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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]

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]

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 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]

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]

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]

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]

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]

• An efficient method to simulate axial multiple transducer arrays is proposed. • In-depth investigation on the excitation of quasi-axisymmetric torsional waves. • Validated analytical and numerical simulations of torsional wave modes along pipes. • Sensitivity analysis for part-circumferential crack detection in numerical models. In pipe inspection using ultrasonic guided wave technique, the current commercial transmitters are designed for the unidirectional guided wave excitation using multiple circular piezoelectric transducers arrays in the axial direction. However, the source with many individual transducer elements in arrays has difficulty in achieving an axisymmetric loading perfectly for defect detection. Therefore, a quasi-axisymmetric wave is formed due to many undesired wave modes are launched instead of a pure axisymmetric wave at a given excitation frequency. In this paper, a realistic superposition model of axial multiple transducer arrays is proposed. The model has many potential applications; one example is investigating the source influence on the generated quasi-axisymmetric wave effect. The analytical model is employed to achieve the predictions for investigating a transmitter's influence for the unidirectional enhancement of torsional T(0,1) guided wave mode excitation in a pipe inspection system composing of three piezoelectric transducer ring arrays. The excitation function with variable power levels among transducers in arrays is also introduced. The predictive results using the analytical model for the distribution of circumferential displacement amplitudes over time are verified using the finite element method and a CLV-3D laser vibrometry measurement on a 219.1-mm-outer-diameter steel pipe without defect. A comparison between calculated and test results has been analysed quantitatively. The respective results are in good agreement. Thus, predictions for the superposed wavefield can be used to analyse the realistic characterisation of the excitation function in axial multiple transducer arrays. Additionally, a sensitivity analysis for part-circumferential crack detection using the quasi-axisymmetric torsional modes generated is also evaluated using finite element modelling. [ABSTRACT FROM AUTHOR]

A series of integral heat transfer measurements in a square annular flow passage was performed for bulk water temperatures of 175-400°C with upward mass velocities of 300 kg/m2 s and 1000 kg/m2 s and heat fluxes of 0, 200 kW/m2, and 440 kW/m2, all at a pressure of 25 MPa. Mean and turbulent velocities measured with a two-component laser Doppler velocimetry system along with simulations using the computational fluid dynamics (CFD) code FLUENT were used to explain the deterioration and enhancement of heat transfer in supercritical pressure water. At low mass velocities, the integral heat transfer measurements exhibited large localized wall temperature spikes that could not be accurately predicted with Nusselt correlations. Detailed mean and turbulent velocities along with FLUENT simulations show that buoyancy effects cause a significant reduction in turbulent quantities at a radial location similar to what is the law of the wall region for isothermal flow. At bulk temperatures near the pseudocritical temperature, high mass velocity integral heat transfer measurements exhibited an enhanced heat transfer with a magnitude dependent on the applied heat flux. Measured mean and turbulent velocities showed no noticeable changes under these conditions. FLUENT simulations show that the integrated effects of specific heat can be used to explain the observed effects. The experimentally measured heat transfer and local velocity data also serve as a database to compare existing CFD models, such as Reynolds-averaged Navier-Stokes (RANS) equations and possibly even large Eddy simulations (LES) and direct numerical simulations (DNS). Ultimately, these measurements will aid in the development of models that can accurately predict heat transfer to supercritical pressure water. [ABSTRACT FROM AUTHOR]