Airflow Acceleration Research Articles

Theoretical assessment of unsteady aerodynamic effects in phonation

This paper ranks the importance of unsteady aerodynamic mechanisms in glottal flow. Particular emphasis is given to separation point motion, acceleration of glottal airflow by vocal fold motion, and viscous blockage. How nondimensional parameters such as the Reynolds, Strouhal, and Womersley numbers help in this ranking is also addressed. An equation of motion is derived which includes terms explicitly describing the effects of interest, assuming (1) a symmetrical glottis, (2) zero pressure recovery downstream of the vocal folds, and (3) a quasisteady glottal jet. Estimating the order of magnitude of the terms in this equation, it is shown that the flow is characterized by two temporal regimes: (1) a flow initiation/shutoff regime where local unsteady acceleration and wall motion dominate, and (2) a "quasisteady" regime where the flow is dominated by convective acceleration. In the latter case, separation point motion and viscous blockage are shown to be out of phase with motion of the vocal folds, thereby impacting the shape of the glottal volume flow waveform. The analysis suggests that glottal flow may be considered quasisteady only insofar as traditional assumptions concerning glottal jet behavior can be confirmed.

Scottish landform example 38: The windblown sands of An Teallach

Click to increase image sizeClick to decrease image sizeKey words: Aeolian sedimentplateau erosionLittle Ice Agesand sheets

Validation of a non-hydrostatic numerical model to simulate stratified wind fields over complex topography

A non-hydrostatic numerical model developed from a general purpose Navier–Stokes solver (CFDS-FLOW3D) has been proposed in order to simulate atmospheric flows over complex topography. In the validation tests presented here, the 3D numerical model has been run to simulate neutral and stratified wind fields over a 2D theoretical bell-shaped mountain. Model results have been compared to analytical solutions, obtained from linear mountain wave theory for the two approximations of (a) neutral flow and (b) stratified flow with atmospheric conditions leading to hydrostatic waves production. In both cases, the model results were in very good agreement with the analytical solution. For atmospheric conditions where non-hydrostatic effects become dominant, the model also proved to be able to reproduce trapped lee waves located downwind of the mountain. For highly non-linear atmospheric conditions, we have tried to reproduce the well-documented severe windstorm which was registered in January 1972 in the region of Boulder (Colorado), during which extreme horizontal wind values of more than 60 m/s were measured. To this purpose, the model was initialised with temperature and wind speed profiles from the meteorological soundings registered at Grand Junction station, located 300 km upwind of Boulder. A comparison of the model calculated potential temperature and horizontal wind component with the observations for this event shows the model ability to reproduce the very strong tropospheric air descent and flow acceleration over the mountain.

Current advances in rhinomanometry.

Current advances in rhinomanometry were reviewed in this paper. Active posterior rhinomanometry with a "head-out" body plethysmography may be the least invasive method currently available for measuring nasal patency. In general, active anterior rhinomanometry with a face mask or a nasal nozzle has been employed in various studies throughout the world. Nasal resistance as calculated from the equation R = 0.78 (delta P/V)1.33 at any points on a pressure/flow curve, or averaged nasal resistance may be the most suitable expression for nasal patency. Values for nasal resistance at delta P 100 Pa in Japanese patients or delta P 150 Pa in Caucasians have been widely employed as standard objective data for nasal obstruction, although rhinomanometric results sometimes do not agree with subjective evaluation of nasal obstruction. Nasal airflow acceleration or peak flow index during nasal breathing at rest can be applied as warranted to confirm an objective diagnosis of symptomatic nasal obstruction. Further, nationality and anthropological characteristics can be related to the severity and type of stuffiness.

Introductory analysis of boundary-layer development on de/anti-icing fluid

When aircraft are kept on the ground for a significant period of time under cold precipitation, anti-icing fluids are used to prevent ice buildup. Unfortunately, at the time of takeoff, the residual fluid on wings modifies the boundary layer of the air and causes lift loss. The purpose of this work was to study the boundary-layer development of the air flowing above a horizontal flat plate covered with a de/anti-icing fluid film. The objective was to find the relationship between the air boundary layer and the geometric and dynamic characteristics of the air/fluid interface. This work consists of numerical and experimental studies. The experimental work contains a rheological study of the fluid and wind-tunnel tests on flat plates in order to describe the movement of the fluid during airflow acceleration. The numerical modeling is used for the prediction of the wave characteristics at the interface and for the determination of the integral relationships for rough boundary-layer conditions. The model of stability gave a good correlation between theory and experiment for the waveform at the air/fluid interface. A simple integral model determines an equivalent flat plate roughness that produces the same boundary layer as with the fluid. This equivalent roughness corresponds, in general, to the waveform, which indicates that the influence of the fluid seems to be only geometrical in nature.

Airflow and roughness characteristics over partially vegetated linear dunes in the southwest Kalahari Desert

There is little understanding of the flow-field surrounding semi-vegetated linear dunes, and predictions of dune mobility are hampered by a lack of empirical data concerning windflow. In an attempt to characterize the near-surface airflow upwind of and over partially vegetated linear dunes in the southwest Kalahari Desert, this study presents measurements of vertical and horizontal wind velocity profiles across cross-sectional transects of seven partially vegetated linear dunes. Vegetation surveys combined with velocity measurements from vertical arrays of cup-anemometers, placed up to 2·3 m above the ground surface, were used to gain information concerning the modification of airflow structure caused by the intrusion of the dunes into the atmospheric boundary layer and to predict the variability of aerodynamic roughness (z0) from interdune to crest. The results suggest an acceleration of flow up the windward slopes of the dunes and, as such, the data correspond to classical theory concerning flow over low hills (essentially Jackson and Hunt (1975) principles). Where the theory is incapable of explaining the airflow structure and acceleration characteristics, this is explained, in part, by the presence of a spatially variable vegetation cover over the dunes. The vegetation is important both in terms of the varying aerodynamic roughness (z0) and problems concerning the definition of a zero-plane displacement (d). It is considered that any attempts to characterize surface shear stress over the Kalahari linear dunes, in order to predict sand transport and dune mobility, will be hampered by two problems. These are the progressively non-log-linear nature of the velocity profiles over the dunes caused by flow acceleration, and the production of thin near-surface boundary layers caused by areally variable aerodynamic roughness as a result of the partially vegetated nature of the dunes.

鼻腔通気度測定法の最近の進歩

At the present, the most reasonable method of determining nasal patency is nasal resistance at point of ΔP100Pa or point of peak flow calculated from an equation R=0.78 (ΔP/V)1.33 or time-averaged nasal resistance measured by active posterior rhinomanometry with a full face capsule or a headout plethysmograph. While employing active anterior rhinomanometry, bilateral nasal resistance at point of peak flow should be estimated from the modified equation of Ohm's law for parallel resistors: T=0.96[R×L/(R+L)]0.92. In Japan, nasal resistance calculated from an equation R=ΔP/V at the point of ΔP100Pa using nozzle active anterior rhinomanometry may be appropriate for clinical use. Ten minutes while at rest in the sitting position is long enough for measuring nasal resistance.Peak flow index and nasal airflow acceleration are useful indicators of nasal breathing for objective evaluation of nasal patency.

Nasal Patency: Subjective and Objective

Nasal airflow resistances (cm H2O/L/sec), accelerations (L/sec2), alteration of transnasal differential pressure, duration (sec) of inspiration and expiration and peak flow index were measured in 31 adult patients referred to our nasal airflow laboratory. Measurements by posterior rhinomanometry using a head-out body plethysmograph were compared with symptomatic severity of nasal stuffiness. Symptomatic severity of nasal stuffiness, which is a subjective perception, did not reveal a significant correlation with nasal resistances and alteration of transnasal differential pressure on quiet breathing. Acceleration of inspiratory airflow through the nose showed a direct relationship with symptomatic severity of nasal stuffiness (p < 0.04) but acceleration of expiration was not related to obstructive symptoms. Peak flow indices on expiration in the patients who did not complain of nasal stuffiness were significantly less than those on inspiration; however, as symptoms of nasal stuffiness increased, the differences between inspiratory and expiratory indices decreased. Duration of the respiration cycle showed no particular relationship with severity of obstructive sensation. We think that acceleration of nasal airflow and peak flow index can be applied to complement the diagnosis of subjective nasal stuffiness.

Winds and subsurface currents in the False Bay region, South Africa

Four current-meter moorings placed in False Bay between February and May 1985 revealed a tendency towards cyclonic motion, but with poleward flow along the western boundary. Data from six anemometers situated around the Bay showed periodic acceleration of northward air flow associated with south-easterly wind events during ridging of the South Atlantic high pressure cell round the continent. A clear pattern of cooling and warming of water at the current-meter sites was observed, corresponding to the acceleration and decay phases of south-easterly wind over periods of a few days. There was a suggestion of subsidence of warm water along the western boundary when the wind relaxed.

TOTAL RESPIRATORY INERTANCE AND ITS GAS AND TISSUE COMPONENTS IN NORMAL AND OBESE MEN.

Total respiratory inertance may be defined as that component of the total impedance to breathing that relates to acceleration of respiratory gas and of all tissue elements (lungs, rib cage, diaphragm, and abdominal contents) that move during respiration. It is expressed in units of pressure required to overcome this inertial component of the total impedance and produce air flow acceleration of 1 L per second per second. Thus its units are centimeters H2O per liter per second2. Intuitively, one would suspect that the inertance of the chest and the abdomen should be increased in severely obese subjects. In investigations of total respiratory mechanics in excessively obese persons, we made measurements of total respiratory inertance. In addition, we attempted to separate the total respiratory inertance into its gas and tissue (including lung tissue, chest wall, and abdominal) components in three normal and three excessively obese subjects. These data form the substance of this report. Inertance data on the normal human respiratory system were first published by DuBois, Brody, Lewis, and Burgess (1) in 1956. These authors, assuming that the respiratory system behaves mechanically as a simple or lumped physical system, determined the total compliance and the natural frequency of the respiratory system. They then calculated the total inertance of the respiratory system by using the simple physical relationship by which the natural frequency of a system may be predicted if its elastic and inertial characteristics are known: fn = 1/274 1/jI *C, where fn