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NomenclatureM -Mach number p -static pressure, psia pt = total pressure, psia r -radius, in. r c = throat wall radius of curvature, in. rth = wall radius at throat, in. Tt = stagnation temperature, °R z -axial distance from throat, in. 7 = specific heat ratio Introduction T HE important parameter that governs the isentropic flowfield in the transonic region of a supersonic nozzle with a circular-arc throat is the ratio of throat radius of curvature to throat radius, r c /r t h. For values of r c /r t h considerably greater than unity, i.e., gradual throat contour, the flow is essentially one-dimensional. Two-dimensional flow effects become important as the ratio r c /r t h decreases. Provided that r c /r t h is not less than about 2, existing twodimensional flow theories 1 " 3 adequately predict the transonic flowfield as indicated by the wall static pressure measurements. 4 However, for nozzles with tighter throats (r c /r^ < 1), such as are found in some rocket engines, these theories do not apply. This Note presents some internal flow measurements in the transonic region of a nozzle with a small ratio of r c /r ih (0.625) and compares some recently developed prediction methods of other investigators with the data. Experimental ApparatusThe conical nozzle used in these experiments had halfangles of convergence and divergence of 45° and 15°, respectively. The static pressure in the flowfield was measured within ±0.2 psi through a 0.006-in.-diam hole drilled radially through the wall of a 0.035-in.-diam tube that extended axially through the nozzle. The tube, which was under tension to hold it taut, was remotely supported in a plenum chamber upstream and in a vacuum chamber downstream. Axial traverses were made along the centerline and at five radial locations in the nozzle throat region. The incremental axial distances traversed and the locations of the wall static pressure taps were measured within 0.002 in. However, the coordinates of the static pressure hole were known only within 0.01 in.The tests were conducted with air at a stagnation pressure of 70 psia and a stagnation temperature of 540°R. The boundary layer 1.4 in. upstream of the nozzle inlet was turbulent and had a thickness of about 5% of the duct radius. The momentum thickness Reynolds number was 2100 as deduced from the velocity distribution measured with a 0.004-in.-high, flattened-tip pitot probe. The actual boundary-

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Number 6 fuel oil was heated, sprayed, and burned in an enclosure using a small commercial oil burner. Samples of residues that emerged from the flame were collected at various locations outside the flame and observed by a scanning electron microscope. Porous cenospheres, larger globules (of size 80 μm to 200 μm) that resemble soap bubbles formed from the very viscous liquid residue, and unburned oil drops were the types of particle collected. Qualitative relationships of the morphology of these particles to the temperature history to which they were subjected were made.

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