Two-dimensional Laser Doppler Velocimeter Research Articles

Ground vehicle gravimetry system based on SINS and two-dimensional LDV integration: error analysis and verification

As an effective tool for refining local gravity data with mGal accuracy, vehicle gravimetry system usually consists of Strapdown Inertial Navigation System (SINS) and Global Navigation Satellite System (GNSS). However, the traditional system is unable to achieve gravimetry in an environment without GNSS signal dues to heavy dependence on GNSS signal. To solve this problem, this study proposed a gravimetry method specifically for the environment without GNSS signal, which consists of the high-precision Strapdown Inertial Navigation System (SINS) and Laser Doppler Velocimeter (LDV) developed by our unit. Based on the error analysis, the system index requirements were proposed, and the relevant indexes of the LDV are verified through simulation and vehicle experiment. The simulation results for different velocimeter accuracies show that the internal accord accuracy of the system is within 1mGal when the velocimeter accuracy is 1 ‰, and the internal accord accuracies of the system are more than 1mGal when the velocimeter accuracies are 5 ‰ and 10‰. The results of the vehicle experiment for different dimensional velocimeters show that when the spatial resolution is 1.7 km, the SINS/LDV (2D) and SINS/GNSS integrated systems have an internal accord accuracy of 0.68 mGal and 0.54 mGal, respectively, while the SINS/LDV (1D) integrated system has an internal accord accuracy of 1.50 mGal. The feasibility of the SINS/LDV system and the necessity of the SINS/LDV system for the dimension and accuracy of the velocimeter are illustrated.

Strapdown vehicle autonomous gravimetry method based on two-dimensional laser Doppler velocimeter

Strapdown vehicle autonomous gravimetry method based on two-dimensional laser Doppler velocimeter

基于二维激光多普勒测速仪建立新组合导航系统的方法

基于二维激光多普勒测速仪建立新组合导航系统的方法

Two-dimensional laser Doppler velocimeter and its integrated navigation with a strapdown inertial navigation system.

In the field of land navigation, a laser Doppler velocimeter (LDV) can be used to provide the velocity of a vehicle for an integrated navigation system with a strapdown inertial navigation system. In order to suppress the influence of vehicle jolts on a one-dimensional (1D) LDV, this paper designs a split-reuse two-dimensional (2D) LDV. The velocimeter is made up of two 1D velocimeter probes that are mirror-mounted. By the different effects of the vertical vibration on the two probes, the velocimeter can calculate the forward velocity and the vertical velocity of a vehicle. The results of the vehicle-integrated navigation experiments show that the 2D LDV not only can actually suppress the influence of vehicle jolts and greatly improve the navigation positioning accuracy, but also can give high-precision altitude information. The maximum horizontal position errors of the two experiments are 2.6m and 3.2m in 1.9h, and the maximum altitude errors are 0.24m and 0.22m, respectively.

陆用组合导航中二维激光多普勒测速仪的标定方法

陆用组合导航中二维激光多普勒测速仪的标定方法

Two-dimensional laser Doppler velocimeter using polarized beams and 90° phase shift for discrimination of velocity direction

A laser Doppler velocimeter (LDV) for two-dimensional velocity measurement using a simple optical configuration without any optical modulator is proposed. The structure using polarized beams and the 90° phase shift of the reference beam is used to discriminate the direction of velocity. The analytical relation among beat frequencies and velocity components is derived and the characteristics of the proposed LDV are simulated. The simulation results indicate that the direction of velocity can be discriminated by the proposed LDV as well as the magnitudes of the components of the velocity.

Mean Velocity Profile in Confined Turbulent Convection

In this Letter, highly resolved measurements of the horizontal velocity inside the boundary layer of turbulent Rayleigh-Bénard convection are reported. They were performed in a cylindrical box with an aspect ratio Gamma=1.13 which was filled with air with a Prandtl number Pr=0.7. The horizontal velocity was measured along the central axis close to the cooling plate in a range of Rayleigh numbers between Ra=10;{11} and Ra=10;{12} using a two-dimensional laser Doppler velocimeter. We demonstrate that the profile of the mean velocity strongly differs from that of classical shear flows like the Blasius shape of a laminar flat plate boundary layer or a turbulent logarithmic velocity profile with standard coefficients.

Vortex Motion in a Swirling Flow of Surfactant Solution with Drag Reduction

Surfactants are well known as additives which induce drag reduction in the straight (nonswirling) pipe flow. However, in industrial applications of the drag-reducing effect, many flow fields besides the straight pipe flow need to be considered. The purpose of this study is to investigate the flow characteristics of the surfactant solution in swirling pipe flow. The drag-reducing effect is estimated from the measurement of wall pressure drop and velocity profiles on various pipe sections by two-dimensional LDV (Laser Doppler Velocimeter). Since the surfactant solution has viscoelasticity, interesting flow characteristics are obtained. The decay of swirl, the vortex type and the turbulence intensity are discussed, compared with the swirling flow of the water. As the results, it is concluded that the change from Rankin’s combined vortex to the forced vortex at a more upstream section by suppressing progress of free vortex and stretch of forced vortex introduces considerable drag reduction. Oscillation of the vortex core is also investigated, and it is found that the oscillation is independent of swirl number.

Effects of viscosity of fluids on centrifugal pump performance and flow pattern in the impeller

Centrifugal pump performances are tested using water and viscous oil as working fluids whose kinematic viscosities are 1 and 48 mm2/s, respectively, the flows in the centrifugal pump impeller are also measured accurately by using a two-dimensional laser Doppler velocimeter (LDV) in best efficiency and part-loading points, while the pump is handling two kinds of working fluids. The effects of the viscosity on the performance and flow pattern within the impeller are established based on the experimental results. The high viscosity results in rapid increases in the disc friction losses over outsides of the impeller shroud and hub as well as the hydraulic losses in flow channels of the pump. The flow patterns near the impeller outlet are little affected by the viscosity of the fluids, but those near the impeller inlet are greatly affected by the viscosity. There is a wide wake near the blade suction side of the centrifugal pump impeller. The flow pattern is essentially different from the well-known jet/wake model.

Velocity and Density Measurements in Supersonic High-Temperature Exhaust Plumes

A two-dimensional laser Doppler velocimeter and a Rayleigh scattering system were used to measure the mean velocities, turbulence quantities, and mean density In a supersonic high-temperature exhaust plume with and without an annular base flow. The distributions of mean temperature and Mach number were inferred. For both cases, the potential core of the supersonic jet extends about 6 nozzle diameters, and the flow remains supersonic until about 15 nozzle diameters. The mean axial velocity, turbulence kinetic energy, shear stress, and temperature become self-similar downstream of the flow. Similarities of turbulence quantities develop slower than the mean velocity, whereas the temperature similarity is established upstream of the velocity. Near the nozzle base of the coaxial jets, one and a half recirculation zones are formed, which represents an extreme of the central-jet-dominated coaxial flows

Influence of inlet pressure conditions on supersonic turbulent mixing layers

The effect of nonisobaric initial conditions on a highly compressible ( M c = 1), supersonic mixing layer is studied experimentally. Mean flow characteristics and turbulent fields are measured with a two-dimensional laser Doppler velocimeter in a high Reynolds number supersonic wind tunnel. Mean longitudinal velocity profiles, vorticity thickness growth rate, longitudinal and lateral turbulent intensities, shear stress, and flatness and skewness factors of longitudinal velocities fluctuations are given for the isobaric and nonisobaric configurations. Results show that the asymptotic state of the mixing layer is the same whatever the inlet pressure condition is (in the range covered by the present experiment). The only apparent effect of the initial pressure ratio is to accelerate the transition between the initial boundary-layer state and the asymptotic mixing-layer configuration. The present results are also compared with existing literature. Both the isobaric and nonisobaric data collapse quite well with other experiments. It has to be noted that the present results confirm that the Reynolds stress tensor anisotropy seems to be unaffected by compressibility until convective Mach number close to unity.

Model study of bubble and liquid-flow characteristics in a bottom blown bath under reduced pressure

Gas injection techniques are widely used in metals refining processes. Pressure on the bath surface of reactors is sometimes highly reduced to enhance the efficiency of refining. Many fundamental and practical investigations have been made to clarify the effects of reduced surface pressure on the mixing time and reaction rates of decarburization or desulfurization in the bath. However, details of these effects are not fully understood yet. Since the mixing time and chemical reaction rates are closely associated with fluid flow phenomena in the bath, information on, for example, the total surface area of bubbles rising in the bath and liquid flow induced by the buoyancy force of the bubbles should be accumulated as much as possible. In this study, the so-called water-model experiments were carried out to reveal the effects of reduced surface pressure on the bubble and liquidflow characteristics using a two-needle electroresistivity probe and a two-dimensional laser Doppler velocimeter. At an axial position near the nozzle, each bubble expanded to a volume corresponding to the hydrostatic pressure. The bubble and liquid-flow characteristics in the axial region located farther than this axial position were found to be approximately the same as those obtained under an atmospheric surface pressure.

Experimental and Numerical Study of Orifice Discharge Coefficients in High-Speed Rotating Disks

Experimental and numerical results of the flow through orifices in rotating disks are presented, with emphasis on basic physical phenomena. It is shown that rotational effects strongly influence the massflow discharged, a phenomenon that cannot be modeled by a stationary setup. The study includes the determination of discharge coefficients under variation of the length-to-diameter ratio, pressure ratio, and rotational speed. The pressure ratio covers low as well as critical values, the maximum rotational speed is 10,000 rpm, which is equivalent to a tangential velocity of 110 m/s. In order to understand the flow structure, local flow velocities were measured by means of a two-dimensional Laser-Doppler Velocimeter. Phase-resolved measurements have been carried out in front of and behind the orifices. A three-dimensional Finite-Volume Code with body-fitted coordinates in a rotating frame of reference is employed for the numerical analysis and the verification of its possibilities and limitations. The results reveal a very complex flow field, which is dominated by high velocity gradients in close vicinity to the orifices. The comparison of the computational solutions with the experimental data shows good agreement. Based on the measurements in combination with the numerical solution, a detailed insight into the physical properties of the flow is achieved.

Experimental and numerical study of a premixed flame stabilized by a rectangular section cylinder

A numerical and experimental study of a turbulent reactive zone stabilized by a rectangular cross-section cylinder positioned in a fully developed turbulent channel flow of a propane-air mixture is presented. Such a flow geometry has been chosen because it features most of the phenomena (recirculation zones, flame stabilization, wall-flame interactions) present in systems of practical interest. The flow is experimentally investigated with a two-dimensional laser Doppler velocimeter and thin compensated thermocouples. The modeling of the reactive flow is based on a modified Bray-Moss-Libby combustion model associated with a Reynolds-stress turbulence model. The resulting set of equations is solved by a finite-difference Navier-Stokes code on a rectilinear mesh. The comparison between numerical and experimental results shows that the use of a full second-order model with dedicated equations for both the Reynolds stresses and the scalar turbulent flux does not lead to a significant improvement of the numerical results. Indeed, although the longitudinal scalar turbulent flux exhibits a nongradient behavior, the evolution of the mean progress variable introduced by the Bray-Moss-Libby model appears to be controlled mainly by the transverse scalar gradient that follows, in all cases, a gradient-like behavior. Additional measurements and calculations are required to find the exact range of mass flow rate, equivalence ratio, and obstacle bluffness overwhich such a tendency can be observed. Nevertheless, the tentative conclusion of this study is that, as soon as a refinement of the modeling of reactive flows in combustors that involve flameholders similar to the one investigated in this study is needed, the use of a Reynolds-stress model should be the first necessary step. Then, depending on the exact nature of the flow geometry, a second phase should consist of evaluating the need for the use of a full second-order model such as the one presented in this study.

Measurement of particle flow properties in a suspension by a laser system

Particle cloud density and velocity in a gaseous suspension with a particle size distribution were determined by a two-dimensional laser system. Measurements were made possible by the combined use of a two-dimensional laser Doppler velocimeter and a phase Doppler particle analyzer. The results and data system show the feasibility of determining average and fluctuating properties and Reynolds stresses.

Bubble and liquid flow characteristics in a vertical bubbling jet

A vertical bubbling jet was formed in a cylindrical water bath by injecting air from a centric single-hole nozzle. Bubble characteristics, such as gas holdup (void fraction), bubble frequency, mean bubble rising velocity, mean chord length, were measured using a two-needle electro-resistivity probe. In addition, liquid flow characteristics, represented by the axial mean velocity, rms values of axial and radial turbulence components, Reynolds shear stress, effective kinematic viscosity, skewness and flatness factors for axial and radial turbulence components, were measured with a two-dimensional laser Doppler velocimeter. The flow field in the bubbling jet was essentially classified into two regions with respect to the axial distance from the nozzle exit. One is located near the nozzle where the inertia force of injected gas plays an important role. The other is located far from the nozzle in which the buoyancy force of bubbles governs the flow. In this study the experimental results of liquid flow characteristics in the latter region were compared with those for a single-phase round jet. Turbulence production in the bubbling jet was found to mainly occur in the wake of bubbles and to be approximately two times as large as the turbulence production in the single-phase round jet. The turbulence structures for the two jets also were different from each other.

Turbulent flows in smooth-wall open channels with different slope

One-dimensional and two-dimensional Laser Doppler Velocimeter (LDV) were used respectively to measure velocity of smooth-wall open channel flows with channel bed slopes varying between 0.25% and 3%. Turbulent flows were all supercritical with Froude numbers varying from 1.5 to 3.5 and Reynolds number having a magnitude of 105. Using 1-D LDV the law of the wall and the law of the wake were examined and the von Karman constant K was verified to be 0.4 universally, while the integral constant A might change with distance from the side wall. The law of the wake exists clearly with a wake strength Π of about 0.3. Moreover, from the 2-D LDV measurements, the influence of channel slopes on the turbulent characteristics were fully investigated.

Effect of Secondary Flow on Wall Shear Stress and Velocity Profile in Right-Angle Branch.

The axial and transverse velocity components in a right-angle branch have been measured using a two-dimensional laser Doppler velocimeter. The radius Rs of curvature along the upstream corner of the side branch is one half of trunk diameter D0. The experiment has been carried out for two flow division ratios at the Reynolds number of 800. Consequently, it is clarified that the sinusoidal variation of wall shear stress along the proximal wall of the side branch is induced by the secondary helical flow transferred from the trunk. The wall shear stress estimated from the axial velocity profile near the tube wall at the common median plane agrees fairly well with the result measured by the electrochemical method, employed in the previous study. Therefore, the electrochemical method is one of the most suitable methods for the measurement of wall shear stress in the range of liquid laminar flow.

空気の底吹きによって撹拌される円筒容器内の水の平均流と乱れ

Cold model experiments based upon aqueous systems were carried out to study the mean velocity and turbulence intensity in a cylindrical bath. The axial and radial velocity components in the cylindrical bath agitated by air injection through a centered single-hole bottom nozzle were measured using a two-dimensional laser Doppler velocimeter. The spatial mean kinetic energy for the time-averaged component km, v and that for the turbulence component kt, v were obtained. It was found that km, v and kt, v depended on 0.60 and 0.72 powers of the injected gas flow rate, respectively. The energy supplied by the injected gas into the bath therefore was more consumed to maintain turbulent motions than to do the mean flow, i.e., the circulating flow as the gas flow rate increased. Measured values of the spatial mean velocity Vm, v=(2km, v)1/2 were satisfactorily approximated by an empirical correlation proposed so far, but the dependence of the present Vm, v values on the bath depth Hw and bath diameter D was different from this correlation. The spatial mean turbulence intensity Tuv=(kt, v/km, v)1/2 was above unity under the present experimental conditions.

Simultaneous measurement of liquid and bubble velocities in a cylindrical bath subject to centric bottom gas injection

A vertical bubbling jet was generated in a cylindrical bath by injecting air cA vertical bubbling jet was generated in a cylindrical bath by injecting air bubble and liquid in the vertical bubbling jet were measured simultaneously using an electro-resistivity probe and a two-dimensional laser Doppler velocimeter. The output signal of the LDV was processed on a personal computer at a sampling frequency of 2 kHz. Hold signals were eliminated. Discrimination of the bubble and liquid velocities was made by referring to the output signal of the electro-resistivity probe. The accuracy of the present velocity measurement of bubbles and liquid was found to be satisfactory from a comparison with results obtained using an image processing technique for high-speed video pictures, a laser void meter or a two-dimensional electro-resistivity probe.