Laser Doppler Anemometer Research Articles

Final report on EURAMET project No. 827: LDA-based intercomparison of anemometers

A regional air speed comparison between six EURAMET laboratories used an ultrasonic anemometer and a laser Doppler anemometer (LDA) at air speeds between 0.2 m s−1 and 40 m s−1. Based on periodic calibrations at the pilot laboratory (PTB), the uncertainty contributed to the comparison by the LDA was 0.2% and the uncertainty contributed by the ultrasonic anemometer depended on the air speed and varied between 2.95% and 0.11%. The degrees of equivalence between the participants were notably better for the laser Doppler anemometer data than for the ultrasonic anemometer data. For example, using the 95% chi-squared consistency check, 16 of the original 59 participant data points were removed as discrepant from the ultrasonic data set, but only one point was discrepant in the LDA data. A possible explanation is that the LDA is non-intrusive and therefore does not alter the velocity field in the wind tunnel whereas the ultrasonic device does produce blockage effects. The results of this comparison (and prior EURAMET and CIPM comparisons) indicate a need for more attention to blockage effects during air speed calibrations and their effect on air speed uncertainty statements.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Optimization of the Flow Rate Meter Based on Laser Doppler Anemometer and Evaluation of High Pressure Fuel Injection Rate

Optimization of the Flow Rate Meter Based on Laser Doppler Anemometer and Evaluation of High Pressure Fuel Injection Rate

Strong correlation between the drag coefficient and the shape of the wind sea spectrum over a broad range of wind speeds

Momentum transfer across the wind‐driven breaking air‐water interface under strong wind conditions was experimentally investigated using a high‐speed wind‐wave tank together with field measurements at normal wind speeds. An eddy correlation method was utilized to measure roughness length and drag coefficient from wind velocity components measured by laser Doppler and phase Doppler anemometers. As a result, a new model for the roughness length and drag coefficient was proposed for predicting momentum transfer across the sea surface under both normal and strong wind conditions using the universal relationship between energy and significant frequency of wind waves normalized by the roughness length. The model shows that the roughness length and drag coefficient are uniquely determined at all wind speeds by energy and significant frequency of wind waves, and they can be given againstU10only from the measurements of the wave parameters and one‐point mean air velocity in the logarithmic law region.

Numerical and experimental investigation of flow and scour around a half-buried sphere

The paper describes the results of a numerical and experimental investigation of flow and scour around a half-buried sphere exposed to a steady current. Hot-film bed shear stress and Laser Doppler Anemometer measurements were made with a half sphere mounted on the smooth bed in an open channel. The hydrodynamic model is a 3-D general purpose N–S flow solver. The k-omega SST turbulence model was used for closure. The flow model was used to study the horseshoe vortex and lee-wake vortex flow processes around the sphere. The flow model was coupled with a morphologic model to calculate scour around the half-buried sphere in currents. The morphologic model includes a sediment-transport description, and a description of surface-layer sand slides for bed slopes exceeding the angle of repose. The sediment transport description includes, for the first time, the effect of externally-generated turbulence (induced by the horseshoe-vortex flow and the lee-wake flow processes) on sediment transport. The results show that the scour depth increases and time scale decreases when the effect of externally-generated turbulence is incorporated in the calculations. Empirical expressions representing the numerically obtained data on the equilibrium scour depth and the time scale are presented. The results show that the equilibrium maximum scour depth in the live-bed regime can be approximated by 0.5 D in which D is the sphere diameter.

A wind tunnel study of particle kinematics during crust rupture and erosion

Sediments with protective crusts of varying type were subjected to particles fed from an upwind source during wind tunnel experiments carried out to compare their ability to resist erosion and alter the kinematics of the saltation cloud. A laser Doppler anemometer measured the distribution of particle velocity for saltators impacting each crusted surface and for particles ejected from this same surface, inclusive of ricochets. Biotic crusts grown on sand in an environmental chamber were able to withstand erosion over several hours of continuous particle impact, as compared to brittle salt crusts, which, regardless of wind speed or sodium chloride concentration, eroded fully within one half hour. Despite the appearance of deep pits and grooves on the ruptured crusts, loss of mass dominated over particle trapping on these rough surfaces. While decreasing salt concentration between 320gkg−1 and 80gkg−1 generally was found to be associated with an increase in the mass flux of particles ejected from the surface, little to no correlation with either wind speed or particle impact speed was observed. The range over which varying salt concentration affects the momentum of ejected particles is rather narrow, within 160gkg−1. Temporal changes in the velocity distribution of ejected particles with crust rupture and deflation are complicated by variations in crust strength with depth. This is especially true of biotic crusts and weak salt crusts. Fast moving particles associated with the upper 40% of the cumulative velocity distribution generally demonstrate little variation from the control surfaces, and probably represent ricochets. In comparison, those within the lower 60% of the distribution are significantly affected by crust rupture and erosion, and may include low energy rebounds as well as the entrainment of new particles loosened from within the crust. While such measurements are exceedingly rare, they are needed for the validation of physically based models of crust erosion.

Chaotic Analysis of the Velocity Signal in Impinging Stream Mixer

The velocity signal of the flow field in Impinging Stream Mixer (ISM) was measured with Laser Doppler Anemometer. A de-noising method for velocity signal in ISM based on wavelet threshold was used. It is obtained that the attractor of the system possess infinite self-similar nested structure by comparing the strange attractor before and after de-noising, which is based on phase space reconstruction theory. It is shown that K entropy and the largest Lypunov exponents have the similar tendency in spatial distribution through scientific computation, however, the stratification of K entropy is more obvious. The value of K entropy and the largest Lypunov exponents are both positive, proving that the system is chaotic. The results indicate that K entropy and Lyapunov exponents can be increased by improving the rotating speed, the disorder and unpredictability of chaos system will increase homogeneously, so as to promote the micro-mixing and improve work efficiency

Boundary‐layer turbulence characteristics during aeolian saltation

A great deal of effort has been expended in measuring turbulence phenomena in clean air flows. However, no previous measurements have been successfully made of the vertical distributions of turbulence intensity and Reynolds stress in a fully adjusted boundary‐layer flow saturated with saltating particles. The present wind tunnel study addresses this knowledge gap using a custom designed laser‐Doppler anemometer (LDA). The amount of turbulence is found to increase with the introduction of saltating particles to the airflow. Over the lowest 15% of boundary layer, vertical profiles of the streamwise wind speed provide friction velocities that lie well within the narrow range of those derived from direct measurement of the Reynolds stress. Relative to clean air, aeolian saltation is demonstrated to increase the magnitude but not the frequency of burst‐sweep events that primarily contribute to the total fluid stress. Within several millimeters above the bed surface, all vertical profiles of wind speed converge upon a focal point, as the local fluid stress declines toward the mobile bed.

Laser velocimetry of a plane mixing layer with a specific initial condition for study of turbulence characteristics of enhanced growth rate

Mixing layers are sensitive to the mixing angle and turbulence in the primary streams. Although there is extensive available research on this rather basic flow, there are still no suggestions for a clearly best configuration. For example, the combination of a laminar initial boundary layer and a large mixing angle has received little attention. In this work we test a new experimental configuration with large mixing angle and laminar/turbulent initial boundary layer that was not examined experimentally by LDA and PIV. This setup is expected to be a representation of the initial conditions that must result in better mixing. A plane mixing layer with a velocity ratio of 0.6 is produced by rebuilding an open circuit wind tunnel. Extensive calibration tests on velocity profiles and Reynolds stresses established the position of the self similar region. Velocity field measurements with laser Doppler anemometer (LDA) and particle image velocimeter (PIV) showed enhanced mixing layer growth. PIV plots showed the presence of stream-wise and cross stream vortices in the self-similar region without any considerable change in turbulence characteristics to that of reported in the literature. The article presents a combination of different experimental results that give a deeper understanding of this very configuration.

Experimental and numerical investigation of flow around a sphere with dimples for various flow regimes

Flow over a sphere is a typical bluff-body flow with many engineering applications. However, it has not been studied in depth, as compared to flow over a circular cylinder, because of the difficulties in the experimental set-up as well as in the computational approach for studying flow over a sphere. The main challenges are to understand the flow hydrodynamics and to clarify the flow pattern around a dimpled sphere because the flow pattern complying with the dimple structure on its surface is very complicated. In this paper experimental and numerical investigations of the fluid flow around a sphere with dimples, are represented. The sphere with dimples is placed in a quadratic cross section duct (measuring section) and numerical simulation results are obtained by solving RANS equations. Furthermore, experimental measurements are carried out using a Laser-Doppler Anemometer (LDA). Experimental and numerical results of flow velocity fields were compared for three different flow regimes (Re=8×103, 2×104 and 4×104). Numerical investigation was performed for wide range of Reynolds numbers (Re=270%106). The final purpose of this paper is experimental and numerical determination of velocity field, separation point, pressure and drag coefficient, the length of reverse flow region in the wake and RANS turbulent model which gives the best results for engineering practice.

Application of the Flow Rate Meter Based on Laser Doppler Anemometer to High Pressure Fuel Injection Rate Measurement

Application of the Flow Rate Meter Based on Laser Doppler Anemometer to High Pressure Fuel Injection Rate Measurement

Experimental Investigation of Particle Deagglomeration using Turbulence

The effect of turbulence on powder aerosol deagglomeration was investigated. Two impinging jets were used to generate turbulence. Lactose particles, whose fully dispersed fine particle fraction (FPF) - number percentage of the particles whose diameter smaller than 5 μm- is above 90 %, were applied as aerosol powder. The particle size distribution after the dispersion unit were measured by using phase Doppler anemometer (PDA) and turbulence level were quantified at the impingement point of two jets with laser Doppler anemometer. As the turbulence level increases turbulent time and length scales decrease, and the ratio of fine particle fraction (FPF) increases from 36% to 86%.

Direct numerical simulation of a high-Froude-number turbulent open-channel flow

In this study, we successfully conducted a direct numerical simulation of a high-Fr turbulent open-channel flow at a Froude number of 1.8 and a Reynolds number of 2325 based on bulk velocity, gravitational acceleration, water depth, and kinetic viscosity, using the multi-interface advection and reconstruction solver (MARS). We confirmed that typical wall-bounded turbulent structures were observed in this high-Fr open-channel flow. On the other hand, near free-surface, surface deformations are constituted of large-scale gentle bumpy waves with the maximum wave height corresponding to approximately 4% of the water depth and small-scale isotropic waves on the large-scale waves. The large-scale waves would generate the high-speed streaky structures near the free-surface and the scale of the small waves would be equivalent to the near free-surface turbulent kinetic energy. Near the free-surface, wall-normal turbulent intensity and energy-dissipation rates increase toward the free-surface, and the tendencies of turbulent statistical quantities near the free-surface are in good agreement with the experimental measurements obtained using a laser Doppler anemometer (LDA) (Nakayama and Nezu, “Bursts near the free-surface in open-channel flows and their relationships with turbulence structures,” J. Hydraulic, Coastal and Environmental Eng. JSCE 635/II, 31 1999). As well as the rigid-lid turbulent open-channel flow, turbulent intensity distribution from the vertical component to the streamwise one is predominant beneath the free-surface.

Fluid flow characteristics for shell side of double-pipe heat exchanger with helical fins and pin fins

To improve understanding of the heat transfer enhancement for shell side of a double-pipe heat exchanger with helical fins and pin fins, the three-dimensional velocity components for the shell side with and without pin fins were measured experimentally by using laser Doppler anemometer (LDA) under cylindrical coordinate system and the fluid flow characteristics, i. e., the distributions of the axial velocity, secondary flow, stream function as well as vorticity were analyzed by employing orthogonal helical coordinate system. The results showed that, for the shell side only with helical fins at large pitch, there was a pair of vortex near the upper and lower edge of the rectangular cross section; the weakest secondary flow occurred at the center. By pin fins being installed, the three-dimensional velocity components in the helical channel were strongly changed. The extra two vortices emerged at the center of the cross sections. The fluctuation of the velocity at the center of the cross sections before and behind a pin was increased sharply by the pin, especially for the situation behind a pin.

Mixing in the three-dimensional wake of an experimental modelled vehicle

Experimental results on tracer gas diffusion within the near wake of a simplified model car (Ahmed model with a rear slant angle of 25°) are presented. Pollutant emission is simulated using heated air injected through a small pipe at one side of the model base. Fine cold wire thermometry is used to measure instantaneous temperature excess and variance of temperature gradient in the near wake. Measurements of the three mean velocity components were made using a laser Doppler anemometers system. Characteristics of the mean and fluctuating temperature fields, time-averaged flow streamlines and scalar dissipation measurements are presented and discussed. The local mixing time scale is determined from the measured mean dissipation rate of temperature variance. Its value shows that micromixing is not a limiting phenomenon for chemical reactions in the near wake.

Effect of finite cavity width on flow oscillation in a low-Mach-number cavity flow

The current study is focused on examining the effect of the cavity width and side walls on the self-sustained oscillation in a low Mach number cavity flow with a turbulent boundary layer at separation. An axisymmetric cavity geometry is employed in order to provide a reference condition that is free from any side-wall influence, which is not possible to obtain with a rectangular cavity. The cavity could then be partially filled to form finite-width geometry. The unsteady surface pressure is measured using microphone arrays that are deployed on the cavity floor along the streamwise direction and on the downstream wall along the azimuthal direction. In addition, velocity measurements using two-component Laser Doppler Anemometer are performed simultaneously with the array measurements in different azimuthal planes. The compiled data sets are used to investigate the evolution of the coherent structures generating the pressure oscillation in the cavity using linear stochastic estimation of the velocity field based on the wall-pressure signature on the cavity end wall. The results lead to the discovery of pronounced harmonic pressure oscillations near the cavity’s side walls. These oscillations, which are absent in the axisymmetric cavity, are linked to the establishment of a secondary mean streamwise circulating flow pattern near the side walls and the interaction of this secondary flow with the shear layer above the cavity.

Effects of Hot and Cold Foods on Signals of Heart Rate Variability and Nail Fold Microcirculation of Healthy Young Humans: A Pilot Study

In traditional Chinese medicine, hot- and cold-attribute of food ingredients are a major part of dietary therapy. The aim of this study was to establish a suitable scientific methodology to define the attributes of food ingredients by investigating the relationship between food attributes and the physiological signals produced in healthy young subjects with different constitutions. Thirty subjects were grouped into hot and cold constitutions by Chinese medical doctors. Every subject took water, aged ginger tea and coconut water, which are well recognized as having neutral-, hot- and cold-attribute, respectively, on different visits. The different physiological signals induced by the samples were observed using skin and axillary temperature sensors, a heart rate variability analyzer and a laser Doppler anemometer. We found that the capillary red blood cell (RBC) velocity in nail fold microcirculation (NFM) of the subjects with hot constitution accelerated significantly after taking the hot-attribute aged ginger tea, which might be the result of elevated vagal activity leading to arteriole dilation in these subjects. In contrast, in subjects with cold constitution, capillary RBC velocity decelerated significantly and skin temperature decreased markedly after taking the cold-attribute coconut water, which might have been induced by sympathetic nerve activation causing the arteriole to be constricted. Accordingly, the use of capillary RBC velocity of NFM measured by laser Doppler anemometer may be a promising way to classify attributes of food ingredients commonly used in Chinese medicine dietary therapy in accordance with different personal constitutions.

Measuring substance velocity in zone of gravitational turbulent gas mixing at low Reynolds numbers

We have measured the distribution of the velocity of a tracking substance in the zone of the gravitational turbulent mixing of two gases with different densities, which is caused by the development of Rayleigh-Taylor instability in the gravitational field. The velocity field has been studied using a single-component laser Doppler anemometer, which allowed the temporal variation of the moduli of vertical and horizontal components of the tracking substance velocity projection to be determined in unstable mixing systems with the Atwood numbers of 0.23 and 0.83.

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.

FLUID FORCES ACTING ON A CUBE AND A STRIP ROUGHNESS SUBMERGED IN OPEN CHANNEL FLOW

The flow induced forces on a cube and a strip roughness placed submerged on the bed in open channel flow were measured by using the three-component load cell. The flow around the cube were measured by using a laser doppler anemometer and a particle image velocimeter and were simulated with a k-epsilon; turbulence model. The drag and lift force coefficients of the cube and strip roughness in the open channel flow with free surface become large with increase of the ratio of cube height h and water depth d (h/d). The equivalent roughness ks for the strip roughness were also estimated by the measured drag forces acting on a strip roughness.

Computational analysis of incompressible turbulent flow in an idealised swirl combustor

Isothermal turbulent swirling flow in a water test rig, representing an idealised swirl combustor, has been investigated experimentally and numerically. The Reynolds number based on combustor inlet diameter and mean axial velocity was 4600. Two cases were investigated at two different swirl intensities. Time-averaged velocities and RMS turbulence intensities were measured by Laser Doppler Anemometer (LDA), along radial traverses at different axial stations. In the three-dimensional, transient computations, Large Eddy Simulations (LES) and URANS Reynolds Stress Models (RSM) have basically been employed as modelling strategies for turbulence. To model subgrid-scale (SGS) turbulence for LES, the models owing to Smagorinsky and Voke were used. In one of the cases, Detached Eddy Simulations (DES) were also applied. The predictions have been compared with the measurements. It has been observed that LES provides the best overall accuracy, where no significant differences between the Smagorinsky and Voke models could be discerned.