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The problem of aliasing in real time photon correlators is discussed theoretically and the phenomenon is verified experimentally for the Malvern digital correlator. It is suggested that the appearance of fold-over or beat frequencies can be utilized-in certain cases-to extend the effective upper frequency limit of a photon correlator and to facilitate accurate determination of the Doppler frequency in a laser Doppler anemometer system.

properties of various types of flat light-scattering media, diagrams were constructed of the characteristic manifestations of these properties. The procedure developed makes it possible to classify various types of scattering objects whose optical properties lie in a region specified by certain limiting situations and whose polarization characteristics are most pronounced and acquire diagnostic significance.

A Fabry-Perot laser-Doppler anemometer for the quasi-simultaneous detection of two velocity components is described. This anemometer requires only one Fabry-Perot and photodetection system. Measurements of two velocity components in a free jet were made to demonstrate the technique.

A device to measure water particle velocity in two directions under a breaking water wave was developed using single‐mode, polarization‐preserving fibers in conjunction with a two‐color, three‐beam laser‐Doppler anemometer. The sensor uses backscatter method with two beams frequency shifted to measure velocity reversal in both directions.

Describes a special optical system which has the simultaneous advantages of a scattering volume microscopic in three dimensions and a wide working distance. The optical device is briefly described, together with the hydraulic system. Some measurements, taken with pure water to test the system, are given.

A Laser Doppler Anemometer and a high speed data logging system are used to study the details of flow in the die land region. An abrupt entry cylindrical glass die, 6 mm I.D. and 210 mm long, is used. A 9.7 poise Newtonian Silicone Oil and a highly elastic polymer solution are investigated under low Reynolds number flow conditions (NRe < 1).

Because fluid motions inside an engine cylinder exert a strong influence on combustion and consequent engine performance, measurements of in-cylinder flow fields can be valuable input to the design of better internal-combustion engines. Laser Doppler anemometry provides a means of measuring the in-cylinder gas velocities in both motoring and firing engines. This paper reviews the state-of-the-art of LDA (laser Doppler anemometer) measurements in engine cylinders. Representative LDA systems and some of the practical problems encountered in their application to engines are described. In an engine, the inlet flow is highly three-dimensional with a very complicated in-cylinder flow. After the inlet flow stops, the fluid motions tend to become more organized; a precessing vortical flow is typically observed. Sample flow-field measurements are presented for some different engine types. Alternative data-reduction schemes and their identification of mean velocity and turbulence are discussed, along with examples of the same data reduced in different ways.Because fluid motions inside an engine cylinder exert a strong influence on combustion and consequent engine performance, measurements of in-cylinder flow fields can be valuable input to the design of better internal-combustion engines. Laser Doppler anemometry provides a means of measuring the in-cylinder gas velocities in both motoring and firing engines. This paper reviews the state-of-the-art of LDA (laser Doppler anemometer) measurements in engine cylinders. Representative LDA systems and some of the practical problems encountered in their application to engines are described. In an engine, the inlet flow is highly three-dimensional with a very complicated in-cylinder flow. After the inlet flow stops, the fluid motions tend to become more organized; a precessing vortical flow is typically observed. Sample flow-field measurements are presented for some different engine types. Alternative data-reduction schemes and their identification of mean velocity and turbulence are discussed, along with examples ...

The purpose of this study is to explore the effect of tapering upon the tendency of flow to become turbulent in straight symmetric tubes. Velocity was measured with a flow to become turbulent in straight symmetric tubes. Velocity was measured with a laser Doppler anemometer in plexiglass tubes which tapered 0.5 deg, 1.5 deg, and 2.5 deg measured from the centerline to the wall. These angles were comparable to the angles of tapering observed in the abdominal aorta of normal subjects, 1.5 deg +/- 0.2 deg (mean +/- SEM) (range 0 deg to 3 deg). The transition Reynolds number (based on the diameter of the tube at the point of measurement) increased as the angle of tapering increased. When the angle of tapering was constant, the transition Reynolds number increased with increasing distance into the tapered section. These observations suggest that tapering of the abdominal aorta tends to promote laminar flow.

The evidence for hypothesizing a relationship between hemodynamics and atherogenesis as well as the motivation for selecting the carotid bifurcation for extensive fluid dynamic studies has been discussed in Part I of this two-paper sequence. Part II deals with velocity measurements within the bifurcation model described by Fig. 1 and Table 1 of the previous paper. A plexiglass model conforming to the dimensions of the average carotid bifurcation was machined and employed for velocity measurements with a laser-Doppler anemometer (LDA). The objective of this phase of the study was to obtain quantitative information on the velocity field and to estimate levels and directions of wall shear stress in the region of the bifurcation.

The self-cleaning prosthetic heart valve was tested under pulsatile flow conditions. The velocity field in the vicinity of the valve was investigated using a laser doppler anemometer. The areas of stagnation are minimum and the wall shear rate is in a physiologically acceptable range for a prosthetic device.

Laser-Doppler anemometry is relatively new technique which is used for measuring velocity fields. It has major applications in the field ofin vitro biofluid mechanics. The laser-Doppler anemometers have many advantages compared with the traditional hot-wire or hot-film anemometers which are still mainly used in studies of biofluid mechanics. A laser-Doppler anemometer (I.d.a) system which can be used to measurein vitro velocity and shear-stress profiles in the vicinity of prosthetic heart valves is described. Accurate velocity measurements in the vicinity of prosthetic heart valves are very scarce, and the use of I.d.a systems will facilitate acquisition of these data.

The effects of unevenly distributed flow were investigated in a symmetrically branched tube with an angle of branching and branch-to-trunk area ratio that were comparable to the human descending aorta. Profiles of velocity were measured at the vertex of the bifurcation with a laser Doppler anemometer during pulsatile flow as well as steady flow. The mean Reynolds numbers were 500, 1000, and 1500. When flow in the branches was equal, reversals were present along the outer wall during the minimal phase of the flow cycle at a Reynolds number of 500. Such reversals were absent at higher Reynolds numbers. When flow in the branches was unequal, reversals occurred only in the branch with the lower flow. Such reversals occurred at all of the Reynolds numbers studied. Pulsatile flow separation, however, did not occur at any Reynolds number when the flow in the branches was equal. Pulsatile flow separation occurred in the partially occluded branch when flow in the branch was ≤8% of the total flow only at Reynolds numbers of 1000 and 1500. A prominent difference between pulsatile and steady flow was that reversals along the outer wall occurred during pulsatile flow at percentages that were prominently higher than the percentage of flow in the branch that produced reversals during steady flow. These observations may be pertinent to understanding the potential of characteristics of flow in the genesis of atherosclerosis in the region of the bifurcation of the aorta.

The purpose of this study was to measure velocity profiles in a symmetrically branched tube with an area ratio (0.8) and angle of branching (70°) that were comparable to the bifurcation of the human descending aorta. Velocity profiles were measured in steady and pulsatile flow with a laser Doppler anemometer. In the branch near the vertex of the bifurcation the profiles were markedly skewed toward the inner wall during both steady and pulsatile flow. Points of inflection in the velocity profiles, where the profiles changed from convex to concave, occurred downstream from the vertex of the bifurcation. A region of transient flow reversal was found along the outer wall during minimal flow in the pulsatile cycle at mean Reynolds numbers below 1000. These observations are pertinent in understanding flow at bifurcations with a branch-to-trunk area ratio of less than one, as occurs at the aortic bifurcation.

An experimental investigation is made of the behavior of the flow field of a laminar boundary layer of a suspension along a flat plate. Velocity fields of both the fluid and the solid particles and the density field of the solid particles are simultaneously obtained by the use of a two-dimensional Laser-Doppler anemometer, a feat virtually impossible to attain by conventional techniques. To validate the technique, the velocity field of a single-phase laminar boundary layer is measured and results are found to agree closely with the classical Blasius solution. The measured results strongly support the model of migratory effects being caused by the hydrodynamic lift forces acting on the solid particles as introduced by the first author and his other coworkers in their recent theoretical investigations of flows of such suspension.

Laser Doppler Anemometry, or LDA, is a widely accepted tool for fluid dynamic investigations in gases and liquids. It is a well-established technique that gives information about flow velocity. This project is based on an LDA (Laser Doppler Anemometry) simulator that models a real system based on the estimation of a speed component. The main functioning of this system is based on the detection of changes in the frequency of scattered light, Doppler effect, by the particles of the fluid illuminated by a coherent light source. In order to carry out this simulation, the Matlab software tool will be used and its graphical user interface (GUI). Previously, a theoretical study is carried out and, subsequently, the code necessary for the creation of the simulator is implemented. This simulator must be able to estimate the speed component by adding noise by varying the SNR, consider a certain threshold to detect the signal, do the spectral analysis to find the Doppler frequency, study the different trajectories of the particles within the measurement volume and analyse the results of such simulations. La anemometría Láser Doppler o LDA, es una técnica utilizada para la investigación de procesos dinámicos en fluidos (gases y líquidos). Esta técnica proporciona información sobre la velocidad de un fluido. Este proyecto se basa en realizar un simulador LDA (Laser Doppler Anemometry) que modele un sistema real basado en la estimación de una componente de velocidad del fluido a medir. Este sistema está basado en la detección de los cambios en la frecuencia de la luz dispersada mediante el efecto Doppler producida por las partículas del fluido, iluminadas por una fuente de luz coherente. En caso que la partícula tenga un diámetro más pequeño que la longitud de onda, se puede estimar la velocidad mediante el modelo de franjas. Para llevar a cabo la realización de este simulador LDA, se hará uso del software Matlab y se presentará mediante la interfaz gráfica de usuario (GUI) que lleva integrada, para generar un entorno gráfico, sencillo y visual. Previamente, se realiza un estudio teórico y luego, se implementa el código necesario para la creación del simulador. Este simulador ha de ser capaz de estimar una componente de velocidad del fluido a medir con y sin ruido (SNR), realizar el análisis espectral para determinar la frecuencia Doppler, estudiar las diferentes trayectorias de las partículas dentro del volumen de medida y analizar los resultados de dichas simulaciones. Tras el análisis de los diferentes casos, se hace una comparación de las medidas obtenidas con el simulador respecto a los datos teóricos. En este documento se presentaran los resultados obtenidos en las simulaciones realizadas y la configuración del escenario, así como los parámetros utilizados.

We report on a full characterization of a laser Doppler anemometer to evaluate an end-to-end model. This model is used to assess the design and predict the performance of an airborne airspeed detector. © 2019 The Author(s)

We report on a scalable data processing scheme of a multi-channel laser Doppler anemometer for the application as an optical air data sensor. The pipelined continuous processing enables dead time free measurements. © 2019 The Author(s)

The paper depicts air velocity values, reproduced by laser Doppler anemometer (LDA) and ultrasonic anemometer (UA), relations with calculated ones from flow rate measurements using the gas meter which calibration uncertainty is ± (0.15 – 0.30) %. Investigation had been performed in channel installed in aerodynamical facility used as a part of national standard of air velocity. Relations defined in a research let us confirm the LDA and UA for air velocity reproduction to be the most advantageous measures. The results affirm ultrasonic anemometer to be reliable and favourable instrument for measurement of mean velocity or control of velocity stability in the velocity range of 0.05 m/s – 10 (15) m/s when the LDA used. The main aim of this research is to investigate low velocity regularities, starting from 0.05 m/s, including region of turbulent, laminar and transitional air flows. Theoretical and experimental results and brief analysis of it are given in the paper. Maximum and mean velocity relations for transitional air flow having unique distribution are represented. Transitional flow having distinctive and different from laminar and turbulent flow characteristics experimentally have not yet been analysed., {"references":["Bertašienė A., Daugelė A., Janušas V. Laser Doppler anemometer\napplication in the air velocity national standard // Advances in Heat\nTransfer. Proc. of V-th Baltic Heat Transfer Conference. Saint-\nPetersburg, September 19-21, 2007. P. 487 - 494.","Janušas V., Ilgarubis V., Daugelė A. Oro greičio verčių atkūrimo tyrimas\n// Matavimai.-2004.- Nr.2 (30). P.11-14.","Bertašienė A., Daugelė A., Janušas V. Investigation of practical\napplication of laser Doppler anemometer // Matavimai. 2006. Nr.2 (38),\nP. 5-10.","Euromet Key Comparison M. FF - K3 - Draft A - February, 2008.","Zhukauskas A. Convective transfer in heat exchangers. Science. 1982, p. 472.","H. Schlichting boundary layer theory. Science. 1974 S. 712.","Jakevi─ìius L., Butkus J., Janu┼ías V., Ilgarubis V. The influence of\nflattened flow profile to the airflow velocity measurement by ultrasound\n// Ultragarsas. 2005. Nr.4(57). P.18-21."]}

The effect of a near-free surface disturbance imposed on an open channel flow in the presence of low and high background turbulence is studied using a two-component laser Doppler anemometer. A bluff body located near the entrance of the flume was used to generate the free surface disturbance and the velocity characteristics were measured at a downstream location where the flow is fully developed. Experiments were conducted in two sets of flow fields. In the first set, the basic condition was an undisturbed open channel flow on a smooth bed, which is then compared with a flow with free surface disturbance. In this set, the turbulence levels are relatively lower and comparable with typical laboratory flume conditions. In the second set, the basic condition is a flow over a train of fixed two-dimensional bed forms, which is then compared with a flow with both bed forms and free surface disturbance. In the presence of the bed forms, there is continuous generation and sustenance of turbulence resulting in sign...

A working laser doppler anemometer has been developed in which the laser light has been frequency shifted by an acousto-optical method. The advantages are that it can determine the sign of the velocity component measured and allows measurements to be made in highly turbulent flows.

The laser doppler anemometer is a comparatively new tool for flow measurements. This article outlines the principles behind `dual-beam' laser anemometry using the fringe model and relates the role of l.d.a. in fluid dynamics research. The techniques are illustrated with reference to systems available at University College, Cardiff