The behavior of recirculating flows typical of advanced air-breathing and rocket injectors has been experimentally investigated. The configuration used consisted of a circular duct having a sudden increase of its diameter. Step size and flow velocity were chosen to be of a magnitude representative of “sudden-dump” combustion chambers. The recirculation, which occurred in the separation region behind the sudden expansion, was investigated using a laser-Doppler velocimeter. Detailed measurements of mean axial velocities were made. Sets of partial differential equations—including continuity, axial and transverse momentum, turbulence energy, and turbulence dissipation—were simultaneously solved using finite differencing techniques. Predictions made using these equations were brought into good agreement with the data taken from the recirculating flows under investigation by selection of appropriate “constants” in the models.

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A one-dimensional flow model of the chemical laser, from combustor to subsonic diffuser, is developed for the study of laser pressure recovery. Combustor and flow chemistry effects, nozzle and cavity boundary-layer losses, laser cavity combustion, and nozzle, cavity, and diffuser geometry influences are included in the analysis. The results from experimental tests on a laser nozzle array with a constant area diffuser are presented. Diffuser exit pressures as high as 263 Torr were measured during these experiments. The one-dimensional flow model is shown to be in agreement with the measured diffuser exit pressures over the full range of test conditions. A AR C D Hpp Nomenclature = area = nozzle area ratio =yth station molar heat capcity, 2J XjiC pi -cavity exit hydraulic diameter = ith specie heat of formation =yth station sensible enthalpy, 2y \ C pi dT =yth station stagnation enthalpy, h } + 1/2 M wj U 2 j =yth station enthalpy, H 0j ; + £j X^hî =yth station total enthalpy, nfij = mass flow = Mach number, U/(yRT) l/2 =yth stream molecular weight,2j XjiM wi -molar flow ' = fluorine available in cavity as F 2 , 1/2 n p ? + n p¥l = pressure = cavity heat release = normalized heat release, Q/n p p 2 = gas constant = cavity mixture ratio, n sr>2 /n p p 2 = temperature = velocity = mole fraction, /i_////i/; X p = n p /n 3 , X s = n s /n 3 = mass fraction, myjmj -fluorine dissociation, 1/2 n pP /n p p 2 = deuterium dissociation, n 4D /n pF = specific heat ratio = laser specific power, (9^/m 3 =yth stream dilution level,^ ^/ 5 T = secondary, fuel stream = second throat diffuser m M M n n P Q q R R L T U y a \l/j Subscripts 0= stagnation state 1-7 = flow stations; Fig. 1

A new Chemical Oxygen-Iodine Laser (COIL) has been developed and demonstrated at chlorine flow rates up to 1 gmol/s. The laser employs a cross flow jet oxygen generator operating with no diluent. The generator product flow enters the laser cavity at Mach 1 and is accelerated by mixing with 5 gmol/s, Mach 5 nitrogen diluent in an ejector nozzle array. The nitrogen also serves as the carrier for iodine. Vortex mixing is achieved through the use of mixing tabs at the nitrogen nozzle exit. Mixing approach design and analysis, including CFD analysis, led to the preferred nozzle configuration. The selected mixing enhancement design was tested in cold flow and the results are in good agreement with the CFD predictions. Good mixing was achieved within the desired cavity flow length of 20 cm and pressure recovery above 90 Torr was measured at the cavity exit. Finally, the design was incorporated into the laser and power extraction as high as 20 kw was measured at the best operating condition of 0.9 gmol/s. Stable resonator mode footprints showed desirable intensity profiles, with none of the sugar scoop profiles characteristic of the conventional COIL designs.

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