on the order of milliseconds. A demonstration of PTMST at cryogenic measurement is shown by transition detection of PTMST-coated NACA64A012 model in JAXA 0.1m Transonic Cryogenic Wind Tunnel. PTMST detects a natural transition as well as a forced transition induced by a roughness at the leading edge at Mach 0.4, total temperature 200 K, and total pressure 120 kPa.

B305 大型低温風洞で用いる感温塗料の開発

A new Temperature-Sensitive Paint (TSP) technique for boundary-layer transition detection in a production-type large cryogenic wind tunnel is present. The formulation of Ruthenium complex TSP system has been optimized in terms of luminescence intensity and robustness. The optimum dye-binder-solvent combination has been determined through systematic sample tests. A new binder has been introduced and the resulting coating was found free from cracking at cryogenic temperatures. This is contrary to the silicone-based cryogenic TSPs that are subject to micro cracks at reduced temperatures. The new TSP can meet the root-mean-square roughness requirement less than 0.15 ?m. We applied this TSP in the JAXA 0.1-m Transonic Cryogenic Wind Tunnel, and then European Transonic Windtunnel (ETW). A variety of transition patterns have been successfully visualized.

低温風洞PSP計測への位相法の適用

The phase-based technique has been applied to pressure-sensitive paint (PSP) measurement in a cryogenic wind tunnel. In this method, surface pressure can be obtained from the phase shift between modulated excitation light and PSP emission. We constructed a laser scanning system for two types of PSP, polymer-based and anodized-aluminum based, and applied it to arc bump model tests in the 0.1-m Transonic Cryogenic Wind Tunnel at National Aerospace laboratory. A comparison of the two paints showed that the polymer-based PSP had higher sensitivity to oxygen and lower spatial variation than anodized aluminum PSP. The pressure distribution on the bump model at Mach 0.82 and 100 Kelvin was successfully obtained using the polymer-based PSP and the laser scanning system. The data obtained with this technique agreed well to pressure tap measurement but contained larger noise than those obtained with the intensity method, mainly due to the interference between reflected excitation light and luminescence.

新色素を用いた感圧塗料の低温風洞への適用

A new type of pressure-sensitive paint for pressure measurement in a cryogenic wind tunnel is present. This paint is composed of Pyrene-based luminophores adsorbed onto anodized aluminum surface (AA-PSP). Various derivatives of Pyrene were calibrated by changing the mole fraction of oxygen in the 0.1 m Transonic Cryogenic Wind Tunnel (TCWT) at National Aerospace Laboratory (NAL). It has been verified that Pyrene-based AA-PSPs show high oxygen sensitivity in the 02 concentration range from 4 to 1000ppm. These AA-PSPs were applied to a 14%-thick circular arc-bump model and tested in TCWT at 100 Kelvin. Surface pressure distributions on the model were clearly imaged with high spatial resolution and S/N ratio. A comparison of the measured intensity data with the pressure tap measurements has suggested that the in situ calibration can be used to obtain quantitative pressure data.

Similarity rule for jet-temperature effects on transonic base pressure

On the basis of the similarity rule for jet interaction, a hot jet can be simulated in a cryogenic wind tunnel with a test gas at ambient or moderately elevated temperatures. By using this approach, jet-temperature effects on the base pressure of a cylindrical afterbody model at transonic speeds have been investigated in the 0.1-m transonic cryogenic wind tunnel at the National Aerospace Laboratory. Mixtures of nitrogen and either methane, argon, or helium at varying temperatures were used as a jet gas to determine separate effects of jet temperature, specific heat ratio, and gas constant. It has been found that data obtained for various jet conditions can be correlated very well with two similarity parameters : the plume maximum diameter for the plume shape effect and the jet to freestream mass flux ratio for the jet entrainment effect. To verify this similarity rule, the same model was tested in an ambient wind tunnel. It was found that an ambient temperature gas having low molecular weight could simulate the jet temperature effects on the transonic base pressure.

Turbulence measurements and noise generation in a transonic cryogenic wind tunnel

A high-frequency combination probe was used to measure dynamic flow quality in the test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe measures fluctuating stagnation (total) temperature and pressure, static pressure, and flow angles in two orthogonal planes. Simultaneous measurements of unsteady total temperature and pressure were also made in the settling chamber of the tunnel. The data show that the stagnation temperature fluctuations remain constant, and the stagnation pressure fluctuations increase by a factor of two, as the flow accelerates from the settling chamber to the test section. In the test section, the maximum rms value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients failed to show vorticity, entropy, or sound as the dominant mode of turbulence in the tunnel.

Cryogenic tunnel measurement of total temperature and pressure

A newly developed, 3-mm-diam, dual hot-wire aspirating probe was used to measure the time-resolved stagnation temperature and pressure in a transonic cryogenic wind tunnel. Measurements were taken in the freestream of the settling chamber and test section. Data were also obtained in the unsteady wake shed from an airfoil oscillating at 5 Hz. The investigation revealed the presence of large fluctuations in the settling chamber occuring at the blade passing frequency of the driving fan of the tunnel. These fluctuations decrease at the test section. The rms value of the fluctuating stagnation pressure decreased from 17.5 percent in the settling chamber to 3.7 percent in the test section. Fluctuating stagnation temperature decreased from 12.3 percent to 8.4 percent. Measurements in the wake of the oscillating airfoil showed a fluctuating stagnation temperature of as much as 42 K in rms value.