Exploration of Liquid Mass Distribution for Liquid Jets in Subsonic Crossflows Using X-Ray Radiography

Abstract

Spray structures of liquid jets in subsonic crossflows were characterized using X-ray radiographyat the 7-BM beamline of the Advanced Photon Source at Argonne National Laboratory. A small-scale wind tunnel with a test section of 2” (H)  2” (W)  6” (L) provided a freestream flow up to Mach 0.3. The wide windows of the test section are fitted with a thin Polyimide film for high X-ray transmittance. An axisymmetric aerated-liquid injector fitted with an exchangeable adaptor was used to generate a pureor aerated-liquid jet at the desired injection conditions. The obtained line-of-sight radiography signals were processed to give quantitative liquid mass distributions within the spray at various injection conditions. The present results were also used to derive spray penetration heights for comparison with predictions from the existing correlations. The present study shows that the present measurements can quantify liquid mass distributions within both near field, such as the jet column, and far field of liquid jets in subsonic crossflows. In the near field, deformation of the liquid column for the pure-liquid jets and the co-annular-like column structure for the aerated-liquid jets can also be quantitatively depicted by the present experimental approach. In the far field, the present efforts to compare the measured penetration heights, based on various threshold values, with the predictions from the existing penetration height correlations, give a new perspective in characterizing spray penetrations in crossflows. In general, the penetration heights predicted from shadowgraph-based correlations are in agreement with the time-average water mass contours and can account for the majority of the injected liquid mass in the far field. The penetration heights predicted from PDPA-based correlations are in agreement with the standard deviation water mass contours and are more indicative of the outer boundary for droplet presence. NOMENCLATURE d0 = injector exit orifice diameter EPL = equivalent path length GLR = aerating gas-to-liquid mass ratio I = intensity of the transmitted light I0 = intensity of the incident light L = passage length M = freestream Mach number; also projected medium density in X-ray beam in Eq. (1) mL = liquid mass flow rate q = jet-to-freestream momentum flux ratio x = freestream position from the injector exit; also X-ray beam path length y = transverse position from the injector exit  = linear attenuation coefficient  = mass attenuation coefficient