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The study of high-pressure sound velocity is an important part of shock wave physics, and the study of ultra-high pressure sound velocity of iron is of great significance to many research fields such as geophysics, solid state physics, and crystallography. At present, the measurement of sound velocity is usually carried out by the catch-up sparse wave method and windowed VISAR technology, which is complex in structure and not highly adaptable. In particular, for the ultra-high pressure sonic velocity measurement of metals, it is limited by the loading platform and window materials and cannot realize the high temperature and high-pressure environment of the earth's inner core. In this paper, the sound velocity measurement of iron under high temperature and high-pressure environment (78 GPa) is realized based on the two-stage light gas cannon experimental platform. The side-side sparse wave method was used to establish a coupling model of high-spatially resolved optical group and fiber bundle. A multiplexed all-fiber laser interferometry velocity measurement system (DISAR) was built, and the spatial resolution was better than 20 μm. In this paper, we will provide a feasible route for a method for measuring the high spatiotemporal resolution velocity. [ABSTRACT FROM AUTHOR]

The study of high-pressure sound velocity is an important part of shock wave physics, and the study of ultra-high pressure sound velocity of iron is of great significance to many research fields such as geophysics, solid state physics, and crystallography. At present, the measurement of sound velocity is usually carried out by the catch-up sparse wave method and windowed VISAR technology, which is complex in structure and not highly adaptable. In particular, for the ultra-high pressure sonic velocity measurement of metals, it is limited by the loading platform and window materials and cannot realize the high temperature and high-pressure environment of the earth’s inner core. In this paper, the sound velocity measurement of iron under high temperature and high-pressure environment (78 GPa) is realized based on the two-stage light gas cannon experimental platform. The side-side sparse wave method was used to establish a coupling model of high-spatially resolved optical group and fiber bundle. A multiplexed all-fiber laser interferometry velocity measurement system (DISAR) was built, and the spatial resolution was better than 20 μm. In this paper, we will provide a feasible route for a method for measuring the high spatiotemporal resolution velocity.

Laser Doppler velocimetry (LDV) based on a differential laser Doppler system has been widely used in fluid mechanics to measure particle velocity. However, the two outgoing lights must intersect strictly at the measurement position. In cross-interface applications, due to interface effects, two beams of light become easily disjointed. To address the issue, we present a laser velocimeter in a coaxial arrangement consisting of the following components: a single-frequency laser (wavelength λ = 532 nm) and a Twyman–Green interferometer. In contrast to previous LDV systems, a laser velocimeter based on the Twyman–Green interferometer has the advantage of realizing cross-interface measurement. At the same time, the sensitive direction of the instrument can be changed according to the direction of the measured speed. We have developed a 4000 m level laser hydrothermal flow velocity measurement prototype suitable for deep-sea in situ measurement. The system underwent a withstand voltage test at the Qingdao Deep Sea Base, and the signal obtained was normal under a high pressure of 40 MPa. The velocity contrast measurement was carried out at the China Institute of Water Resources and Hydropower Research. The maximum relative error of the measurement was 8.82% when compared with the acoustic Doppler velocimeter at the low-speed range of 0.1–1 m/s. The maximum relative error of the measurement was 1.98% when compared with the nozzle standard velocity system at the high-speed range of 1–7 m/s. Finally, the prototype system was successfully evaluated in the shallow sea in Lingshui, Hainan, with it demonstrating great potential for the in situ measurement of fluid velocity at marine hydrothermal vents. [ABSTRACT FROM AUTHOR]

We propose the use of a second surface mirror as a displacement plate-beamsplitter to provide significant simplification and cost reduction of time-of-flight anemometry (ToFA), without sacrificing precision and accuracy. These benefits are most pronounced for long-range applications. Our method's principle benefits are due to the few and simple components it requires as well as low sensitivity to both temperature effects and light source incoherence. We found that precise and accurate results are possible using a common consumer mirror as the main optical element and an inexpensive diode laser as the light source, which could broaden access to laser anemometry and make many industry applications economically feasible. The nature of the design also permits an increase in range for a given laser power since the method can utilize the entire optical area of the focusing lens/mirror independent of other design considerations and the cost of a flat second-surface mirror is usually negligible. To characterize the performance of this method, we develop a Cramer–Rao bound (CRB) for a general class of ToFA's with multiple Gaussian beams under signal-independent Gaussian white noise. For a given measurement volume, the lowest velocity uncertainty is achieved by creating a standard two-sheet geometry: power-matching the first two beams by adjusting the beamsplitter and blocking the rest of the beams is optimal. However, keeping the higher order beams permits determination of flow direction. Conditions to achieve beam power-matching are given. An anemometer is built using a diode laser with 12 mw 405 nm beam using a total of just three transmitting optical components. Our setup has an accuracy of 99.1%. The worst-case precision of 96.7% nearly achieves the CRB, although optimizing the setup more can lower the bound, and therefore allow increase in the performance by an order of magnitude or more. [ABSTRACT FROM AUTHOR]

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Photon counting heterodyne can provide extremely high sensitivity while allowing to reduce the local oscillator power as low as 1 pW, which will promote the advantage in flash coherent imaging. To explore the receiver bandwidth under different count rates in photon counting heterodyne applications, an AMCW-based single photon mechanism is proposed and experimentally demonstrated in this letter. With amplitude-modulated continuous wave (AMCW) technique, an AMCW optical signal with single frequency and low DC component is generated for receiver bandwidth exploration. Afterwards, the spectrum is recovered from the photon arrival sequence under different count rates. Experimental results show that a receiver bandwidth of up to 1 GHz can be estimated from the photon arrival sequence when the count rates ranges from 2 Mcps to 8 Mcps. [ABSTRACT FROM AUTHOR]

A frequency-modulated continuous-wave (FMCW) lidar is proposed to avoid signal aliasing in the measurement of distance and velocity. In the transmitter, a lightwave is amplitude-modulated in a Mach-Zehnder modulator by a linear-frequency modulated (LFM) waveform. The modulated light is used as a probe signal. The reflected optical signal beats with a local optical (LO) signal in a phase-diversity coherent optical receiver. The in-phase and quadrature components of the output signal are simultaneously recorded. The distance is extracted from the sum of the squares of the two components, while the velocity is calculated from the ratio of them. An experiment is carried out, in which the real-time distance and velocity of a spinning disk are measured. The proposed method can be used to solve the problems of signal aliasing which may lead to the ambiguity of distance and velocity measurements in traditional FMCW lidars. Moreover, the impacts of optical phase fluctuations are removed from the distance measurement in the proposed method. [ABSTRACT FROM AUTHOR]

This paper is an experimental study on electroconvective flows produced by an asymmetric electric field in a cavity. It is part of a scientific project aiming to develop electrohydrodynamic (EHD) flow actuator in order to enhance heat transfer and mixing efficiency in fluidic and microfluidic systems. In this study, the EHD flow is obtained by applying a dc voltage between two electrodes (cylinder/plane) immersed in a working liquid. The produced velocity fields strongly depend on the applied voltage. Whatever may be the applied voltage, the fluid goes from the cylinder toward the plate or the other way round. The velocity fields obtained by particle image velocimetry for different potentials are analyzed in both cases with the usual mechanisms (injection and conduction) at the origin of the motion of the liquid. A discussion on the transition between injection and conduction phenomena is finally presented. [ABSTRACT FROM AUTHOR]

A robust nonfragile observer-based controller for a linear time-invariant system with structured uncertainty is introduced. The H∞ robust stability of the closed-loop system is guaranteed by use of the Lyapunov theorem in the presence of undesirable disturbance. For the sake of addressing the fragility problem, independent sets of time-dependent gain-uncertainties are assumed to be existing for the controller and the observer elements. In order to satisfy the arbitrary H2-normed constraints for the control system and to enable automatic determination of the optimal H2/H∞ bound of the performance functions in disturbance rejection control, additional necessary and sufficient conditions are presented in a linear matrix equality/inequality framework. The H2/H∞ observer-based controller is then transformed into an optimization problem of coupled set of linear matrix equalities/inequality that can be solved iteratively by use of numerical software such as Scilab. Finally, concerning the evaluation of the performance of the controller, the control system is implemented in real time on a mechanical system, aiming at vibration suppression. The plant under study is a multi-input single-output clamped-free piezo-laminated smart beam. The nominal mathematical reduced-order model of the beam with piezo-actuators is used to design the proposed controller and then the control system is implemented experimentally on the full-order real-time system. The results show that the closed-loop system has a robust performance in rejecting the disturbance in the presence of the structured uncertainty and in the presence of the unmodeled dynamics. [ABSTRACT FROM AUTHOR]

Laser Doppler velocimetry (LDV) is a high precision instrument based on the Doppler effect of a laser, and it would greatly improve the performance of vehicle navigation and vehicle velocity metrology for its advantages. To reduce the measurement error produced by a jolt of a vehicle, a novel Janus‐configured all fibre LDV is designed. The system comprising two independent interferometers is connected by 1.55 μm single mode fibre devices. Road experiments are carried out to compare the performances of the microwave radar, single beam LDV and Janus‐configured LDV. The Janus‐configured LDV is reliable to measure the velocity of the vehicle and its root‐mean‐square error is 0.0222 m/s, while it is 0.0284 m/s for the single beam LDV. The results validate that the designed LDV can achieve improved performance of vehicle velocity measurement. [ABSTRACT FROM AUTHOR]

The contact electrification of aerosolized micro particles has been studied using a novel technique involving laser velocimetry. This has allowed the simultaneous determination of size and electrical charge of individual silica microspheres (in the range 1 – 8 µm). Interestingly the particles interacting with the injector tube have been seen to become electrified with a relatively narrow range of surface charge concentration of around Q/4πr 2 ~ −100 e - /µm 2 (~ −0.02 mC/m 2 ) for all particle sizes. Several combinations of aerosol particle and injector tube composition were also investigated, some of which led to positive particle electrification and all of which resulted in similar values of measured surface charge concentration. The electrification was not seen to be strongly affected by gas composition and is in reasonable agreement with the expected maximum surface charge observed in previous experiments (<0.1 mC/m 2 ). Possible explanations for this effect are discussed, including the possibility of field emission at the contact site. In the future this technique is intended also to be applied to particle-particle induced contact electrification and its material dependence. [ABSTRACT FROM AUTHOR]

Since the beginning of the Mars planet exploration, the characterization of carbon dioxide hypersonic flows to simulate a spaceship’s Mars atmosphere entry conditions has been an important issue. We have developed a Tunable Diode Laser Absorption Spectrometer with a new room-temperature operating antimony-based distributed feedback laser (DFB) diode laser to characterize the velocity, the temperature and the density of such flows. This instrument has been tested during two measurement campaigns in a free piston tunnel cold hypersonic facility and in a high enthalpy arc jet wind tunnel. These tests also demonstrate the feasibility of mid-infrared fiber optics coupling of the spectrometer to a wind tunnel for integrated or local flow characterization with an optical probe placed in the flow.

We demonstrate a flow-meter sensor using a bare laser diode (LD) as a self-mixing interferometer and no additional lens nor optical component. The diode is placed directly on the edge of the duct, exploiting the natural laser divergence. The flow measurement is based on the Doppler shift induced by the scattering particles inside the fluid and read by the self-mixing effect inside the LD. The proposed approach has been modeled by a numerical simulator in order to find the best signal processing algorithm. A set of measurements on blood proves good performances as a flow meter, while simulations confirm the system robustness to mechanical misalignments and changes in liquid properties. [ABSTRACT FROM PUBLISHER]

The performance and exit flow characteristics of two mixed-flow turbines have been investigated under steady-state conditions. The two rotors differ mainly in their inlet angle geometry, one has a nominal constant incidence (rotor B) and the other has a constant blade angle (rotor C), but also in the number of blades. The results showed that the overall peak efficiency of rotor C is higher than that of rotor B. Two different volutes were also used for the tests, differing in their cross-sectional area, which confirm that the new larger area volute turbine has a higher efficiency than the old one, particularly at lower speeds, and a fairly uniform variation with velocity ratio.

The Stanford Cylindrical Cusped Field Thruster (CCFT) has been experimentally and numerically investigated with particular focus on the exit plane acceleration region near the top magnetic cusp. Time-averaged xenon ion laser-induced fluorescence measurements using the 5d[4]7/2 - 6p[{3}]5/2 ( $\lambda = 834.72$ -nm air) Xe II transition have mapped the total ion velocity vectors in this region. The thruster is also simulated using the fully kinetic 3-D particle-in-cell code F3MPIC. The consistent experimental and numerical results give physical insight into the mechanisms of ion acceleration and the role of the magnetic field topology in determining ion trajectories and plume divergence. The electrons are strongly magnetized and follow the magnetic field structure, grouping near the cusps. A steep potential drop over a few millimeters near the exit plane follows the magnetic separatrix of the top cusp, and is consistent with measured ion velocity vectors. A characteristic conical region of high ion density, peak ion velocity, and visible emission is observed in the experimental and simulated plume, with an estimated divergence half-angle of 30°. [ABSTRACT FROM PUBLISHER]

The fluctuation-dissipation theorem establishes the fundamental links between thermomechanical noise and damping. In this paper, we bridge the gap between theory and practice by developing protocols for estimating dissipation in low-loss microresonators by measuring thermomechanical noise using laser Doppler vibrometry. The measurement does not require external actuation of the device and damping can be estimated without relying upon knowledge of material properties, device dimensions, or structural stiffness. The power spectral density of velocity and displacement noise is computed using a direct method that avoids segmenting the measurements in the time domain, thereby avoiding any bias in the estimation of the quality factor. We demonstrate the implementation of the protocol by measuring damping at room temperature and low pressure in four silicon-based microcantilever resonators with natural frequencies ranging from 17.6 to 26.7 kHz and quality factors ranging from 2×104 to 2×105 . The accuracy of noise-based estimates is evaluated by comparison with values of the log decrement measured under free decay. [ABSTRACT FROM AUTHOR]

In this work a brief experimental investigation of velocity changes on a fluid flow by means of a noncontactive optical method based on the Non-steady-state photo-electromotive force (P-EMF) effect is presented. Evidence of linear dependence of P-EMF signal on fluid flow for low velocities as compared with a Laser Doppler Anemometry test is shown and discussed. [ABSTRACT FROM AUTHOR]

Terahertz frequency quantum cascade lasers (THz QCLs) are compact sources of coherent THz radiation with potential applications that include astronomy, trace-gas sensing, and security imaging. However, the reliance on slow and incoherent thermal detectors has limited their practical use in THz systems. We demonstrate THz sensing using self-mixing (SM) interferometry, in which radiation is reflected from an object back into the QCL cavity, causing changes in the laser properties; the THz QCL thus acts simultaneously as both a source and detector. Well-established SM theory predicts a much weaker coupling in THz QCLs than in diode lasers, yielding a near-linear relationship between the phase of SM signals and the external cavity length. We demonstrate velocimetry of an oscillating reflector by monitoring SM-induced changes in the QCL drive voltage. We show that this yields data equivalent to that obtained by sensing the emitted THz power, thus allowing phase-sensitive THz-SM sensing without any external detector. We also demonstrate high-resolution SM-imaging at a round-trip distance of 21 m in air—the longest-range interferometric sensing with a THz QCL to date. [ABSTRACT FROM PUBLISHER]

The possibility of creating unsteady distortions of the tip shock by waves emitted from an aircraft is assessed experimentally. The model chosen is a cylindrical fore body equipped with a spike. This configuration is known for generating an important level of unsteadiness around the spike in supersonic regime. The wind tunnel Mach number is equal to 2. The experiments show that waves emitted from this source propagate along the tip shock and interact with it. It is then assessed that this interaction produces a periodic distortion of the shock that propagates to the external flow. Unsteady pressure sensors, high speed schlieren films, hot wire probing and laser Doppler velocimetry are used as complementary experimental means. The final result is a coherent representation of the complex mechanism of wave propagation that has been evidenced. The principle of creating unsteady shock deformation by onboard equipments could be examined as a possibly promising method of sonic boom control. [ABSTRACT FROM AUTHOR]

Abstract: A Laser Doppler Velocimetry (LDV) technique was implemented to simultaneously measure the gas and particulate phase velocities in a high-speed jet plume in a two-dimensional (2D) bubbling fluidized bed. The gas and particulate phase velocity profiles are presented and analyzed. This includes similarity profile scaling as well as volume fraction, mass flow, and momentum transport calculations for the two phases. Furthermore, applying the Eulerian equation of motion to the particulate phase with the measured velocity profiles, the bed particle drag coefficient is recovered and is found to be consistent with the established empirical value. [Copyright &y& Elsevier]

Abstract: In the present work, the effect of emulsion fluidization on the gas and particle phase transport in a high-speed gas jet plume in a bubbling bed is examined. Implementing a Laser Doppler Velocimetry (LDV) technique, the gas and particulate phase velocities of a gas jet injected into a bubbling bed of 838μm high-density polyethylene (HDPE) micropellets were measured. These velocity profiles were used to determine the volume fraction, mass flow, and momentum transport rate for each phase at various axial locations as well as an average particle drag coefficient in the measurement region of the plume. Maintaining consistent gas jet inlet conditions, the HDPE emulsion fluidization was varied from a spouted bed to 50% beyond minimum fluidization. In addition to the integral flow values, centerline phase velocity scaling is also examined. The scaling is based on the development of similarity velocity profiles for the two phases. Additional experiments to investigate this idea were carried out with 1) the particle emulsion and fluidization level is held constant while the jet inlet velocity is varied and 2) the jet inlet velocity and fluidization ratio is held constant while the bed particles are varied. [Copyright &y& Elsevier]

Theoretical and experimental analysis of the spectral characteristics of the signal acquired from self-mixing laser Doppler of extracorporeal blood flow is presented. The theoretical spectrum of the predetected signal is calculated in the single scattering approximation and assuming a parabolic velocity profile in the duct. The resulting signal is mixed in a diode laser cavity to generate the sensor output. Theoretical predictions are verified by measurements performed on blood and phantoms flowing in an extracorporeal circulation system. [ABSTRACT FROM PUBLISHER]

Velocimetry of ceramic particles ejected via cathode spot eruption on the surface of a biased electrode in the presence of a low-density plasma has been carried out. Witness plate measurements indicated the rate of powder removal to be greater than 3.0 mg/s. An expanded laser beam and fast frame-rate camera were used to perform laser-illuminated particle imaging velocimetry measurements. The velocity distribution for 45- \mu\m-diameter ceramic particles was found to range between 0.2 and 1.5 m/s in the plane of view as they are ejected from the electrode surface. Nonuniform powder ejection in the horizontal plane is shown to be related to the presence of an applied magnetic field. [ABSTRACT FROM AUTHOR]

Basilar-membrane responses to white Gaussian noise were recorded using laser velocimetry at basal sites of the chinchilla cochlea with characteristic frequencies near 10 kHz and first-order Wiener kernels were computed by cross correlation of the stimuli and the responses. The presence or absence of minimum-phase behavior was explored by fitting the kernels with discrete linear filters with rational transfer functions. Excellent fits to the kernels were obtained with filters with transfer functions including zeroes located outside the unit circle, implying nonminimum-phase behavior. These filters accurately predicted basilar-membrane responses to other noise stimuli presented at the same level as the stimulus for the kernel computation. Fits with all-pole and other minimum-phase discrete filters were inferior to fits with nonminimum-phase filters. Minimum-phase functions predicted from the amplitude functions of the Wiener kernels by Hilbert transforms were different from the measured phase curves. These results, which suggest that basilar-membrane responses do not have the minimum-phase property, challenge the validity of models of cochlear processing, which incorporate minimum-phase behavior. [ABSTRACT FROM PUBLISHER]

Abstract: A new experimental method to measure the velocity and fluctuations of a solid–liquid suspension is proposed in this work. This method based on laser anemometry with Doppler effects consists of an association of laser velocimetry and an electronic logic circuit placed at the reception. This circuit was developed in order to distinguish between signals from the continuous phase (water) and those of the solid particles (glass beads) and therefore to detect the presence of large particles (larger than the laser wavelength) in the measurement volume. The present experimental method is limited to small volumetric concentrations lower than 2%. Indeed, when the value of 2% is exceeded, the suspension becomes a very diffusing medium and prevents the propagation of laser beams in the flow in an ascending vertical glass pipe. The results show that a fine particle suspension, which represents a tracer, behaves as a homogeneous fluid. For large particles, we confirmed the existence of a slip velocity and the effect of particle concentration on the turbulence intensity. [ABSTRACT FROM AUTHOR]

Since the beginning of the Mars planet exploration, the characterization of carbon dioxide hypersonic flows to simulate a spaceship's Mars atmosphere entry conditions has been an important issue. We have developed a Tunable Diode Laser Absorption Spectrometer with a new room-temperature operating antimony-based distributed feedback laser (DFB) diode laser to characterize the velocity, the temperature and the density of such flows. This instrument has been tested during two measurement campaigns in a free piston tunnel cold hypersonic facility and in a high enthalpy arc jet wind tunnel. These tests also demonstrate the feasibility of mid-infrared fiber optics coupling of the spectrometer to a wind tunnel for integrated or local flow characterization with an optical probe placed in the flow. [ABSTRACT FROM AUTHOR]

Basilar membrane responses to clicks and to white noise were recorded using laser velocimetry at basal sites of the chinchilla cochlea with characteristic frequencies near 10 kHz. Responses to noise grew at compressive rates and their instantaneous frequencies decreased with increasing stimulus level. First-order Wiener kernels were computed by cross-correlation of the noise stimuli and the responses. For linear systems, first-order Wiener kernels are identical to unit impulse responses. In the case of basilar membrane responses, first-order Wiener kernels and responses to clicks measured at the same sites were similar but not identical. Both consisted of transient oscillations with onset frequencies which increased rapidly, over about 0.5 ms, from 4-5 kHz to the characteristic frequency. Both first-order Wiener kernels and responses to clicks were more highly damped, exhibited slower frequency modulation, and grew at compressive rates with increasing stimulus levels. Responses to clicks had longer durations than the Wiener kernels. The statistical distribution of basilar membrane responses to Gaussian white noise is also Gaussian and the envelopes of the responses are Rayleigh distributed, as they should be for Gaussian noise passing through a linear band-pass filter. Accordingly, basilar membrane responses were accurately predicted by linear filters specified by the first-order Wiener kernels of responses to noise presented at the same level. Overall, the results indicate that cochlear nonlinearity is not instantaneous and resembles automatic gain control. [ABSTRACT FROM AUTHOR]

Abstract: Selectivity of fishing gears like trawls is obviously conditioned by the fish behaviour but also by the net and the flow. As well, flow may affect fish behaviour. With the aim of a better understanding of the flow in presence of a net and a catch, we suggest, through the experimental study below, to determine and to analyze the flow over a rigid cod-end in two configurations: with a closed and an open net entrance. Trials took place in a free surface flume tank and the flow characteristics were determined from velocity measurements obtained by laser velocimetry (inside, outside and through the meshes of the stiff cod-end). The experimental device, the measures and their analyzes are given here. [Copyright &y& Elsevier]

In this work, an experimental method based on laser anemometry with Doppller effects is developed. This allows the measurement of velocities and their fluctuations in a flow of solid-liquid suspension in an ascendant vertical pipe. In order to distinguish between the signals coming from the continuous phase, water and those of the glass bead particles larger than the Kolmogorov length scale, an electronic logic circuit was incorporated in the measuring equipment. This enabled the study of both the slip velocity of the solid-liquid suspension and the influence of the large particles on turbulence. The results show that a fine particle suspension, which represents a tracer behaves as a homogeneous fluid. For large particles, we confirmed the existence of a slip velocity and the effect of particle size on the turbulence. The use of two distinct measurement volumes produces good results for the direct measurement of the turbulent length scales. The results show that the presence of solid particles modifies the turbulence characteristics. [ABSTRACT FROM AUTHOR]

The design and development of a new fiber-optic sensor for measuring the velocity of a continuous material (also called a web) in material processing systems is described. The development of the proposed sensor is based on the dual beam laser Doppler velocimetry technique and the unique properties of different types of optical fibers. The developed sensor is capable of measuring the true web transport velocity as opposed to the existing methods which infer web transport velocity based on the roller angular speed. Since the sensor design utilizes fibers, signal processing can be performed away from the measurement area, and as a result the sensor can be used in harsh environments within the web processing line. The proposed sensor has been constructed and experiments have been conducted on an experimental web platform. The performance of the sensor is evaluated for a range of web velocities and different web materials. Sensor design, its construction, and a representative sample of the results are presented and discussed. [ABSTRACT FROM PUBLISHER]

The parametric three-dimensional geometric model of twin-screw supercharger rotors of any aspect ratio was developed. For model validation through visualization, computer-aided design (CAD) rotor models with scalable data were generated in commercial CAD software and calibrated experimentally by laser Doppler velocimetry (LDV) tests. Calibrated rotor profile data can be transferred into CAD-CFD interface for flow simulation for performance optimization. [ABSTRACT FROM AUTHOR]

We present a rate equation model of a single mode vertical-cavity surface-emitting laser (VCSEL) with two states of linear polarization, subject to Doppler-shifted optical feedback. Recent experimental work has shown that the polarization bistability often observed in VCSELs can be exploited to enhance the responsivity of these semiconductor lasers in speed-sensing applications. We review these experimental results briefly and use the rate equation model to explain the increased signal-to-noise ratio. [ABSTRACT FROM PUBLISHER]

Laser Doppler velocimetry (LDV) has been widely used for many years in fluid mechanics to measure particle velocity. However, in most applications, i.e., in industrial processes, such a system is often too expensive. This paper discusses a technique based on the use of an analog phase-locked loop and an analog integrator system for processing laser Doppler velocimeter data to infer particle velocity. This method appears to be suitable for designing low-cost integrated LDV sensors. A SIMULINK program has been written in order to validate the method for velocities in the 10-80 mm/s range. Finally, the performance of the estimator is illustrated by Monte-Carlo simulations obtained from synthesized Doppler signal. [ABSTRACT FROM PUBLISHER]

This paper presents a review of theoretical and experimental results on stability and other unsteady properties of aircraft wakes. The basic mechanisms responsible for the propagation and the amplification of perturbation along vortices, namely the Kelvin waves and the cooperative instabilities, are first detailed. These two generic unsteady mechanisms are described by considering asymptotic linear stability analysis of model flows such as vortex filaments or Lamb–Oseen vortices. Extension of the linear analysis to more representative flows, using a biglobal stability approach, is also described. Experimental results obtained using LDV, hot wire and PIV in wind tunnels are presented and they are commented upon the light of theory. [Copyright &y& Elsevier]

The average velocity field at the pump-turbine interface in a scaled version of a truck torque converter was studied. Seven different turbine-to-pump rotational-speed ratios were examined, ranging from near stall (0.065) to overspeed (1.050) so as to determine the effect of the speed ratio on the flow field and on the mass flow rate. Laser velocimetry was used to measure the flow velocity through the pump's exit and the turbine's inlet plane. At the pump's exit, as the speed ratio increases, the high velocities move to the pressure-shell corner and then to both the core-suction and the pressure-shell corners. Concentrated velocity gradients are largest at the lowest speed ratio, but areas of velocity gradients are largest near the coupling point. Near the coupling point, the flow field is most nonuniform, which yields a highly periodic flow into the turbine inlet. Above the coupling point, the high velocity remains in the pressure-shell corner but separation is seen to develop at the highest speed ratio. At the turbine's inlet, reverse flow is seen at low speed ratios and is an indicator of flow leakage through the core. Velocity gradients are very large at low speed ratios. As the speed ratio increases to the coupling point, the high velocities remain on the shell side. Above the coupling point, the high-velocity flow migrates from the shell side to the core side. The mass flow rate decreases significantly and nonlinearly with the increase of the speed ratio, but for speed ratios greater than 1.000, the negative slope decreases. [ABSTRACT FROM AUTHOR]

The flow around two airfoils in the vicinity of stall has been experimentally investigated in the ONERA/CFM F2 wind tunnel. The aim of this study was to provide a detailed and well established database for CFD validation, in low speed conditions (M∞=0.15) for a fixed Reynolds number of 2.1×106 based on the chord. The 2D single element models were fitted with wall pressure taps allowing the measurement of pressure distributions and the determination of the lift coefficient. Measurements over a wide range of angles of attack provided a global view of the phenomena. The first airfoil typically exhibits an abrupt stall, while the second one is characterized by a very mild one. The main part of this study was a very careful survey of the suction side boundary layer and near wake, using the F2 LDA system in a 2D configuration. This first part deals with the boundary layer surveys. A companion paper presenting the wake results will be issued later. [Copyright &y& Elsevier]