Kenneth J. De Witt

Intraglottal pressure profiles for a symmetric and oblique glottis with a divergence angle of 10 degrees.

Human phonation does not always involve symmetric motions of the two vocal folds. Asymmetric motions can create slanted or oblique glottal angles. This study reports intraglottal pressure profiles for a Plexiglas model of the larynx with a glottis having a 10-degree divergence angle and either a symmetric orientation or an oblique angle of 15 degrees. For the oblique glottis, one side was divergent and the other convergent. The vocal fold surfaces had 14 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. Results indicated that for either the symmetric or oblique case, the pressure profiles were different on the two sides of the glottis except for the symmetric geometry for a transglottal pressure of 3 cm H2O. For the symmetric case, flow separation created lower pressures on the side where the flow stayed attached to the wall, and the largest pressure differences between the two sides of the channel were 5%-6% of the transglottal pressure. For the oblique case, pressures were lower on the divergent glottal side near the glottal entry and exit, and the cross-channel pressures at the glottis entrance differed by 27% of the transglottal pressure. The empirical pressure distributions were supported by computational results. The observed aerodynamic asymmetries could be a factor contributing to normal jitter values and differences in vocal fold phasing.

Intraglottal pressure distributions for a symmetric and oblique glottis with a uniform duct (L)

A Plexiglas model of the larynx, having a uniform duct shape and minimal diameter of 0.04 cm, was used to obtain wall pressure distributions resulting from internal airflow. Both a symmetric glottis (obliquity of 0 degrees) and a slanted glottis (obliquity of 20 degrees) were used. The oblique glottis (i.e., a glottis that slants relative to the axial tracheal flow) is present in both normal and abnormal phonation. Obliquity has been shown to create unequal cross-channel pressures on the vocal fold surfaces [Scherer et al., J. Acoust. Soc. Am. 109, 1616 (2001)], and the study here continues this line of research. For the oblique glottis, one side was divergent and the other convergent. Transglottal pressures from 3 to 15 cm H 2 O using constant airflows were used. Results indicated that the pressure distributions on the two sides of the glottis were essentially equal for the symmetric uniform case (pressures differed slightly near the exit due to asymmetric flow downstream of the glottis). For the oblique glottis, the pressures on the vocal fold surfaces at glottal entry differed by 21.4% of the transglottal pressure, suggesting that this oblique glottis creates upstream glottal pressures that may influence out-of-phase motion of the two vocal folds.

Low-density nozzle flow by the direct simulation Monte Carlo and continuum methods

Two different approaches, the direct simulation Monte Carlo (DSMC) method based on molecular gasdynamics, and a finite-volume approximation of the Navier-Stokes equations, which are based on continuum gasdynamics, are employed in the analysis of a low-density gas flow in a small converging-diverging nozzle. The fluid experiences various kinds of flow regimes including continuum, slip, transition, and free-molecular. Results from the two numerical methods are compared with Rothes experimental data, in which density and rotational temperature variations along the centerline and at various locations inside a low-density nozzle were measured by the electron-beam fluorescence technique. The continuum approach showed good agreement with the experimental data as far as density is concerned. The results from the DSMC method showed good agreement with the experimental data, both in the density and the rotational temperature. It is also shown that the simulation parameters, such as the gas/surface interaction model, the energy exchange model between rotational and translational modes, and the viscosity-temperature exponent, have substantial effects on the results of the DSMC method.

Three-Dimensional Steady Flow Through A Bifurcation

Steady flow of an incompressible, Newtonian fluid through a symmetric bifurcated rigid channel was numerically analyzed by solving the three-dimensional Navier-Stokes equations. The upstream Reynolds number ranged from 100 to 1500. The bifurcation was symmetrical with a branch angle of 60 deg and the area ratio of the daughter to the mother vessel was 2.0. The numerical procedure utilized a coordinate transformation and a control volume approach to discretize the equations to finite difference form and incorporated the SIMPLE algorithm in performing the calculation. The predicted velocity pattern was in qualitative agreement with experimental measurements available in the literature. The results also showed the effect of secondary flow which can not be predicted using previous two-dimensional simulations. A region of reversed flow was observed near the outer wall of the branch except for the case of the lowest Reynolds number. Particle trajectory was examined and it was found that no fluid particles remained within the recirculation zone. The shear stress was calculated on both the inner and the outer wall of the branch. The largest wall shear stress, located in the vicinity of the apex of the branch, was of the same order of magnitude as the level that can cause damage to the vessel wall as reported in a recent study.

New Concept in Runback Water Modeling for Anti-Iced Aircraft Surfaces

A numerical simulation of the anti-icing of aircraft surfaces is presented. The simulation utilizes the breakup of a uniformly thin liquid film into individual streams or rivulets separated by dry spaces to more accurately describe the physics of runback water. A two-dimensional heat transfer approach is used to calculate the temperature distributions in the runback water and in the solid wall. The model allows a multilayer representation of the solid wall with the possibility of heating the surface by means of electrical heating elements embedded within the layers or by means of convective heating of the surface from the inside using compressor bleed air. Parametric studies are performed to investigate the effects of some of the problem variables on the results.

The effect of exit radii on intraglottal pressure distributions in the convergent glottis

Phonation depends upon the dynamic distribution of glottal air pressures that act upon the vocal folds, as well as tissue properties of the vocal folds. The glottal wall pressures depend upon the shape, size, and diameter of the glottis for a given flow. This study examined how the radius of curvature of the glottal exit in the converging glottis affects the wall pressures in the glottis. The following exit radii were used: 0.0908 cm, 0.0454 cm, and 0.0050 cm for the 10° case, and 0.0841 cm, 0.021 025 cm, and 0.0050 cm for the 20° case. Minimal glottal diameter and flow were held constant at 0.02 cm and 73.2 cm3/s, respectively. The computational fluid dynamics code FLUENT was used to obtain the pressure profiles. Both the transglottal and intraglottal pressures increased as the exit radius decreased, resulting in an increase in flow resistance and an increase in the outward pressure forces on the vocal folds. The results suggest that the glottal exit curvature should be well specified when building compu...

Experimental Frossling Numbers for Ice-Roughened NACA 0012 Airfoils

Experimental Frossling numbers are presented for two aluminum castings of ice-roughened NACA 0012 airfoil surfaces at 0-deg angle of attack for chord Reynolds number ranging from 4.00 £ £10 5 to 1.54£10 6 . The castings were meticulously obtained from actual ice accretions representing mildly rough glaze and rough glaze ice with horns. A modie ed investment casting technique wasused to capture all of the surface roughness details. The rough glaze ice with horns produced higher heat-transfer rates than those for the mildly rough glaze ice, especially at the horns. Immediately downstream of the horns, stagnation air gaps resulted and caused lower heat-transfer coefe cients. For both types of ice, higher Reynolds numbers in general produced higher heat-transfer coefe cients. For the samechord Reynoldsnumberand at thesameposition on the airfoil, theFrossling numbersweregenerally higher than those for the smooth case and those for the hemispherical roughness elements of previous studies. A maximumincreaseofapproximately306%overthesmoothcaseand192%overthedensehemisphericalroughness case was recorded at one rough glaze ice horn. This work provides some directly measured values of the Frossling number needed to improve the prediction of some icing codes. Such icing codes help in the effective design of some deicing systems of aircraft.

Numerical simulation of rarefied gas flow through a slit

Two different approaches, the finite-difference method coupled with the discrete-ordinate method (FDDO), and the direct-simulation Monte Carlo (DSMC) method, are used in the analysis of the flow of a rarefied gas from one reservoir to another through a two-dimensional slit. The cases considered are for hard vacuum downstream pressure, finite pressure ratios, and isobaric pressure with thermal diffusion, which are not well established in spite of the simplicity of the flow field. In the FDDO analysis, by employing the discrete-ordinate method, the Boltzmann equation simplified by a model collision integral is transformed to a set of partial differential equations which are continuous in physical space but are point functions in molecular velocity space. The set of partial differential equations are solved by means of a finite-difference approximation. In the DSMC analysis, three kinds of collision sampling techniques, the time counter (TC) method, the null collision (NC) method, and the no time counter (NTC) method, are used.

Heat transfer measurements from a smooth NACA 0012 airfoil

Local convective heat transfer coefficients were measured from a smooth NACA 0012 airfoil having a chord length of 0.533 m. Flight data were taken for the smooth airfoil at Reynolds numbers based on chord in the range 1.24 to 2.50 million and at various angles of attack up to 4 deg. During these flight tests, the freestream velocity turbulence intensity was found to be very low. Wind tunnel data were acquired in the Reynolds number range 1.20 to 4.52 million and at angles of attack from -4 to +8 deg. The turbulence intensity in the IRT was 0.5-0.7 percent with the cloud-generating sprays off. A direct comparison between the results obtained in flight and in the IRT showed that the higher level of turbulence intensity in the IRT had little effect on the heat transfer for the lower Reynolds numbers but caused a moderate increase in heat transfer at the higher Reynolds numbers. Turning on the cloud-generating spray nozzle atomizing air in the IRT did not alter the heat transfer. The present data were compared with leading-edge cylinder and flat plate heat transfer correlations that are often used to estimate airfoil heat transfer in computer codes.

Numerical analysis of hypersonic low-density scramjet inlet flow

Hypersonic low-density flow around a two-dimensional scramjet inlet model has been analyzed using the direct simulation Monte Carlo (DSMC) method. The predominant features of hypersonic flows, such as a thick viscous layer due to the low-density fluid together with shock-boundary-layer interaction and shock impingement as well as shock-induced separation, are encountered in this type of flowfield. Three hypersonic flowfields with different degrees of rarefaction are investigated. The freestream Knudsen numbers of the flowfields based on the height of the duct passage are in the range of 0.02-0.12. Conventional continuum gasdynamics based on the concept of a local equilibrium may not be adequate to describe this type of flowfield accurately. The pressures obtained by the DSMC simulation are compared with available experimental data. Good agreement is obtained with previous experimental data and with theoretical solutions for similar wedge flow cases near the leading edge of the ramp centerbody. Good agreement is observed with the experimental data of Minucci and Nagamatsu except for some discrepancies, especially in the lower-density cases, which may be partially attributed to three-dimensional effects and/or to experimental uncertainty.