Measurement of recovery temperature on an airfoil in the Langley 0.3-m transonic cryogenic tunnel

Johnson, C. B.; Adcock, J. B.

doi:10.2514/6.1981-1062

Cited by 7 publications

(1 citation statement)

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“…However, only the spectral characteristics of IR radiation and of the specific IR system in use can provide the necessary information to analyze a particular application. Planck's law indicates that spectral emissive power of IR radiation peaks at Gun) = 28987 r(K) (4) this relationship being known as Wien's displacement law. For example, the IR radiation of a body at 300 K peaks at 9.7 jum, whereas at 100 K it peaks at 29.0 /mi.…”

Section: Ir Radiation At Low Temperaturesmentioning

confidence: 98%

Boundary-layer transition detection with infrared imaging emphasizing cryogenic applications

Gartenberg

Wright

1994

AIAA Journal

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This paper reviews the technique of boundary-layer transition detection using infrared (IR) imaging, emphasizing cryogenic wind-tunnel testing. With the exception of the low-temperature effects on the IR radiation, the discussion is relevant to conventional wind-tunnel and flight testing as well. At low temperatures, IR imaging encounters a reduction in the radiated energy throughout the IR spectrum, combined with a shift to longer wavelengths of the bulk of the radiation. This radiation behavior affects the minimum resolvable temperature difference (MRTD) of the IR imaging system because of its fixed wave band sensitivity. In the absence of commercial long wavelength IR imaging systems, operating at wavelengths longer than 13 jim, some measures can be taken to alleviate the problem caused by the MRTD limitation. The thermal signature of transition can be enhanced by allowing a small and controlled temperature increase of the wind-tunnel flow that induces a transient heat transfer to the model. This action temporarily reveals the model area under the turbulent regime through its higher heating rate compared with the laminar regime. The contrast between the areas exposed to the two regimes can be enhanced by subtraction of thermograms (the equilibrium thermogram from the transient thermogram). Further visual improvement can be obtained through shade stretching or binary shading. Nomenclature A = detector area c = speed of light D* = detectivity of IR detector e = emissive power h = Planck constant / = in-band detectable blackbody radiance, w/m 2 sr k = Boltzmann constant M = Mach number MRTD = minimum resolvable temperature difference at 50% signal modulation, see also appendix A N = photon emission number NEP = noise equivalent power of detector n = refraction index, c 0 /c P = Prandtl number (P = IR incident power at detector p = IR detectable power at detector R = Reynolds number S/N = signal-to-noise ratio T = temperature t = time U = velocity x = local coordinate, or unit length a = angle of attack, or thermal diffusivity 7 = specific heats ratio A/ = amplifier bandwidth d = velocity boundary-layer thickness e = emittance X = wavelength, or spectral property (subscript) /x = viscosity, or micro (10~6) Experimental Testing Technology Division, MS 234. r = transmittance, or imager optics transmission co = acceptance solid angle, sr Subscripts aw = adiabatic wall b = blackbody c = chord r = recovery value in the boundary layer ref = temperature reference conditions, 303 K t = total property t -I = difference between turbulent and laminar values 0 = vacuum conditions oo = freestream value

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Section: Ir Radiation At Low Temperaturesmentioning

confidence: 98%