Laser Doppler Velocimetry System Research Articles

Experimental investigation of flows in a high-head pump-turbine draft tube at turbine mode

The accurate prediction of flow patterns is essential during the optimization design of a pump-turbine. To determine the flow patterns and validate the flow simulation inside a pump-turbine, Laser Doppler Velocimetry (LDV) measurements and 3D flow simulation in the draft tube cone of a high-head pump-turbine model have been performed at normal operating conditions in turbine and pump modes. Velocity distributions were measured for operating conditions covering the speed factor nED=0.21 and 0.19 at turbine mode for loads ranging from 40% to 100% the rated power as well as best efficiency point. Measurements of unsteady flows inside the draft tube cone were conducted at a high precision hydraulic model test rig with LDV system from TSI Co. The 3D flows through the pump-turbine model were numerically simulated with ANSYS/CFX® software at all the measured operating points. Both measured and simulated velocity profiles are presented and analyzed to show the influence of operating parameters on the velocity and swirl characteristics in draft tube inlet. Comparison of the measurement and simulation shows rather good agreement at the best efficiency point and full load but clear discrepancies at part load. The experiment data such as the velocity profiles, pressure signals, and amplitude and frequency characteristics of the instantaneous tangential velocity at various loads offers the possibility to assess the precision in performance prediction in the pump-turbine using the numerical simulation methods. The measured instantaneous tangential velocity at part loads reveals a periodic peak, which is asynchronous to that of runner’s rotating speed and can be used to determine the characteristic frequency of rotating vortex rope at part loads. Axial and tangential velocity fields obtained from LDV measurements at normal operating points can be used to validate the numerical simulation in optimization design.

Bed shear stress and turbulence characteristics under unsteady flows

A series of laboratory experiments were conducted to investigate the turbulence and bed shear stress characteristics under solitary waves and dam break flows. The Laser Doppler velocimetry (LDV) systems were used to measure the velocity profile very near the bottom. A method was developed to find the wave-induced bed shear stress over a smooth bed from the measured velocities within or near the viscous sub-layer. A unified 2D numerical model was developed to simulate the entire flow field from bottom to free surface. The model solves the Reynolds Averaged Navier-Stokes (RANS) equations, with the BSL k-ω turbulence closure model that can capture the turbulence inside and outside of boundary layer. The numerical results were compared to the experimental data and available theories in terms of free surface displacement, mean velocity, turbulence intensity, and bed shear stress. Discussions were made on the effects of the turbulence characteristics on changing the patterns of mean velocity profile and bed shear stress. Further efforts were made to revisit the existing boundary layer theories, trying to quantifying the role of free stream velocity and acceleration as well as eddy viscosity in modifying the response properties of the bed shear stress under unsteady flows. A formula was proposed to calculate the instantaneous bed shear using the free stream velocity and acceleration. The results using the present formula are compared to those from the earlier works for solitary wave, dam break wave, and saw-tooth wave.

Investigating the flow characteristics of air-lift pumps operating in gas–liquid two-phase flow

Abstract Experiments were conducted to investigate the flow characteristics in the riser pipe and the suction pipe of airlift pump at a series of air flow rates and submergence ratios by using a high speed camcorder and a Laser Doppler Velocimetry system (LDV). A modified model was developed to predict the performance of airlift pump operating in gas–liquid two-phase flow. The results show that an unstable flow structure composed by a water falling film, a bubbly mixture, a water ascending film appearing alternately in riser pipe dominates the performance of airlift pump at large air flow rates. The bubbly mixture with a strongest capacity for pumping water first increases to its maximum and then slightly decreases. In suction pipe, the average velocity shows a flat profile and increases with increasing submergence ratio. Moreover, the predicted results of modified model are in good agreement with the experimental data in a margin of ± 12%.

Camera-based assessment of arterial stiffness and wave reflection parameters from neck micro-motion

The feasibility of a camera-based extraction of carotid distension waveforms offers the prospect of a user-friendly alternative to laser Doppler velocimetry (LDV) or accelerometry-based systems. Upon supplementary calibration of vessel wall displacement to arterial pressure, our system may also be an appealing alternative to applanation tonometry for extracting cardiac-related features from the central pulse pressure waveform. Objective: This paper describes the application of camera-based micro-motion imaging to extract health-related features from the contour of the carotid displacement waveform. Approach: We build on the assumption that the cardiac-related frequency components of the skin motion (sMOT) waveform, as acquired at the vicinity of the carotid artery under uneven illumination, receive a dominant contribution from the carotid wall displacement. We propose a two-step approach at which sMOT signals are queried based on the local amplitude of remote-photoplethysmography sensors spanning the neck’s skin and then ensemble-averaged for cardiovascular health assessment. Main results: The feasibility of the system is demonstrated for assessing stiffness index, augmentation pressure, augmentation index and reflection magnitude on a dataset comprising 28 participants (ages 23 to 62 yrs; 22 males). Significance: Although presented here as a standalone system, micro-motion imaging can be an auxiliary technique for improving sensor placement and signal quality of tonometric or LDV technologies.

Turbulence measurements in an axial rotary blood pump with laser Doppler velocimetry.

The implantation of rotary blood pumps as ventricular assist devices (VADs) has become a viable therapy for quite a number of patients with end-stage heart failure. However, these rotary blood pumps cause adverse events that are related to blood trauma. It is currently believed that turbulence in the pump flow plays a significant role. But turbulence has not been measured to date because there is no optical access to the flow space in rotary blood pumps because of their opaque casings. This difficulty is overcome with a scaled-up model of the HeartMate II (HM II) rotary blood pump with a transparent acrylic housing. A 2-component laser Doppler velocimetry (LDV) system was used for the measurement of time resolved velocity profiles and velocity spectra upstream and downstream of the rotor blades. Observing similarity laws, the speed and pump head were adjusted to correspond closely to the design point of the original pump - 10,600 rpm speed and 80 mmHg pressure head. A model fluid consisting of a water-glycerol mixture was used. The measured velocity spectra were scalable by the Kolmogorov length and the Kolmogorov length was estimated to be between 14 and 24 µm at original scale, thus being about 1.5 to 3 times the size of a red blood cell. It can be concluded that turbulence is indeed present in the investigated blood pump and that it can be described by Kolmogorov's theory of turbulence. The size of the smallest vortices compares well to the turbulence length scales as found in prosthetic heart valves, for example.

Laser doppler velocimetry and confined flows

Finding the mode, in which two component laser Doppler velocimetry can be applied to flows confined in cylindrical tubes or vessels, was the aim of this study. We have identified principle issues that influence the propagation of laser beams in laser Doppler velocimetry system, applied to flow confined in cylindrical tube. Among them, the most important are influences of fluid and wall refractive indices, wall thickness and internal radius ratio and beam intersection angle. In analysis of the degrees of these influences, we have applied mathematical model, based on geometrical optics. The separation of measurement volumes, that measure different velocity components, has been recognized as the main drawback. To overcome this, we propose a lens with dual focal length ? primary focal length for the measurement of one velocity component and secondary focal length for the measurement of the other velocity component. We present here the procedure for calculating the optimal value of secondary focal length, depending on experimental set-up parameters. The mathematical simulation of the application of the dual focal length lens, for chosen cases presented here, confirmed the accuracy of the proposed procedure.

Glial Endothelin-1 Regulates Retinal Blood Flow During Hyperoxia in Cats.

To investigate the role of endothelin-1 (ET-1) in retinal glial cells in regulating retinal blood flow (RBF) during hyperoxia in cats. We measured the vessel diameter (D), blood velocity (V), and blood flow (F) simultaneously in first-order retinal arterioles using a laser Doppler velocimetry system. The animals were under general anesthesia during hyperoxia (100% oxygen) for 10 minutes 24 hours after intravitreal injection of L-2-aminoadipic acid (LAA), a gliotoxic compound, or diluted hydrochloric acid (0.01 N) used as the vehicle control. We also measured the changes in the RBF after intravitreal injection of BQ-123, a specific ET type A receptor antagonist, in LAA-treated eyes. To examine if endothelin-converting enzyme-1 (ECE-1), as an ET-1-generating enzyme located in retinal glial cells, immunohistochemical examinations with costaining of antiglial fibrillary acidic protein (GFAP) antibody and anti-ECE-1 antibody were performed in whole-mount retinas. During hyperoxia, the decreases in D, V, and F in response to hyperoxia were attenuated significantly (P < 0.01 for all comparisons) in the LAA-treated eyes compared with the vehicle control (LAA, D, -8.5 ± 1.5%; V, -13.8 ± 1.5%; F, -27.8 ± 3.0% versus vehicle control, D, -16.8 ± 1.3%; V, -26.3 ± 2.0%; F, -48.9 ± 2.4%). In LAA-treated eyes, intravitreal injections of BQ-123 did not change the rate of hyperoxia-induced RBF compared to LAA-treated eyes. The anti-ECE-1 antibody was costained with anti-GFAP antibody in the whole-mount retinas. The current findings suggest that retinal glial ET-1 may play an important role in regulating RBF during hyperoxia in cats.

Dynamic strain measurements of marine propellers under non-uniform inflow

An experimental investigation was conducted to determine the dynamic strain characteristics of marine propellers under non-uniform inflow. Two 7-bladed highly skewed model propellers of identical geometries, but different elastic characteristics were tested at various rotational speeds and free stream velocities in the water tunnel. Two kinds of wire mesh wake screens located 400mm upstream of the propeller plane were used to generate four-cycle and six-cycle inflows. A laser doppler velocimetry (LDV) system located 100mm downstream of the wake screen plane was used to measure the axial velocity distributions produced by the wake screens. Strain gauges were bonded onto the propeller blades in different positions. A customized underwater data acquisition system which can record data off-line was used to record the dynamic strain. The results show that the frequency properties of the blade dynamic strain are determined by the harmonics of the inflow and that the stiffness of the propeller has an essential effect on the dynamic strain amplitudes.

A comparative experimental evaluation of uncertainty estimation methods for two-component PIV

Uncertainty quantification in planar particle image velocimetry (PIV) measurement is critical for proper assessment of the quality and significance of reported results. New uncertainty estimation methods have been recently introduced generating interest about their applicability and utility. The present study compares and contrasts current methods, across two separate experiments and three software packages in order to provide a diversified assessment of the methods. We evaluated the performance of four uncertainty estimation methods, primary peak ratio (PPR), mutual information (MI), image matching (IM) and correlation statistics (CS). The PPR method was implemented and tested in two processing codes, using in-house open source PIV processing software (PRANA, Purdue University) and Insight4G (TSI, Inc.). The MI method was evaluated in PRANA, as was the IM method. The CS method was evaluated using DaVis (LaVision, GmbH). Utilizing two PIV systems for high and low-resolution measurements and a laser doppler velocimetry (LDV) system, data were acquired in a total of three cases: a jet flow and a cylinder in cross flow at two Reynolds numbers. LDV measurements were used to establish a point validation against which the high-resolution PIV measurements were validated. Subsequently, the high-resolution PIV measurements were used as a reference against which the low-resolution PIV data were assessed for error and uncertainty. We compared error and uncertainty distributions, spatially varying RMS error and RMS uncertainty, and standard uncertainty coverages. We observed that qualitatively, each method responded to spatially varying error (i.e. higher error regions resulted in higher uncertainty predictions in that region). However, the PPR and MI methods demonstrated reduced uncertainty dynamic range response. In contrast, the IM and CS methods showed better response, but under-predicted the uncertainty ranges. The standard coverages (68% confidence interval) ranged from approximately 65%–77% for PPR and MI methods, 40%–50% for IM and near 50% for CS. These observations illustrate some of the strengths and weaknesses of the methods considered herein and identify future directions for development and improvement.

Experimental and numerical studies on the flow-induced vibration of propeller blades under nonuniform inflow

This article presents the experimental and numerical studies on the flow-induced vibration of propeller blades under periodic inflows. A total of two 7-bladed highly skewed model propellers of identical geometries but different elastic characteristics were operated in four-cycle and six-cycle inflows to study the blade vibratory strain response. A total of two kinds of wire mesh wake screens located 400 mm upstream of the propeller plane were used to generate four-cycle and six-cycle inflows. A laser Doppler velocimetry system located 100 mm downstream of the wake screen plane was used to measure the axial velocity distributions produced by the wake screens. Strain gauges were bonded onto the propeller blades in different positions. Data from strain gauges quantified vibratory strain amplitudes and excitation frequencies induced by the wake screens. The propellers were accelerated through the flexible propeller’s fundamental frequency to investigate the effect of resonance on vibratory strain response. The numerical work was conducted using large eddy simulation and moving mesh technique to predict the unsteady forces acting on the propeller blade when operating in a nonuniform inflow.

Structures of Methane-Air and Propane-Air Turbulent Premixed Bunsen Flames

ABSTRACTStructures of turbulent Bunsen flames in the corrugated-flamelet regime were investigated by use of a three-color six-beam laser-Doppler velocimetry system. Four different mixtures with identical laminar burning velocities (0.34 m/s) were selected to facilitate comparisons—lean and rich methane, and lean and rich propane. A bimodal distribution, not previously reported in the literature on turbulent Bunsen flames, was observed in the radial component of gas velocity off-axis in the turbulent flame brush. Our previous measurements enabled the low-velocity mode to be identified as velocity fluctuations of the unburned mixture and the high-velocity mode as fluctuations of the burned-gas radial velocity. Favre-averaged and Reynolds-averaged reaction-progress variables were then calculated from these bimodal distributions, identifying an initially unexpected region near the flame tips where, at a fixed radius, the average progress variable decreased (rather than increasing) with increasing height over a short distance, likely through enhanced flamelet flapping, which has not been predicted by modeling but which appears to occur quite generally for sufficiently tall turbulent Bunsen flames in quiescent ambient environments, for the corrugated-flamelet regime. Conditioned and unconditioned Favre-average velocity components and intensities also were calculated from the data for future tests of modeling. The distributions of the progress variables also clearly showed that the turbulent burning velocity of the rich propane flame was appreciably larger than that of any of the other three, as was its radial flame-brush thickness at any given height, and its high-radial-velocity mode had a higher average velocity magnitude than the others. Similarly, the turbulent burning velocity and flame-brush thickness appear to be smaller for the lean propane flame. These differences can be attributed to influences of preferential oxygen diffusion to turbulence-induced flamelet bulges, not included in existing modeling approaches, for the rich propane flames, and to a corresponding inhibition of fuel diffusion to the bulges in the lean flames. The former phenomenon is related to but different from the well-known cellular-flamelet instability, these effects occurring for flames that are stable to diffusive-thermal disturbances. It was concluded that a greater fraction of the total amount of heat release occurs in the upstream half of the turbulent flame brush in the rich propane flame, producing enhanced flow divergence in the upstream region, while the reduced ability of the slowly diffusing fuel to reach bulges in the lean flame generates the opposite effect. The results point to directions in which turbulent-combustion modeling needs to be improved, and an approach to modeling this type of preferential-diffusion effect is suggested.

Comparison of Flame Stability Under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame

The flame characteristics of a pilot-scale swirl burner for air and oxy-fuel combustion of pulverized coal are investigated. The local burner air (or oxygen) ratio λ and the oxygen concentration have been systematically varied. The investigated flames were characterized recording UV emissions originating from OH* chemiluminescence indicating the reaction zone in the gas phase, measuring the axial and tangential velocities using an laser Doppler velocimetry (LDV) system and analyzing the composition of the flue gas. A change of the flame structure was revealed from the conducted measurement: the “regular” flame for the investigated burner is characterized by a cone-shaped swirling combustion zone with a distinct inner recirculation zone. Reducing the oxidizer flows through the burner leads to a breakdown of the inner recirculation zone and a significant change of the flame pattern. This change was identified by the LDV measurements as well as from the chemiluminescence images, and it was found to be closely related to the momentum flow through the burner into the main combustion zone.

An improved instantaneous laser Doppler velocity system

In this paper, improvements made on a single velocity component instantaneous laser Doppler velocimetry (ILDV) system are detailed. The ILDV system developed in this research effort is capable of measuring a single velocity component at a rate as high as two megahertz. The current system accounts for the effects of the laser intensity variation on the measured velocity and eliminates the use of a Pockels cell used in previous ILDV systems. The system developed in the current effort was tested using compressible, subsonic jet flows. The ILDV system developed would be most beneficial where a high data capture rate is needed such as in shock tubes, and high-speed wind tunnels.

An In Vitro Hemodynamic Flow System to Study the Effects of Quantified Shear Stresses on Endothelial Cells

Numerous in vitro systems have previously been developed and employed for studying the effects of hemodynamics on endothelial cell (EC) dysfunction. In the majority of that work, accurate flow quantification (e.g., uniformity of the flow over the ECs) remains elusive and wall shear stress (WSS) quantifications are determinedusing theoreticalrelationships (without considering theflow channelaspect ratio effects).In addition, thoserelationships are not applicable to flows other than steady laminar cases.The present work discusses the development of a novel hemodynamic flow system for studying the effects of various well-quantified flow regimes over ECs. The current work presents a novel hemodynamic flow system applying the concept of a parallel plate flow chamber (PPFC) with live microscopy access for studying the effects of quantified WSS on ECs. A range of steady laminar, pulsatile (carotid wave form) and low-Reynolds number turbulent WSSs were quantified throughvelocity field measurements by a laser Doppler velocimetry (LDV) system, to validate the functionality of the current hemodynamic flow system. Uniformity of the flow across the channel width can be analyzed with the current system (e.g., the flow was uniform across about 65-75% of the channel width for the steady cases). The WSS obtained from the experiments had higher values in almost all of the cases when compared to the most commonly-used theoretical solution (9%<error<16%), whereas another relationship, which considers the channel dimensions, had better agreement with the experimental results (1%<error<8%). Additionally, the latter relationship predicted the uniform flow region in the PPFC with an average difference of <5% when compared to the experimental results. The experimental data also showed that the WSS at various locations (D, E and F) at the test section differed by less than 4% for the laminar cases representing a fully developed flow. WSS was also determined for a low-Re (Re=2750) turbulent flow using (1) the Reynolds shears stress and (2) the time-averaged velocity profile gradient at the wall, with a good agreement (differences <16%) between the two where the first method returned a higher value than the second. Porcine aortic endothelial cell (PAEC) viability in the system and morphological cell response to laminar WSS of about 11 dyne/cm(2), were observed. These results provideperformance validationof this novelin vitrosystem with many improved featurescompared to previous similarprototypes for investigation of flow effects on ECs. The integration of the LDV technique in the current study and the comparison of the results with those from theory revealed that great care must be taken when using PPFCs since the commonly used theoretical relation for laminar steady flows is unable to predict the flow uniformity (which may introduce significant statistical bias in biological studies) and the predicted WSS was subjected to greater error when compared to a more comprehensive equation presented in the current work. Moreover, application of the LDV technique in the current system is essential for studies of more complex cases, such as disturbed flows, where the WSS cannot be predicted using theoretical or numerical modelling methods.

Beam pointing angle optimization and experiments for vehicle laser Doppler velocimetry

Beam pointing angle (BPA) is one of the key parameters that affects the operation performance of the laser Doppler velocimetry (LDV) system. By considering velocity sensitivity and echo power, for the first time, the optimized BPA of vehicle LDV is analyzed. Assuming mounting error is within ±1.0 deg , the reflectivity and roughness are variable for different scenarios, the optimized BPA is obtained in the range from 29 to 43 deg. Therefore, velocity sensitivity is in the range of 1.25 to 1.76 MHz/(m/s) , and the percentage of normalized echo power at optimized BPA with respect to that at 0 deg is greater than 53.49%. Laboratory experiments with a rotating table are done with different BPAs of 10, 35, and 66 deg, and the results coincide with the theoretical analysis. Further, vehicle experiment with optimized BPA of 35 deg is conducted by comparison with microwave radar (accuracy of ±0.5% full scale output). The root-mean-square error of LDV’s results is smaller than the Microstar II’s, 0.0202 and 0.1495 m/s , corresponding to LDV and Microstar II, respectively, and the mean velocity discrepancy is 0.032 m/s . It is also proven that with the optimized BPA both high velocity sensitivity and acceptable echo power can simultaneously be guaranteed.

Experimental and Computational Investigations of a Normal-Hole-Bled Supersonic Boundary Layer

A series of experiments have been conducted on a bleed hole array spanning the width of the Cambridge University Engineering Department supersonic wind tunnel at Mach numbers of 1.8 and 2.5. The wind tunnel was run with varying levels of suction, and the flow structure over the bleed array was subsequently mapped with a laser Doppler velocimetry system at a resolution of 0.25 hole diameters or better. The same wind-tunnel setup was simulated using the OVERFLOW Navier–Stokes equation solver. The information obtained was used primarily in qualitative comparisons of flow patterns. Overall good agreement was found in the definition of the expansion fan and barrier shock pattern produced by flow entering the normal holes, as well as three-dimensional flow patterns. Both studies agreed well in terms of measured mass flow rates, to within 1% of the boundary-layer mass flow. The presence of the barrier shock standing off the downstream edge of the bleed holes corresponded with a jet of upward flow, which may provide a mechanism for the generation of streamwise vortices.

Correlation of frictional drag and roughness length scale for transitionally and fully rough turbulent boundary layers

This study investigates zero-pressure-gradient turbulent boundary layers for several rough surfaces in the transitionally rough and fully rough flow regimes. The tested surfaces include, but are not limited to marine antifoulings as irregularly rough engineering surfaces. The boundary layer profiles were measured by using a two-dimensional Laser Doppler Velocimetry system. The coatings were applied with different procedures to simulate the effect of different application types. An attempt was made to find a new roughness length scale which provides a good correlation to represent the roughness functions for both transitionally and fully rough flow regimes. Surface roughness measurements with a laser profilometer device were carried out to determine several roughness parameters to be used in the calculation of the roughness length scale. Different roughness calculation methods, with varying low-pass filter window lengths and sampling lengths, were applied to determine their effect on the roughness parameters and hence the roughness function correlations.The paper presents a new definition for the roughness length scale and covers the details of the measurements, analyses, discussions regarding the differences between the surfaces, the effect of the roughness calculation methods and application type of the antifouling coatings.

Relationship Between Retinal Blood Flow and Serum Adiponectin Concentrations in Patients With Type 2 Diabetes Mellitus.

To study the relationship between retinal microcirculation and serum adiponectin, an important adipocytokine secreted by adipocytes, concentrations in patients with type 2 diabetes mellitus. Using a laser Doppler velocimetry system, we simultaneously measured the retinal blood flow (RBF) values and retinal vessel diameter and blood velocity in 64 consecutive Japanese patients (mean age ± SD, 59.8 ± 10.4 years) with type 2 diabetes with no or mild nonproliferative diabetic retinopathy. We compared the values with the RBF and serum adiponectin concentrations in these patients. The patients were divided into two groups based on sex (33 males, 31 females). The plasma adiponectin concentrations were correlated positively with the retinal vessel diameter (r = 0.480; P = 0.005), retinal blood velocity (r = 0.399; P = 0.02), and RBF (r = 0.518; P = 0.002) and correlated negatively with the retinal arterial vascular resistance (r = -0.598; P = 0.0002) in males, but not females, with type 2 diabetes with early-stage diabetic retinopathy. Multiple regression analysis showed that the plasma adiponectin level was independently and positively correlated with RBF and negatively correlated with retinal arterial vascular resistance. Our results indicated that a high concentration of serum adiponectin may be associated with increased RBF, probably via the increased blood velocity and dilated vessel diameter in males with type 2 diabetes with early-phase diabetic retinopathy.

High-resolution in-situ LDV monitoring system for measuring velocity distribution in blood vessel

We herein describe a cross-sectional multiple-point laser Doppler velocimetry (CS-MLDV) system for monitoring blood vessels that are sutured and connected during an operation. In order to observe the condition of a blood vessel during an operation, the previously developed linear MLDV (L-MLDV) system can realize velocity distribution imaging of the carotid artery in a living mouse by means of traverse laser light. We subsequently developed a CS-MLDV system, which can measure the instantaneous two-dimensional (2D) flow velocity, by upgrading the optical components and signal processing used in L-MLDV. The validity of the CS-MLDV results was verified through comparison with the results of a computational fluid dynamics (CFD) analysis. The results of the CFD analysis were similar to the experimental results obtained under the same flow field condition. Moreover, an instantaneous 2D velocity distribution can be obtained even for the case of flowing blood. Finally, we carried out in-vivo measurement in a mesenteric vessel of a mouse in order to demonstrate the potential of the CS-MLDV for use in surgery.

Intermittency in the Transition to Turbulence for a Shear-Thinning Fluid in Hagen-Poiseuille Flow

Since Reynolds original experiments in 1883, very few studies have been carried out on the transition to turbulence for shear thinning fluid in Hagen-Poiseuille. Compared to the Newtonian fluids, the results showed two interesting phenomenon: a delay in transition to turbulence and the appearance of an asymmetry in the mean axial velocity profiles. In this study, we measured experimentally the fraction factor and axial velocity profiles using Laser Doppler Velocimetry system (LDV) at different Reynolds numbers. It is shown an axisymmetric in the mean axial velocity profiles for laminar and turbulent regimes and an increasing asymmetry profile with increasing Rew for transition regime. Two different stages are clearly identified during transition to turbulence. The first stage which we called it pre-transition, took place only in the non Newtonian fluids while the second stage correspond to the appearance of turbulent puffs. Another objective of this study is the statistical analysis of the axial velocity fluctuation. In the transition regime, power spectra identified the existence of a weak turbulence. It is generated by the shear-thinning character of the fluid, which follows a power law with an exponent close to -3 (f -3).