Working Section Research Articles

Effect of Acoustic Radiation on DMA Resolution

Acoustic waves produced by pressure fluctuations in the turbulent exhaust region of differential mobility analyzers (DMAs) are radiated upstream, making the flow in the working region slightly unsteady and reducing DMA resolution. This claim is demonstrated in a variety of settings. First, a resonance has been observed in several DMAs where the resolution decreases drastically in a narrow range of flow rates. This resonance can only be acoustic, and must be excited by flow unsteadiness, which is only present downstream. Second, non-idealities observed in two very different DMAs are suppressed when they are operated under transonic conditions. This is consistent with the inability of acoustic waves to propagate upstream against a supersonic flow. Third, these non-idealities decrease when the turbulent exhaust region from which acoustic radiation would originate is not in direct sight with the DMA's working section. These findings suggest new strategies to achieve DMA resolving powers approaching 100 under ...

Response of a Laminar Separation Bubble to an Impinging Wake

Laminar separation and transition phenomena were investigated experimentally in the wake-disturbed flow over a 2.4 m long flat plate. A controlled diffusion pressure distribution, representative of that on a compressor blade, was imposed but with sufficiently strong loading to cause laminar separation. Boundary layer velocity traverses were performed at several longitudinal stations. Wakes were generated upstream by a single rod, parallel to the leading edge, attached to a rotating disk mounted flush in the sidewall of the working section. Data are presented in the form of velocity traces and contours of velocity and turbulent intermittency. The results highlight the interaction between the incoming wake and the natural boundary layer, which features a long and thin laminar separation bubble; they demonstrate that wind tunnel experiments provide a good representation of boundary layer behavior under wake disturbances on turbomachinery blading. The calmed region behind the disturbance is a feature that is even stronger behind a wake interaction than behind a triggered turbulent spot. Intermittency values for the undisturbed flow in the separation bubble reattachment region are well represented by Narasimha’s universal intermittency distribution, lending support to the use of intermittency-based predictive routines in calculations of blade boundary layers.

Study of Interaction of Disturbances in an Internal Flow

Data on narrow‐band acoustic disturbances that arise in manifold pipes with one or two blind branches and in wind tunnels with an open working section are analyzed. The ranges of acoustic instability that correspond to excitation of self‐oscillations in a flow in the cases mentioned are determined. The dependence of the intensity of acoustic radiation in two blind branches and in the manifold between them on the multiplicity of the length of the resonance section to the length of halfwaves of resonance frequency is considered. The possibility of attenuation of self‐oscillations by organizing hydrodynamic structures that interact with formations generating acoustic oscillations is determined.

Aerodynamics of spinning and non-spinning tennis balls

The aerodynamic properties of a tennis ball are obtained using wind tunnel measurements. In the first phase of this study, the drag coefficient of a variety of new and used non-spinning tennis balls was measured. The measurements were conducted in the Reynolds number range of 85×10 3< Re<250×10 3, which corresponds to a velocity range of 20< U<60 ms −1 (45< U<135 mph). The data for the new tennis balls revealed that all balls have similar drag coefficients, within the repeatability of the experiment. However, it was shown that a heavily worn ball exhibits a significant decrease in drag coefficient. A simple trajectory plot was used to illustrate the significance of this drop in C D, on a typical tennis stroke. It was shown that if the drag coefficient of the worn ball was reduced even further, then the ball would travel faster through the air, and give the receiver a significantly shorter time to react to the shot. In the second phase of this study, the drag and lift coefficients of new and used spinning tennis balls was measured. This testing was conducted by placing the ball inside the working section of the wind tunnel, held between two horizontal shafts. The ball was spun at rates up to 2750 rpm, which is representative of a typical top spin shot hit by a professional player. The data showed that the lift coefficient for all the new balls was identical. However, the lift coefficient was generally lower for the heavily worn ball compared with the new ball. A trajectory plot was calculated to illustrate the effect of the lower drag and lift coefficients of the worn ball, compared to the new ball. It was shown that the lift coefficient value has little effect on the reaction time of the receiver. It was also shown that a lower lift coefficient reduces the window of opportunity for the server because the player is less able to utilise the spin to control the shot to ensure that the ball both clears the net and also lands in the service box. This highlights the fact that it may not be in the manufacturers interest to produce a ‘faster’ tennis ball with a lower drag coefficient, because the ball may also have a lower lift coefficient, thus reducing the players ability to play certain strokes.

A wind-tunnel based study of helicopter tail rotor blade vortex interaction

AbstractThe interaction of a helicopter tail rotor blade with the tip vortex system from the main rotor is a significant source of noise and, in some flight states, can produce marked reductions in control effectiveness. This paper describes a series of wind-tunnel tests to simulate tail rotor blade vortex interaction with a view to providing data for the development and validation of numerical simulations of the phenomenon. In the experiments, which were carried out in the Argyll wind-tunnel of Glasgow University, a single-bladed rotor located in the tunnel’s contraction was used to generate the tip vortex which travelled downstream into the working section where it interacted with a model tail rotor. The tail rotor was instrumented with miniature pressure transducers that measured the aerodynamic response during the interaction. The results suggest that the rotor blade vortex interaction is similar in form to that measured at much higher spatial resolution on a fixed, non-rotating blade. The combination of the two datasets, therefore, provides a valuable resource for the development and validation of predictive schemes.

Behaviour controls post-settlement dispersal by the juvenile bivalves Austrovenus stutchburyi and Macomona liliana

Post-settlement dispersal is a key process affecting the population dynamics of many soft sediment benthic invertebrates. Despite its importance, few studies have quantified those factors that influence juvenile dispersal. In a laboratory flume, we examined the effects of three flow velocities and two substrate types on the dispersal of two common intertidal bivalves: the deposit-feeding wedge shell Macomona liliana and the suspension-feeding cockle Austrovenus stutchburyi. Juveniles of three size classes (<2, 2–4 and 4–8 mm shell length) were added to cores of defaunated natural sediment or glass beads. We recorded the number of bivalves remaining in cores versus those recovered downstream either on the flume floor, in bedload traps or in a plankton net at the end of the working section of the flume after 48 h at three freestream velocities (4.8, 11.0 and 16.6 cm s −1). At flow speeds of 4.8 cm s −1, <5% of individuals were recovered outside the cores for both species. At higher flows, the dispersal mode (crawling, bedload or in suspension) and frequency of dispersal differed markedly between species. Austrovenus dispersed primarily by crawling in the low flow treatments. The frequency of dispersal increased substantially (2–6×) between 11.0 and 16.6 cm s −1, and most Austrovenus were found in bedload traps at the highest flow. At the highest flow, twice as many Austrovenus individuals left the glass bead treatment as from the natural sediment. The number of dispersing Macomona also increased with increasing flow from the natural sediment, but numbers dispersing from glass beads were similar for the two higher flows (11.0 and 16.6 cm s −1). Macomona dispersal mode was associated with size; smaller size classes were collected in the bedload traps and the plankton net in approximately equal proportions, while only a small proportion of the largest size class were collected in the plankton net. In contrast to flume dispersal experiments with live bivalves, most dead Austrovenus did not move at the highest flow speed, while most dead Macomona were transported at the highest flow speed. The live–dead comparisons, in conjunction with our primary experimental results, imply that there are active behavioural components to both water column and bedload transport. Our research emphasises that both species actively influence post-settlement transport in response to both substrate type and flow regime, and that bedload transport, often categorised as a passive transport process, is also greatly influenced by active behavioural processes.

Fracture properties of a fiber-metal laminates based on magnesium alloy

Fiber-metal laminates (FMLs) are high performance laminated structures based on stacked arrangements of composite material and aluminum alloy. Currently, a glass fiber reinforced epoxy/aluminum alloy FML (GLARE) is being considered for use in the manufacture of the upper fuselage of the A380 Airbus aircraft [1]. Previous work on FMLs has shown that they combine the excellent durability and machinability common to many metals with the superior fatigue and fracture properties offered by many fiber-reinforced composites [2–4]. Krishnakumar [2] tested a Kevlar fiber FML (ARALL) and showed that its ultimate tensile strength is considerably greater than that of a conventional aluminum alloy. Vogelsang [3] conducted tension-tension fatigue tests on a number of FML systems as well as a plain aluminum alloy and showed that crack growth rates in the former were significantly less than those in the plain aluminum alloy. Several workers have investigated the impact response of aerospace-grade fiber-metal laminates [5, 6]. Vlot et al. [5] conducted low and high velocity impact tests on a GLARE system, a plain aluminum alloy and a carbon fiber reinforced thermoplastic. Their results showed that the FML offered the highest damage threshold energy of all the systems considered. The aim of the present work is to investigate the fracture properties of a novel fiber-metal laminate based on a lightweight magnesium alloy and a carbon fiber reinforced plastic. Magnesium alloys offer a number of advantages over many metals including their low density (thirty percent lower than an aluminum alloy), their superior corrosion resistance and their excellent electromagnetic shielding ability. Currently, magnesium alloys are being used in the automotive industry in the manufacture of transmission casings and in the aerospace industry for the manufacture of gearboxes and other lightweight components. The fiber-metal laminates examined in this study were based on 0.5 mm thick magnesium alloy sheets (AZ31 alloy from Advance Metals International Ltd.) and a woven carbon fiber reinforced toughened epoxy (Stesapreg EP121-C15-53 from Stesalit Ltd, Switzerland). The composite and metal plies were placed in a picture frame mold with dimensions 240 × 200 mm and cured for 4 h at 125 ◦C. All of the laminates tested in this research project were based on a 2/1 configuration (two magnesium alloy skins either side of a carbon fiber reinforced epoxy core). Table I summarizes the stacking configurations investigated in this study. The composite volume fraction within the FMLs was varied by increasing the number of composite plies between the two outermost magnesium alloy skins from two to eight. The tensile properties of the FMLs and the magnesium alloy were evaluated using 20 mm wide rectangular samples at a crosshead displacement rate of 2 mm/min. The initial strain history in each sample was recorded using a clip-on extensometer fixed to the specimen edge. The extensometer was incapable of measuring large strains. In such cases, the crosshead displacement was normalized by the length of the working section to yield a nominal strain (this was only undertaken when a complete stress-strain curve was required). The energy-absorbing properties of the fiber-metal laminates were evaluated through a series of single edge notch bend (SENB) tests on specimens with dimensions 100 × 18 mm × thickness. Prior to testing, a 9 mm long pre-crack was introduced at the mid-span. The precrack was sharpened by swiping a sharp razor blade along the tip of the stress concentration. The SENB specimens were positioned on two simple supports positioned 72 mm apart and loaded at a crosshead displacement rate of 5 mm/min. The work of fracture was then determined by dividing the area (energy) under the load-displacement curve by the cross-sectional area of the fractured ligament. Fig. 1 shows typical stress-strain (nominal) curves for the three FMLs and the plain magnesium alloy. The stress-strain curve for the plain magnesium alloy indicates that although its tensile strength is below that of the FMLs, it does exhibit quite a high degree of ductilty beyond the elastic limit. The stress-strain curves for all of the FMLs exhibited an almost linear response up to maximum stress at which point the composite layers fractured in a brittle manner. An examination

Flame characteristics, temperature - time curves, and rate of spread in fires propagating in a bed of Pinus pinaster needles

An extensive set of experiments was carried out in order to collect data to validate fire propagation models being developed in the context of an European research project. The experiments were performed in a dedicated burning tray (2.0 m × 0.70 m working section), where wind velocity, fuel moisture content and slope were varied to study fire propagation in beds of Pinus pinaster needles. All the runs were videotaped and, from the recordings, information on flame geometry (i.e. flame height, flame length and flame angle) and rate of spread was obtained. Temperature measurements were also carried out by a small tower of six thermocouples at different heights above the fuel bed. Results show that headfire rate of spread increases steeply with wind speed for wind-driven fires but does not depend on wind speed for backing fire spread rates. Rate of spread increases slightly with slope for up-hill propagation, and is not slope dependent for down-hill cases. Rate of spread decreases when fuel moisture content increases. Flame angle and flame height are also dependent on wind velocity, slope, and fuel moisture content. The importance of temperature for fire propagation is discussed, emphasizing the role of radiation heat transfer in the process. Correlations between temperature and other indicators of fire behaviour (namely the rate of spread) are presented. Results are discussed and compared. The results obtained provide a good database for the assessment of fire propagation models.

Surge instability on a cavitating propeller

This study details experiments investigating a previously unrecognized surge instability on a cavitating propeller in a water tunnel. The surge instability is explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Similarities between the instability and previously documented cavitation phenomena are noted. Measurements of the radiated pressure are obtained, and the acoustic signature of the instability is identified. The magnitudes of the fluctuating pressures are very large, presumably capable of producing severe hull vibration on a ship.The origins of this instability are explored through separate investigation of the cavitation dynamics and the response of the water tunnel to volumetric displacement in the working section. Experiments are conducted to quantify the dynamics of the propeller cavitation. Finally, a model is developed for the complete system, incorporating both the cavitation and facility dynamics. The model predicts active system dynamics (linked to the mass flow gain factor familiar in the context of pump dynamics) and therefore potentially unstable behaviour for two distinct frequency ranges, one of which appears to be responsible for the instability.

Influence of diet on dispersal of horse mussel Atrina zelandica biodeposits

Benthic suspension feeders repackage particulate matter into organic-rich biodeposits (feces and pseudofeces) that are released into near-bottom flows. Where suspension feeders are found in dense assemblages, they physically alter the near-bottom flow field and thus may affect the local pattern of particle deposition. This dispersal pattern will control the spatial flux of biodeposits, and potential effects on sediment properties and surrounding benthic fauna. We quantified the downstream dispersal of biodeposits produced by an array of horse mussels Atrina zelandica fed either cultured phytoplankton (P) or a mixture of phytoplankton and silt (PS), a diet range that mim- ics the natural variation in near-bed seston quality. Experiments were run in a laboratory flume at a free-stream velocity of 4.5 cm s -1 , a value typical of field conditions. Diet had a significant effect on A. zelandica feeding activity and the dispersal of biodeposits. Compared to the P biodeposits, a greater fraction of the PS biodeposits was ejected well above the horse mussel array into the acceler- ated overlying flow layer (62% compared with 35%). However, more of the PS biodeposits settled either within the A. zelandica array or in the 120 cm working section downstream of the array (43 vs 17% of P biodeposits). Despite overall similarity in size, PS biodeposits had a settling velocity twice that of the P biodeposits. Of biodeposits settling downstream of the array, more than 70% settled within 20 cm of the trailing edge, regardless of diet. The density of biodeposits decreased exponen- tially with distance from the array at a rate that was similar for both diets. Monte Carlo simulations with a simple boundary layer model generally reproduced this pattern, but also highlighted the importance of initial height above bottom as well as flow complexities in the downstream wake region. Thus, the quality and quantity of A. zelandica biodeposits reaching the bed depends on the interaction among behavioral responses to available diet, settling velocity and boundary layer flows. Such interactions should have strong but localized effects on the incorporation of pelagic productiv- ity into the sediments and their consequent impacts on benthic community structure.

Influence of the Curvature of an Airfoil on the Structure of Transonic Flow

A study is made of the dependence of the pattern of transonic flow about an airfoil on the change in its shape and in the parameters of the incoming air flow. Consideration is given to a family of airfoils in a channel modeling the working section of a wind tunnel. The formation and propagation of weak shock waves in local supersonic regions near the central part of the airfoil has been investigated numerically. The finite-difference method based on a substantially nonoscillatory scheme of second order of accuracy has been employed to solve the Euler equations describing nonviscous gas flow. It has been shown that the sensitivity of the flow pattern to a change in the Mach number of the free flow substantially increases with decrease in the curvature of the airfoil.

Trial of controlled partial recirculation of ventilation air at Mount Isa Mines

The ventilation and cooling of deep, hot mines present particular problems in Australia as a consequence of the surface climate, the size of the underground voids, the degree of mechanization and the cost of power in remote areas. A preliminary investigation of the effects of controlled partial recirculation of air was conducted in Mount Isa Mines' Deep Copper section. Gas and dust concentrations were measured in the exhaust air of the major working section to assess the potential for recirculating exhaust air to the intake airways to reduce the cost of providing an acceptable working environment in the deep parts of the mine. Studies were undertaken of airborne dust deposition in vertical airways and the efficiency of usage of the ventilation air in diluting contaminants. It was established that 45% of the respirable dust was deposited in a 130-m vertical raise and 60% of the air supplied to the section could be reused or recirculated.The first major field trial of a controlled partial recirculation system in Australia was undertaken in the light of these results and demonstrated excellent potential for significant reduction in ventilation costs. Gas and dust contaminant levels were well below the threshold limit values during the trial. It is concluded that controlled partial recirculation can be a practical, effective and safe aid to normal ventilation practice in Australian deep, hot mines.

Long-lived sensors with replaceable surface for stripping voltammetric analysis: Part I

This study was inspired by the need of solving main problems of stripping voltammetry involving a short lifetime of electrodes, the necessity of mechanical regeneration of their surface and toxicity of mercury. The proposed electrodes (sensors) consist of a tungsten wire or a carbon-containing filament (thread). The latter was modified using one of the following methods: electroplating with mercury “in situ” or beforehand, or deposition of an insoluble mercury-organic complex on the filament surface beforehand and electrochemical reduction of the complex during analysis. Rotating disk tungsten electrodes, impregnated graphite disk electrodes and thick-film graphite electrodes were used to choose the solution composition and potential waveforms, and to compare the efficiency of the proposed sensor and earlier sensors. It was shown that long-lived mercury-free tungsten electrodes may serve to determine copper ions over the concentration interval from 10 to 1000 μg l −1. The carbon-containing filament may be used to determine copper, lead and cadmium concentrations at the level of μg l −1. A total of 10 measurements can be made using one and the same section of the electrode. Relative standard deviations of concentrations found range from 0.026 to 0.14 for various versions of electrodes and concentration intervals. The lifetime of the sensor is determined by the length of the wire or the thread and the replacement frequency of the working section. The obtained data confirm the reliability of the long-lived sensors. All the sensors, except the carbon-containing filament modified “in situ”, do not contaminate the environment with mercury. The long-lived sensors can be installed in flow-through systems designed for use under laboratory conditions and for remote unattended environmental monitoring.

Optimum wind tunnel regulation

The regulation of a wind tunnel system using minimum control effort is considered. A theory enabling input-output models to be employed in the design process is outlined. The procedure is applied to the regulation of the airspeed within the tunnel working section enabling turbulent conditions to be replicated, using a Dryden wind gust generator. Optimum dynamic control with least control effort is achieved using a simple closed-loop structure. The penalties involved in selecting a non-optimum design are commented on.

Dynamics of Explosive Boiling of Toluene

We carried out experimental investigations of the dynamics of heterogeneous pool boiling of toluene. A platinum wire of diameter 100 μm and length 68 mm served as a working section. Nonstationary heating of the working section was used to attain high levels of the metastability of liquid. The working section was also used as a resistance thermometer to determine the temperature of the heat transfer surface. High-speed motion-picture photography of the processes investigated was made. The experiments were carried out at a pressure in the working volume from 1.6 kPa to 76 kPa and subcoolings from 4 K to 83 K. Comparison was made between the experimental data for the speed of the evaporation front with calculations made by the model suggested by the present authors earlier. The discrepancy did not exceed 15%.

The Design and Construction of a Vertical Wind Tunnel for the Study of Untethered Firebrands in Flight

The design and construction of a wind tunnel with a vertical working section, which was used successfully for the study of untethered firebrands at their terminal velocity, is described. Two unique features in this tunnel design set it aside from previous vertical wind tunnels: the vertical working section has a divergent taper that allows a firebrand to find its terminal velocity within a velocity gradient, and the velocity of the boundary layer of the working section has been forced to a higher speed than the central zone to stop the firebrand impacting on the working section walls. These features in combination with a responsive speed control on the fan allow observation of burning firebrands throughout their viable lifetime in freefall with changing terminal velocities. This paper is intended as a synthesis of wind tunnel design and as a guide to researchers considering building similar devices to study the untethered flight characteristics of local species of firebrands.

Investigation of the Heat of Polymorphous Transformation in Zirconium by the Method of Pulsed Electric Heating

Results are given of the determination of the heat of polymorphous transformation in zirconium during resistive electric heating of specimens at rates from 103to 104K/s. A comparative analysis of the time dependences of temperature and resistance is used to demonstrate that the beginning and completion of phase rearrangement occur nonsimultaneously over the entire working length of the specimen. A procedure is suggested for obtaining refined data on the thermal effect, based on the calculation of the fraction of the working section, which has completely passed over to a new phase during a time interval identified by the heating thermogram. The mean value of the heat of α–β phase transition obtained by this procedure is 55.4 J/g. The obtained data are compared with those available in the literature.

Procedimiento para la planeación agregada en la pequeña y mediana industria manufacturera

The investigation work was developed taking like reference mark the state of the art on the Aggregate production Planning in the universal context and in the South American context, to end up studying to depth the behavior of the Colombian productive culture regarding the Gliding, the Programming and the Control of the production, in particular, the development level in the investigation and the application reached in the PYME (Small and Medium Company) in the specific field of the Aggregate production Planning, working in agreement with the government politicians about productivity and competitiveness, as well as in the observation about the necessity of to develop and to apply appropriate proceduresfor the sector manufacturer and the benefits that these they will generate in the Colombian economic and social context. For the position of the procedures one kept in mind, besides the state of the art in Aggregate production Planning, precedent works developed by the author, as well as their professional activity in the consultancy field, that which allowed to visualize the existent problem in the PYME. It is as well as you arrives to the position of a procedure for the Aggregate production Planning of Materials, which allows to determine the gross necessities of the different required raw materials during the planning horizon, a procedure for the Aggregate Capacities Planning that generates the gross capacity required in each one of the working sections during the time of planning, and a procedure for the Aggregate Planning of shifts, machines and labor force. These results allow the PYME to have a good support for the taking of decisions in minimum time, that which constitutes a contribution of high novelty and applicability in the Colombian environment. All the outlined procedures were developed making partial applications in different companies of the sector PYME, corroborating this way the coherence of their position so much mathematical as practical. The application of the procedures required the assembly of an appropriate system of information, as well as the development of software for the prosecution of the information and the obtaining of results.

Finding an efficient profile for the working (roughing) section in plane periodic rolling

Finding an efficient profile for the working (roughing) section in plane periodic rolling

SPECIAL ISSUE ON SENSITIVE SKIN

Sensitive Skins are large-area, flexible arrays of sensors integrated onto the entire surface of machines. Sensitive skin will endow these machines with the senses of proximity, touch, pressure, temperature, and chemical/biological agents. Thus Sensitive Skin will make possible the use of unsupervised machines in unstructured, unpredictable surroundings. Sensitive Skin will make machines "cautious" and thus friendly to their environment. Sencitive Skin will revolutionize service industries, make important contributions to human prosthetics, and augment human sensing when fashioned into clothing. Being transducers massive data flow, Sensitive Skin devices will make yet another advance in the information revolution. The National Science Foundation (NSF) and the Defense Advanced Research Projects Agency (DARPA) sponsored the NSF-DARPA Sensitive Skin Workshop that took place on October 14 and 15, 1999, at the Key Bridge Marriott Hotel in Arlington, Virginia. The purpose of the Workshop was to find consensus on the nascent Sensitive Skin technology, and provide recommendations for the research community and government agencies. The Workshop covered principles, methodology, and prototypes of sensing skin-like devices and related intelligence and software. It drew more than 40 participants from universities, companies, government laboratories, and government research agencies. Sensitive Skin devices present a new paradigm in sensing and control. Sensitive Skin is an enabling technology with far reaching applications — from medicine and biology to industry and defense — which are not possible today. Systems based on Sensitive Skin will be pivotal for progress in two broad areas. 1) Machines in unstructured environments. Sensitive Skin will enable moving machinery to acquire real-time information about surrounding objects. Hence, use it to operate safely in unstructured environments that cannot be modified at will and must be accepted as they are (in contrast to structured environments, such as a factory floor, whose design or redesign is only a matter of cost and effciency). 2) Augmentation of human sensing. In limb prosthetics and artificial skin grafts, Sensitive Skin will supplant the sensing ability of human skin. In wearable sensor clothing, Sensitive Skin will augment human sensing with full-body sensors and will provide sensing beyond human capability and wireless communication. The workshop participants discussed potential applications of Sensitive skin; envisioned skin materials, for embedding sensors, wiring, and control electronics; packaging; sensor layout, devices, and on-sensor signal processing; and research directions and goals. During the Workshop the participants alternated between working together in one single group, and splitting into four working sections — Materials, Devices, Signal Processing, and Applications — to chart a roadmap for research and development on the new sensing paradigm represented by sensitive skin systems. Because the workshop was held in one-and-a-half days, this report should be viewed as a first effort to map out new territory, and as an invitation to join the exploration!