Dual-Measurement-Method and its extension for accurately resolving the secondary flows in LDA (Laser Doppler Anemometry) applications

In LDA (Laser Doppler Anemometry) applications in flow measurements, it is always inevitable that small deviations between the LDA and the flow coordinate systems occur. This will lead to a velocity shift in each measured velocity component. In the cases where the secondary flows are of many orders smaller than the main flow, the velocity shift embedded in the measurements can be as large as the actual secondary flow itself. The secondary flow structure could then be totally distorted through the measurements.In order to accurately resolve the secondary flow structures across the main flow, a method known as the Dual-Measurement-Method (DMM) has been developed and shown to be very efficient. The method is based on the “reflection design” of the LDA layout and aims to find out the velocity shift existing in the measurement results. For situations where the “reflection design” of the LDA layout is restricted, the Dual-Measurement-Method has been extended in a way that three arbitrary measurements have to be carried out. The calculation processes in finding out the velocity shift from three such measurements have been outlined and validated. An example of use indicates that just in that case the secondary flows have to be resolved as accurately as possible.     

μPIV measurement of grease velocity profiles in channels with two different types of flow restrictions

Grease is commonly used to lubricate various machine components such as rolling bearings and seals. In this paper the flow of lubricating grease passing restrictions is described. Such flow occurs in rolling bearings during relubrication events where the grease is flowing in the transverse (axial) direction through the bearing and is hindered by guide rings, flanges etc, as well as in seals where transverse flow occurs, for example during so-called breathing caused by temperature fluctuations in the bearing. This study uses a 2D flow model geometry consisting of a wide channel with rectangular cross-section and two different types of restrictions to measure the grease velocity vector field, using the method of Micro Particle Image Velocimetry. In the case of a single restriction, the horizontal distance required for the velocity profile to fully develop is approximately the same as the height of the channel. In the corner before and after the restriction, the velocities are very low and part of the grease is stationary. For the channel with two flow restrictions, this effect is even more pronounced in the “pocket” between the restrictions. Clearly, a large part of the grease is not moving. This condition particularly applies to the cases with a low-pressure drop and where high consistency grease is used. In practice this means that grease is not replaced in such “corners” and that some aged/contaminated grease will remain in seal pockets.     

Combination of the optical analyzer technique and multiply photon doppler velocimetry to measure the sound velocities in shock-compressed metals

It is proposed to combine the optical analyzer technique (OAT) and multiply photon Doppler velocimetry (MPDV) in every explosive experiment in order to overcome the reported discrepancies in the sound velocities measured in shock-compressed metals using different techniques. Such a combination is demonstrated to be efficient in explosive experiments with stepped samples of 12Kh18N10Т austenitic stainless steel and high-purity Mg95 magnesium under their shock-wave loading in ranges of 60–120 and 20–30 GPa, respectively. The OAT ensures classical recording of the longitudinal and bulk sound velocities. Depending on the loading intensity, the MPDV technique recorded temporal changes in the velocity of the “sample–indicator” interface or temporal changes in the shock-front velocity in the indicator. These data were used to monitor the parameters of the shock-compressed sample and to determine the instant when the first characteristic of the rarefaction-wave fan overtakes the shock-wave front in the indicator. Within the range of relatively low loads where the indicating fluid remains transparent and acts as a window material, the MPDV registers temporal variations in the velocity of the “sample–indicator material” interface. The OAT ensures reliable registration in the range of high-intensity loads, while the MPDV ensures time-resolved registration of the steady-shock-wave front velocity in the indicator up to the instant of its overtaking by a rarefaction wave. Both techniques are observed to work well in the intermediate range of loads. Combining these techniques enhanced the reliability of the obtained consistent data on the sound velocities in shock-compressed structural materials and also allowed a decreased number of explosive experiments with samples of toxic materials.     

Use of gas bubbles for ultrasound Doppler flow velocity profile measurement

Ultrasonic velocimetry based on the Doppler shift effect accurately provides quasi-instantaneous flow fields for fluids with a sufficiently high acoustic scattering level. However, ultrasonic velocity instruments are known to perform poorly in clear water with low acoustic scattering level, which are frequent conditions in laboratory applications. This work confirms a technique to solve the problem by seeding the flow with micro hydrogen bubbles, generated by means of electrolysis.This paper investigates the influence of gas bubbles density on the quality of the ultrasound Doppler based velocity profiles in an open channel flow. The bubbles are generated by electrolysis of water using different magnitudes of electrical current. The estimation of the number of bubbles in the measurement volume confirms that the bubble diameter is similar to that of the wire used for electrolysis. This enables to determine the minimum density of gas bubbles needed to obtain a reasonably good echo and therefore an accurate velocity profile.     

The characterization of internal combustion engine bores

In recent years the production of cylinder bores has received much attention by manufacturers. The finishing processes used include boring, honing and plateau honing. A feature of the surface changes which occur during running is related to the wearing action caused by the piston ring on the bore. This action very rapidly causes a “transitional topography” where the surface generated exhibits the influence of the piston ring which modifies the machined surface. The transitional surface although modified still retains significant characteristics of its initially machined state.Plateau honing is a finishing process which attempts to impart a transitional topography which may be considered partially “run in” and hence provides a condition which is part way towards the fully run-in state.In this paper the methods of producing engine bores are considered, the surface profiles obtained by these methods are examined and attempts to characterize their surface topography are made. The effects of wear are studied and from a consideration of the surface topography of the initial machining process a characterization technique is proposed.It is shown in the paper that the assessment of R_a, or preferably R_q, is sufficient to monitor final machining and functional wear on a cylinder bore provided that the general shape of the initial surface is known.     

A new velocity estimation method using spectral identification of noise

In all measurement techniques one seeks accuracy and precision. In ultrasonic Doppler velocimetry, those qualities strongly depend on signal to noise ratio of the Doppler signal and on the performance of the velocity estimator. The most widely used estimation method in ultrasonic coherent Doppler velocimetry is the pulse pair method. Its success is due to the computation efficiency of the algorithm combined to an unbiased estimator. Unfortunately, for a wide range of experimental fluid flows, the pulse pair estimation is less efficient, especially for clear water or concentrated mud where the signal to noise ratio can be very low, or for highly turbulent flows where the Doppler signal has a broad spectrum. Our approach is based on the treatment of the Doppler spectral information. It uses a simple parametric identification inspired by theoretical models and experimental observations. It acts through noise subtraction and subsequent cutting. Thus, we have developed a fast velocity estimation algorithm superior to the pulse pair one in terms of accuracy. The robustness of the method was evaluated by adding different levels of white Gaussian noise to an experimental Doppler signal. The results demonstrate an increase of noise immunity up to one decade compared to the pulse pair method.     

Flume experiments for assessing the dye-tracing technique in rill flows

Flow velocity controls hillslope soil erosion and is a key hydrodynamic variable involved in sediment transport and deposition processes. The dye-tracer technique is one of the most applied methods for measuring velocity of shallow interrill and rill flow. The technique is based on the injection of a tracer in a specific point and the measurement of its speed to travel the known distance from the injection point to a given channel section. The dye-tracer technique requires that the measured surface flow velocity has to be corrected to obtain the mean flow velocity using a correction factor which is generally empirically deduced. The technique has two sources of uncertainties: i) the method applied for measuring the travel time of the dye-tracer and ii) the estimate of the correction factor, which is the ratio between the mean flow velocity and the surface velocity, in different flow conditions. In this paper the results of a wide experimental investigation, carried out using a fixed bed small flume simulating a rill channel, are presented. At first, the comparison between a chronometer-based (CB) and video-based (VB) technique was carried out for establishing the influence of the travel time measuring technique. For each experimental run, which was characterized by a sample of 20 measurements carried out with the same values of slope and discharge, the developed analysis showed that the empirical frequency distribution of the ratio between the single measurement and the sample mean (i.e., the average of 20 measurements) is more uniform for the VB technique than for the CB one. In any case, this sample mean was representative of surface flow velocity for both the CB and the VB technique. Furthermore, the mean value obtained by the CB measurements lightly underestimated (−1.7%) the corresponding mean obtained by the VB technique. Finally, the effects of slope (0.1–8.7%), flow Reynolds number (3462–10040), Froude number (1.44–5.17) on the correction factor are presented. The analysis demonstrated that the correction factor is independent of flow Reynolds number while a relationship with a Froude number, obtained by surface velocity measurement, or channel slope can be established.     

轴伸式贯流泵装置全流场三维湍流数值模拟

为探讨轴伸式贯流泵装置双向运行时的内部流动结构并进行性能预测,应用三维湍流Navier-Stokes、Realizable 两方程湍流模型、壁面函数法和滑移网格技术,进行泵装置双向运行时的全流场三维湍流数值模拟研究。计算所采用的模型贯流泵具有特定的S形叶片及正向运行时的后置弯曲导叶。研究结果揭示了贯流泵装置正、反向运行时的全流道速度等值线、静压等值线、出水流道断面矢量及出水流道的流线形状特征,探讨在泵装置实际安装条件下泵与流道的相互影响,进行泵装置性能的数值模拟预测,并与试验结果进行比较分析。数值模拟结果表明,泵段的出口流态及导叶对流道的流动结构有很大的影响,扩散形流道对流道进口流态反映敏感,无导叶的直形泵装置出口扩散流道内的流动为轴向旋涡、环形旋涡、轴向流动的叠加,数值模拟计算预测泵装置性能的方法是有效、可行的,能够满足工程需要。     

Infrared and Visible Images Fusion with Multi-visual Cues

Image fusion is an important technique which combines the original information from multiple input images into a single composite image. The fused images will be more beneficial to human visual perception or further computer processing tasks than any individual input. Most of the traditional infrared and visible fusion approaches perform the fusion on the assumption that the original information is measured by local saliency features such as contrast or gradient. There is little consideration of the “interesting” or “useful” information in global. In this paper, an infrared and visible image fusion method is proposed by considering the final aim of image fusion, the human visual perception and further image processing tasks. The fusion is implemented under the non-subsampled contourlet transform based image fusion framework. The low frequency sub-band coefficients which represent the intensity of the scene are fused with the weight map which is constructed by considering both visual saliency uniqueness and task-oriented objectness, and refined by spatial consistency with guide filter. The new fusion strategy ensures that the objects being “interesting” or “useful” are preserved in the fused image. Sixteen pairs of infrared and visual images are used to test the validation of the proposed method. The experimental results show obvious improvement of the proposed method in terms of both objective and subjective quality measurements corresponding to other methods.     

ITER-relevant calibration technique for soft x-ray spectrometer

The ITER-oriented JET research program brings new requirements for the low-Z impurity monitoring, in particular for the Be—the future main wall component of JET and ITER. Monitoring based on Bragg spectroscopy requires an absolute sensitivity calibration, which is challenging for large tokamaks. This paper describes both “component-by-component” and “continua” calibration methods used for the Be IV channel (75.9 ?) of the Bragg rotor spectrometer deployed on JET. The calibration techniques presented here rely on multiorder reflectivity calculations and measurements of continuum radiation emitted from helium plasmas. These offer excellent conditions for the absolute photon flux calibration due to their low level of impurities. It was found that the component-by-component method gives results that are four times higher than those obtained by means of the continua method. A better understanding of this discrepancy requires further investigations.     

Load Capacity Estimation of Foil Air Journal Bearings for Oil-Free Turbomachinery Applications

This paper introduces a simple “Rule of Thumb” (ROT) method to estimate the load capacity of foil air journal bearings, which are self-acting compliant-surface hydrodynamic bearings being considered for Oil-Free turbomachinery applications such as gas turbine engines. The ROT is based on first principles and data available in the literature and it relates bearing load capacity to the bearing size and speed through an empirically based load capacity coefficient, D. It is shown that load capacity is a linear function of bearing surface velocity and bearing projected area. Furthermore, it was found that the load capacity coefficient, D, is related to the design features of the bearing compliant members and operating conditions (speed and ambient temperature). Early bearing designs with basic or “first generation” compliant support elements have relatively low load capacity. More advanced bearings, in which the compliance of the support structure is tailored, have load capacities up to five times those of simpler designs. The ROT enables simplified load capacity estimation for foil air journal bearings and can guide development of new Oil-Free turbomachinery systems.     

The application of erosion slowness theory to prediction of surface contour generation during particulate ablation of solids

The theory of surface contour modification resulting from ablation processes in which the local erosion rate is a function of the angle between the surface and the eroding flux which has previously been applied to chemical dissolution and atomic particle impact etching processes is described and its relevance to surface ablation resulting from macroparticle or fluid attack is explored. It is shown how predictions of the dynamic evolution towards possible steady state conditions can be obtained from this “erosion slowness theory” and applications to the erosion of hemispheres and undulatory surface waveforms are considered both theoretically and experimentally. Attention is directed towards examination of the case where the eroding agent flux is spatially uniform, but extrapolation of the technique to spatially non-uniform flux is also outlined.     

Two-point correlation estimation of turbulent shear flows using a novel laser Doppler velocity profile sensor

In this paper we describe, for the first time, a new method of two-point correlation estimations of turbulent flows using a laser Doppler velocity profile sensor. For the spatial correlation estimations the laser Doppler velocity profile sensor offers unique opportunities since a high spatial resolution of approximately 20 micron within the measurement volume is achieved. Furthermore, the low relative velocity measurement uncertainty of about 0.1% yields a high resolution of small velocity fluctuations and, therefore, allows correlation investigations where such high resolution is required. Moreover, a new virtual detection volume technique is presented which is only applicable in conjunction with the laser Doppler velocity profile sensor and offers the potential to achieve highly precise spatial correlation estimations. Measurements have been carried out in the turbulent wake of a circular. Both temporal as well as spatial correlation estimations have been calculated from the acquired velocity data yielding a longitudinal Taylor microscale of 3.53 mm and a transverse Taylor microscale of 1.84 mm.     

The Externally Pressurized,Porous Wall,Gas-Lubricated Journal Bearing.

The externally pressurized, gas-lubricated journal bearing consisting of a porous bushing, through which gas enters the clearance space, is analyzed. The classical Reynolds' equation for laminar, isothermal, compressible flow in a finite journal bearing is modified to allow for the local mass flow through the porous bushing into the clearance space due to the difference between the constant supply pressure and the pressure within the bearing. At low mass flow rates, it is assumed that the flow in the porous bushing obeys the Darcy equation for isothermal, compressible “creeping flow.” The analysis is extended to include bearings with higher flow rates by a simple modification of the Darcy equation.

The modified Reynolds' equation is solved for the case where the shaft does not rotate by perturbing the mass flow rate through the bearing using the eccentricity ratio as a small parameter. An asymptotic solution for the “short bearing” and the “maximum load-carrying capacity” is determined independent of the perturbation technique. The results of the perturbation technique are compared numerically with the results of the asymptotic solution, and they are found to be in agreement.     

Automated extraction of free surface topography using SfM-MVS photogrammetry

This paper describes a spatial measurement technique to measure the free surface of natural fluid flows in laboratory applications. This effective solution is based on “Structure-from- Motion/Multi-view Stereo” (SfM-MVS) photogrammetry and is capable of reconstructing water surface morphology, both at an instant and with a high spatial resolution. The efficiency and accuracy of the method is dependent upon the acquisition of high quality imagery (i.e. sharply focussed, no motion blur) with appropriate multi-frame camera coverage and configuration, and data processing must utilise appropriate camera calibration data. The potential of the technique for developing hydraulic understanding is demonstrated using two contrasting approaches. First, the water surface behind a living vegetation element is analysed along a single transect. Second, the full three-dimensional characteristics of the captured water surfaces are examined using statistical methods which demonstrate surface dissimilarity between vegetated and non-vegetated cases. The technique is transferable to real-world field sites.     

Fault detection for quality control of household appliances by non-invasive laser Doppler technique and likelihood classifier

This paper addresses the problem of developing an on-line diagnostic system for mechanical quality control of household appliances. The selection of a suitable measurement technique for feature extraction is discussed; the choice of a laser Doppler vibrometer technique and a laboratory measurement station for washing machines is presented. Vibration velocity and displacement are measured over a grid of points on the machine surface and data are stored in a database suitable for processing, both with good appliances and with defect ones with known defects. Features from the vibration velocity spectrum are used as the input to a likelihood classifier, which is shown to achieve very good classification scores.     

Measurement of fast-changing low velocities by photonic Doppler velocimetry

Despite the increasing popularity of photonic Doppler velocimetry (PDV) in shock wave experiments, its capability of capturing low particle velocities while changing rapidly is still questionable. The paper discusses the performance of short time Fourier transform (STFT) and continuous wavelet transform (CWT) in processing fringe signals of fast-changing low velocities measured by PDV. Two typical experiments are carried out to evaluate the performance. In the laser shock peening test, the CWT gives a better interpretation to the free surface velocity history, where the elastic precursor, main plastic wave, and elastic release wave can be clearly identified. The velocities of stress waves, Hugoniot elastic limit, and the amplitude of shock pressure induced by laser can be obtained from the measurement. In the Kolsky-bar based tests, both methods show validity of processing the longitudinal velocity signal of incident bar, whereas CWT improperly interprets the radial velocity of the shocked sample at the beginning period, indicating the sensitiveness of the CWT to the background noise. STFT is relatively robust in extracting waveforms of low signal-to-noise ratio. Data processing method greatly affects the temporal resolution and velocity resolution of a given fringe signal, usually CWT demonstrates a better local temporal resolution and velocity resolution, due to its adaptability to the local frequency, also due to the finer time-frequency product according to the uncertainty principle.     

Application of surface velocimetry in estimating rating curves in compound channels

Discharge estimation in natural rivers with geometrically irregular cross-sections and roughness differences between different parts of the wetted perimeter is complex. Therefore a compound channel can be used as a model of these rivers. Although assesing the behavior of rating curves in compound channels is very difficult and time-consuming, taking photographs of a floating object with a specified time interval is a method by which the velocity of the water surface can be estimated. The flow rate is first calculated using the isovels passing through the measured surface velocity. Then, the estimated discharge at a water level is applied to evaluate the rating curve. A compound channel model is built in the laboratory to carry out this experiment, and then the experimental results are obtained from rating curves. For the first time this paper uses surface water velocityto estimate the discharge and rating curve based on the SPM method introduced in 2003 and 2017, respectively. Also, an experimental setup consisting of a compound channel with a two-stage floodplain is another innovative feature of the current work that has not been previously explored. The results of discharge estimation based on the isovels and surface velocity show that the average error does not exceed 12%. Finally, the average statistical parameters of MAPE and NRMSE are obtained 6.4% and 0.045, respectively, for the estimated rating curve using the available data.     

A review of the measurement of blood velocity and related quantities using Doppler ultrasound

Ultrasound systems can be used to investigate blood flow by use of the Doppler effect. The flow information may be displayed as either a real-time sonogram or a two-dimensional colour image. Estimates of maximum velocity using commercial systems are in error by typically 10-100 per cent; this is associated with the inability of the single-beam Doppler method to measure the true direction of flow, and with geometric spectral broadening. Vector Doppler systems acquire Doppler information along two beam directions and are able to measure accurately the velocity and direction of motion within the scan plane. The small beam width of modern Doppler systems means that the condition of uniform insonation, required for estimation of mean velocity from mean frequency shift, is not valid except for the very smallest vessels. Other quantities related to the velocity may also be estimated, such as the volumetric flow and wall shear stress. Flow visualization using colour flow imaging suffers from dependence of the displayed colour on the direction of blood motion. The vector Doppler technique may be extended to colour flow to give improved visualization of flow, in which there is no angle dependence within the scan plane.