Optical Measurements of the Temperature in a Supersonic Jet

Abstract

In this study a nonintrusive method for temperature measurement is investigated. The technique involves a two-beam schlieren system based on the measurement of angular beam dee ection across an axisymmetric e ow. The mean temperature is obtained by the Abel transform using the Gladstone approximation. Fluctuating temperatures are estimated by statistical processes of the beam dee ections. Validation is e rst performed in subsonic e ow, where schlieren data are compared with those obtained using classical probe. Finally, the schlieren method is successfully applied on supersonic jets approaching space launcher conditions. In the case of perfectly expanded jets, comparison between numerical and optical data shows good agreement. Nomenclature D = nozzle diameter, m J = Gladstone’ s constant, K LC = length of the potential core, m l = length scale, m M = Mach number n = refractive index P = pressure, Pa R = gas constant, J/mol ¢K r = radial component, m T = temperature, K V = jet velocity, m/s y = axial component, m ° = ratio of the specie c heats 2 = angle of beam dee ection, rad Ω = density, kg/m 3 ? = e uctuation rate of temperature Subscripts a = ambient condition i = stagnation condition j = perfectly expanded condition o = centerline component s = static component t = transverse component Superscripts N = time average 0 = e uctuating component