Time-resolved Particle Image Velocimetry Measurements Research Articles

The near wake of a sinusoidal wavy cylinder with a large spanwise wavelength using time-resolved particle image velocimetry

The near wake of a sinusoidal wavy cylinder is investigated using time-resolved particle image velocimetry (TR-PIV). The wavy cylinder has a large spanwise wavelength of six mean diameters. TR-PIV measurements are taken in three orthogonal planes in the near wake at a Reynolds number Re = 3.0 × 103. Flow structures are documented in detail, in terms of time-mean flows, Reynolds stresses, and dominant structures. A substantially long recirculation bubble is observed downstream of the saddle and node planes, corroborating the fact that fluid forces are largely reduced. Furthermore, different frequencies of vortex shedding at the saddle and node are observed for the first time, that is, vortical structures shed from the saddle and node at higher and lower frequencies, respectively. In the cross-stream plane, time-mean streamwise vorticities concentrate between the saddle and node and show an alternating pattern along the spanwise direction. Moreover, results from proper orthogonal decomposition (POD) analyses reveal distinct characteristics in the lower POD modes for the saddle and node planes; meanwhile, upwash/downwash flows downstream of the saddle, together with streamwise vortices, are associated with the lower POD modes in the cross-stream plane. Comparison is made between the present results and that for a wavy cylinder with a relatively small wavelength at similar Reynolds numbers.

Synchronization of multi-plane measurement data by means of POD: application to unsteady boundary layer transition

Time-resolved particle image velocimetry measurements have been performed on the suction side of a low-pressure turbine cascade perturbed by periodic unsteady incoming wakes. The flow field has been investigated in two orthogonal planes. A wall-normal and a wall-parallel plane have been considered to identify and characterize the dimensions of the coherent structures developing within the boundary layer at the different wake passing phases. A new proper orthogonal decomposition (POD)-based procedure has been developed to sort the data acquired in the two planes. Particularly, the temporal coefficients of the POD modes related to wake migration have been used to provide phase-averaged data and synchronize the information obtained in the two measurement planes. It is shown that this technique does not require an external trigger, typically requested by previous available multi-plane phase-locking strategies. Moreover, POD has been applied to sub-ensembles of data at the same relative phase within the wake passing cycle. Thanks to the proposed procedure, the characteristic dimension of the eddies caused by the wake–boundary layer interaction has been investigated: at each phase of the wake passing cycle, the POD provides the representation of the most relevant flow features. It has been possible to observe the presence of boundary layer streaks and when they first occur within the wake passing period. One-dimensional auto-correlations of the velocity fields in the wall-parallel plane have been performed following the periodic perturbation induced by the passing wake in space and time. The auto-correlation provides the spacing between streaks, that, once scaled with the local boundary layer displacement thickness measured at the same phase in the wall-normal plane, is consistent with the available literature data for steady flows.

Stereoscopic TR-PIV measurements of mixed convection flow in a vertical channel with an open cavity with discrete heating

An experimental investigation of opposing mixed convection is carried out using stereoscopic time-resolved particle image velocimetry (TR-PIV) to assess the thermal effects on the flow structure over an open cubical cavity that lies at the midsection of a vertical water channel. The ratio between the channel and cavity depth is of 1, the wall facing the opening is isothermal and all other walls are adiabatic. The complex interaction between the induced incompressible forced flow at ambient temperature and buoyancy-induced flow from the heated wall of the cavity are studied experimentally for fixed Prandtl number of Pr=7, buoyancy strength or Richardson number in the range 0 ≤ Ri ≤ 20, and two Reynolds numbers defined with the channel hydraulic diameter and the mean velocity in the upstream channel of Re=1500 and 4500 that correspond to laminar and turbulent upstream boundary layers, respectively. The 3D flow features are presented in the form of mean statistics and instantaneous flow properties in planes normal to the cavity floor. It is found that the shear layer development is highly 3D due to the confinement effect induced by the lateral walls. We also show the modulation effect of opposing buoyancy on the flow distributions and the time-evolution of the shear layer. Also, the complex dynamics of the coherent structures in the region surrounding the cavity show that the entrainment rate is modified with increasing buoyancy. Root-mean-square contours of the fluctuating laminar velocity fields have been obtained, and Reynolds stress distribution and proper orthogonal decomposition analysis for the turbulent case show that an increase in the fractional energy of the characteristic POD modes takes place for increasing Ri numbers.

Unsteady Flow Physics of Airfoil Dynamic Stall

A series of wind-tunnel experiments was conducted on a dynamically pitching NACA 0012 airfoil in order to understand the unsteady flow physics associated with dynamic stall at a transitional Reynolds number of . The airfoil was pitched about the quarter-chord axis following a linear ramp maneuver at . A series of high-frequency unsteady surface pressure measurements were acquired in order to investigate the time-dependent behavior of the flow in the immediate vicinity of the airfoil. These surface pressure measurements actively displayed the evolution of the airfoil boundary layer, leading-edge laminar separation bubble, and dynamic stall vortex. A detailed time-frequency analysis of surface pressure measurements was performed in order to identify the dominant frequencies associated with the unsteady laminar separation bubble. This analysis was also used to study the evolution of the length scales associated with flow structures near the airfoil leading edge, which emerged before the formation of the dynamic stall vortex. Finally, time-resolved particle image velocimetry measurements were acquired to study the evolution of the off-body flowfield during the development of dynamic stall.

Time-resolved PIV measurement of influence of upstream roughness on separated and reattached turbulent flows over a forward-facing step

This study reports an experimental investigation of the effects of upstream roughness on a low Reynolds number turbulent boundary layer over a forward-facing step. Two types of upstream roughness were investigated, including a transitionally rough 16-grit sandpaper (ks+ ≈ 69) and fully rough staggered cubes (ks+ ≈ 500). A two-dimensional two-component time-resolved particle image velocimetry (2D-2C TR-PIV) method was used to measure the time-averaged mean velocities, Reynolds stresses, temporal auto-correlations and frequency spectra of the flow field to quantify the influence of upstream roughness on the downstream evolution of the turbulence over the step. The results indicate that upstream roughness decreased the vortex shedding frequency. Roughness also decreased the reattachment length by enhancing the streamwise turbulence intensity level, reducing the magnitude of backflow and suppressing the vortex shedding frequency in comparison to the smooth wall. In the recirculation region, upstream roughness reduced the mean streamwise velocity only in the outer layer. The Reynolds stresses remained relatively unchanged by the sandpaper roughness but were significantly modified by the cube roughness. Downstream of the leading edge, the staggered cubes increased the streamwise Reynolds stress both near the wall and outside the shear layer but decreased the wall-normal Reynolds stress and Reynolds shear stress within the shear layer. These modifications are inversely proportional to distance in the recirculation region. The life times of the streamwise and wall-normal velocity fluctuations increase with streamwise distance and are much longer in the redevelopment region than in the recirculation region. Quadrant decomposition and joint probability density functions of the velocity fluctuations were also measured to characterize upstream roughness effects on the downstream evolution of the dominant motions producing the Reynolds shear stress.

Experimental study of human thermal plumes in a small space via large-scale TR PIV system

In small occupied spaces such as vehicle cabins, in-depth information about human thermal plumes can be important for designing ventilation systems, especially in the case of displacement ventilation. In this study, large-scale time-resolved particle image velocimetry measurements were performed to reveal airflow characteristics of thermal plumes inside a small space with high temporal and spatial resolutions. The measured time-averaged velocity showed that the development of thermal plumes was limited by the small space, with maximum vertical velocity of 0.184 m/s above the head. The standard deviation of velocity and the turbulence intensity (TI) indicated high fluctuation characteristics, with TI of approximately 0.4 in the mainstream area. With these time-resolved data, the integral, Taylor and Kolmogorov scales were calculated, which provided recommended grid sizes and time steps for different numerical simulations. For investigation of instantaneous characteristics and vortex structures, three vortex identification parameters were compared. The vorticity index identified bulky attached and detached vortexes around the head; the Q-criterion revealed that the mainstream area was controlled mainly by deformation structures; and the λci criterion, which was the most effective means of identification, avoided the influences of deformation structures and focused only on the rotation structures with directions of rotation. Furthermore, multi-scaled characteristics of thermal plumes were revealed by proper orthogonal decomposition, and the period of ascending plumes was estimated as 5 s.

Time-resolved PIV measurements in a low-aspect ratio facility of randomly packed spheres and flow analysis using modal decomposition

This work experimentally investigated the flow characteristics in a facility with randomly packed spheres at a low-aspect ratio of 4.4. Velocity fields in the near-wall region and in the pores between spheres were obtained by employing the matched-index-of-refraction (MIR) and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of 340, 520, and 720. From the obtained TR-PIV velocity vector fields, flow characteristics including first- and second-order statistics, such as mean velocity, root-mean-square fluctuating velocity, and Reynolds stress profiles, were computed. The effects of the wall enclosure and Reynolds numbers on the flow patterns were investigated by comparing the computed flow statistics and evaluating two-point cross correlations of the velocities measured adjacent to and far from the wall. Comparisons of the mean velocities, root-mean-square fluctuating velocities, and Reynolds stress component showed an increase in flow mixing and turbulent intensity in the gaps between spheres in the packed bed. The re-circulation-region sizes, however, were found to be independent from an increase in Reynolds numbers. Finally, flow modal decompositions, such as the proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), were applied to the vorticity fields extracted from sub-regions located near and far from the wall to reveal the most dominant POD and DMD flow structures.

Pulse-burst PIV of an impulsively started cylinder in a shock tube for Re > 105

The impulsive start of a circular cylinder in a shock tube was characterized with time-resolved particle image velocimetry measurements (TR-PIV) at 50 kHz using a pulse-burst laser. Three Reynolds numbers Re of 1.07, 1.63 and 2.46 × 105 were studied adding insight into the transient process near the drag crisis. In all cases, vorticity was maximum in the first pair of vortices formed. In a fashion analogous to previous studies at Re ≤ 104, a single symmetric vortex pair was first shed from the cylinder at Re = 1.07 × 105 prior to the eventual transition to a von Karman vortex street. In contrast, at Re ≥ 1.63 × 105, two or more symmetric vortex pairs were first shed. The non-dimensional time for the wake to begin to exhibit asymmetry was also found to be lower at the two higher Re. The time required to reach a fully antisymmetric wake (peak von Karman shedding) was roughly five times the asymmetric onset time. Altogether, the study indicates a transformation in the impulsive wake structure and associated time scales to occur at Re near 1.6 × 105.

Secondary instabilities in the wake of an elongated two-dimensional body with a blunt trailing edge

The secondary instability in the wake of a two-dimensional blunt body with a chord to thickness ratio of 46.5 was experimentally investigated for Reynolds numbers of 3500, 5200 and 7000 based on the blunt trailing edge height $h$. Planar, stereoscopic and high-speed particle image velocimetry (PIV) measurements were performed to characterise the wake and upstream boundary layer. The same mode B secondary instability that is found in the cylinder wake was found to be present in the wake of the elongated body studied here. The most probable wavelength of the secondary instability, defined as the spanwise distance between adjacent streamwise vortex pairs in the wake, was found to range from $0.7h$ to $0.8h$ by applying a spatial autocorrelation to the spanwise–wall-normal instantaneous fields of the $Q$-criterion. The temporal evolution of the secondary wake vortices was investigated using time-resolved stereoscopic PIV measurements and it was shown that the vortices maintain both their directions of rotation and spanwise positions during the primary vortex shedding cycles. In agreement with previous literature, the secondary instability did not greatly change as the upstream boundary layer transitioned from laminar to turbulent. Moreover, any upstream boundary layer structures were found to rapidly evolve into wake structures just past the blunt trailing edge. The wavelength of the secondary instability was shown to match the spanwise distance between adjacent low-speed zones of streamwise velocity in the wake. These undulating velocity patterns proved to be a viable method for determining the secondary instability wavelength; however, this type of analysis is highly sensitive to the energy content used for data reconstruction when proper orthogonal decomposition is applied beforehand.

Assessment of human left ventricle flow using statistical shape modelling and computational fluid dynamics

Blood flow patterns in the human left ventricle (LV) have shown relation to cardiac health. However, most studies in the literature are limited to a few patients and results are hard to generalize. This study aims to provide a new framework to generate more generalized insights into LV blood flow as a function of changes in anatomy and wall motion. In this framework, we studied the four-dimensional blood flow in LV via computational fluid dynamics (CFD) in conjunction with a statistical shape model (SSM), built from segmented LV shapes of 150 subjects. We validated results in an in-vitro dynamic phantom via time-resolved optical particle image velocimetry (PIV) measurements. This combination of CFD and the SSM may be useful for systematically assessing blood flow patterns in the LV as a function of varying anatomy and has the potential to provide valuable data for diagnosis of LV functionality.

On Street-Canyon Flow Dynamics: Advanced Validation of LES by Time-Resolved PIV

The advanced statistical techniques for qualitative and quantitative validation of Large Eddy Simulation (LES) of turbulent flow within and above a two-dimensional street canyon are presented. Time-resolved data from 3D LES are compared with those obtained from time-resolved 2D Particle Image Velocimetry (PIV) measurements. We have extended a standard validation approach based solely on time-mean statistics by a novel approach based on analyses of the intermittent flow dynamics. While the standard Hit rate validation metric indicates not so good agreement between compared values of both the streamwise and vertical velocity within the canyon canopy, the Fourier, quadrant and Proper Orthogonal Decomposition (POD) analyses demonstrate very good LES prediction of highly energetic and characteristic features in the flow. Using the quadrant analysis, we demonstrated similarity between the model and the experiment with respect to the typical shape of intensive sweep and ejection events and their frequency of appearance. These findings indicate that although the mean values predicted by the LES do not meet the criteria of all the standard validation metrics, the dominant coherent structures are simulated well.

Double helix vortex breakdown in a turbulent swirling annular jet flow

Double helical vortex breakdown is rarely observed in experiments and is mostly reported for laminar flows. A double helical breakdown structure in a turbulent annular jet is identified and its dynamics analyzed based on time-resolved tomographic particle image velocimetry measurements.

Aeroacoustic analysis of an airfoil with Gurney flap based on time-resolved particle image velocimetry measurements

Particle image velocimetry for the experimental assessment of trailing edge noise sources has become focus of research in recent years. The present study investigates the feasibility of the noise prediction for high-lift devices based on time-resolved particle image velocimetry (PIV). The model under investigation is a NACA 0015 airfoil with a Gurney flap with a height of 6% of the chord length. The velocity fields around and downstream of the Gurney flap were measured by PIV and used to compute the corresponding pressure fields by solving the Poisson equation for incompressible flows. The reconstructed pressure fluctuations on the airfoil surface constitute the source term for Curle's aeroacoustic analogy, which was employed in both the distributed and compact formulation to estimate the noise emission from PIV. The results of the two formulations are compared with the simultaneous far-field microphone measurements in the temporal and spectral domains. Both formulations of Curle's analogy yield acoustic sound pressure levels in good agreement with the simultaneous microphone measurements for the tonal component. The estimated far-field sound power spectra (SPL) from the PIV measurements reproduce the peak at the vortex shedding frequency, which also agrees well with the acoustic measurements.

Assessment of the pseudo-tracking approach for the calculation of material acceleration and pressure fields from time-resolved PIV: part II. Spatio-temporal filtering

The present study characterises the spatio-temporal filtering associated with pseudo-tracking. A combined theoretical and numerical assessment is performed that uses the relatively simple flow case of a two-dimensional Taylor vortex as analytical test case. An additional experimental assessment considers the more complex flow of a low-speed axisymmetric base flow, for which time-resolved tomographic PIV measurements and microphone measurements were obtained. The results of these assessments show how filtering along Lagrangian tracks leads to amplitude modulation of flow structures. A cut-off track length and spatial resolution are specified to support future applications of the pseudo-tracking approach. The experimental results show a fair agreement between PIV and microphone pressure data in terms of fluctuation levels and pressure frequency spectra. The coherence and correlation between microphone and PIV pressure measurements were found to be substantial and almost independent of the track length, indicating that the low-frequency behaviour of the flow could be reproduced regardless of the track length. It is suggested that a spectral analysis can be used inform the selection of a suitable track length and to estimate the local error margin of reconstructed pressure values.

Unsteady behavior of a sweeping impinging jet: Time-resolved particle image velocimetry measurements

The unsteady behavior of a sweeping impinging jet is measured experimentally using time-resolved particle image velocimetry. For the configuration with a jet-to-wall spacing ratio L/dh = 8, an approximately linear increase in the sweeping frequency is observed with Reynolds numbers (Re) between 2.7 × 103 and 9.3 × 103, especially at high Reynolds numbers. The saturation of the sweeping jet, at which the maximum deflection angle is reached, occurs at Re = 6.7 × 103. Special focus is then placed on the spatial and temporal variations of unsteady flow fields at two Reynolds numbers Re = 4.0 × 103 and 9.3 × 103. The unsteady behavior in the near-exit region is first compared. At a higher Reynolds number, the jet in the near-exit region remains at the maximum deflection angle for a longer time during one oscillation cycle with more concentrated jet momentum, resulting in a faster switching process. In the near-wall region at Re = 4.0 × 103, the sweeping impinging jet exerts a large region of influence due to the oscillation motion of the impact region along the wall. The time-averaged velocity components and velocity fluctuating components near the wall show double peaks on both outer sides and a minimum in the middle of the near-wall region. At Re = 9.3 × 103, due to the rapid and intensive sweeping process, the jet column breaks in the near-exit region, resulting in a weak flow in the middle of the near-wall region. Accordingly, the profiles of the time-averaged velocity components and velocity fluctuating components show higher double-peak values but an even lower minimum value. Finally, the state-of-the-art dynamic mode decomposition method is used to capture the main flow behavior of distinct frequencies at these two selected Reynolds numbers. Bounded by the breaking location of the jet column, the flow with a superharmonic oscillation frequency in the middle of the near-wall region disappears at Re = 9 × 103. Therefore, the energetic flow patterns are found to be more evenly distributed in the near-exit region than in near-wall region. The phase correlation between the captured flow patterns is determined by projecting the phase-averaged flow fields onto the most energetic modes.

Vortex dynamics behind a self-oscillating inverted flag placed in a channel flow: Time-resolved particle image velocimetry measurements

The unsteady flow behind an inverted flag placed in a water channel and then excited into a self-oscillating state is measured using time-resolved particle image velocimetry. The dynamically deformed profiles of the inverted flag are determined by a novel algorithm that combines morphological image processing and principle component analysis. Three modes are discovered with the successive decrease in the dimensionless bending stiffness: the biased mode, the flapping mode, and the deflected mode. The distinctly different flow behavior is discussed in terms of instantaneous velocity field, phase-averaged vorticity field, time-mean flow field, and turbulent kinetic energy. The results demonstrated that the biased mode generated abundant vortices at the oscillating side of the inverted flag. In the deflected mode, the inverted flag is highly deflected to one side of the channel and remains almost stationary, inducing two stable recirculation zones and a considerably inversed flow between them. In the flapping mode, the strongly oscillating flag periodically provides a strengthened influence on the fluid near the two sidewalls. The reverse von Kármán vortex street is well formed and energetic in the wake, and a series of high-speed impingement jets between the neighboring vortices are directed toward the sidewalls in a staggered fashion.

Analysis of the pressure fields in a swirling annular jet flow

In this paper, we investigate the flow structures and pressure fields of a free annular swirling jet flow undergoing vortex breakdown. The flow field is analyzed by means of time-resolved tomographic particle image velocimetry measurements, which enable the reconstruction of the three-dimensional time-resolved pressure fields using the governing flow equations. Both time-averaged and instantaneous flow structures are discussed, including a characterization of the first- and second-order statistical moments. A Reynolds decomposition of the flow field shows that the time-averaged flow is axisymmetric with regions of high anisotropic Reynolds stresses. Two recirculation zones exist that are surrounded by regions of very intense mixing. Notwithstanding the axisymmetric nature of the time-averaged flow, a non-axisymmetric structure of the instantaneous flow is revealed, comprising a central vortex core which breaks up into a precessing vortex core. The winding sense of this helical structure is opposite to the swirl direction and it is wrapped around the vortex breakdown bubble. It precesses around the central axis of the flow at a frequency corresponding to a Strouhal number of 0.27. The precessing vortex core is associated with a low-pressure region along the central axis of the jet and the maximum pressure fluctuations occur upstream of the vortex breakdown location, where the azimuthal velocity component also reaches peak values as a result of the inward motion of the fluid and the conservation of angular momentum. The POD analysis of the pressure fields suggests that the precessing helical vortex formation is the dominant coherent structure in the instantaneous flow.

Flow structures behind a vibrissa-shaped cylinder at different angles of attack: Complication on vortex-induced vibration

Complementary experimental studies have been conducted with a vibrissa-shaped cylinder at different angles of attack, through vortex-induced vibration (VIV) test in a wind tunnel, along with extensive measurements of wake dynamics in a water channel using time-resolved particle image velocimetry (TR-PIV). The VIV responses of an elastically mounted vibrissa-shaped cylinder are experimentally compared at various angles of attack in the range of θ = 0°–90°. At the reduced velocity of U0/f0Dh = 3–10 (f0 being the system's natural frequency), the cross-flow displacement of the cylinders convincingly demonstrates that the vibrissa-shaped cylinder at a small angle of attack (θ ≤ 30°) is stable, and without appreciable displacement. Beyond θ = 30°, a prominent three-branched VIV response is readily identified, and increasing the angle of attack results in an upward shift of the synchronized region and a considerable intensification of the peak amplitude. Subsequently, TR-PIV measurements are made of the wake flow behind the vibrissa-shaped cylinder, to determine the spatio-temporally varying flow fields in two spanwise planes, i.e., the saddle and the nodal planes. Four systems with different angles of attack are chosen for comparison at ReD = 1.8 × 103, i.e., θ = 0°, 30°, 60° and 90°. In the two systems with θ = 0° and 30°, the wake regions feature weak velocity fluctuations in highly limited areas. However, increasing the angles of attack (to θ = 60° and 90°) gives rise to expanded recirculation zones, highly unstable flow reversals immediately behind the cylinder, and strengthened velocity fluctuations in the bulk wake regions. Cross-correlation of the fluctuating longitudinal velocities shows that at θ = 60° and 90° the energetic large-scale vortical structures form earlier, and they exert considerable influence on the near-wake fluid behind the cylinder. Finally, a sophisticated data-driven dynamic mode decomposition (DMD) process is used to extract the dominant unsteady structures in the four systems with different angles of attack. In the system with θ = 0°, two dominant DMD modes at frequencies St = 0.23 and 0.30 are identified in the saddle and the nodal planes, respectively, and those frequencies are St = 0.18 and 0.19 in the system with θ = 30°. The interaction between these dominant events at different frequencies tends to disrupt the formation of a strong vortex-shedding process. Therefore, the hydrodynamic force on the cylinder does not make a concerted contribution to suppressing the VIV behavior along the spanwise direction. In the systems with θ = 60° and 90°, the corresponding DMD modes exhibit much more synchronous, organized characteristics in the saddle and nodal planes, and unsteady events at the same frequencies are detected in both planes, reaching St = 0.14 (for θ = 60°) and 0.12 (for θ = 90°). These effects, along with the intensified vortex-shedding processes in the saddle and nodal planes, exert a concerted hydrodynamic force on the cylinder, causing it to start with an oscillatory state.

Wake characterization methods of a circulation control wing

We propose a three-pronged methodology to characterise the wake behind a circulation control wing. The study relies on time-resolved particle image velocimetry (TR-PIV) measurements in a water tunnel for a range of blowing intensities. The first method is the well-known proper orthogonal decomposition (POD). The second tool is a new implementation of the power spectrum. Finally, a modified Q-criterion vortex detection and quantification method is presented. The results show the complementary advantage of the three methods in analysing wake flows with varying conditions.

Stereoscopic particle image velocimetry measurements of flow in a rod bundle with a spacer grid and mixing vanes at a low Reynolds number

In this study, we experimentally investigate the flow field characteristics in a fuel rod bundle with a spacer grid and split-type mixing vanes at a low Reynolds number of 14, 000. Time-resolved stereoscopic particle image velocimetry (TR-SPIV) measurements were performed in a matched-index-of-refraction facility, and taken downstream of the mixing vanes. Velocity measurements were performed along the vertical-horizontal planes in the inter-channels between the fuel rods. From the obtained TR-SPIV velocity vector fields, the full-field flow statistics such as the mean velocity and Reynolds stresses were computed. Moreover, spectral analysis, squared coherent functions and spatial-temporal velocity cross correlations were performed on the TR-SPIV velocity snapshots. A variety of integral length scales estimated from the two-point spatial cross-correlations have shown that the flow downstream of the mixing vanes was strongly anisotropic. Vortex shedding frequencies were found to contribute to the peaks of coherent functions computed from the fluctuating velocity. This work is the first experimental evidence confirming the findings and discussions from previous numerical studies about the anisotropy flow and a wide range of turbulence length scales generated by the mixing vanes.