Modeling the human larynx can provide insights into the nature of the flow and pressures within the glottis. In this study, the intraglottal pressures and glottal jet flow were studied for a divergent glottis that was symmetric for one case and oblique for another. A Plexiglas model of the larynx (7.5 times life size) with interchangeable vocal folds was used. Each vocal fold had at least 11 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. The glottis had an included divergent angle of 10 degrees. In one case the glottis was symmetric. In the other case, the glottis had an obliquity of 15 degrees. For each geometry, transglottal pressure drops of 3, 5, 10, and 15 cm H2O were used. Pressure distribution results, suggesting significantly different cross-channel pressures at glottal entry for the oblique case, replicate the data in another study by Scherer et al. [J. Acoust. Soc. Am. 109, 1616-1630 (2001b)]. Flow visualization using a LASER sheet and seeded airflow indicated separated flow inside the glottis. Separation points did not appear to change with flow for the symmetric glottis, but for the oblique glottis moved upstream on the divergent glottal wall as flow rate increased. The outgoing glottal jet was skewed off-axis for both the symmetric and oblique cases. The laser sheet showed asymmetric circulating regions in the downstream region. The length of the laminar core of the glottal jet was less than approximately 0.6 cm, and decreased in length as flow increased. The results suggest that the glottal obliquity studied here creates significantly different driving forces on the two sides of the glottis (especially at the entrance to the glottis), and that the skewed glottal jet characteristics need to be taken into consideration for modeling and aeroacoustic purposes.

Flow visualization with smoke particles illuminated by a laser sheet was used to obtain a qualitative description of the air flow structures through a dynamically similar 7.5x symmetric static scale model of the human larynx (divergence angle of 10 deg, minimal diameter of 0.04 cm real life). The acoustic level downstream of the vocal folds was measured by using a condenser microphone. False vocal folds (FVFs) were included. In general, the glottal flow was laminar and bistable. The glottal jet curvature increased with flow rate and decreased with the presence of the FVFs. The glottal exit flow for the lowest flow rate showed a curved jet which remained laminar for all geometries. For the higher flow rates, the jet flow patterns exiting the glottis showed a laminar jet core, transitioning to vortical structures, and leading spatially to turbulent dissipation. This structure was shortened and tightened with an increase in flow rate. The narrow FVF gap lengthened the flow structure and reduced jet curvature via acceleration of the flow. These results suggest that laryngeal flow resistance and the complex jet flow structure exiting the glottis are highly affected by flow rate and the presence of the false vocal folds. Acoustic consequences are discussed in terms of the quadrupole- and dipole-type sound sources due to ordered flow structures.

Experimental and numerical investigations are performed and compared for the flow of nitrogen in a small nozzle and in the near field of the plume resulting from expansion into near-vacuum conditions. The experimental data obtained were in the form of pressure measurements using a pitot tube, in the nozzle-exit plane and near field of the plume. Since the flow regimes vary from continuum, at the nozzle throat, to rarefied, in the plume, two different numerical studies are undertaken: the first employs a continuum approach in solving the Navier-Stokes equations, and the second employs a stochastic particle approach through the use of the direct simulation Monte Carlo (DSMC) method. Comparison of the experimental data and the numerical results at the nozzle exit reveals that the DSMC technique provides the more accurate description of the expanding flow. It is discovered that the DSMC solutions are quite sensitive to the model employed to simulate the interaction between the gas and the nozzle-wall surface. It is concluded that the simple fully diffuse model is quite satisfactory for the present application. The study provides the strongest evidence to date that the DSMC technique predicts accurately the flow characteristics of low-density expanding flows.Nomenclature D e = diameter at nozzle exit D p = diameter of probe D t = diameter at nozzle throat M x -Mach number ahead of a shock P x = static pressure ahead of a shock P 0 = total pressure P oy = total pressure behind a shock P x = static pressure ahead of a shock Re p -probe Reynolds number T 0 -total temperature r ref = reference temperature T w = temperature of nozzle wall T x = static temperature ahead of a shock T y = static temperature behind a shock U 0 = thermal velocity at total temperature t/oo = freestream velocity 7 = ratio of specific heats jLt ref = viscosity given by reference temperature H y = viscosity given by temperature behind a shock a?= viscosity temperature exponent Poo = freestream density

The effect of sample size on flash-cooling was assessed using an assortment of Hampton Screen I solutions (Hampton Research). These were cryogenically cooled to ascertain the minimum glycerol concentration needed for vitrification of solutions. Solutions were 'flash-cooled' in 1.0, 0.5 and 0.1 mm commercial cryoloops, using a 100 K nitrogen stream generated by an Oxford 600 Cryostream. The loops were visually examined and then X-ray diffraction data were collected and evaluated for ice formation. The glycerol concentration needed for vitrification was found to decrease significantly as sample size decreased; detailed key data are presented in tabular form. Glass transition temperatures, T g , were measured for solutions leading to successful vitrification in the 1 mm cryoloop. The trends in the required concentration of glycerol and resultant T g can be understood through a simplified heat-transfer analysis. This analysis points to a critical cooling time period for successful vitrification.