Air-liquid two-phase flow is a common flow pattern in industrial area. The relative velocity between the gas phase and the liquid phase in air-liquid two-phase flow should be considered for the two-phase flow. Technically, it is more challenging to study the instability of bubbles than regular and steady gas phase. A novel method combining electromagnetic test and cross correlation has been carried out in order to determine the bubble velocity in the air-water flow in vertical upward pipe. Higher excitation frequencies have better receiving signals. The high-frequency (>1 MHz) electromagnetic testing system was designed and two groups of electromagnetic sensors were installed in two parallel sections of the vertical upward pipe, each of which included an excitation coil and a receiving coil. Experimental results were collected and by cross-correlation algorithm, the bubble velocity could be calculated by the time difference of the phase signals on two receiving coils. Three kinds of bubbles with different velocities were distinguished in the experiment. Relative errors of the experimental results were controlled within 10%. The technique which is simple, effective, non-contact and non-invasive provides a new approach for the measurement of bubble velocity in two-phase flow. This method can be improved afterwards for other industrial applications, e.g. bubble parameter measurement in metal liquid.

A fast and accurate gas concentration measurement method by fitting the main peak of the absorption spectrum harmonic signal is proposed for the first time to significantly improve the speed and accuracy of gas concentration measurement by laser wavelength modulation spectroscopy (WMS). In the proposed method, only the main peak of the absorption spectrum harmonic signal is scanned to obtain the peak value of the harmonic signal (WMS-2f/1f). This can greatly improve the scan speed due to the reduction of absorption spectrum scan range. Higher accuracy measurement can be achieved via fitting the main peak of the absorption spectrum harmonic signal (WMS-2f/1f) by a polynomial. The methods for choosing a suitable polynomial's degree and the influence of fitting data length on measurement result are discussed in this paper. The experimental results of carbon dioxide concentration measurement under different conditions validate the effectiveness of the proposed method.

The accurate measurement of particle size distribution and optical constant is of great importance for the prediction of radiative transfer in participating media. In the present work, an improved firework algorithm was applied to estimate the particle size distribution and optical constant simultaneously. At different angles, the time-resolved transmittance of a one-dimensional slab irradiated by laser of different wavelengths was measured. Afterward, the particle size distribution and optical constant were retrieved using the improved firework algorithm. According to the test cases for three different types of particle size distribution functions, it can be concluded that the particle size distribution and optical constant can be retrieved accurately by the proposed improved firework algorithm with assistant of corresponding physical property measurement technique.

Micro structure grating is a widely used electronic component. The geometric parameters of one-dimensional rectangular aluminum matrix grating are inversely estimated using stochastic particle swarm optimization (SPSO) algorithm. The theoretical overview of rigorous coupled wave analysis (RCWA) algorithm and particle swarm optimization algorithm is introduced, and RCWA algorithm is employed to solve the electromagnetic field problem within grating. The objective function is formulated based on the spectral reflectance obtained by the direct problem, and then the SPSO algorithm is used to optimize the objective function. The geometric parameters such as the grating period, ridge width and groove depth are retrieved simultaneously. The effects of population size and searching space on the inverse estimation results are also investigated. The retrieval results show that SPSO algorithm is effective and robust for estimating geometric parameters of grating and the population size is suggested as 30.

To investigate the radiation sampling of the translucent media and optimize the parameters of a plenoptic camera, a backward ray tracing model is established based on the paraxial approximation in this paper. Considering the integrating properties along the sampling path of the translucent media, several indices for evaluating the angular sampling are then proposed such as cone angle of a single pixel and sampling angel of object side. The effects of the positions of the pixels and micro lenses of the plenoptic camera on the radiation sampling and the effects of the optical parameters of the plenoptic camera on ray direction sampling performance are analyzed. The results indicate that, for the light field sampling on flame radiation, a smaller diameter of the micro lens is useful for improving the accuracy of radiation sampling in certain direction and decreasing the size of main lens aperture. Moreover, smaller focal length of main lens is advantageous for improving the sampling angle of object side.

Lamb wave gas sensor has broad industrial application prospects in gas sensing due to its advantages of high sensitivity, low loss and multi-mode characteristic. However, Lamb wave gas sensor is now still in fundamental academic research period. Experiments concerning the sensor are implemented by network analyzers, which means that gas properties cannot be determined automatically but by manual operation. This limits the applications of Lamb wave gas sensor. In this paper, a specified data acquisition instrument designed for Lamb wave gas sensor was developed. The direct digital synthesizer technology and an embedded system were introduced to obtain the information of the amplitude-frequency and phase-frequency of Lamb wave gas sensor. Maximum peaks of all Lamb wave modes were determined by a multi-peak fast search algorithm. To verify the effectiveness of the data acquisition instrument, frequency sweep experiment and algorithm verification experiment were carried out under different modes. The experimental results show that the data acquisition instrument can accurately acquire the frequency characteristics of Lamb wave gas sensor and the information of multiple peaks in a certain frequency range. Then, combining with the models of Lamb wave gas sensing, it can directly output parameter measurement results, and achieve automatic detection of gas parameters.

Research on calibration method of hot-wire probe in compressible fluid is carried out to meet usage requirements of various velocity measurements. The logarithmic calibration mathematical model is studied and it is discovered that there is a problem of matrix singularity in the process of solving calibration coefficients, which results in poor stability in solving linear equations with a small velocity perturbation. The mathematical model is improved by nondimensionalizing the parameters and adding a positive offset to build a dimensionless logarithmic calibration mathematical model. Calibration experiments are conducted with Mach number varying from 0.3 to 0.5 and ejection pressure varying from 150 kPa to 300 kPa. When using the original logarithmic calibration mathematical model, the results of data fitting show that correlation coefficient is 0.997 61 and deviation of fitting velocity in average is 1.378 m/s. Condition number of coefficient matrix in the process of solving calibration coefficients is 1.595×10⁸, which means that the matrix has a strong singularity. After introducing a small velocity perturbation (1 m/s), correlation coefficient becomes 0.379 74 and deviation of fitting velocity in average becomes 43.81 m/s, which shows instability in solving linear equations. When using the dimensionless logarithmic calibration mathematical model, the results of data fitting show that correlation coefficient is 0.998 95 and deviation of fitting velocity in average is 1.203 m/s. Condition number of coefficient matrix in the process of solving calibration coefficients is 3.655×10², which indicates a weak singularity, and the improved mathematical model is not affected by a small velocity perturbation due to selection of dimensionless method. Uncertainty of fluid velocity is analyzed and velocity uncertainty in average is 3.168 m/s, which is obviously greater than the deviation of fitting velocity in average. The experimental results verify the feasibility of application of the dimensionless logarithmic calibration mathematical model to hot-wire probe calibration in compressible fluid.

The temperature of water vapor and moist gas will drop greatly in the sonic nozzle, which leads to the condensation and will have a great effect on the measurements. Aimed at the phenomenon of condensation and self-oscillation of sonic nozzle, an experimental condensation apparatus was set up to observe the condensation of moist air in sonic nozzle, and the pressure distribution under different conditions was obtained. To validate and supplement the experimental data, a gas-liquid two-phase flow Eulerian model was established through numerical analysis of influence factors on condensation. The results show that the inlet pressure, humidity and temperature have a great influence on condensation phenomenon. With the increase of humidity and temperature, the location of condensation moves forward and the intensity also increases. With the increase of the inlet pressure, the location of condensation moves forward, while the intensity weakens. The frequency of self-oscillation is positively related to the humidity and temperature, and negatively related to the inlet pressure. The amplitude is positively related to the inlet pressure, humidity and temperature.

The instantaneous velocity vector fields of the vortex wave field in the channel flow were measured by 2DPIV. The identification of the spanwise vortices is carried out by using the criteria of Reynolds decomposition and swirling strength λ_ci criteria. The distribution characteristics of spanwise vortices are analyzed from scale properties, mechanical properties and motion properties of the counter-clockwise and clockwise vortices identified by swirling strength λ_ci criteria. The results show that the number of clockwise vortices is larger than that of the counter-clockwise vortices in the flow field. The swirling strength of the counter-clockwise vortices is in the form of parabolic shape in the range of normal direction 0.05-0.45, while the clockwise vortices show the overall downward trend. And the average diameter and the long axis of the ellipse of the counter-clockwise vortices increase slowly with the increase of the normal position, while the clockwise vortex tends to decrease. The largest value of the inclination angle of the long axis of the ellipse of the counter-clockwise spanwise vortices is 67.28°. The eccentricity of the equivalent ellipse of the clockwise vortices shows a decreasing trend, and the circularity is better. The contribution of the counter-clockwise spanwise vortices to the total mean 〈vω_z〉 has a maximum value of 61% at normal direction 0.15, and the contribution of the spanwise vortices to the total Reynolds stress is smaller; the population densities of counter-clockwise spanwise vortices in the 0-0.08 normal displacement range have a sharp upward trend, and achieve the maximum 0.36; The distribution of the clockwise spanwise vortices shows the inverted "U"-shape; The population density ratio of spanwise vortices with different directions of swirling to total spanwise vortices is greater than 0.3; the streamwise convective velocity of the spanwise vortices is less than that of the mean velocity of flow field in general, and the difference between them is larger in the central region of the channel. The normal convective velocity of the spanwise vortex increases from negative value to positive value with the increase of normal distance, and two phenomena of ejecting and sweeping occur on the two sides of the central mainstream.

The double coupled Duffing oscillator simulation system is put forward as a method for detecting the signal of gas-liquid two-phase flow patterns in small channel. The double coupled Duffing oscillator simulation and detection system is constructed, which is used to analyze the signal characteristics of flow patterns by the three key parameters:damping rate, coupling coefficient and frequency. The performance of the simulation system is tested by the typical chaotic signal of Lorenz and Rössler. When two-phase flow signal is detected, the eigenvalues are extracted including the instantaneous oscillator velocity and oscillator displacement, and based on the eigenvalues, the further study on flow pattern dynamic characteristics and flow pattern identification was done. The results show that this analysis method has better noise immunity and represents typical chaotic characteristics well through the verification of typical chaotic signals. The two extracted eigenvalues can reveal the mechanism of gas-liquid two-phase flow pattern transition process in small channel. Combining the instantaneous oscillation velocity of oscillator with the oscillator displacement can identify the nitrogen-water two-phase flow pattern in small channel accurately, which will contribute to the characteristic analysis and flow pattern identification of other multi-phase flow of different media.

Aimed at the problem of poor effects of cabin comfort and energy saving caused by constant air supply velocity of bridge air conditioning, in the paper, we built the cabin simulation model adopting the CFD method based on the research object, Boeing 737 passenger cabin. And the validity of the CFD cabin simulation model is verified by experiments. Based on this model, the effects of different air supply velocities on the temperature field, wind velocity field and NO_x concentration field in cabin are studied. Then the functional relationship between the air diffusion perfoumance index (ADPI), the drainage efficiency and the bridge load air conditioning air supply velocity is fitted separately. Meanwhile, the optimal air supply velocity of bridge load air conditioning is obtained through the merit function in response to ADPI and drainage efficiency, which could provide the basis for energy-saving control of bridge load air conditioning unit.

Particle-material impact is popular in the nature and industries. In this work, experimental measurement and numerical calculation were carried out to investigate the particle impinging jet effect on the behaviour of material (304 stainless steel). Herein, particle diameter, particle tracking trajectories, particle-wall collision point distribution were considered to study material loss and the phase change of material structure. In the experimental work, the measurements were carried out for material mass loss, material element X-ray diffractometry (XRD) analysis, surface micro-structure scanning electron microscopy (SEM) observation and so on. In addition, the behaviour of particle impinging jet impact on wall material was studied by numerical simulations. Particularly, flow fields, particle trajectories and wall material loss were obtained. The results show that particle collision point distribution is quite different from their tracking trajectories under particle impinging jet impact, which causes the wear zones on sample surface different from each other obviously. It is concluded that particle-wall impact will not only lead to material loss but also cause the phase change of material structure.

Based on the capacitively coupled contactless impedance detection sensor with radial structure, a new method for the flow pattern identification of ductule gas-liquid two-phase flow is proposed by using wavelet packet analysis and K-means algorithm. Firstly, the real part and the imaginary part of the electrical impedance signal, which can reflect the information of the measured fluid, were obtained by using the developed capacitively coupled contactless impedance detection sensor. Then, the real part of signals and the imaginary part of signals were decomposed into 4 sub-bands by wavelet packet decomposition technique, and energy distributions of different frequency ranges were calculated. By combining the mean and variance of the real part and the imaginary part of the signal, the feature vectors was constructed. Finally, using K-means algorithms to do pattern classification, the flow pattern identification model was built. Experiments were carried out in small glass pipe with different inner diameter of 3.5 mm and 5.5 mm. The results show that the developed capacitively coupled contactless impedance detection sensor, which can obtain the information of the fluid flow, is successful, the proposed flow pattern identification method is effective, and the accuracy of flow pattern identification can be above 88%.

Flow pattern is one of the most important parameters of gas-liquid two-phase flow and has great influence on the flow of gas-liquid two-phase flow. In this paper, gas-liquid two-phase flow patterns in a horizontal pipe are analyzed with capacitively coupled electrical resistance tomography (CCERT) system. Principal component analysis (PCA) method is used to extract the principal components of the electrical conductivity information under different flow patterns, and thus the redundancy of signal between different electrode pairs can be eliminated. The three flow patterns are recognized by using K-means clustering algorithm. The experimental results show that this method has high accuracy. The static identification accuracy for bubble flow, stratified flow and annular flow is 97%, 96% and 99%, respectively, and the dynamic identification accuracy is 92%, 90% and 87%, respectively.

The present paper focused on huge wave's feature parameters (e.g. wave shape, wave amplitude, wave length, wave frequency, etc.) and kinetic properties in gas-liquid two-phase churn flow in vertical pipe under different working conditions and conducted experimental study. The effects of flow parameters on feature parameters and kinetic properties of huge wave were investigated. The results indicate that the competition between gravity and shear force under different flow conditions affects the wave behavior significantly. The huge wave firstly moves downward due to the gravity till it reaches a critical amplitude for the flow reversal, which demonstrates that the flooding of the film is a characteristic of the churn flow throughout the regime and the reason makes churn flow highly disturbed. The shape of huge wave can be described by a normal-distribution function, and the wave amplitude of huge wave is larger than disturbance wave in annular flow. The amplitude and wavelength of huge wave decrease with the increase in gas flow rate but increase with the increasing liquid mass flow rate, which is similar to annular flow. At lower gas superficial velocities, the critical amplitude asymptotically approaches a constant value at greater liquid mass flow rates. The wave frequency is found to be proportional to the gas and liquid velocity.

Wire-driven parallel robot (WDPR) provides a new support method for wind tunnel tests due to its effective simulation of the aircraft model's pose, and has a great application potential. This paper gives details of an investigation of stability and aerodynamic interference referring to the application of WDPR in hypersonic wind tunnel. The parallel support system with 8 wires was constructed, and the 10° cone model was selected as the test model whose position and pose can be adjusted through the wire length. The support system's stability under the action of aerodynamic force is simulated, and the wire diameter is optimized. Based on the constructed three-dimensional model, under the condition of Mach numuber is 7.8, the aerodynamic coefficient of the model suspended with WDPR at different angles of attack is calculated in CFD. The comparison of the simulation result with the result of the same model without wires and the experimental data in reference indicates that, at small angle of attack, the relative error of the aerodynamic interference caused by the wires is small, and the interference increases with the increase of angle of attack. In addition, modal characteristics of the WDPR and the crescent shape support system are analyzed and the natural frequencies of the two support systems are compared. The comparison result shows that the natural frequency and the stiffness of the WDPR are higher than those of the crescent shape support system. The academic research work of this paper provides reference to the application of wire-driven parallel support technology in hypersonic wind tunnel.

In order to explore the feasibility of using injection technology to reduce the start Mach number of hypersonic inlet, the flow field of the two-dimensional hypersonic inlet was calculated by numerical simulation. The effect of injection on the hypersonic inlet was analyzed by comparing the flow field structure, mass-captured coefficient and total pressure recovery coefficient under different working conditions, and the influence of jet velocity, pressure and angle of inclination on starting performance of the inlet was also studied. The analysis results show that the change of original interference form of the shock wave and inlet boundary-layer is the main reason for the reduction of the start Mach number of inlet. The study also shows that increasing jet velocity is conducive to improving the control effect, but increasing jet velocity continuously would result in an increase in the back pressure of the isolation section. This phenomenon is related to the jet pressure, and reducing the jet pressure could expand the effective jet velocity range to start the inlet. At different jet angles of inclination, the above rules are consistent. The simulation results reveal the systematic rule of changes of the inlet starting ability with injection parameters, which can be used to guide engineering design and optimization.

Insects are often disturbed by lateral wind when flying in nature. Thus understanding the variation of aerodynamic force of the flapping wing under the lateral wind is significant to the research on flying mechanism of insects. The fluid fields around the flapping wing under the lateral winds were simulated using the method of computational fluid dynamic (CFD), which were then compared with the hovering situation (with no lateral wind), and the effects of the dynamic characteristics of flapping wing was investigated from two aspects of the strength and direction of the lateral wind. The results indicate that the lateral wind has two contributions to the aerodynamics of the flapping wing:one is "changing-relative-velocity" effect, and the other is "changing-LEV-axial-velocity" effect. Lateral winds in different directions (from wing-tip to wing-root or from wing-root to wing-tip) have obviously different effect on the aerodynamics; however, under lateral winds with different intensities but the same direction, the variations of aerodynamic force are similar, and there are only numerical differences.

Based on the sparsity or compressibility of the signal, compressed sensing (CS) theory can achieve high-accuracy reconstruction of the signal by sampling a small amount of data. In this paper, CS theory was used for the image reconstruction of electrical capacitance tomography (ECT). First, using the fast Fourier transformation (FFT) basis, the gray signals of original images can be transformed into the sparse signals. Then, the random observation matrix of ECT system was designed by rearranging the rows of the sensitivity matrix of ECT in a random order. Finally, interior point method, gradient projection for sparse reconstruction (GPSR) algorithm and greedy algorithm which are the three commonly used reconstruction algorithms of CS were used for ECT image reconstruction and the comparison was made with linear back projection algorithm and Landweber iterative algorithm. Simulation results indicate that reconstructed images with higher accuracy can be obtained using the ECT image reconstruction algorithm based on CS theory. Meanwhile, the advantages and disadvantages of the three CS image reconstruction algorithms were analyzed. The advice of selecting which type of image reconstruction algorithm was given.

Tomographic reconstruction is the core step of tomographic particle image velocimetry (Tomo-PIV) technology to realize the reconstruction of three-dimensional position and intensity information of particles (3D particle field). Compared to the Tomo-PIV based on the multiple conventional cameras, a single focused light field camera can simultaneously record the direction and position information of the scattered light produced by tracer particles. In this paper, a tomographic reconstruction technique based on a single focused light field camera is proposed to reconstruct the three-dimensional position and intensity information of the particles. To verify the feasibility and accuracy of the proposed method, the light field imaging model of the tracer particles is established by the geometrical optics. The imaging of the particle in the focused light field camera is simulated by ray tracing technique. The light field imaging differences of the tracer particles in different depth positions are compared. The tomographic reconstruction based on single focused light field camera is mathematically modeled. A multiplicative algebraic reconstruction technique (MART) is used to reconstruct the 3D particle field by retrieving the simulated light field image. Reconstruction quality of multiple particles is characterized by the normalized correlation coefficient. The reconstruction results show that the position accuracy of a single particle in the Z axis direction is ±0.35 mm, which validates the feasibility of the 3D particle field reconstruction method based on focused light field imaging theory.

Magnetic induction tomography (MIT) has promising applications in biomedical examination and diagnosis. In order to acquire biological tissue characteristic information, a magnetic induction tomography system with multi-excitation frequency mode is designed. The system operates under voltage excitation and voltage measurement mode, and it can select three excitation frequency modes of single frequency, sweep frequency and mixed frequency from 100 kHz to 4 MHz. The system includes excitation source module, sensor coil array, data acquisition and conditioning module, and digital demodulation module, and it uses field-programmable gate array(FPGA) to control multiplexer, programmable amplifier, analog-digital converter and so on. The simulation experiments show that the test data acquired by the system with multi-excitation frequency mode has good consistency, its signal to noise ratio is above 46 dB, and voltage difference acquired at different excitation frequencies can be used to realize the image reconstruction of measured object conductivity distribution.

To ensure that the electrical capacitance tomography (ECT) system meets the requirements of multiphase flow parameter measurement in aerospace field, an ECT system based on the CPCI industrial bus standard is designed. A high-performance field-programmable gate array (FPGA) chip is used as the main control chip to realize the integrated design of signal excitation module, multiplex switch module, data processing module, data demodulation and transmission module. The signal is preprocessed with signal filtering, amplification and phase-sensitive demodulation, and then the demodulated capacitance data is transferred to the host computer through the CPCI industrial bus interface. Finally, the image is reconstructed in the host computer. The experimental results of ECT system show that the image acquisition speed can reach 1 785 frames per second at 1 MHz excitation signal with 8 electrode sensor and 10-cycle test signal for demodulation. The system can operate under a SNR of above 60 dB, while the imaging results have good spatial resolution.

This paper focuses on the lack of the sensitivity coefficient information and the low utilization of the measurement voltage in FCM clustering algorithm in electrical impedance tomography (EIT) technology, and proposes a new imaging algorithm. In the new algorithm, sensitivity matrix information is introduced to correct the voltage of each subdivision unit. And at the same time, we propose to handle the measurement voltage according to its weight coefficient in the total voltage value, and this method can be applied to all EIT classical inversion algorithms. Both the theoretical analysis and numerical simulation results demonstrate that the new algorithm is more accurate in locating two-phase flow patterns than the existing FCM clustering algorithm, the spatial resolution deviation of reconstructed image has been reduced by 5% to 15%, and the correlation coefficient has been increased by 5% to 20%.

The traditional method to measure the phase holdup of three-phase flow is only for some single phase. In order to solve this problem, models to predict the phase holdup were established and a non-invasive method was proposed for the measurement of each phase holdup in three-phase flow based on capacitively coupled electrical resistance tomography (CCERT) and acoustic emission. Firstly, the phase holdup measurement model of gas-water two-phase flow was established by using partial least squares regression method in the static case. Meanwhile, the dynamic experiments that compare the method with the differential pressure method to verify the validity of the modelwere carried out on bubbling bed to fulfill the non-invasive measurement of the two-phase phase holdup. On this basis, the measurement model of gas holdup was established through processing the sound signals collected by acoustic emission system. Then, the gas holdupis measured in three-phase system by using the model and is combined with the non-conductive phase holdup measured by CCERT.Thus each phase holdup in three-phase flow is obtained in a non-invasive way.