Laser Doppler Velocimeter Research Articles

Strength Characteristics of a Heat-Resistant Metal-Matrix Composite Inconel 625–5%NiTi–TiB2 Alloy Fabricated by Direct Laser Deposition under Shock-Wave Loading

The Hugoniot elastic limit and spall strength were measured for a heat-resistant metal-matrix composite Inconel 625–5%NiTi–TiB2 alloy additive manufactured (AM) by direct laser deposition. The strength characteristics of the alloy were obtained from the analysis of the complete wave profiles recorded with a VISAR laser Doppler velocimeter during shock-wave loading of the samples. The samples were loaded using a PP50 pneumatic gun or ad hoc explosive devices along and across the material deposition direction in order to determine the strength anisotropy of the AM alloy under study. The maximum shock compression pressure was ~7 GPa, and the strain rate under tension before spalling varied in the range of 105–106 s–1. Kinetic dependencies of elastic/plastic transition and critical fracture stresses vs. loading conditions were plotted. It was shown that the Hugoniot elastic limit of the alloy under study decreases as the shock wave travels into the sample, while the spall strength increases as the material’s strain rate increases at the moment of spall fracture. A comparison of the strength characteristics of the Inconel 625–NiTi–TiB2 composite alloy with the original Inconel 625 alloy has shown that an addition of 5% of powder based on NiTi-TiB2 leads to a decrease in its elastic limit and critical fracture stresses upon spalling by more than 10%. The alloy under study demonstrates anisotropy of strength properties relative to the material deposition direction.

Influence of Spherical Aberration on the SNR in Single-Beam Laser Doppler Velocimeter for Remote Measurement

Influence of Spherical Aberration on the SNR in Single-Beam Laser Doppler Velocimeter for Remote Measurement

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

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

Research and Flight Test on Airborne Laser Doppler Velocimeter for Unmanned Aerial Vehicles

Research and Flight Test on Airborne Laser Doppler Velocimeter for Unmanned Aerial Vehicles

Online Calibration Method for Pitch-Independent Laser Doppler Velocimeter Based on Improved Integrated Navigation Model

Online Calibration Method for Pitch-Independent Laser Doppler Velocimeter Based on Improved Integrated Navigation Model

Review of laser Doppler velocimeter technology for navigation and localization

Review of laser Doppler velocimeter technology for navigation and localization

Measurement range expansion of single-beam Laser Doppler velocimeter based on a focusing transmitter

The own velocity of a ground vehicle with high precision provided by the single-beam Laser Doppler velocimeters (LDV) promotes the localization accuracy of vehicles efficiently. However, the present LDVs are unable to be mounted on air vehicles for the velocity measurement of vehicles so far because of the restricted working distance. In order to expand the measuring range, a mid-distance LDV is designed in this paper. An optical focusing transmitter that transforms the Gaussian beam waist to the pre-set distance with an appropriate radius is constructed through theoretical simulations. Further experiments show that the mid-distance velocimeter can measure the velocity of moving objects within 50 m and the signal quality of measurement holds at a high level. This improved single-beam LDV with a longer working distance has great potential in acquiring the high-precision velocity of low-altitude air vehicles and many other remote velocity measurement applications.

Flow and heat transfer studies of multijet impingement cooling for different configurations: A review

AbstractIncreasing the gas turbine engine's turbine intake temperature has long been a potential strategy for increasing the specific work output of the engine. However, the melting temperature of the turbine blades and vane material limits the maximum intake temperature. As a result, internal and external cooling techniques are commonly used to maintain the vane material in a safe condition. This study provided an overview of internal impingement cooling to highlight the significance of geometrical variations, such as flat plate, curve plate, and actual vanes. It was observed that flat and curved plate impingement heat transfer studies were reported extensively, whereas limited studies were found on the conjugate effects on airfoil surfaces. The importance of conjugate heat transfer studies and their impact has recently been described in the literature. In most of the literature, a wide range of instruments, such as Laser Doppler Velocimeter, Particle Image Velocimeter, liquid crystal sheets, and so forth, were used for experimental investigations. According to most studies, the local value of internal surface temperature and heat transfer coefficient are vital factors of local flow behavior. Jet‐to‐jet spacing, jet‐to‐plate spacing, jet hole diameter, and jet Reynolds numbers played a crucial role in both numerical and experimental analyses. Different geometric variations strongly influence flow behavior. Therefore, the usual method for determining interior temperature distributions and heat transfer coefficients by considering generalized geometries like the flat and curved plate may not produce accurate conjugate solutions. Most of the computational studies on the flat and curved plate indicate the usage of κ−ω shear stress transport and κ–ε realizable model to predict the heat transfer coefficient.

A Fast Robust In-Motion Alignment Method for Laser Doppler Velocimeter-Aided Strapdown Inertial Navigation System

With ultra-high velocity measurement accuracy, laser Doppler velocimeter (LDV) is promising to replace the odometer to provide vehicle velocity information in the process of land integrated navigation. This paper investigates the fast in-motion initial alignment for LDV-aided strapdown inertial navigation system (SINS). Aiming at the problem that the installation misalignment angles and scale factor error of LDV will reduce the alignment accuracy and the alignment speed, a Robust Double Gain Square-Root Unscented Quaternion Estimator (RDGSR-USQUE) method with good effect at large misalignment angle is proposed. In RDGSR-USQUE, the influence of unknown parameter error is considered in the construction of process model and measurement model and a double gain structure is proposed to improve the convergence speed based on the usually neglected posterior measurement residual information. RDGSR-USQUE method improves the defects of the traditional Unscented Quaternion Estimator (USQUE) method, such as poor noise resistance, slow convergence speed under large misalignment angle and easy to lead to non-positive definite covariance matrix. This will help to estimate and compensate unknown parameter errors while estimating attitude, so as to improve the accuracy of process model and measurement model, and finally improve the accuracy of attitude estimation. The performance of the proposed scheme is verified by vehicle field test. The results show that the proposed method has higher alignment accuracy, faster convergence speed and stronger robustness than three other compared methods, and the estimated installation misalignment angle and scale factor of LDV are satisfactory in general cases.

Effect of Heat Treatment and Test Temperature on the Strength Properties of Cast Heat-Resistant Nickel Base Inconel 718 Superalloy under Shock-Wave Loading

The influence of the heat treatment regime and the initial temperature on the strength characteristics of the cast heat-resistant superalloy Inconel 718 under shock loading has been studied. For samples of four types: in the as-received state, in the as-received state with subsequent heat treatment, in the as-received state after annealing and in the as-received state after annealing and subsequent heat treatment, measurements of the Hugoniot elastic limit and spall strength were carried out, based on the registration and subsequent analysis of the wave profiles in the samples under study. Shock-wave load pulses with an amplitude of ~6.5 GPa were generated using a light-gas gun. Measurement of the evolution of the shock-wave during loading—registration of the velocity profiles of the free surface of all types of samples of different thicknesses was carried out using a laser Doppler velocimeter VISAR. The measurements were carried out at a temperature of 20 °C and 650 °C. The analysis of the results revealed a noticeable effect of heat treatment and temperature on the characteristics of the elastic-plastic transition and the resistance to spalling of the Inconel 718 superalloy.

Laser Doppler velocimetry for three-dimensional distribution measurement of the velocity component by combining two-dimensional spatial encoding and non-mechanical scanning.

We present a differential laser Doppler velocimeter (LDV) for measuring the velocity distribution in a three-dimensional (3D) space. Our conventional research so far has proposed some methods for measuring two-dimensional (2D) distribution measurement. One of the proposed methods was spatial encoding of measurement points arranged on a 2D plane. Besides, we also have proposed laser Doppler cross-sectional velocity distribution measurement based on a non-mechanical scanning method. We propose a 3D method by combining 2D spatial encoding and non-mechanical scanning, in which the measurement points distributed on a 2D plane are spatially encoded with different bias frequencies, and these points are scanned non-mechanically in another direction by changing the wavelength. As a feasibility study of the proposed method, experiments were conducted using a 4×4 channel optical setup and were performed at five wavelengths over 1537-1553 nm. The experimental results indicate that the proposed method could successfully measure the 3D distribution of the velocity component. The spectral peaks of the beat signals for 68 measurement points for the rotational speed of the target of 2.0s-1 and those for 67 measurement points for the rotational speed of -2.0s-1 out of 80 measurement points were successfully observed within the measurement error of 2.8%-4.8%.

Online calibration technology for a one-dimensional laser Doppler velocimeter based on a strapdown inertial navigation system.

In the integrated navigation system, which consists of a laser Doppler velocimeter (LDV) and strapdown inertial navigation system, it is necessary to calibrate the LDV. We propose an online calibration method for a LDV based on the strapdown inertial navigation system. This system uses highly accurate output information in the early stage of the inertial navigation system to carry out coarse calibration for the velocimeter and then employs a Kalman filter to correct the results of coarse calibration to achieve high precision calibration for the velocimeter. Experimental results show that the relative distance error of dead reckoning is less than 0.02%, indicating that the proposed online calibration method can achieve high-precision calibration for the velocimeter.

Research on the characteristics of fluid flow and heat transfer of Al2O3-water nanofluid in an L-shaped chaotic channel

PurposeThis paper aims to investigate the effects of different volume fractions of Al2O3-water nanofluid on flow and heat transfer under chaotic convection conditions in an L-shaped channel, comparing the difference of numerical simulation results between single-phase and Eulerian–Lagrangian models.Design/methodology/approachThe correctness and accuracy of the two calculation models were verified by comparing with the experimental values in literature. An experimental model of the L-shaped channel was processed, and the laser Doppler velocimeter was used to measure the velocities of special positions in the channel. The simulated values were compared with the experimental results, and the correctness and accuracy of the simulation method were verified.FindingsThe calculated results using the two models are basically consistent. Under the condition of Reynolds number is 500, when the volume fractions of nanofluid range from 1% to 4%, the heat transfer coefficients simulated by single-phase model are 1.49%–25.80% higher than that of pure water, and simulated by Eulerian–Lagrangian model are 3.19%–27.48% higher than that of pure water. Meanwhile, the friction coefficients are barely affected. Besides, there are obvious secondary flow caused by lateral oscillations on the cross sections, and the appearance of secondary flow makes the temperature distributions uniform on the cross section and takes more heat away, thus the heat transfer performance is enhanced.Originality/valueThe originality of this work is to reveal the differences between single-phase and two-phase numerical simulations under different flow states. The combination of chaotic convection and nanofluid indicates the direction for further improving the heat transfer threshold.

Effect of shell on performance of heat exchanger with trefoil-hole baffle

The periodic whole cross-section model and the periodic unit duct model were established, and the differences between two models were discussed. The effects of shell wall and baffle edges on the shell side performance of the heat exchanger with trefoil-hole baffle were investigated using both models. Thermodynamics in the shell side and heat transfer coefficient of each tube in different position were discussed. It is found that disparities between the results of the two numerical models decreases with the increase of the inner shell diameter. When the shell diameter is 0.8 m, the disparity is less than 10%, which means that the effects of the shell wall and the edges of baffles become weaker. When the shell diameter is less than 0.8 m, modified correlations for the periodic unit duct model are introduced to quantitatively reveal the effects of shell wall and baffle edges on thermodynamics with the variations of the shell diameter and baffle spacing. The fluid-flow velocities at specific locations on the shell side were measured using a laser doppler velocimeter system. The accuracy of the numerical simulation method was verified by the experimental results.

Height measurement method based on one-dimensional laser Doppler velocimeter and integrated navigation system of single-axis rotation inertial navigation system (invited)

Height measurement method based on one-dimensional laser Doppler velocimeter and integrated navigation system of single-axis rotation inertial navigation system (invited)

In-motion initial alignment method for a laser Doppler velocimeter-aided strapdown inertial navigation system based on an adaptive unscented quaternion H-infinite filter

With its advantages of high velocity measurement accuracy and fast dynamic response, the laser Doppler velocimeter (LDVs) is expected to replace the odometer (OD) in combination with a strapdown inertial navigation system (SINS) to give a higher-precision integrated navigation system. Since a LDV has higher velocity measurement accuracy and data update frequency than an OD and Doppler velocity log, a LDV is used for the first time in this paper to aid a SINS in in-motion alignment. Considering that some approximation is used in the alignment model, the uncertainty noise of the sensors during the motion process and the unknown noise parameters during the filter process, an adaptive unscented quaternion H-infinite estimator (AUSQUHE) is proposed. The proposed AUSQUHE method has high robustness since it combines the advantages of an unscented quaternion estimator and H-infinite filter. The adaptive threshold of the H-infinite filter and the adaptive measurement noise covariance matrix are introduced to make the filter adapt to the changing environment and accelerate the convergence of errors. The performance of the proposed method is verified by a vehicle field test with a normal LDV signal and a vehicle test with the LDV signal disturbed by noise. The results show that the proposed method has higher alignment accuracy, faster convergence speed and stronger robustness than the four other compared methods.

Fluid Flow and Heat Transfer Characteristics Investigation in the Shell Side of the Branch Baffle Heat Exchanger

The branch baffle heat exchanger, being an improved shell-and-tube heat exchanger, for which the flow manner of the shell-side fluid is a mixed flow of oblique flow and local jet. The computational fluid dynamics (CFD) method has been implemented to investigate the fluid pattern and heat transfer performance. The accuracy of the modeling approach has been confirmed by an experimental approach using a Laser Doppler Velocimeter system. Flow field, temperature field, and pressure field are displayed to study the physics behavior of fluid flow and thermal transport. Heat transfer coefficient, pressure drop, and efficiency evaluation criteria are analyzed. In contrast with the shell-and-tube heat exchanger with segmental baffles and shutter baffles, the pressure loss in the proposed heat exchanger with branch baffles has been dramatically improved, accompanied by a slight decrease in heat transfer coefficient under the same volume flow rate. The efficiency evaluation criteria of the heat exchanger with branch baffles are 28%-31%,13.2%-14.1% higher than those with segmental baffles and shutter baffles, respectively. Further analysis in accordance with the field synergy principle illustrates that the velocity and pressure gradients of the heat exchanger with branch baffle have finer field coordination. The current heat exchanger structure provides a reference for the future optimization design to reach energy saving and emission reduction.

Changes in the Environment of Scientific Instruments Development: Investigation of the Development of Domestic Laser Doppler Velocimeter Since 1970s

Currently, the R & D level of scientific instruments in China lags behind advanced countries. The perspective of the history of scientific instrument enables us to investigate the reasons for this situation. This paper presents a study on laser Doppler velocimeter. Based on various historical records, we obtain that the environment of domestic research and development of the instrument has been decreasing since the 1970s; the lack of financial support and other reasons jointly contributed to this change.

Position observation-based calibration method for an LDV/SINS integrated navigation system.

With the advantages of high velocity measurement accuracy and fast dynamic response, the laser Doppler velocimeter (LDV) is expected to replace the odometer to be combined with a strapdown inertial navigation system (SINS) to form a higher precision integrated navigation system. However, LDV scale factor error and misalignment angles between LDV and inertial measurement unit will affect the accuracy of navigation. Considering that not all global navigation satellite system (GNSS) receivers can directly provide velocity information and current mainstream calibration methods are sensitive to the measurement noise and outliers of velocity and position information, a robust calibration method aided by GNSS is proposed in this paper, which is based on position observation. Different from current popular calibration methods, the attitude information of the GNSS/SINS integrated navigation system obtained by an adaptive Kalman filter is used to construct the observation vector together with LDV velocity outputs and GNSS position outputs in this method. The LDV scale factor error and the misalignment angle are determined by the ratio of two observation vector modulus and the Davenport's q-method method, respectively. The accuracy and robustness of the calibration method are verified by one vehicle test with normal GNSS signals and one vehicle test with GNSS signals with outliers. And the horizontal position error of dead reckoning of the calibrated LDV/SINS integrated system are less than 0.0314% and 0.1033% of the mileage, respectively.

Quality Assessment of Nonwoven Air Filters Used in Fertilizer Factories.(Dept.T)

Two experimental techniques used to evaluate fabric filtration efficiency. Gas filtration apparatus and another apparatus used optical techniques based on laser doppler velocimeter are constructed. The filtration efficiency have been measured for a wide varity of non-woven filter fabrics. Excellent agreement has been found between the two techniques. The necessary performance characteristics of air filter fabrics could be selected and arranged carefully in decreasing order of importance. In this paper several methods are used to assess the quality of some nonwoven fabrics as air filters similar to those filters used in the fertilizer factory. Complex evaluation of quality methods have been applied to determine the best filter which can be used in fertilizer factories. Quality assessment methods such as arithmetic mean, geometric mean, harmonic mean, exponential mean, polygon area, guality number and generalized desirability function can be used for assessing the quality ranking of air filter fabrics accurately.