Laser Doppler Anemometry Method Research Articles

Design of a small-scale wind tunnel for the study of horizontal-axis wind turbine blades

The paper considers the details of design and construction of a small-sized wind tunnel with an open circuit and a closed test section for investigating the blades of horizontal-axis wind turbines. The effect of different types of jet straighteners on the turbulence of the flow in the test section has been studied. Turbulence flow distributions Tu at Reynolds numbers Re from 5·103 to 2·104 are obtained using Laser Doppler Anemometry methods. As a result, the wind tunnel design with average flow turbulence of 1.6 % is obtained. The flow visualization of NACA 64-618 airfoil at Re = 5·103 is obtained.

Comparative study of LDA and PIV methods for flow homogeneity measurements

Abstract In the Hydraulic Laboratory of the Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava the distribution of the flow velocity in a shaft intake structure was investigated on a physical model. The homogeneity of the flow velocity distribution in the intakes of turbines has a great influence on the turbine performance. Modern optical methods, particle image velocimetry and laser Doppler anemometry, were used to measure the flow velocity distribution in the model of the turbine intake. The particle image velocimetry method provides a record of the velocity field, while the laser Doppler anemometry method provides an accurate indication of the velocity at a given point. The flow velocity distributions in the examined profiles were measured by the particle image velocimetry and laser Doppler anemometry methods and the results were compared with each other.

Development of laser doppler anemometer method for calculation verification in study of gas motion in controlled turning-and-diverging flow

The laser-Doppler anemometry method was developed for experimental studies on control of turning-and-diverging flow have been carried out; detailed diagnostics of averaged and turbulent characteristics have been made. Numerical modeling and comparison with experimental data based on known up-to-date turbulence models have been performed; comparative analysis of models has been done. The findings may be useful for determination of applicability limits of turbulence models.

Development of the method of laser Doppler anemometry for diagnostics of turbulent flows at high speed

The aim of the work was to develop a laser Doppler anemometry method for high-speed turbulent aerodynamic flow diagnostic. As a result, this allowed us to measure two projections of the velocity vector in the range of 0.1 - 400 m/s with a relative error not exceeding 0.5%. The measurement area was 0.1x0.1x0.5mm. The positioning device moved the measuring unit in the area of 250 x 250 x 250 mm with an accuracy of 0.1 mm. This method also provides the ability to measure local flow rate fluctuations.

LDA diagnostics of the flow structure in the model of an advanced four-vortex furnace

In this work, the internal aerodynamics of a laboratory model of a promising furnace with a four-vortex scheme for burning coal fuel is studied using the method of laser Doppler anemometry (LDA). Distributions of the averaged velocity and velocity pulsations are obtained in various areas of the furnace model in a wide range of regimes. The main features of the flow are identified. The experimental results are compared with the previous measurements by the PIV method; their good agreement is achieved. The data obtained are used to verify the mathematical model in numerical studies of a full-scale furnace.

Kinematic characteristics investigation in a transparent swirler of a vortex tube with square cross-section

The work is devoted to experimental investigation of the vortex effect in the Ranque-Hilsch tube using non-contact methods. The vortex tube, which consists of the slit-type swirler made as accelerating vortex chamber, a working channel with a square cross section, a radial diffuser at the hot outlet and a diaphragm at the cold one was used. For optical diagnostics, the vortex chamber (swirler) was equipped with optical windows. On the basis of measurements by the laser Doppler anemometry method, new experimental information about flow at the entrance of the Ranque-Hilsch vortex tube was obtained.

Velocity Measuring Tool of Projectile in the Barrel: Experimental Research Results of the Valid Layout

The work is devoted to the consideration of the methodology of experimental research of velocity measuring tool of the projectile in the barrel. The content of individual stages of conducting research is outlined. The research of the optical quality of the reflective coating is carried out. It is shown that the use of reflective paint and envelope in the coating of the front part of the projectile provides an effect of retroreflection, sufficient for the Doppler frequency shift. The influence of the retroreflective coating on the ballistic characteristics of the projectile has been investigated. It is defined that the relative increase of the mass and dimensions of the projectile, wich caused by the planted of the retroreflective coating on its front part, does not exceed, in accordance 0,10% and 0,025% of its output mass and length, therefore, the effect of these projectile parameters is too small and unable to exert a noticeable effect on its ballistic characteristics during of movement in barrel. The velocity projectile curves were carried by experimentally on an valid layout of the measuring tool , and their analysis was carried out. The possibility of using the double differential method of laser Doppler anemometry to measure the velocity of the projectile in barrel has been confirmed. Found that form the experimental curves velocity corresponds to the expected nature of the increase velocity of the projectile in the barrel of velocity measuring tool. The adequacy of the mathematical model of the measurement tool which obtained theoretically is confirmed.

Investigation of flow kinematics in the structured multibed catalytic cartridge

The reduction of harmful substances emission into the atmosphere is very important to create compact, energy-efficient catalytic units for afterburning volatile organic compounds. A key component of such units is the catalyst cartridge. The efficiency of its operation is provided by the supply of a gas flow with a uniform velocity field. To solve the problem, the gas flow distributor and an aerodynamic stand for its testing were created. A set of air-flow blades was used to align the velocity profile before the catalyst cartridge. Also flow kinematics inside the cartridge was investigated via laser Doppler anemometry method.

Suppression of vortex core precession in a swirling reacting flow

The influence of combustion effect on unsteady vortex structure in the form of precessing vortex core was studied using the non-intrusive method of laser Doppler anemometry and special procedure of extracting the non-axisymmetric mode of flow fluctuations. The studies show that combustion has a significant effect on the parameters of such a core, reducing the amplitude (vortex deviation from the burner center) and increasing precession frequency. At the same time, the acoustic sensors detect almost an order reduction in the level of pressure pulsations generated by the precessing vortex core. Moreover, distributions of tangential velocity fluctuations and cross-correlation analysis show that vortex precession is quite pronounced even under the combustion conditions, bringing a significant coherent component to distributions of velocity fluctuations.

Method of determining the optimal coordinate domain in the measurement of water flows turbulence using lad-56 in rectangular channels

One of the modern methods of the experimental investigation of water flows turbulence is the method of Laser Doppler Anemometry. At the present time a measuring system “LAD-056” (Russia) is operating in the laboratory of the Department of Hydraulics of MGSU. The authors conducted an analysis of the requirements to experimental data when calculating turbulent characteristics of water flows. The article shows the necessity of checking the database of ripple continuity over time and the required representation of the number of points in the implementation. The results of experiments are presented showing the importance of fixing the length of the implementation and testing time. The authors offered a method of determining the optimal spatial coordinates for the measurement to minimize the time of filling the base of experimental data. According to the methods of defining optimal coordinate domain when measuring turbulent water flows with the use of “LAD-056” in a rectangular channel with glass walls in was established that it is required to conduct measurements within the range from 0 to 120 mm from the closest side wall. In case of greater deepening it is required to use illuminators reducing deflections of laser beams.

Aerodynamics of a promising vortex furnace design

The aerodynamics of a promising vortex furnace design with secondary top blasting has been studied. Flow velocity fields have been measured in an isothermal laboratory model of the furnace using a digital tracer imaging (particle image velocimetry) technique. Three-dimensional diagnostics of flow structure in the combustion chamber has been carried out by the method of laser Doppler anemometry. Processing of the obtained data using the criterion of “minimum total pressure” has been used to visualize the spatial structure of the vortex core.

Investigation of the turbulent swirl flow in pipe generated by axial fans using PIV and LDA methods

In this paper is presented experimental investigation of the turbulent swirl flow in pipe generated by axial fans. Two various models of industrial axial fans are used. One of these is axial fan W30, model AP 400, Minel, Serbia and has seven blades and outer diameter 0.397m. Second axial fan SP30 is model TGT/2-400-6, S&P, Spain, has six blades and outer diameter 0.386m. This results with greater clearance in the second case. Blades were adjusted for both fans at the angle of 30? at the outer diameter. Test rig length is 27.74-D, where D is average inner diameter app. 0.4 m. Measurements are performed in two measuring sections downstream the axial fans (z/D = 3.35 and z/D = 26.31) with one-component laser Doppler anemometry (LDA) system and stereo particle image velocimetry (SPIV). Obtained Reynolds numbers, calculated on the basis of the average axial velocity (Um) in the first measuring section are for fan SP30 Re = 226757, while for fan W30 Re = 254010. Integral flow parameters are determined such as average circulation and swirl number. Significant downstream axial velocity transformation occurs for both fans, while circumferential velocity is decreased, but non-dimensional velocity profile remains the same. Circumferential velocity distribution for both fans in the central zone corresponds to the solid body, while in r/R > 0.4, where D = 2R, distribution is more uniform. Radial velocity in the case of fan SP30 has almost zero values in the measuring section z/D = 3.35, while its values are significantly increased in the downstream section with the maximum in the vortex core region. On the contrary radial velocity decreases downstream for fan W30 and has also maximum value in the vortex core region for both measuring sections. Level of turbulence, skewness and flatness factors are calculated on the basis of the experimental data. The highest levels of turbulence for circumferential velocity are reached in the vortex core region for both fans. It is shown how statistical moments of the third and fourth order differ from the values for normal Gaussian distribution. In this paper are also analyzed velocity fields by use of SPIV.

Diagnostics of swirl flow spatial structure in a vortex furnace model

The method of laser Doppler anemometry was applied for study of the spatial structure of a swirl turbulent flow occurred in isothermal lab-scale model of a vortex furnace (“CBTI design”). The criterion of “minimum of total pressure” was applied for visualization of a vortex core; the latter possesses a W-shaped geometry. Velocity and pressure pulsation spectra were measured for a wide range of operational parameters; these spectra testify about zero precession of a vortex core.

Flow diagnostics in a vortex furnace by particle image velocimetry

The internal aerodynamics of a model vortex furnace for a steam generator with a horizontal axis of flow rotation and distributed input of fuel-air mixture jets has been studied. Average characteristics of the flow velocity field in various cross sections have been determined using a digital tracer imaging (particle image velocimetry) technique. Results are compared to data obtained by the method of laser Doppler anemometry.

Measurement of the radius and slip velocity of a rolling wheel by a laser Doppler anemometer

The use of laser Doppler anemometry methods for determining the radius and slip velocity of rolling wheels is justified theoretically and experimentally. It is demonstrated that these methods allow the wheel radius to be measured with a relative error of 0.05–0.02% for the wheel turning angle of 0.6–4.0°. The slip velocity can be calculated in this case with an error of 20%. The slip velocity of a railroad wheel moving with a velocity of 60 mm/s is found.

A method for measuring particle velocity in thermal spraying

A mechanical method was established to determine the particle velocity in plasma spraying processes based on rotating slotted double cylinders or discs. The particle velocity was found to be a function of the mass of particles penetrating through the slots at different rotating speeds. The results obtained revealed a close agreement with those measured by the laser Doppler anemometry method and scanning confocal Fabry—Perot interferometer. The method provides a simple and accurate way of detecting the particle velocity in thermal spray processes. In addition, the method appears to be a low cost way of establishing measurement unit and high endurance in thermal spraying under such adverse conditions. This may lead to a wide application of the method on an industrial scale.

Distortion of LDA fringe pattern by tracer particles

For precise flow velocity measurements laser Doppler anemometry (LDA) is wide-spread in use in the laboratories of industry and universitarian research institutions. The LDA method has the advantage of being not intrusive and able to discriminate between forward and reverse velocities. So far, laser Doppler anemometry is believed to be one of the most accurate flow measuring techniques. However, recent investigations have shown that the period lengths of LDA signal bursts are not constant within an individual burst. This can induce an additional scatter in the signal frequency and in the determination of the flow velocity. Until now, the reason for the period variations has not been investigated in detail although the problem was observed before. This paper describes experimental investigations which show that the particle passage through the laser beams shortly before the point of superposition, i.e. the LDA measuring volume, yields a distorted LDA fringe pattern. Thus, the signal period length from an individual particle, passing the center of the measuring volume at the same time, varies according to the distortion of the fringe spacing.

Laser Doppler anemometry detection of hydroacoustic particle velocity

The method of Laser Doppler Anemometry (LDA) is applied to the measurement of particle velocity in a hydroacoustic field. The field is created in a USRD type G19 or G40 calibrator. The LDA results are compared with the values for the velocity obtained from the pressure gradient measured by a USRD standard hydrophone. The anemometer is operated in forward scattering mode, and also in backscattering mode through the use of a fiber‐optic transducer. Seeding particles of varying material and size are dispersed in the acoustic medium (water). The influence of these parameters including the particle concentration on the signal quality and detection threshold is discussed. [Work supported by ONR.]

Laser Doppler anemometry detection of hydroacoustic particle velocity

The method of laser Doppler anemometry is applied to the measurement of particle velocity in a hydroacoustic field. The field is created in an Underwater Sound Reference Detachment-type G19 calibrator. The anemometer is operated in the forward-scattering mode. Seeding particles of varying material and size are dispersed in the acoustic medium (water). The laser Doppler anemometry results are compared with the values for the velocity obtained from the pressure gradient measured by a hydrophone.

High-strain-rate free-surface boundary-layer flows

Two-dimensional boundary-layer flows of water down an inclined table were investigated in both the laminar and turbulent regimes. Mean, r.m.s. and skewness and velocity spectra were determined from streamwise velocity measurements. Two laser-Doppler anemometry methods were developed (for studying polymer-solution flows using this same water table) and compared with measurements obtained using hot-film anemometry. All three techniques obtained consistent results.An analysis based on a von Mises transformation is presented which accurately predicts the mean-velocity profile and flow development in the laminar regime. High strain rates are achieved which can be varied independently of Reynolds number, and turbulent flows are easily generated by inserting a disturbance. These turbulent flows are surprisingly similar to more commonly investigated turbulent boundarylayer flows of much greater y+ extent. Turbulent water-table flows typically extend only to y+ = 100, yet mean velocity essentially follows the law of the wall, and intensity and skewness measurements are similar to those obtained in flows much less limited in y+.