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Purpose: This article describes the development and initial validation of an objective measure of nasal air emission (NAE) using nasal accelerometry. Method: Nasal acceleration and nasal airflow signals were simultaneously recorded while an expert speech language pathologist modeled NAEs at a variety of severity levels. In addition, microphone and nasal accelerometer signals were collected during the production of /papapapa/ speech utterances by 25 children with and without cleft palate. Fourteen inexperienced raters listened to the microphone signals from the pediatric speakers and rated the samples for the severity of NAE using direct magnitude estimation. Mean listener ratings were compared to a novel quantitative measurement of NAE derived from the nasal acceleration signals. Results: Correlation between the nasal acceleration energy measure and the measured nasal airflow was high (r = .87). Correlation between the measure and auditory-perceptual ratings was moderate (r = .49). Conclusion: The measure presented here is quantitative and noninvasive, and the required hardware is inexpensive ($150). Future studies will include speakers with a wider range of NAE severity and etiology, including cleft palate, hearing impairment, or dysarthria. Further development will also involve validation of the measure against airflow measures across subjects., Velopharyngeal dysfunction (VPD) occurs as a result of inappropriate opening or closing of the velopharyngeal (VP) port. VPD can be due to structural, neurological, or functional impairments; in particular, 20%-30% [...]

Air-water flows on stepped spillways were investigated experimentally in the last decades with a focus on steep slope chutes equipped with flat horizontal steps. Detailed air-water flow properties were recorded herein with three stepped geometries down a slope of θ = 8.9° with: flat horizontal steps, pooled steps, and a combination of flat and pooled steps. The data included the distributions of basic air-water flow properties, as well as the energy dissipation and flow resistance data deduced from the air-water flow measurements. The results on the flat slope showed that the pooled stepped design enabled a greater rate of energy dissipation, but the pooled stepped geometries were affected by some flow instabilities and unsteady flow processes for a range of flow rates. Key words: air-water flows, turbulence, stepped spillways, pooled steps, flow instabilities, physical modelling, turbulent energy dissipation. De nombreuses recherches ont ete conduites pour etudier l'entrainement d'air sur des coursiers en marches d'escalier durant les dernieres decennies. Ces travaux ont etudie principalement des geometries avec fortes pentes et des marches plates et horizontales. Ici, on presente de nouveaux travaux experimentaux sur une faible pente (θ = 8, 9°) avec trois configurations : marches plates et horizontales, marches avec murets, et combinaison de marches plates et avec murets. Des mesures diphasiques detaillees ont ete conduites. Les resultats indiquent que la dissipation d'energie est maximum en presence de marches avec murets (en continue ou en alternance), mais ces geometries sont sujettes a des instabilites hydrodynamiques tres importantes. Mots-cles: entrainement d'air, turbulence, coursier en marches d'escalier, marches avec murets, instabilites hydrodynamiques, modelisation physique, dissipation d'energie., Introduction Air-water flows on stepped spillways were investigated experimentally in the last two decades (e.g., Chanson 1993, 2001; Ruff and Frizell 1994; Chamani and Rajaratnam 1999; Carosi and Chanson 2008). [...]

Induced velocity gives rise to an important component of the angle of attack experienced by a blade element and, hence, the rotor loads. Finite-state induced-velocity models can be found in rotorcraft codes that require fast computation but cannot replicate real flowfield features. However, they do encapsulate in a simple and intuitive way the impact of real wakes on rotorcraft dynamics and hence are popular in codes that are used to study vehicle flight mechanics such as stability, control, and handling qualities. Explicit verification of these models is not possible, but implicit verification is possible if blade flapping is known; and this paper presents results from flight tests of a light gyroplane fitted with a two-bladed teetering rotor instrumented to measure the rotor flapping behavior. An appropriate model structure is developed to allow calculation of induced-velocity components from steady-flight flapping data recorded across the aircraft's level-flight speed range. Very good agreement is obtained between flight and theory in respect to the uniform and longitudinal components, correlating well with previous studies. However, the lateral component is very poorly correlated, and this is attributed to strong nontrapezoidal behavior in the real wake. Notwithstanding this, it is concluded that the simple finite-state, induced-velocity model is a valid tool for gyroplane flight mechanics studies and rotorcraft autorotation in general.

In this paper, wind-tunnel measurements are presented for the airflow fluctuation detection using pressure optical sensors. Twenty-one wind-tunnel test runs for various Mach numbers, angles of attack, and Reynolds numbers were performed in the 6 x 9 [ft.sup.2] wind tunnel at the Institute for Aerospace Research at the National Research Council Canada. A rectangular finite aspect ratio half-wing, having a NACA 4415 cross section, was considered with its upper surface instrumented with pressure taps, pressure optical sensors, and one Kulite transducer. The Mach number was varied from 0.1 to 0.3 and the angle of attack range was within -3 to 3 deg. Unsteady pressure signals were recorded and a thorough comparison, in terms of unsteady and mean pressure coefficients, was performed between the measurements from the three sets of pressure transducers. Temperature corrections were considered in the pressure measurements by optical sensors. Comparisons were also performed against theoretical predictions using the XFoil computational fluid dynamics code, and mean errors smaller than 10% were noticed between the measured and the predicted data. DOI: 10.2514/1.40715

This article describes the wind tunnel used in the Physics Department of the Ecole Normale Superieure in Paris for undergraduate laboratory courses. By using an active grid, which consists of a grid of shafts fitted with randomly rotating wings, a fully turbulent flow is observed. The velocity of the air flow is measured with a low cost hot wire probe. The Reynolds number is large enough so that predictions of the 1941 Kolmogorov theory of turbulence can be observed, such as the famous k-5/3 spectrum, in spite of the small size of the tunnel. Deviations from the Kolmogorov theory are also observed and quantified. The moderate cost and size of the wind tunnel due to the use of the active grid make it a valuable teaching tool for introducing the phenomenology of turbulence to undergraduates.

The effects of active flow control by oscillatory blowing at the leading edge of a nonslender delta wing with a 50-degree sweep angle have been investigated. Pressure measurements and particle image velocimetry measurements were conducted to investigate the formation of leading-edge vortices for oscillatory blowing, compared with completely stalled flow for the no-blowing case. Stall has been delayed substantially and significant increases in the upper surface suction force have been observed. For a given angle of attack, there is an optimal momentum coefficient, after which forcing at higher momentum coefficients has negligible effect. For the poststall region, as the angle of attack increases, the optimal momentum coefficient increases. Velocity measurements show that the flow reattachment is promoted with forcing, and a vortex flow pattern develops. The time-averaged location of the center of the vortical region moves outboard with excitation. The near-surface flow pattern obtained from the particle image velocimetry measurements shows the reattachment clearly in the forward part of the wing. There is no jetlike axial flow in the core of the vortex, which seems to have breakdown at or very near the apex. Phase-averaged measurements reveal the perturbation due to the pulsed blowing, its interaction with the shear layer and vortex, apparent displacement of the vortex core, and relaxation of the reattachment region. Experiments with excitation from finite span slots located in the forward half of the wing show that partial blowing may be more effective at low momentum coefficients and promote reattachment upstream of the slot.

A Reynolds-averaged Navier-Stokes-based scalar-variance model is described that extends a previous low-speed nonreacting jet model to more generalized high-speed compressible reacting flows. The model is cast in a k-[epsilon] turbulence model framework. Transport equations for energy variance and its dissipation rate are solved to predict temperature fluctuations and provide a thermal time scale for use in calculating a variable turbulent Prandtl number. For multispecies problems, mixture-fraction variance and dissipation rate equations are solved that predict species concentration fluctuations and provide a species mixing time scale for use in calculating a variable turbulent Schmidt number. The formulation accounts for compressibility and near-wall damping effects. A series of high-speed flow simulations are presented for both nonreacting and reacting configurations and the predictions are compared to available measured data and companion LES calculations. Results demonstrate the models' capabilities over a range of conditions and suggest that the proposed formulation will provide improved predictions in practical high-speed aeropropulsive configurations of interest, such as scramjet combustors, where turbulent Prandtl and Schmidt numbers vary substantially. DOI: 10.2514/1.21075

We investigate the performance of two recently developed subgrid-scale models, the approximate deconvolution model and the high-pass filtered Smagorinsky model, in large-eddy simulations of laminar-turbulent transition in a supersonic boundary layer. Subharmonic transition in a boundary layer at a freestream Mach number of 4.5 and a Reynolds number (based on initial displacement thickness) of 10,000 is considered, which has been studied previously in detail by direct numerical simulations. For computational efficiency, the temporal simulation approach has been adopted. The discretization is based on Fourier collocation and various high-order finite difference schemes in the wall-parallel and wall-normal directions, respectively. Large-eddy simulations results are assessed by comparing statistical and instantaneous quantities during transition with data obtained from a sufficiently resolved direct numerical simulation. The results show that the large-eddy simulations accurately reproduce the direct numerical simulations data from the slightly disturbed laminar flow through transition into the turbulent stage, with a computational effort of two orders of magnitude less than the direct numerical simulations. Both subgrid-scale models are formulated locally in space and in a fully three-dimensional manner and do not need an ad hoc adaptation to nonturbulent or near-wall regions. DOI: 10.2514/1.15048

Time-accurate Navier-Stokes flow solvers utilizing Newton and dual-time-step implicit subiteration algorithms have been investigated for both moving-body and deforming-grid applications. A set of relatively simple two-dimensional validation cases has been identified to assess the performance of these unsteady computational fluid dynamics (CFD) solvers with varying time-step size and number of subiterations. These cases demonstrate the advantages of second-order time derivatives and subiterations for unsteady-flow simulations. This investigation also indicates subiteration algorithms and large time steps can be used to reduce the computational cost of a given unsteady-flow simulation.

An adjoint-based error estimation and grid adaptation study is conducted for three-dimensional inviscid flows with unstructured meshes. The error in an integral output functional of interest is estimated by a dot product of the residual error and adjoint variable vector. To suppress excessive mesh refinement in unnecessary regions due to high-frequency noise contained in the residual vector, the flow residual is smoothed using a volume-weighted averaging process. Regions to be adapted are selected based on the error contribution of a local node to the global error. The adaptive regions are refined by the bisection refinement algorithm. The present procedure is applied to three-dimensional transonic inviscid flows around ONERA M6 wing and ONERA M5 airplane models. The same level of prediction accuracy for drag is achieved with much less mesh points than uniformly refined fine meshes. It is found that the residual smoothing strategy remarkably improves the accuracy of error estimation, and there exists an optimum number of smoothing for accurate error estimation.

Flowfield measurements were carried out on the upper surface of a GLC-305 airfoil configured with glaze and rime ice-shape simulations. The mean and ront-mean-square fluctuation of the streamwise velocity were measured using a split-hot-film probe at several chordwise locations. These data were taken at three different angles of attack preceding stall for each iced-airfoil configuration at Reynolds numbers of 3.5 x [10.sup.6] and 6.0 x [10.sup.6] with Mach numbers of 0.12 and 0.21. The velocity measurements confirmed the presence of a large separation bubble downstream of the ice shapes. The separation bubbles for the glaze ice configuration were much larger than those for the rime ice case, resulting from the differences in the ice horn geometry. Other than the differences in size, the integral boundary-layer characteristics were very similar. Changes in Reynolds number did not significantly affect the separation bubble characteristics. However, a larger Mach number did result in a slightly larger separation bubble for the glaze ice case at [alpha] = 6 deg. The root-mean-square velocity distributions had peak values in the separated shear layer, downstream of transition, that compared well with previous work.

A new porous condition has been implemented in the PAB3D solver to simulate flow over porous surfaces. The newly added boundary condition is utilized to compute the flow field of a nonaxisymmetric, convergent-divergent nozzle incorporating porous cavities for shock-boundary layer interaction control. The nozzle has an expansion ratio (exit area/throat area) of 1.797 and a design nozzle pressure ratio (NPR) of 8.78. The flow fields for a baseline nozzle (no porosity) and for a nozzle with porous surfaces (10% porosity ratio) are computed for NPR varying from 2.01 to 9.54. Computational model results indicate that the overexpanded nozzle flow is dominated by shock-induced boundary-layer separation. Porous configurations are capable of controlling off-design separation in the nozzle by encouraging stable separation of the exhaust flow. Computational simulation results, wall centerline pressure, Mach contours, and thrust efficiency ratio are presented and discussed. Computed results are in excellent agreement with experimental data.

The effect of a movable trailing-edge tab on a tip vortex generated by an oscillating NACA 0015 wing was investigated at Re = 1.86 x [10.sup.5] by using a miniature triple hot-wire probe. Both upward and downward tab deflections, actuated with different start times and durations, were tested. The downward tab motion was most effective in displacing the vortex position. The earlier the actuation the larger the displacement. The upward tab motions were, however, found to be more effective in diffusing the tip vortex and rendered a significantly reduced peak tangential velocity and core circulation, compared to an uncontrolled baseline wing. The earlier and longer the upward tab actuations the lower the vortex core strength and peak tangential velocity. The vortex core radius was rather insensitive to the tab motion. The upward tab deflection, however, produced less induced drag compared to a downward deflection.

Transitional supersonic base flows at M = 2.46 are investigated using direct numerical simulations. Results are presented for Reynolds numbers based on the cylinder diameter ReD = 3 X [10.sup.4]-1 X [10.sup.5]. As a consequence of flow instabilities, coherent structures develop that have a profound impact on the global flow behavior. Simulations with various circumferential domain sizes are conducted to investigate the effect of coherent structures associated with different azimuthal modes on the mean flow, in particular on the base pressure, which determines the base drag. Temporal spectra reveal that frequencies found in the axisymmetric mode can be related to dominant higher modes present in the flow. It is shown that azimuthal modes with low wave numbers cause a flat base pressure distribution and that the mean base pressure value increases when the most dominant modes are deliberately eliminated. Visualizations of instantaneous flow quantities and turbulence statistics at [Re.sub.D] = 1 x [10.sup.5] show good agreement with experiments at a significantly higher Reynolds number. For these investigations, a high-order-accurate compressible Navier-Stokes solver in cylindrical coordinates developed specifically for this research was used.

Vortices shed from the tip of a rectangular half-span wing model (NACA 0012) have been investigated with particle image velocimetry at a chord Reynolds number between 3.4 x [10.sup.4] and 26.6 x [10.sup.4] and angles of attack [alpha] = 8 and 16 deg over 0.2 ~ 5 chord lengths downstream of the model. It has been found that the measured wing-tip vortex shows little dependence in the circumferential velocity [v.sub.[theta]] and vorticity [OMEGA], when normalized by their local maximum, on [alpha], Reynolds number, and downstream distance from the wing. Furthermore, the radial distributions of [v.sub.[theta]] and [OMEGA] coincide quite well with the exponential vortex solution, with only a slight departure outside the core region.

Based on a Navier--Stokes/full potential/free wake solver, a new hybrid method was developed for efficient predictions of the three-dimensional viscous flowfield of a helicopter rotor under both hover and forward flight conditions. The developed flow solver was composed of three modules: 1) a compressible Navier-Stokes analysis to model the viscous flow and near wake about the blade, 2) a compressible potential flow analysis to model the inviscid isentropic potential flow region far away from the rotor, and 3) a free wake model to account for tip vortex effects once the tip vortex leaves the viscous flow region and enters the potential flow region. In this hybrid method, a moving embedded grid methodology was adopted that accounts for rigid blade motions in rotation, flapping, and pitching. A dual-time method was employed to fulfill the calculation of the unsteady flowfields of helicopter rotors, and a third-order upwind scheme (MUSCL) and flux-difference splitting scheme without introducing artificial viscosity were used to calculate the flux. To search suitable donor elements in embedded grids to pass information between the viscous flow and potential flow zones, a new searching scheme was implemented. The sectional pressure distributions of a UH-60A helicopter rotor and an AH-1G model rotor in hover and forward flight, with and without the wake model, were calculated, and the developed hybrid model was validated by comparing with available experimental data. The simulated steady and unsteady lifting results of a model rotor with three different blade-tip planforms demonstrate the benefits of the curvilinear swept tip and constant swept tip in suppressing supercritical flows.

Using the finite volume method, the Navier-Stokes equations are solved on a body-fitted structured grid. The low speed and hovering flight of MI-171V5 helicopter are numerically simulated, and the flowfield characteristics around its engine inlet are calculated. Following this, beginning with a prescribed wake model, a semi-empirical correction for the vortex core effect on rotor wake is made, and a free-wake calculation is carried out. The calculated results show that both computational-fluid-dynamics method and free-wake analytical technique can predict the vortex wake flowfield distributions.

A wind-tunnel study of the effects of the addition of movable tip strakes on the aerodynamic characteristics of a rectangular wing model has been conducted. This is a new application of the strake concept for modifying the flowfield around a wing. The addition of sharp-edged slender delta-wing-shaped strakes significantly modified the flow pattern in the vicinity of the wing through generation of vortex lift. The strakes improved the lift-to-drag ratio of the baseline wing by as much as 23%. The method can have potential for lateral control too. Based on limited flow-visualization results, it appears that the strakes favorably influence the near-field roll up of the wing trailing vortices. The approach warrants additional investigations using more advanced measurement and flow-visualization techniques.

The Reynolds number dependence of the near-surface flow structure and topology on a representative unmanned combat air vehicle planform is characterized using a technique of high-image-density particle image velocimetry, to complement classical dye visualization. Patterns of streamline topology, including bifurcation lines, as well as contours of streamwise and transverse velocity, surface-normal vorticity, and Reynolds stress correlation, all immediately adjacent to the surface of the planform, provide quantitative indicators. At low angle of attack, these indicators show significant alterations with Reynolds number, in accord with large variations of patterns of vortex breakdown and vortex interaction visualized by dye and substantial alterations of flow patterns in the crossflow plane, including reattachment phenomena, which are interpreted with patterns of velocity, streamlines, and streamwise vorticity. On the other hand, at moderate angle of attack, the near-surface quantitative indicators show much less sensitivity to Reynolds number, which is in line with weak variations of the onset of vortex breakdown with changes in Reynolds number.

Frequency-domain and time-domain approaches to dynamic response analysis of aeroservoelastic systems to atmospheric gust excitations are presented. The discrete and continuous gust inputs are defined in either time-domain or stochastic terms. The various options are formulated in a way that accommodates linear control systems of the most general form. The frequency-domain approach is based on the interpolation of generalized aerodynamic force coefficient matrices and the application of Fourier transforms for time-domain solutions. The time-domain approach uses state-space formulation that requires the frequency-dependent aerodynamic coefficients to be approximated by rational functions of the Laplace variable. Once constructed, the state-space equations of motion are more suitable for time simulations and for the interaction with control design algorithms. However, there is some accuracy loss because of the rational approximation. The spiral nature in the complex plane of the gust-related aerodynamic terms is discussed, and means are provided for dealing with the associated numerical difficulties. A hybrid formulation that does not require the rational approximation of the gust coefficients is also presented for optional use in discrete gust response analysis. The various methods were utilized in the ZAERO software and applied to a generic transport aircraft model.

An experimental investigation has been carried out to study the effect of nose bluntness on the characteristics of vortex asymmetry and induced side forces on slender cone models at low speeds. Two cone models with semi-apex angles of 8 and 12 deg were utilized, and on each model nose bluntness was varied up to 20% (based on base diameter). Measurements made consisted of six-component balance loads over a wide range of Reynolds number from 0.4 x [10.sup.6] to 5.4 x [10.sup.6]. The results show that the onset of vortex asymmetry with nose blunting correlates with geometrical parameters and is practically independent of Reynolds number. The (maximum) side-force levels decrease initially up to a certain bluntness ratio, then increase, followed by a gradual decrease for large values of bluntness ratios. This decrease or increase in side-force levels with nose blunting is associated with a corresponding increase or decrease, respectively, in the onset of vortex asymmetry. Whereas the increase in side-force level beyond the first minimum is qualitatively similar to that observed in earlier studies, the present data definitely indicate that there is a progressive decrease in side-force levels to relatively low values for large bluntness ratios, which could form an important design input. The bluntness ratio corresponding to the occurrence of the first minimum in (maximum) side force depends on the cone angle and is nearly independent of Reynolds number.

Through the evolution of natural flight systems, it is expected that many have been optimized to provide enhanced efficiency. With this in mind the current study was conducted to determine whether flight configurations found in nature might be appropriately applied to fixed-wing mechanical flight systems to provide performance improvements through energy savings. Four different biologically inspired wings were designed and experimentally tested against a planar elliptic configuration used as a baseline. Two of the configurations show performance improvements over the baseline, using two different comparison techniques. Surface oil flow visualizations at the wingtips highlight differences that provide insight into the flow physics of the improvements.

The application of overset grid methods to studying the flowfield of the FANTAILTM antitorque system of the RAH-66 rotorcraft is described. The FANTAIL itself and the experimental program used to design it are described first. Then, OVERFLOW-D, an overset grid-based, Navier-Stokes computational fluid dynamics code is reviewed, and its adaptation to the ducted fan geometry of the FANTAIL is explained. The modeling of the FANTAIL using OVERFLOW-D, including grids and boundary conditions, is explained in detail. The results of numerical studies of the hovering FANTAIL are presented and are shown to compare well with experiment. Flowfield visualizations are presented and are used to explain how the blade tip vortices combine with the adverse pressure gradient beneath the rotor disk to impact flow along the duct wall beneath the disk.

Accurate prediction of flutter speeds is essential to efficient and safe flight testing for envelope expansion. Such accuracy is particularly difficult to obtain when analyzing flight data from speeds well below the critical speed at which flutter occurs. The flutterometer was introduced as a tool that could predict the onset of flutter even at low-speed conditions; however, the conservatism in those predictions reduced testing efficiency. A method to augment the flutterometer to decrease the conservatism, and consequently increase the accuracy, of the predicted flutter speeds is presented. The method incorporates a scheme for model updating that ensures consistency between the analytical dynamics and the flight data. The tool is used to compute flutter speeds for the aerostructures test wing. The speeds predicted with the model updating scheme are very close to the actual flutter speed and demonstrate the benefits for improving efficiency of envelope expansion.

A systematic investigation of cross-flow fan performances is presented according to an original criterion for the parameterization of fan geometry. Test facility and procedures are set up following ISO standards. The aim is to find which are the parameters most affecting fan performances and the effects of their design choice. Indications are found to design fans according to the desired objectives, such as maximum total pressure, total efficiency, and flow rate. [DOI: 10.1115/1.1593710]

The dependence of an interrupting capability on the spatial distribution of airflow velocity was investigated in an air-blast flat-type quenching chamber. To obtain a various distribution of airflow velocity, the axial position of a nozzle and the inlet width of the nozzle were varied. For each of the axial positions and each of the inlet widths, arc interruption tests for ac currents were performed to measure the interrupting capability. Furthermore, the distribution of airflow velocity in the quenching chamber was calculated intentionally in the absence of the arc. From the test and calculation results, we found out a definite relationship between the velocity distribution and the interrupting capability. Index Terms--Airflow, arc discharges, correlation, interrupting capability, vortex.

Detailed measurements of the flow field within the entire 2nd stage of a two-stage axial turbomachine are performed using particle image velocimetry. The experiments are performed in a facility that allows unobstructed view on the entire flow field, facilitated using transparent rotor and stator and a fluid that has the same optical index of refraction as the blades. The entire flow field is composed of a 'lattice of wakes,' and the resulting wake-wake and wake-blade interactions cause major flow and turbulence nonuniformities. The paper presents data on the phase averaged velocity and turbulent kinetic energy distributions, as well as the average-passage velocity and deterministic stresses. The phase-dependent turbulence parameters are determined from the difference between instantaneous and the phase-averaged data. The distributions of average passage flow field over the entire stage in both the stator and rotor frames of reference are calculated by averaging the phase-averaged data. The deterministic stresses are calculated from the difference between the phase-averaged and average-passage velocity distributions. Clearly, wake-wake and wake-blade interactions are the dominant contributors to generation of high deterministic stresses and tangential nonuniformities, in the rotor-stator gap, near the blades and in the wakes behind them. The turbulent kinetic energy levels are generally higher than the deterministic kinetic energy levels, whereas the shear stress levels are comparable, both in the rotor and stator frames of references. At certain locations the deterministic shear stresses are substantially higher than the turbulent shear stresses, such as close to the stator blade in the rotor frame of reference. The nonuniformities in the lateral velocity component due to the interaction of the rotor blade with the 1st-stage rotor-stator wakes, result in 13 percent variations in the specific work input of the rotor. Thus, in spite of the relatively large blade row spacings in the present turbomachine, the nonuniformities in flow structure have significant effects on the overall performance of the system. [DOI: 10.1115/1.1509077]

This article demonstrates an innovative method for the observation of vertical air motion and raindrop size distribution in precipitation using a 94-GHz Doppler radar. The method is particularly appealing since it is based on fundamental physics--the scattering of microwave radiation by large particles (Mie scattering). The technique was originally proposed in 1988 by Dr. Roger Lhermitte, who ironically pioneered the development of 94-GHz Doppler radars for the study of nonprecipitating clouds. Since then, no real effort for the evaluation and demonstration of the technique was undertaken. In this article, observations from stratiform rain are presented to illustrate the potential and accuracy of the method. The retrievals from this technique provide vertical air motion to an accuracy of 5-10 cm [s.sup.-1]. Despite attenuation, the Doppler velocity measurements remain unbiased and the data revealed high-resolution kinematical and microphysical structures within the stratiform precipitation for the first time. This article will hopefully expose the potential of this technique to the meteorological community and will serve as another example of the visionary contributions that Dr. Lhermitte has made to radar meteorology.

In November of 1999, four permanent surface stations were installed in the vicinity of the surface ozone monitoring station on the summit of the Cerro Tololo (2200 m MSL) in Chile at 30[degrees]S. These stations were used to study the atmospheric flow conditions, which are important for the interpretation of the ozone measurements at Cerro Toloto. In addition, radiosonde ascents were performed in March of 2000 near the coast and about 60 km inland. Different wind regimes were distinguished. Above 4 km MSL, large-scale westerly winds prevailed, while northerly winds were observed in a band along the coastline between 2- and 4-km-MSL height. The upper boundary of the northerly wind regime corresponded to the mean height of the Andes mountain range. This wind regime resulted from the westerly winds being blocked and forced to flow in parallel to the Andes (when Froude number is less than 1). The phenomenon was also confirmed by model simulations. Seasonally varying, thermally induced valley winds and a sea breeze developed below the northerly wind regime. In summer, the valley winds reached the Cerro Tololo. Diurnal variation of the top boundary of the valley winds also influenced the lower boundary of the northerly wind regime, which was less than 2 km MSL during the night and greater than 2 km MSL during the day. Thus, this observational and modeling study has shown that in summer the baseline ozone monitoring site at Cerro Tololo can be contaminated by polluted air that is transported from the plains by the thermally induced wind systems.

Steady divergent flow (inspiration directed) is measured using Laser Doppler Velocimetry in a large-scale model carefully mimicing the morphometry of small human airways. The anatomical features, which induced vorticity in the flow from vorticity free entrance flow, are evaluated under conditions of convective similitude. The flow pattern in the daughter tubes is typical of laminar flow within the entrance to sharp bends (Dean number >500) with rapid development of strong secondary flows (maximum secondary velocity is 45 percent of mean axial velocity). The secondary flow consists of two main vortices, with two smaller and weaker secondary vortex activities toward the inner wall of curvature. There appears to be time dependent interaction with these vortices causing warbling at specific flow conditions. The calculated vorticity transport along the flow axis showed interaction between the viscous force at the new boundary layer development along the carinal wall and centrifugal force of curvature, with a significant influence by the upstream flow prior to entering the actual flow division. This interplay results in an overshoot of the calculated vorticity transport comparable to flow entering curved bends and suppression for the tendency to separate at the inner wall of these tight bends. The maximum primary flow velocities are skewed toward the carinal side (outer wall of curvature) and development of a second peak occurred with convection of the high velocity elements toward the inner wall of curvature by the strong secondary flow.

A previously reported method for nonequilibrium quantitation of air-borne volatiles from air streams by solid-phase microextraction (SPME) was improved by broadening its scope. The original method was defined for the 100-(mu)m poly(dimethylsiloxane) fiber type for a wide range of analytes, sampling temperatures, and sampling times, but only for four specific airflow configurations. The present study extends the choice of volumetric airflow rates to a continuous range between 2 and 220 mL/min. Kinetics of absorption was characterized for 21 different airflow rates within this range using n-alkanes of 11-18 carbons. Nonlinear regression analysis was used to develop a relationship between airflow rate and absorption kinetics and then to integrate these results into the previous model. The overall model (with 8 fitted degrees of freedom and based on 2240 measurements) had an r(super 2) value of 0.9972 and residual variability (RSD) of 9.75%, which compared favorably with the sampling precision of SPME (approximately 5%). The method allows absolute quantitation by SPME for a broad range of analytes and sampling parameters without prior calibration of the individual fiber and regardless of whether equilibration is complete. Simulations are presented that demonstrate how the choice of airflow rate can affect quantitation.

Ozone tagging velocimetry (OTV) is a nonintrusive time-of-flight velocity measurement method. It is composed of a write step, where a 193-nm pulsed excimer laser creates an O3 line through O2 uv absorption, and a subsequent read step, where a 248-nm excimer laser photodissociates the O3 and fluoresces the vibrationally excited O2 product, indicating the tag line displacement. Instantaneous OTV images and velocity measurements were obtained for the first time in airflows at room temperature.

This paper reports an experimental investigation on centrifugal compressor surge. The compression system consists of a four-stage blower with vaned diffusers and a large plenum discharging into the atmosphere through a throttle valve. Measurements of unsteady pressure and flow rate in the plant, and of instantaneous velocity in the diffusers of the first and fourth compressor stage, are performed during deep surge, at several valve settings and three different rotation speeds. Additional tests have been carried out on a different system configuration, i.e., without plenum, in order to obtain the steady-state compressor characteristics and to collect reference data on stall in surge-free conditions. In this configuration, a fully developed rotating stall was detected in the compressor diffusers, while during surge it affects only a limited part of the surge cycle. The goal of the present experimental work was to get a deeper insight into unstable operating conditions of multistage centrifugal compressors and to validate a theoretical model of the system instability to be used for the design of dynamic control systems.

Research was conducted to examine the flow and heat transfer behavior in various convex-louver arrays. Flow visualization, core pressure-drop measurements and local convective data are taken into consideration and compared with similar measurements from a related offset-strip geometry. Results illustrate the effects of boundary layer restarting, spanwise vortices, shear-layer unsteadiness, reattachment, recirculation and separation on heat transfer.

Air permeability of soil is an important parameter for soil aeration and contaminant remediation techniques such as soil vacuum extraction. Transient-flow air permeameters are inexpensive and portable, but have been shown to be sensitive to small changes in temperature in the air tank induced by the changing air pressure. We have developed a simple and inexpensive modification to the design of transient-flow air permeameters that improves both the accuracy and precision of the method. The apparatus was modified by the addition into the air tank of a heat capacitor, i.e., fiberglass insulation. The fiberglass insulation filling the tank acts as a uniformly distributed heat source-sink (capacitor) and thereby dampens the temperature changes. Data from the near-isothermal air tank design were compared with data from the standard air tank design and data from a method that uses the standard air tank design but measures both pressure and temperature simultaneously. An air permeability value determined with a steady-state flow method was used as a reference. The results show that nonisothermal air tank data can produce large inaccuracies relative to the steady-state permeability. Applying a temperature correction to the nonisothermal air tank data improved the results considerably, but this method requires additional temperature and pressure measurements of extreme precision. The permeabilities produced with the 'nearly isothermal' air tank closely matched the steady-state values without having to apply any correction to the data. It is therefore recommended that the air tank of transient air permeameters be filled with a heat capacitor, such as fiberglass insulation.

This paper considers a linear hydrostatic model of a stable, uniform, constant rotational airflow over three-dimensional, elliptic, cross-sectional families of mountains in a z system. The surface pressure and the winds that are induced around the mountain chain are deduced using Fourier representation in both horizontal directions. The surface pressure perturbations and the induced wind intensities are linked to 1) the incoming airmass thermodynamic properties through Froude and Rossby numbers, 2) the geometrical aspect ratio of the mountain, 3) the direction of incidence of the incoming flow relative to the mountain orientation, and 4) the Coriolis effect through the Rossby number. The balance between the different factors that contribute to the morphology of the pressure and wind fields was established for northerly and southerly incoming flows that were blocked by an elliptical barrier resembling the Pyrenees mountain chain. Fair agreement was found between the results of the model and the experimental data collected during PYREX (Pyrenees experiment) intensive operational periods, with special regard to the asymmetry of the lateral flow for northerly incoming air masses.

Limited data are available on spatial variation in hydrologic behavior of soil macropores. This study examined field variation of soil water release and permeability in the pressure head range that influences macropores. One hundred twenty-seven undisturbed soil cores were collected from a no-tillage field containing a Lobdell silt loam (fine-loamy, mixed, mesic Fluvaquentic Eutrochrept) soil. An air flow device that eliminates the gravitational gradient was used to measure water release, [Theta](h), and air permeability, [k.sub.a](h), in the pressure head, h, range of 0 to -240 mm. Mean air-filled porosity, [[Epsilon].sub.a], of 0.044 [m.sup.3] [m.sup.-3] and geometric mean [k.sub.a] equal to 1.3 [Mu][m.sup.2] at h = [Theta] indicated that macroporosity in a majority of these cores failed to exhibit negative air-entry pressure heads. Generalized scaling of water release curves and air permeabilities using water contents expressed as degree of capillary saturation ([[Theta](h) + [[Epsilon].sub.a]/[[Theta].sub.s]) yielded considerable scatter reduction, implying a high degree of pore geometry and flow similarity for this soil. The spherical semivariogram model of water release scaling factors, [Alpha][(h).sub.r], had a range of 14.1 m, whereas the linear semivariogram of air permeability scaling factors, [Alpha][([k.sub.a]).sub.r], had a range of 21.1 m. Further, sill values for [Alpha][([k.sub.a]).sub.r] were 7.6 times greater than for [Alpha][(h).sub.r]. The poor correlation, dissimilar statistical distributions, and dissimilar spatial dependence of scaling factors suggested that characteristic lengths related to total macroporosity and fluid-conducting macroporosity were substantially different.

Wall-pressure fluctuations in a Mach 3 flow over a blunt fin are analysed using continuous wavelet transform The study gives a new insight into the problem of inferring flow structure from the wall-pressure signal. Details of the study are presented.

The air moving capacity of a transverse-inlet multiple-disk fan has been measured experimentally and the results successfully collapsed with a simple scaling law. The disk fan studied was an array of several hundred closely spaced plastic disks that rotated about a common axis inside an approximately semi-cylindrical housing. A splitter plate lying parallel to the axis of rotation and tangent to the disks separated the inflow and outflow streams. The volume flow rate of air per unit length along the axis of rotation was measured using standard LDV techniques. For disk spacings greater than 1 mm, the volume flow rate was found to be essentially proportional to [Omega][square root of h[R.sup.3]], where [Omega] = radian rotation rate of the disks, h = disk spacing, and R = disk radius. This scaling law was derived from a simple force balance for a small fluid element moving between rotating disks. The Reynolds number of the experiments, [Omega] [square root of [h.sup.3]R/[Nu]], was varied from 2 x [10.sup.2] to [10.sup.3]. In addition, the air-moving capability of the disk fan was found to be nearly independent of the geometrical placement of the rotating disks within the fan housing.

Measurements of the 3-d velocities, total and static pressures have been made in a 0.89 m diameter commercial pump impeller, using air as the working fluid. Results at the peak efficiency operating point show separation of the flow near the shroud on the pressure side of the blade at the leading edge. This separation results in a low energy region which initially travels axially through the impeller to form a wake in the suction side shroud corner region. A region of reversed radial velocity is observed at the outlet, which is due to high blade sweep angle together with the poor guidance given to the flow by the blades in the mid-passage region.

This paper considers the measurement and prediction of the additional total pressure losses of subsonic steady airflow in sharp-cornered bends, similar to those present in the secondary air cooling systems of gas turbine engines. The bends examined ranged between 30 to 150 in 30 deg increments and were circular in cross section. Experimental results covering a wide speed range up to choking are presented for five different bend geometries. An analytical flow model provided results in fairly good agreement with the measurements obtained and equally compared favourably with the experimental findings of other researchers at low Mach numbers. The highest attainable upstream Mach number ([M.sub.U]) of the average upstream flow was 0.57 for the 30 deg bend. The maximum possible values of [M.sub.U] represent a limiting condition dictated by downstream choking of the flow. The compressible flow coefficients, caused by the presence of the bends, can be expected to be between 10 to 20 percent higher than those for incompressible flow.

The calculated thrust and mass flow rate of a nozzle depend on the uniformity of the entering flow. The one-dimensional flow equations are extended to arrive at analytic expressions for the predicted performance of a nozzle processing two streams whose properties are determined ahead of the throat. The analysis approach forms the basis for the understanding of flows which have more complex distributions of total pressure and temperature. The uncertainty associated with mixing is examined by the consideration of the two limiting cases: compound flow with no mixing and completely mixed flow. Nozzle discharge and velocity coefficients accounting for non-uniformity are derived. The methodology can be extended to experimentally measured variations of flow properties so that proper geometric design variables may be obtained.

This study is concerned with numerical analysis of laminar separated flow in symmetric, two-dimensional, straight-walled diffusers. With Reynolds numbers Re = 56 and 114 and expansion ratios ER = 3 and 4, totally, there are four cases considered. At the low Reynolds number and the low expansion ratio the flow in the diffuser is nearly symmetric to the center line, irrespective of the diffusion angle. As Reynolds number or expansion ratio increases, a large recirculation region forms at one side wall and a small one at the other side. For the case with Re = 114 and ER = 4 the small recirculating flow disappears at small diffusion angles and a third recirculating flow appear in the same side of the small main recirculation region for large diffusion angles. The pressure recovery reaches its peak value somewhere downstream of the reattachment point of the large recirculating flow. The effectiveness of the diffuser deteriorates as the diffusion angle increases, apart from that at Re = 56 the effectiveness increases from [Theta] = 15 to 30 deg. Symmetric flow solutions can be obtained by incorporating a symmetric relaxation method. The pressure recovery is higher for the symmetric flow than that for the asymmetric flow owing to the weaker recirculating strength in the former.