Time-resolved temperature characterization of a hypersonic shock layer using a single high-speed color camera for aerospace design applications

Abstract

Two-color ratio pyrometry (TCRP) using a high-speed color camera has been used for temperature characterization of a hypersonic shock layer. The camera, used as a pyrometer, was calibrated in-house using a monochromator to determine its spectral responsivity and was used to acquire time-resolved images of the flow field over test models at a frame rate of 20 000 fps to understand the evolution of temperature inside the shock region. The optical efficiency of the monochromator and other optical equipment were determined separately and corrected for. Two test models, a flat-faced cylinder of diameter 70 mm and a hemisphere of diameter 80 mm, were used for the experiments to study the effect of geometry on the results. Experiments were performed in a free-piston-driven shock tunnel at a stagnation enthalpy of 5.2 MJ kg−1. The average steady-state temperature in the stagnation region in the cylinder was about 3650 K ± 3% (uncertainty in the shock layer due to camera noise), and for the hemisphere it was 3300 K ± 6%. The resolved temperature was 14% higher than that obtained from a similar, but time-integrated, measurement obtained using a digital single lens reflex (DSLR) camera. Steady 2D numerical simulations were performed to reconstruct the 3D flow assuming azimuthal symmetry, and an algorithm was developed to use the shape of the temperature profile along the line-of-sight (LOS) derived from simulations to predict the actual stagnation-plane temperature from the experimental LOS-integrated TCRP-derived temperature. The actual temperature in the stagnation region on the vertical plane of symmetry (stagnation plane) for the cylinder and the hemisphere were higher by 2.76% and 1.77%, respectively, than the corresponding TCRP-derived LOS-integrated temperature. The results are promising for future use in determining intense temperature gradients and heat flux in the vicinity of space vehicles and for the design of efficient thermal protection systems.

A novel multi-band plenoptic pyrometer for high-temperature applications

“…Figure 6 shows the effects of noise on both the accuracy and uncertainty of temperature measurements at four different signal-to-noise ratios (SNRs). In this simulation, the wavelength range of the measurement varied from 650 nm to 800 nm in increments of 25 nm to emulate the qualitites of the camera used here and temperature range was between 625 • C and 1100 • C. The SNR is calculated using equation (7),…”

“…more wavelengths/bands to determine temperature and estimate emissivity. Multispectral instruments can be used in many areas such as measuring temperature distribution of surfaces [1][2][3][4][5][6][7] and sooty flames [8][9][10][11], along with many industrial applications [10,[12][13][14][15]. A few examples of these applications in more detail include Zhang et al [13] who used a monochromatic pyrometer for temperature measurements of casting billets, where an emissivity estimation was provided by a separate dual-wavelength colorimetric thermometer.…”