Aerodynamic Conditions Research Articles

An automated system for the acoustical and aerodynamic characterization of small air moving devices

A plenum fixture for use in the measurement of acoustic emissions of air moving devices used to cool electronic equipment under the actual aerodynamic conditions of operation has been standardized in ISO 10302 and ANSI S12.11. This fixture has proven to be a valuable tool for use in the characterization of these devices. However, as many in industry have discovered, the construction of the plenum to the standardized specifications can quite complex, and the use of the plenum to fully characterize air moving devices can be quite laborious and tedious. Under contract to the NASA Glenn Research Center, which has a significant interest in the acoustic emissions of the air moving devices it uses to cool racks and payloads that are installed on the International Space Station, the authors have developed a fully automated fan test plenum that operates under software control. This plenum has been developed to facilitate rapid acoustic characterization of fans and other air moving devices, both independently and when operating into real world inlet conditions, obstructions and aerodynamic loads. The plenum slider has been calibrated to allow full development of fan curve data in parallel with acoustic emission data.

Segmental and prosodic effects on coda glottalization

This paper examines effects of segmental context and prosodic phrasing on the occurrence of coda glottalization in American English. On the basis of acoustic data from six female speakers, it is argued that the main effect of following segmental context on the occurrence of coda glottalization is due to anticipatory coarticulation, with anticipation of following sonorant consonant articulations favoring the aerodynamic conditions for glottalized voicing. The cross-dialect propensity to have high coda glottalization rates before sonorant consonants can then be understood to arise as a phonetically natural consequence of normal coarticulation processes. This coarticulatory account is supported by the fact that when an intonation phrase (IP) boundary intervenes between the coda consonant and a following sonorant, the contextual effect on glottalization rates is weakened. Our data also suggest that, all else being equal, presence of an IP boundary favors the occurrence of glottalization. These patterns are compatible with an account in which a glottal constriction goal on the coda consonant is optional in the linguistic representation. The optionality of this goal is somewhat problematic for many models of phonetic knowledge, but the coarticulatory explanation of the sonorancy effect helps to insightfully simplify any account of the distribution of glottalization.

Aerodynamic Experiment on an Ejector-Jet

Characteristics of an ejector-jet were investigated experimentally. Evaluation of a new, one-dimensional model of suction performance under the aerodynamic choking condition and observation of mixing conditions through the pseudo-shock were primary subjects of study. Supersonic primary rocket exhaust was simulated by air, and secondary airflow was simulated by nitrogen. Parameters were the ratio of the total pressure of the secondary flow to that of the primary flow, the ratio of the entrance area of the secondary flow to that of the primary flow, and the Mach number of the primary flow. A throttling valve downstream of the mixing region simulated subsonic combustion and subsequent choking, and the throttling created a pseudo-shock ahead of the valve. The suction performance increased with increased total pressure of the secondary flow, the increase of the Mach number of the primary flow, or the increase of the area of the secondary flow. The calculated results on the suction performance agreed well with these measured values. When the gases became subsonic due to throttling, the primary and secondary fluids mixed well through the pseudo-shock and became almost uniform ahead of the downstream choking position. The mixing progressed quickly in the pseudo-shock. Nomenclature A = cross section H = height M = Mach number ˙ m = mass flow rate P = pressure Pt = total pressure r = ratio of the mass flow rate of the secondary flow to that of the primary flow T = temperature Tt = total temperature u =v elocity x = streamwise coordinate from the entrance of the test section y =v ertical coordinate from the primary-flow sidewall z = spanwise coordinate from the center plane of the test section γ = ratio of specific heats ρ = density ω = mass fraction of the secondary flow

Blade-tip heat transfer in a transonic turbine

The blade-tips of high-pressure turbine blades in a gas turbine engine are subjected to strong convective heat transfer and continued to present a significant design challenge to manufacturers. This paper is concerned with developing an understanding of the unsteady flow physics that influences the blade-tip heat transfer. Experimental investigations of bladetip heat transfer and aerodynamics have been conducted in a transonic turbine stage test facility. The data reveal the effect of vane-rotor interactions on the unsteady heat transfer along the blade-tip mean camber line. In particular, the vane shock and potential field interaction establish characteristic unsteady heat transfer signatures at different axial positions along the blade-tip. The fluctuations in heat transfer are discussed in terms of vane-periodic changes in both relative total temperature and aerodynamic conditions.

Flexible Launch Vehicle Attitude Control Design Using Coevolutionary Algorithm

Launch vehicles in general are slender and flexible. The flexibility of the launch vehicle easily induces instability to the total launch vehicle system. There is also a high rate of change in mass and aerodynamic conditions. These conditions require an attitude controller which is robust to various system parameter changes and disturbances. In this paper, the launch vehicle's attitude controller is optimized by the coevolutionary algorithm. The attitude controller structure must be determined and the performance index is set according to the user needs. The coevolutionary algorithm can find the gains of the controller which gives the best performance. The controller is robust over a wide range of the system uncertainties. Also these uncertainties are controlled by the adaptive control using neural networks.

헬리콥터 로터 시험장치의 개발 및 공력소음특성의 측정

본 논문에서는 축소형실험을 통하여 제자리 비행하는 헬리콥터 주로터에서 발생하는 소음의 특성을 측정하는 실험을 수행하였다. 이를 위하여 구동장치에서의 발생소음이 적은 저소음 로터시험장치를 설계/제작하였으며, 아울러 로터의 공력특성을 측정하기 위하여 작동조건에서의 회전수, 추력 및 토크를 함께 계측하였고 이에 대한 문제점을 검토하였다. 사용된 하중 측정장치의 교정을 통하여 이의 정확도를 확인하였으며, 두개의 블레이드로 구성된 직경 1.2m의 축소형 로터를 이용한 실험에서 측정된 추력값이 이론적 계산값과 비교하여 비교적 잘 일치함을 알 수 있었으나 토크 측정값은 잘 일치하지 않음을 확인하였다. 소음 측정실험을 통하여 로터 구동장치로 인한 배경소음이 로터 소음에 비하여 현저히 작음을 확인하였고, 각 로터 발생소음원의 특성에 따라 날개끝 속도에 의하여 달리 무차원화 됨을 확인하였고 방향성 특성도 변화함을 확인하였다. In this paper the aeroacoustic characteristics of a helicopter main rotor system is measured by using a pair of scaled rotor blades. A low noise rotor test jig is developed for noise measurement and the rotational speed, thrust and torque are measured simultaneously in order to match the aerodynamic conditions with the full scale rotor. The accuracy of the force measurement device was checked through a calibration procedure. The measured thurst and torque with a 1.2m rotor are compared to the results of analytical prediction and showed that the thrust data at various rotational speed followed the prediction relatively well, but the torque data considered less accurate. It is also found that the background noise level of the test rig is sufficiently low, and the measured noise level from the rotor can be scaled with rotor tip speed. However, the Mach number dependancy and the directivity changes depend on the noise source characteristics.

Trapping of hydride forming elements within miniature electrothermal devices: part I. investigation of collection of arsenic and selenium hydrides on a molybdenum foil strip

The interaction of selenium and arsenic hydrides with surface of bare and modified (Pt, Ir and Rh) strips of the molybdenum foil was investigated by atomic absorption spectrometry employing miniature hydrogen diffusion flame as a simple atomizer and by radiotracer technique using 75Se-radionuclide as an indicator. In contrast to the recently reported data for tungsten atomizers, enhanced trapping was observed at the temperatures above 1000 °C, close to 1100–1200 °C, for the bare and modified molybdenum foil strips, irrespective of the analyte, and amount and type of the modifier deposited. When using a 75Se-radiotracer, the same selenium trapping efficiency of approximately 30% was found for the bare and rhodium-treated foils at the temperature of 1200 °C. Trapping isotherms of both analytes appeared to be very close to the linear fit even up to the upper limit of the analytical relevancy of 100 ng of an analyte, indicating a very high trapping capacity of the bare and modified surfaces. The influence of injection gas flow rate and capillary distance suggested that aerodynamic conditions of the injected gas near the molybdenum surface play significant role in trapping both analytes. The maximum trapping efficiency was reached for flow rates close to 60–70 ml min −1 and for a relatively short distance of 1–2 mm between the capillary orifice and the foil surface. Radiography experiments with 75Se-radiotracer showed that a major part of selenium was collected on a relatively small area, in the central part of the strip, opposite the orifice of the injection capillary. After trapping and vaporization steps, deposits of the selenium tracer were also found on the quartz tube wall of the trap chamber, close to the heated part of the strip.

An Improved Shape Memory Alloy Actuator for Rotor Blade Tracking

The design, analysis, and testing of an improved Shape Memory Alloy (SMA)-based tracking tab actuator is described in this paper. The goal of the actuator is to provide in-flight tracking capability for a helicopter rotor in order to minimize 1/rev vibrations due to rotor dissimilarities. Previous SMA-based actuator designs demonstrated the potential for in-flight rotor tracking but admitted drawbacks that led to inconsistent operation under air-loads. The current research builds upon the existing knowledge base and addresses the challenges encountered in previous designs. The objective is to achieve a deflection of 58 with an accuracy of 0:18 under realistic aerodynamic loading conditions. The present actuation concept is based on the bidirectional motion of a pair of antagonistic SMA wires, with a passive friction brake to lock the tab position. A theoretical model of the actuator was developed based on Brinson’s thermomechanical model. The model was used to predict the behavior of the actuator under external loading and applied as a design tool to identify optimal actuator parameters. The actuator was integrated into a NACA 0012 12 in. chord blade section and tested in an open-jet wind tunnel at speeds of up to 120 ft/s (0.107 M) and at angles of attack up to 158. Closed-loop tracking was implemented using a PID controller with gains selected by Ziegler-Nichols tuning. The improved SMA actuator meets the project goals by achieving repeatable tab deflection of up to 58with an average accuracy of 0.058. Position hold under power-off conditions and a duty cycle of 20 cycles/h were also demonstrated.

Analysis of hysteresis and phase shifting phenomena in unsteady three-dimensional wakes

The aerodynamic characteristics of automobiles are greatly influenced by the unsteady change in the direction of relative airflow. The aim of this paper is to analyse how such a change influences vehicle wake flow patterns. An analysis was conducted on a simplified model capable of reproducing the typical structures encountered under the aerodynamic conditions of an automobile. The results were processed by mapping the steady and unsteady total pressure losses around the model. The findings should enable automobile development engineers inter alia to identify and analyse the physical phenomena that occur when a vehicle is subjected to a sudden gust of side wind.

Experimental transfer function for a low-pressure differential mobility analyzer by use of a monodisperse C 60 monomer

A C 60 monomer as an inherently monodisperse standard particle was produced by a C 60 vapor source equipped with an 241 Am neutralizer, and its mobility spectrum was measured by using a low-pressure differential mobility analyzer (LPDMA). The transfer function was derived from the mobility spectrum and was measured as dependences on aerodynamic and electrodynamic conditions. The experimental transfer function thus obtained was compared with the theoretical transfer function.

An Experimental Assessment of Numerical Predictive Accuracy for Electronic Component Heat Transfer in Forced Convection—Part I: Experimental Methods and Numerical Modeling

Numerical predictive accuracy is assessed for component-printed circuit board (PCB) heat transfer in forced convection using a computational fluid dynamics (CFD) software for the thermal analysis of electronic equipment. This is achieved by comparing numerical predictions with experimental benchmark data for three different components, mounted individually on single-component PCBs, and collectively on a multi-component PCB. Benchmark criteria are based on measured steady-state component junction temperature and component-PCB surface temperature profiles. The benchmark strategy applied permits the impact of both aerodynamic conditions and component thermal interaction on predictive accuracy to be quantified. In the accompanying Part II of this paper, the experimental measurements are reported and numerical predictive accuracy is assessed.

Analysis of aerodynamic problems with geometrically unspecified boundaries using an enhanced Lagrangian method

This paper presents solutions for several 2-D aerodynamic problems with geometrically unspecified boundaries. These solutions are obtained with an enhanced Lagrangian method based on stream function and Lagrangian-distance coordinates, which includes special procedures to substantially improve the numerical resolution of the shock waves and for the numerical implementation of the aerodynamic conditions defining the geometrically unspecified solid or fluid boundaries. The method is first validated for flows with specified solid boundaries by comparison with exact analytical solutions and with previous computational results obtained by numerical methods using Eulerian formulations. In all cases, this enhanced Lagrangian method displayed a very good accuracy and computational efficiency and a sharp numerical resolution of shock waves. Then this method is used to obtain solutions for problems with geometrically unspecified boundaries, such as: (i) indirect problems of determining the geometrical shape of airfoils and nozzle walls for a specified pressure distribution; (ii) supersonic nozzle design problem for a specified uniform flow at the nozzle outlet based on reflection-suppression condition; (iii) analysis of flexible-membrane airfoils; and (iv) analysis of jet-flapped airfoils.

Heat Transfer in High-Temperature Fibrous Insulation

The combined radiation/conduction heat transfer in high-porosity, high-temperature fibrous insulations was investigated experimentally and numerically. The effective thermal conductivity of fibrous insulation samples was measured over the temperature range of 300-1300 K and environmental pressure range of 1.33 x 10(exp -5)-101.32 kPa. The fibrous insulation samples tested had nominal densities of 24, 48, and 72 kilograms per cubic meter and thicknesses of 13.3, 26.6 and 39.9 millimeters. Seven samples were tested such that the applied heat flux vector was aligned with local gravity vector to eliminate natural convection as a mode of heat transfer. Two samples were tested with reverse orientation to investigate natural convection effects. It was determined that for the fibrous insulation densities and thicknesses investigated no heat transfer takes place through natural convection. A finite volume numerical model was developed to solve the governing combined radiation and conduction heat transfer equations. Various methods of modeling the gas/solid conduction interaction in fibrous insulations were investigated. The radiation heat transfer was modeled using the modified two-flux approximation assuming anisotropic scattering and gray medium. A genetic-algorithm based parameter estimation technique was utilized with this model to determine the relevant radiative properties of the fibrous insulation over the temperature range of 300-1300 K. The parameter estimation was performed by least square minimization of the difference between measured and predicted values of effective thermal conductivity at a density of 24 kilograms per cubic meters and at nominal pressures of 1.33 x 10(exp -4) and 99.98 kPa. The numerical model was validated by comparison with steady-state effective thermal conductivity measurements at other densities and pressures. The numerical model was also validated by comparison with a transient thermal test simulating reentry aerodynamic heating conditions.

Aerodynamic characteristics of trills and phonological patterning

The present study attempts to characterize the aerodynamic conditions required for the production of apical trills and to account for some universal tendencies in the patterning of trills in terms of their aerodynamic and distinctiveness requirements. In order to ascertain the aerodynamic conditions required for trills, oropharyngeal pressure ( P o) and airflow were recorded simultaneously in two subjects producing voiced and voiceless trills. The backpressure during trills was intermittently bled with catheters of varying diameter, and thus impedance. It was found that (1) voiceless trills show a higher P o and a larger rate of flow than voiced trills, which generates friction noise across the lingual constriction; (2) voiceless trills are more robust to changing aerodynamic conditions but less distinct auditorily, as inferred from acoustic data; (3) the P o and airflow conditions for voiced trills and fricatives show very similar values, with trills showing a narrower range of allowable variation. The behavior of trills in varying aerodynamic conditions accounts for observed phonological patterns: the universal preference for voiced trills, the alternation between trills and fricatives, trill devoicing, and the lack of nasal trills.

On the effect of the local turbulence scales on the mixing rate of diffusion flames: assessment of two different combustion models

A mathematical model for the prediction of the turbulent flow, diffusion combustion process, heat transfer including thermal radiation and pollutants formation inside combustion chambers is described. In order to validate the model the results are compared herein against experimental data available in the open literature. The model comprises differential transport equations governing the above-mentioned phenomena, resulting from the mathematical and physical modelling, which are solved by the control volume formulation technique. The results yielded by the two different turbulent-mixing physical models used for combustion, the simple chemical reacting system (SCRS) and the eddy break-up (EBU), are analysed so that the need to make recourse to local turbulent scales to evaluate the reactants' mixing rate is assessed. Predictions are performed for a gaseous-fuelled combustor fired with two different burners that induce different aerodynamic conditions inside the combustion chamber. One of the burners has a typical geometry of that used in gaseous fired boilers—fuel firing in the centre surrounded by concentric oxidant firing—while the other burner introduces the air into the combustor through two different swirling concentric streams. Generally, the results exhibit a good agreement with the experimental values. Also, NO predictions are performed by a prompt-NO formation model used as a post-processor together with a thermal-NO formation model, the results being generally in good agreement with the experimental values. The predictions revealed that the mixture between the reactants occurred very close to the burner and almost instantaneously, that is, immediately after the fuel-containing eddies came into contact with the oxidant-containing eddies. As a result, away from the burner, the SCRS model, that assumes an infinitely fast mixing rate, appeared to be as accurate as the EBU model for the present predictions. Closer to the burner, the EBU model, that establishes the reactants mixing rate as a function of the local turbulent scales, yielded slightly slower rates of mixture, the fuel and oxidant concentrations which are slightly higher than those obtained with the SCRS model. As a consequence, the NO concentration predictions with the EBU combustion model are generally higher than those obtained with the SCRS model. This is due to the existence of higher concentrations of fuel and oxygen closer to the burner when predictions were performed taking into account the local turbulent scales in the mixing process of the reactants. The SCRS, being faster and as accurate as the EBU model in the predictions of combustion properties appears to be more appropriate. However, should NO be a variable that is predicted, then the EBU model becomes more appropriate. This is due to the better results of oxygen concentration yielded by that model, since it solves a transport equation for the oxidant concentration, which plays a dominant role in the prompt-NO formation rate. Copyright © 2002 John Wiley & Sons, Ltd.

Static, seismic and stability analyses of a prototype wind turbine steel tower

Selected results of a study concerning the load bearing capacity and the seismic behavior of a prototype steel tower for a 450 kW wind turbine with a horizontal power transmission axle are presented. The main load bearing structure of the steel tower rises to almost 38 m high and consists of thin-wall cylindrical and conical parts, of varying diameters and wall thicknesses, which are linked together by bolted circular rings. The behavior and the load capacity of the structure have been studied with the aid of a refined finite element and other simplified models recommended by appropriate building codes. The structure is analyzed for static and seismic loads representing the effects of gravity, the operational and survival aerodynamic conditions, and possible site-dependent seismic motions. Comparative studies have been performed on the results of the above analyses and some useful conclusions are drawn pertaining to the effectiveness and accuracy of the various models used in this work.

Explaining learning curves for wind power

Due to environmental concerns and the fact that fossil energy sources are non-renewable, there is a growing interest in alternative energy sources. One of these sources is wind. The utilisation of wind energy differs greatly between countries, both due to different aerodynamic conditions and to differing policies. This article compares the learning curves for wind power in three countries, Denmark, Germany and the United Kingdom. The study reveals that policies that enhance competition probably can result in large cost reductions, but that they may hamper diffusion of wind power. Using price systems that guarantee wind turbine owners a certain price for each kW h generated, Germany and Denmark have created stable market conditions, and thereby increased the capacity installed, although costs have fallen less.

A non-linear integrated aeroelasticity method for the prediction of turbine forced response with friction dampers

The aim of this paper is to describe an integrated aeroelasticity model for turbine blade forced response predictions. Such an approach requires a successful integration of the unsteady aerodynamics with non-linear structural dynamics, the latter arising from the use of root friction dampers to dissipate energy so that the response levels can be kept as low as possible. The inclusion of friction dampers is known to raise the resonant frequencies by up to 20% from the standard assembly frequencies, a shift that is not known prior to the aeroelasticity calculations because of its possible dependence on the unsteady excitation. An iterative procedure was therefore developed in order to determine the resonance shift under the effects of both unsteady dynamic loading and non-linear friction dampers. The iterative procedure uses a viscous, non-linear time-accurate flow representation for evaluating the aerodynamic forcing, a look-up table for determining the aerodynamic boundary conditions at any speed, and a time-domain friction damping module for resonance tracking. The methodology was applied to a high-pressure turbine rotor test case where the resonances of interest were due to first torsion and second flap blade modes under 40 engine-order excitation. The forced response computations were conducted using a multi-bladerow approach in order to avoid errors associated with “linking” single bladerow computations since the spacing between the bladerows was relatively small. Three friction damper elements, representing one actual friction damper, were used for each rotor blade. The number of rotor blades was decreased by 2–90 to obtain a cyclic sector of 4 stator and 9 stator blades. Such a route allowed the analysis to be conducted on a much smaller domain, hence reducing the computational effort significantly. However, the stator blade geometry was skewed in order to adjust the mass flow rate. Frequency shifts of 3.2% and 20.0% were predicted for the 40 engine-order resonances in torsion and bending modes, respectively. The predicted frequency shifts and the dynamic behaviour of the friction dampers were found to be within the measured range. Furthermore, the measured and predicted blade vibration amplitudes showed a good agreement with available experimental data, indicating that the methodology can be applied to typical industrial problems.

Particle separation from gases using cross-flow filtration

Most filters used in solid/gas separation are applied in the “dead-end” mode, where the aerosol particles arrive at the filter on trajectories that are approximately perpendicular to it. This study concerns the alternative method of cross-flow filtration, which is in common use for filtering liquids. In this mode, previously studied by Menard et al. [Powder Technol. 71 (1992) 263], Thomas et al. [Powder Technol. 76 (1993) 79] and Ferrer et al. [Powder Technol. 113 (200) 197], some of the flow passes through the filter, depositing particles on the surface, while some sweeps past the surface, causing shear on the deposited cake. Depending on the operating conditions, particle aggregation can occur on the surface and the resulting aggregates can be removed by the through-flow and collected in a downstream device. Laboratory scale equipment has been set up in which a cross-flow filter module is coupled to a cyclone postseparator to separate the aggregates leaving the filter. The filters used were ceramic tubes of 6 cm outside diameter, 4 cm inside diameter and variable lengths. An aerosol of limestone dust particles (mmd=5.0 μm) in ambient air enters the inside of the filter along the axis; due to the aerodynamic conditions within the filter some of the particles are deflected towards the filter and are captured. The results show that the cake is detached in the form of loose agglomerates rather than individual particles, which are easily collected by means of the cyclone. The collection efficiency shown by the cross-flow filter/cyclone combination is over 99% for 5.0 μm (mmd) particles under optimum conditions compared to ≈90% shown by the stand-alone cyclone. This separation efficiency is comparable to that of a surface filter and the pressure loss savings with this system make it an attractive gas cleaning option.

A PROCEDURE FOR THE EVALUATION OF INSTALLED PROPELLER NOISE

A method for the prediction of the acoustics of a propeller in the flow-field of a wing is presented. The method is used to study the noise generated by the unsteady loading induced on the propeller as it passes through the wing flow-field. Both the aerodynamic and acoustic methods are previously proven techniques, the aerodynamic method being based on a combination of free wake analysis and a three-dimensional boundary element method, while the acoustic calculation is a full-surface, moving medium form of the Ffowcs Williams–Hawkings equation. Calculations are presented for a reference case of a four-bladed low-speed propeller in forward flight. The acoustic predictions are supplemented with retarded time results which relate the radiated noise to the aerodynamic conditions on the blade at the time of noise emission. The noise data and the retarded time results are discussed and related to previous aerodynamic work.