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The velocity profiles and volumetric concentrations were measured using a laser doppler anemometer for a vertically ascending two-phase liquid–liquid droplet flow in a cylindrical tube, where the density difference between the phases is relatively small. This regime simulates the flow of a two-phase gas–liquid mixture in microgravity. The small phase slip velocity was experimentally measured. New methods have been developed for using a laser doppler anemometer to measure the velocity and volumetric concentration of phases in a dispersed two-phase flow. [ABSTRACT FROM AUTHOR]

We study the possibility of application of the methods of laser Doppler anemometry for the noncontact measurement of the velocity of moving media in various phase states. We mention the specific features of the conditions of application of laser Doppler anemometers and, in particular the fact that, in numerous cases there exist restrictions on the use of photomultipliers. With an aim to find an alternative to the classical photomultiplier of a laser Doppler anemometer, we study three types of photomultipliers: classical electric vacuum photomultipliers, silicon avalanche multipixel photomultipliers, and photomultipliers with microchannel plate. We performed physical experiments aimed at measuring the velocity of aero- and hydrodynamic flows by laser Doppler anemometers with photomultipliers of the indicated three types. Actually, we measured the velocities of a rotating glass disk, of an aerodynamic flow in a channel with rectangular cross section, of an aerosol flow, and of a flooded hydrodynamic jet. The accumulated experimental data are analyzed according to the criteria of evaluation of the quality (efficiency) of operation and the ranges of applicability of the specified photomultipliers. By analyzing the physical properties of the investigated photomultipliers, we clarify their efficiency characteristics in different experiments. The ranges of efficient applications of these photomultipliers are determined for a broad class of physical experiments. The obtained results are of high importance for the researchers involved in the study of aero- and hydrodynamic flows in which it is necessary to have accurate and reliable result of measurements of the flow velocity. The optimal choice of a photomultiplier for the laser anemometers makes it possible to increase the accuracy, simplify the procedure of collecting the experimental data, and to reduce the cost of the final equipment. [ABSTRACT FROM AUTHOR]

Gas–liquid separation at natural gas wellheads has always been a key technical problem in the fields of natural gas transportation and storage. Developing a gas–liquid separation device that is both universal and highly efficient is the current challenge. A new type of combined gas–liquid separation device was designed in this study, and the efficiency of the separator was studied using a laser Doppler anemometer and phase Doppler particle analyzer at a flow rate of 10–60 Nm3/h. The results showed that the separation efficiency of the combined separator was above 95% at each experimental flow rate, verifying the strong applicability of the combined separator. Moreover, the separation efficiency was as high as 99% at the flow rates of 10 and 60 Nm3/h, thereby realizing efficient separation. This study is significant to the development of gas–liquid separation devices. [ABSTRACT FROM AUTHOR]

The temperature stability of the laser wavelength is an important characteristic of a laser Doppler anemometer with chromatic channel separation. This work presents experimental studies of the 660-nm wavelength shift of a semiconductor laser diode as a function of temperature and laser radiation power. It is established that the temperature drift of the wavelength lies within 0.2 nm/ C. It is shown that the use of semiconductor diodes of this type in laser Doppler anemometers with chromatic channel separation is possible, but requires careful selection of optical filters. [ABSTRACT FROM AUTHOR]

The primary goal of wound healing therapy is to quickly close the wound and form healthy and functional scar tissue. As capillary system regeneration is an important condition for skin wound healing, it is important to dynamically monitor angiogenesis with multiple methods based on the 3D reconstruction of dermal microcirculation. In this study, we established a quantitative system to comprehensively evaluate angiogenesis and perfusion during wound healing. Full-thickness skin wounds were generated on the back of rats. Laser Doppler anemometer (LDA), laser speckle contrast imaging (LSCI), and medical electronic dermoscopy (MED) are used to observe the vasculature from the horizontal plane and quantify blood perfusion in wounds. We combined immunofluorescence staining and two-photon excited fluorescence microscopy (TPEF) to reconstruct 3D vessels for longitudinal quantification. These results indicated that new blood vessels around the wound grew parallel to the wound surface. The shape of the blood vessels changed from curved to straight, and the density of the surrounding vascular network gradually decreased as manifested by a decrease in the nodes and branches and the total length of the blood vessels. There were dense blood vessels that grew vertically to the wound surface in the center of the wound. This study established a real-time, non-invasive system to monitor re-epithelialization and angiogenesis and quantitatively assess blood vessels during wound healing, which facilitates the evaluation of new treatments for wound healing.

The characteristics of the trapezoidal weir flow are measured using a one-dimensional laser Doppler anemometer for two different flow conditions. The governing equations of the flow are solved using Standard k–ε, Realizable k–ε, Modified k–ω and Reynolds Stress Model based on the Reynolds-Averaged Navier–Stokes Equations and by Large Eddy and Detached Eddy Simulations. ANSYS-Fluent package program is used for the numerical analysis of flow with the same experimental conditions. The free surface of the trapezoidal weir flow is computed by the volume of fluid method. The effect of the selected grid structure on the numerical results is examined by Grid Convergence Index. Moreover, two-dimensional (2D) and three-dimensional (3D) analyses of the trapezoidal weir flow are included to estimate the effects of side walls. Experimental results of the velocity field and free surface profiles are compared to the numerical results of 2D and 3D simulations for the validation purposes. From the comparisons it is concluded that the Reynolds Stress Model estimates the flow field more accurately compared with those of the other models used in the present study. Furthermore, the flow characteristics such as turbulence kinetic energy, energy spectrum and pressure distributions for different flow rates are presented. Lastly, the discharge coefficients for different flow–weir configurations are compared experimentally and numerically. [ABSTRACT FROM AUTHOR]

Abstract The type of fan-blade skew used in axial fans has a strong impact on the sound field, the flow field and their interrelations. In this study, the sound emission and the velocity distributions of three low-pressure axial fans with a similar design point and forward-, backward- and unskewed fan blades are investigated. The forward skewed fan is found to have best aerodynamic performance as well as the least sound emission over a broad operating range. More detailed investigations at the fan design point, based on sound pressure spectra and beamforming evaluations, reveal very dominant subharmonic narrowband components and increased turbulence-ingestion noise for the backward- and the unskewed fan. Moreover, an increase in the meridional velocity in the tip region is observed for the forward-skewed fan, which weakens the tip-vortex formation. For the backward- and the unskewed fan however, a reduced meridional velocity in the tip region is found, which is an indicator of an intensified tip gap flow. Additionally, values of the turbulent kinetic energy are substantially increased for the backward- and the unskewed fan, which also hints at unsteady flow phenomena in the tip region. These flow processes are linked to the subharmonic narrowband sound emission. Finally, unsteady flow features in the tip region lead to an increase in turbulence-ingestion noise. [ABSTRACT FROM AUTHOR]

The subject matter of the article concerns velocities/flow rate measurements in the area of disturbed flows-behind the 90° bend. They were conducted by means of an ultrasonic flowmeter with clamp-on sensors on pipeline, for water and two different Reynolds numbers of 70,000 and 100,000, corresponding to two velocities of approximately 1.42 m/s and 2.04 m/s. The tests were carried out at 12 distances from the disturbance. Sensors on the circumference of the pipeline were mounted 30° each. The correction factor values were calculated for the given measurement geometry. The measurements have shown that the values of this coefficient are always greater than 1, which means that the ultrasonic flow meter understates the speed values. They also showed that already at a distance of 8 nominal diameters from the disturbance, the correction factor does not exceed 1.02, so the measurement errors are within the maximum permissible error (MPE) of a typical ultrasonic flow meter. For distances less than eight nominal diameters from the disturbance, not taking the correction factor value into the account can lead to systematic errors of up to 10.8%. Studies have also proved that in each measurement plane behind the disturbance there are two mounting angles for the ultrasonic sensors, 60° and 240° respectively, for which the correction factor values are minimal. Additionally, using the laser Doppler anemometry (LDA) method, velocity solids were determined at individual distances from the disturbance, and the projections of velocity blocks on the appropriate plane represented velocity profiles and indicated the distances from the disturbance at which these profiles stabilise.

The direct measurement of emissions from naturally ventilated dairy barns is challenging due to their large openings and the turbulent and unsteady airflow at the inlets and outlets. The aim of this study was to quantify the impacts of the number and positions of sensors on the estimation of volume flow rate and emissions. High resolution measurements of a naturally ventilated scaled building model in an atmospheric boundary layer wind tunnel were done. Tracer gas was released inside the model and measured at the outlet area, using a fast flame ionization detector (FFID). Additionally, the normal velocity on the area was measured using laser Doppler anemometry (LDA). In total, for a matrix of 65 × 4 sensor positions, the mean normal velocities and the mean concentrations were measured and used to calculate the volume flow rate and the emissions. This dataset was used as a reference to assess the accuracy while systematically reducing the number of sensors and varying the positions of them. The results showed systematic errors in the emission estimation up to +97%, when measurements of concentration and velocity were done at one constant height. This error could be lowered under 5%, when the concentrations were measured as a vertical composite sample.

Abstract The calibration of Laser Doppler Velocimeters (LDVs) is of a great importance for the accurate measurement of the fluid flow rate and the speed of moving objects. In this paper, a simple, low-cost and portable calibration system for LDV is introduced. This system, which is based on a commercial optical chopper, can offer calibration uncertainty of (0.048%) (σ = 2) for velocities up to 1914 m/min and dynamic lengths of up to 15.4 km, which is better than the uncertainties reported by similar systems with a much complicated design. Therefore, this calibration system can be implemented easily by any calibration laboratory or even by national metrology institutes. [ABSTRACT FROM AUTHOR]

This paper presents results from an experimental study which was conducted at Technical University Delft, Netherland. The research was made on obstructions resembling weirs in an open channel. This weir-type obstruction was a representative of groyne/dike in a natural channel. The experimentation was performed in the laboratory for different values of inflow (25 l/sec and 40 l/sec), weir with and without vegetation and with different leeward slopes of the weir (1:4 and 1:7). The results were obtained for Reynolds normal stresses, longitudinal and vertical velocities. A comparison was made between the results of 1:4 and 1:7 leeward slope ratios. The data was collected with a LDA (Laser Doppler Anemometer). The vegetation was modeled with vertical circular rods placed over the crest of the weir. The blockage area due to this vegetation was 25% of the total area. The velocity data was gathered at around ten locations both at upstream and downstream the weir to get an insight into the flow structure. The results have been presented in the shape of vertical profiles both for velocities as well as Reynolds stresses at different locations of the channel.

Wall jet in heading face has both mean and turbulence characteristics that makes it have replacement and mixing effects on the air flow field. Thus，wind fluctuations play critical roles in the transportation and diffusion of gas and dust，for example，dust suspension entirely depends on that effect. However，the available experimental data on the subject are rather limited due to the limitations of experimental equipment and its complexity. This paper studies the turbulence characteristics of wall jet in heading face. For this purpose，the authors carried out some measurements of instantaneous 3D velocity in experimental model by using a three-dimensional laser doppler anemometer. After that，the authors have studied the distribution and scale of the turbulence intensity that calculated from the experiment data based on the statistical theories of turbulence. The experimental results indicate that there are serious wind fluctuations not only in the jet zone but also in the recirculation zone affected by the return flow and the side walls. The turbulence intensity in three directions are anisotropy but in the same order. Besides，the authors noticed that turbulence intensity increases firstly and then decreases with the distance from the axis of the jet reached the recirculation zone where the turbulence intensity are closer to the magnitudes of the mean air velocity. According to the analysis，shear instability that caused by velocity gradient between the flow layer is an important factor to cause the violent turbulence. At last，the authors suggest that a full attention should be given to the fluctuation term in motion equations when a further study of ventilation efficiency and migration law of gas and dust in heading face is made by any means. [ABSTRACT FROM AUTHOR]

Background: According to the clinical data, flow conditions play a major role in the genesis of intracranial aneurysms. The disorder of the flow structure is the cause of damage of the inner layer of the vessel wall, which leads to the development of cerebral aneurysms. Knowledge of the alteration of the flow field in the aneurysm region is important for treatment.Objective: The aim is to study quantitatively the flow structure in an patient-specific aneurysm model of the internal carotid artery using both experimental and computational fluid dynamics (CFD) methods with Newtonian and non-Newtonian fluids.Methods: A patient-specific geometry of aneurysm of the internal carotid artery was used. Patient data was segmented and smoothed to obtain geometrical model. An elastic true-to-scale silicone model was created with stereolithography. For initial investigation of the blood flow, the flow was visualized by adding particles into the silicone model. The precise flow velocity measurements were done using 1D Laser Doppler Anemometer with a spatial resolution of 50 μ m and a temporal resolution of 1 ms. The local velocity measurements were done at a distance of 4 mm to each other. A fluid with non-Newtonian properties was used in the experiment. The CFD simulations for unsteady-state problem were done using constructed hexahedral mesh for Newtonian and non-Newtonian fluids.Results: Using 1D laser Doppler Anemometer the minimum velocity magnitude at the end of systole -0.01 m/s was obtained in the aneurysm dome while the maximum velocity 1 m/s was at the center of the outlet segment. On central cross section of the aneurysm the maximum velocity value is only 20% of the average inlet velocity. The average velocity on the cross-section is only 11% of the inlet axial velocity. Using the CFD simulation the wall shear stresses for Newtonian and non-Newtonian fluid at the end of systolic phase (t= 0.25 s) were computed. The wall shear stress varies from 3.52 mPa (minimum value) to 10.21 Pa (maximum value) for the Newtonian fluid. For the non-Newtonian fluid the wall shear stress minimum is 2.94 mPa; the maximum is 9.14 Pa. The lowest value of the wall shear stress for both fluids was obtained at the dome of the aneurysm while the highest wall shear stress was at the beginning of the outlet segment. The vortex in the aneurysm region is unstable during the cardiac cycle. The clockwise rotation of the streamlines at the inlet segment for Newtonian and non-Newtonian fluid is shown.Conclusion: The results of the present study are in agreement with the hemodynamics theory of aneurysm genesis. Low value of wall shear stress is observed at the aneurysm dome which can cause a rupture of an aneurysm. [ABSTRACT FROM AUTHOR]

In mixing ventilation systems, diffusers are often located on side walls and supply quasi-free air jets above the occupied zone. The aim of the current research was to create a new CFD 3D benchmark with two well-defined characteristic zones in the room, i.e., the quasi-free jet zone and the occupied zone. The measurements were performed in a physical scale model (1:5) of the room. The kinematic similarity criterion was fulfilled by the equality of the Reynolds numbers in the model and in the prototype. Measurement methods adequate for air velocity and speed measurement were applied: laser Doppler anemometry for the axial velocity component in the jet and low velocity thermal anemometry for the air speed in the occupied zone. The novelty of the paper is the identification of the evolution of the air mean velocity distribution with distance from the supply opening. In the distance of 15–30 equivalent diameters, the jet behaves as a free turbulent axisymmetric jet; its momentum flux is conserved and fixed at approximately 80% of the inlet momentum flux. At higher distances from the inlet, the confinement effect of partitions is observed. The CFD results validation and reporting methods applicable for the benchmark data are proposed. The new 3D benchmark can be useful for CFD researchers, engineers and students for testing different CFD modelling aspects and thus may contribute to the improvement of CFD prediction accuracy. The benchmark results are available in the Data in Brief article. [ABSTRACT FROM AUTHOR]

This paper presents a review of the state-of-the-art of methods for obtaining maximum likelihood estimates of signal parameters of Doppler lidars and laser Doppler anemometers. [ABSTRACT FROM AUTHOR]

The delay time of ignition of a composite propellant based on ammonium perchlorate by a CO-laser is measured at various pressures and radiant flux densities. The characteristics of the propellant at the moment of ignition are calculated. The obtained rate constants of the reactions in the propellant are compared to the respective rate constants of the reactions in the c-phase occurring during the combustion of the composite propellant. [ABSTRACT FROM AUTHOR]

The author presented the features of hydraulic and hydro-technological investigations at the laboratory of fluid mechanics and hydraulics, including scientific technical works of the students, Master students, postgraduate students and doctoral students of the department of hydraulics and water resources and the department of hydraulic engineering MGSU. The modern equipment of hydraulic laboratory is reflected. The attention is drawn to the most important investigation topics, which included in the formed scientific schools and directions. The methodological aspects of the stated tasks in frames of scientific and educational process are considered.