Large-scale Turbulent Structures Research Articles

Spatial and spectral investigation of turbulent kinetic energy in cavitating flow generated by Clark-Y hydrofoil

In the present paper, the turbulent cavitating flow generated by a Clark-Y hydrofoil is investigated by large eddy simulation (LES) combined with Zwart-Gerber-Belamri (ZGB) cavitation model. In order to shed light on the influence of cavitation on turbulent energy distribution among scales, energy spectrum obtained from the three-dimensional velocity field is firstly applied to turbulent cavitating flow. Spatial and spectral distributions of turbulent kinetic energy are studied for both non-cavitating flow and cavitating flow. Cavitation is found to have a significant effect on the original turbulent flow by inducing more large-scale turbulent structures. The energy spectrum of cloud cavitating flow also experiences a periodic evolution as cavitation develops, and a large amount of turbulent kinetic energy is found to generate as the first shedding, cutoff and second shedding of cavities happen.

Turbulent Properties of Triple Elliptic Free Jets With Various Nozzle Orientation

Abstract An experimental investigation of nozzle orientation effects on turbulent characteristics of elliptic triple free jets was carried out for three nozzle configurations. The first configuration had each nozzle oriented along the minor plane (3_Minor), the next had two nozzles oriented along the minor plane and one along the major plane (Min_Maj_Min) and the last configuration had one nozzle oriented along the minor plane and two along the major plane (Maj_Min_Maj). The experiments were conducted using modified contoured nozzles with a sharp linear contraction for a nozzle spacing ratio of 4.1d, a nozzle equivalent diameter of 9 mm, and Reynolds number of 10,000. Nozzle orientation effects on the mean velocity, turbulent intensity, and Reynolds shear stress were discussed. The velocity decay, jet spread, merging point (MP), combined point (CP), and potential core length were used to characterize the effects of nozzle orientation on the mixing performance. The 3_Minor configuration had shorter potential core length and closer MP location which are indicative of a faster mixing in the converging region. The early merging of 3_Minor led to higher levels of streamwise turbulent intensity. One-dimensional plots revealed that jets approached self-similarity at a faster rate in the major axis. The orientation of the middle jet was found to be a key factor in determining transverse diffusion of the Reynolds shear stress in the plane of observation. Two-point correlations were used to provide insight into the effects of nozzle orientation on the spatial coherence of the large-scale turbulence structure and integral length scale.

Investigating channel flow using wall shear stress signals at transitional Reynolds numbers

Time-resolved wall shear stress measurements are conducted to investigate channel flow at transitional Reynolds numbers. Constant temperature anemometry (CTA) is employed to measure the instantaneous wall shear stress using glue-on hot films as the sensing probes. Pressure-drop measurements are conducted to calibrate the mean hot-film voltage signals and to ensure that the pressure drop is measured in the so-called “fully-developed” region of the channel, a study of effect of entrance length on the pressure-drop measurements is carried out. Time history and higher order statistics of wall shear stress fluctuations reveal that the flow remains laminar until Reτ(=uτh/ν)≈43 in our channel flow facility, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. Third and fourth order moments of wall shear stress jump at the onset of transition and increase significantly until they reach maxima at about Reτ ≈ 48. After this Reynolds number, these two higher order moments start to decrease gradually with increasing Reynolds number and after Reτ≈73−79, any significant dependence of these two moments on Reynolds number disappears. Multiple hot-film measurements, which are located at different spatial locations, are conducted to characterize the large-scale turbulent structures. It is observed that there are structures, at least 7h wide, for Reτ between 46.8 and 53.9. Two-point spatial correlations reveal that on average these large structures are angled at approximately 17o for Reτ=46.8 and roughly between 32o and 37o for 48.7 < Reτ < 53.9 relative to the streamwise direction.

DNS of plane Couette flow with surface roughness

Direct numerical simulation of fully developed turbulent plane Couette flow (pCf) has been performed to investigate the effect of surface roughness. Flow characteristics in a statistically stationary field are then compared with the smooth pCf data. The present study considers a case, where the bottom wall is fixed, while the top wall is moving with a constant velocity $$U_{\mathrm{w}}$$ in the flow direction. For roughening, square ribs are placed on the stationary wall with a streamwise pitch $$\lambda = 5k$$, where $$k = 0.2h$$ is the roughness height and h is half the height between the walls. In the present study, we examined the flow and pressure fields around the ribs. For the pitch $$\lambda = 5k$$, a single recirculation zone is observed in the cavity between any two consecutive ribs. In addition, the profiles of the mean data in the channel core region at different streamwise locations are shown to collapse with each other, indicating that the flow is quasi-homogeneous in the streamwise direction. Further, counter-rotating secondary roll cells or Taylor–Gortler-like vortices, which evolve temporally and oriented along the flow direction, are also observed in the rough pCf. In addition, the large-scale turbulent structures are distorted into fine-scale motion around the ribs. Furthermore, the skin friction coefficient and the mean pressure fields are qualitatively similar to a rough Poiseuille flow (with ribs only on one wall).

Simulation of stochastic pressure loads on a medium head Francis runner

In recent years, major advances have been made in simulating dynamic and transient flows in hydraulic turbines. Overall, computational fluid dynamics (CFD) and finite element analysis (FEA) simulations have been quite successful and have helped to advance knowledge beyond the best efficiency point. The simulation of transient operations like startup and runaway has nearly become part of the standard toolbox. However, numerically predicting stochastic flows, such as those occurring during speed-no-load (SNL) regime, remains a challenge. Since these flows can have a significant impact on turbines’ life expectancy, CFD methods need to be improved. In this paper, we examine the SNL regime in a Francis turbine in which extensive dynamic fluctuations were measured. The approach used was to first focus on the CFD methodology required to better predict stochastic pressure loads with hybrid turbulence models such as the Scale-Adaptive Simulation–Shear-Stress Transport (SAS-SST) model and the relatively new Stress-Blended Eddy Simulation (SBES) model. This will then allow us to determine the amount of LES content required to accurately predict large-scale turbulent structures and the corresponding pressure fluctuations that they generate on blades.

Modification to Improved Delayed Detached-Eddy Simulation Regarding the Log-Layer Mismatch

The wall-modeled large-eddy simulation branch of the widely used improved delayed detached-eddy simulation (IDDES) method is supposed to resolve the problems of log-layer mismatch and underprediction of skin friction, as claimed by the authors of the IDDES (Shur, M. L., Spalart, P. R., Strelets, M. K., and Travin, A. K., "A Hybrid RANS-LES Model with Delayed DES and Wall-Modeled LES Capabilities," International Journal of Heat and Fluid Flow, Vol. 29, 2008, pp. 1638–1649). But, some researchers did meet these problems when using the IDDES. Aiming at finding out the reason and seeking a remedy, an analysis of the IDDES is carried out that focuses on the relation between the wall-parallel grid size and the length scale of the energetic turbulent structures at the Reynolds-averaged Navier–Stokes (RANS)/large-eddy simulation (LES) interface, and it reveals that the flaw of the IDDES arises from the fact that, in the IDDES approach, the energetic, large-scale, and stress-carrying turbulent structures in the vicinity of the RANS/LES interface are essentially impossible to well resolve by the LES mode. On the basis of the analysis, a modification to the IDDES is proposed by moving the RANS/LES interface further away from the wall so that, at the RANS/LES interface, the wall-parallel grid size is sufficient to resolve the turbulent structures. The modification is simple in form but has clear physical meaning. Through a series of sensitivity tests, it can be concluded that the modified IDDES does resolve the problems of log-layer mismatch and underprediction of skin friction, and it is applicable to low-, moderate-, and high-Reynolds-number flat plate boundary-layer flows without exception.

Effect of fluid injection on turbulence and noise reduction of a supersonic jet.

Supersonic jets, such as the ones used in high-performance military aircraft, have both downstream and upstream noise components due to the large-scale turbulent structures and the presence of shock cells in the jet plume. The fluid insert technology is a noise reduction method that has been shown to effectively reduce both these noise components. This paper analyses the unsteady flow changes associated with different fluid insert configurations with a goal of helping to understand the detailed noise reduction mechanisms. Using direct cross-correlations of the near-field data with the far-field microphone signals, it is found that even the use of a single injector as a fluid insert helps break up the large-scale structures of the flow. However, a more azimuthally distributed blowing is required to reduce the upstream broadband shock-associated noise (BBSAN). Addition of upstream injectors at each azimuthal location further enhances the BBSAN reduction. Decomposition of the jet flow-field into hydrodynamic and acoustic modes shows that fluid insert nozzles reduce the amplitude and convection speed of the coherent acoustic mode in the plane of highest noise reduction. This article is part of the theme issue 'Frontiers of aeroacoustics research: theory, computation and experiment'.

Analysis of turbulence in convergent-divergent nozzles with fluid insert noise reduction technology

The noise generated by tactical fighter aircraft engines is harmful to personnel working in the vicinity of the aircraft and can cause annoyance to communities in the vicinity of air bases. The primary noise sources in supersonic jets are related to the supersonic convection of large-scale turbulent structures, which generate intense noise in the jet downstream direction, and the interaction of the turbulence with the jet’s shock cell structure that results in broadband shock-associated noise, which radiates predominantly in the sideline and upstream directions. The use of fluid inserts in the divergent section of variable area exhaust nozzles has been shown experimentally, at small and moderate scale, to reduce noise radiation from both noise sources. To understand the fluid insert noise reduction mechanisms, a Large Eddy Simulation database is developed and analyzed. The focus is on differences between turbulence properties in a baseline and a fluid insert nozzle. The flow database is analyzed using Spectral Proper Orthogonal Decomposition and Doak’s Momentum Potential Theory. The latter theory permits the decomposition of the flow into hydrodynamic, thermal and acoustic components. The changes in the acoustic component are related to the observed changes in the radiated noise.

Application of hybrid RANS-LES models to the prediction of flow behaviour in an industrial crystalliser

Knowledge of the residence time and shear rates in industrial crystallisers is critical for any assessment of the performance of these vessels from a chemical engineering perspective. It is unlikely that the range of expected residence time behaviours, or the shear rates can be predicted accurately with a RANS model. In the current study, a wide range of hybrid RANS-LES models, including Stress-Blended Eddy Simulation (SBES), were used to predict the flow field in a laboratory-scale alumina precipitator with the objectives of both quantifying the accuracy of the models and assessing if the hybrid models provide significant improvement over a previous RANS modelling study. Predicted mean and fluctuating velocities have been compared with Laser Doppler Velocimetry (LDV) data from a laboratory-scale alumina precipitator. The results achieved show that hybrid RANS-LES models can accurately predict both the mean and fluctuating velocities in the precipitator vessel. Importantly, as the mesh is refined, agreement with experimental data improves and differences between model predictions reduce, showing that sensitivity to the sub-grid scale model reduces if all the relevant large-scale turbulence structures are explicitly resolved. Prediction of fluctuating velocities is found to be more accurate than that achieved in a previous RANS modelling study. The SBES results are found to be mesh-independent, and to give closer agreement with experimental data, on a coarser mesh than both the SST-DDES and SST-SAS approaches as the model formulation allows rapid transition to an explicit LES model immediately outside the wall boundary layer. This is an important result for industrial simulation due to the significant reduction in simulation times needed.

Three-Dimensional Experimental Study of Compressibility Effects on Turbulent Free Shear Layers

Turbulent planar mixing layers of varying compressibility levels have been studied experimentally via flow visualization techniques, pressure measurements, and stereoscopic particle image velocimetry. The experiments were conducted for five different convective Mach numbers (, 0.38, 0.55, 0.69, and 0.88). For each case, inflow conditions were thoroughly documented with planar particle image velocimetry. Results indicate that the incoming boundary layers are thin (less than or equal to 9% of channel height) and fully developed. Schlieren and Mie scattering images show that for increased levels of compressibility the large-scale turbulent structures are less organized, and the Brown–Roshko rollers that are dominant in the incompressible case are not found. Three-component velocity measurements made on the spanwise-central plane () via stereo particle image velocimetry confirm the reduction in the normalized growth rate with increasing that has been agreed upon widely. Turbulence statistics results show that the peak (normalized) streamwise normal kinematic Reynolds stress remains constant, while the spanwise normal, transverse normal, and primary shear kinematic Reynolds stress peak values all decrease with increasing . In addition, knowledge of all three normal stress components allows for the calculation of the full Reynolds stress anisotropy tensor, a novel result for compressible mixing layer experiments. Each anisotropy component remains constant across the shear layer center. As compressibility in the mixing layer increases, the streamwise normal stress anisotropy increases, transverse and spanwise normal stress anisotropies decrease, and the shear stress anisotropy remains constant. Conversely, the Reynolds stress correlation coefficient remains constant across all cases at approximately 0.47.

Unmanned aerial vehicles reveal the impact of a total solar eclipse on the atmospheric surface layer.

We use unmanned aerial vehicles to interrogate the surface layer processes during a solar eclipse and gain a comprehensive look at the changes made to the atmospheric surface layer as a result of the rapid change of insolation. Measurements of the atmospheric surface layer structure made by the unmanned systems are connected to surface measurements to provide a holistic view of the impact of the eclipse on the near-surface behaviour, large-scale turbulent structures and small-scale turbulent dynamics. Different regimes of atmospheric surface layer behaviour were identified, with the most significant impact including the formation of a stable layer just after totality and evidence of Kelvin-Helmholtz waves appearing at the interface between this layer and the residual layer forming above it. The decrease in surface heating caused a commensurate decrease in buoyant turbulent production, which resulted in a rapid decay of the turbulence in the atmospheric surface layer both within the stable layer and in the mixed layer forming above it. Significant changes in the wind direction were imposed by the decrease in insolation, with evidence supporting the formation of a nocturnal jet, as well as backing of the wind vector within the stable layer.

Large-scale turbulence structures in a laboratory-scale boundary layer under steady and gusty wind inflows

Experiments on turbulence structures and features of a wind field under steady inflow and gusty wind inflows were implemented in a straight-through wind tunnel. Streamwise and wall-normal velocity components were measured using a streamline constant temperature anemometer (streamline CTA). Power spectra analyses revealed the existence of very large-scale motions (VLSMs) under both steady and gusty wind inflows; but new gusty scale motions (GSMs) were revealed under only gusty wind inflows. The GSMs might originate from an ordered external driving force that forces hairpin packets to align coherently in groups with a length scale related to the gust inflow condition. The streamwise wavelength of VLSMs is independent of inflow conditions, while the turbulent energy of VLSMs is associated with the wall-normal height and local mean streamwise velocity. In particular, the streamwise wavelength of GSMs increases linearly with the average value and period of sinusoidal gusty wind inflows, and the turbulent energy of GSMs is sensitive to the wall-normal height and all characteristic parameters of gusty wind inflows, including the average value, amplitude and period. Considerable wall-normal airflows induced by gusty wind inflows were detected and these are negatively correlated with the variation in gusty streamwise velocity, and root mean square (RMS) values of the gusty wall-normal velocity tended to increase linearly with the average value and amplitude of gusty wind inflows.

Gusty wind disturbances and large-scale turbulent structures in the neutral atmospheric surface layer

This study analyzes the contribution of large-scale turbulent structures, including very large-scale and large-scale motions, to the streamwise turbulent kinetic energy and momentum flux in comparison with the contribution of the gusty wind disturbances based on the high-quality data obtained from the field measurements conducted in the near-neutral surface layer. The results of this study denote that the gusty wind disturbances contain only a portion of the energy contained in very large-scale motions and do not contain any of the information contained in large-scale motions. The amount of lost contributions to the streamwise turbulent kinetic energy and momentum flux increases linearly with the friction velocity, eventually becoming 53% and 67%, respectively. This indicates that large-scale turbulent structures (very large-scale motions and large-scale motions) better describe the coherent structures in the atmospheric surface layer when compared with the gusty wind disturbances.

The meandering behaviour of large-scale structures in turbulent boundary layers

This paper quantifies the instantaneous form of large-scale turbulent structures in canonical smooth-wall boundary layers, demonstrating that they adhere to a form that is consistent with the self-sustaining streak instability model suggested by Flores &amp; Jiménez (Phys. Fluids, vol. 22, 2010, 071704) and Hwang &amp; Cossu (Phys. Fluids, vol. 23, 2011, 061702). Our motivation for this study stems from previous observations of large-scale streaks that have been spatially locked in position within spanwise-heterogeneous boundary layers. Here, using similar tools, we demonstrate that the randomly occurring large-scale structures in canonical layers show similar behaviour. Statistically, we show that the signature of large-scale coherent structures exhibits increasing meandering behaviour with distance from the wall. At the upper edge of the boundary layer, where these structures are severely misaligned from the main-flow direction, the induced velocities associated with the strongly yawed vortex packets/clusters yield a significant spanwise-velocity component leading to an apparent oblique coherence of spanwise-velocity fluctuations. This pronounced meandering behaviour also gives rise to a dominant streamwise periodicity at a wavelength of approximately $6\unicode[STIX]{x1D6FF}$. We further statistically show that the quasi-streamwise roll-modes formed adjacent to these very large wavy motions are often one-sided (spanwise asymmetric), in stark contrast to the counter-rotating form suggested by conventional conditionally averaged representations. To summarise, we sketch a representative picture of the typical large-scale structures based on the evidence gathered in this study.

POD-Based Data Mining of Turbulent Flows in Front of and on Top of Smooth and Roughness-Resolved Forward-Facing Steps

A new application of proper orthogonal decomposition (POD) to uncover the relation of the instantaneous energetic large-scale turbulent structures to the dominant POD modes had been reported. Motivated on this method, the data mining from the velocity vector fields measured by the particle image velocimetry and structural analysis on the selected POD-based reconstructed turbulent flows in front of and on top of smooth and roughness-resolved forward-facing steps (FFSs) has been performed. The velocity fields containing the most energetic large-scale structures are conditionally chosen. The conditional criterion is that the chosen velocity fields whose POD temporal coefficients of the first or second mode are correspondingly larger than twice of their root mean square values. Typically, the most energetic instantaneous structures are the large-scale second-quadrant (Q2) or fourth-quadrant (Q4) events and the mostly open separation bubbles in front of these FFSs; while the large-scale structures behave as a strong shear layer, and near or in which are a few spanwise prograde or retrograde vortices; and sometimes the alternating node and saddle points appeared. Similarly, for the flow on top of the FFSs, the most energetic structures are presented as a great many large-scale Q4 or Q2 events and a few secondary vortices at the very near wall; while the large-scale structures are overall exhibited as a strong shear layer, and in which a large number of vertex structures are created. These energetic large-scale structures here are not only sensitive to the surface roughness conditions but also to the spanwise locations.

Study of identification of large-scale turbulence structures in drag-reducing turbulent boundary layer flow by means of stereoscopic PIV measurements

Study of identification of large-scale turbulence structures in drag-reducing turbulent boundary layer flow by means of stereoscopic PIV measurements

Towards the prediction of the convective and the radiative heat fluxes in turbulent buoyant flames

The present paper aims at describing the flow dynamics of turbulent buoyant flames encountered in gaseous or liquid pool fires or horizontally oriented solid materials. Indeed, the predictive simulations of liquid pools or solid fuel fires requires the prediction of the thermal stress received by the evaporating liquid or the pyrolysing material, and therefore a fine description of the surrounding flame. Yet, reactive Large Eddy Simulation is a powerful tool in fluid mechanics to correctly simulate turbulent flows such as large-scale buoyant flames, so long as the discretization and the numerical schemes allow to resolve the large scale turbulent structures which determine the global flame shape.Thus, this study is divided into two steps. In the first step, Large Eddy Simulations of the SANDIA FLAME methane pool fire are performed using the CALIF3S-ISIS software, for different grid refinements and convective schemes. The ability of the different numerical choices in correctly describing this flame is compared in terms of velocity variance-to-average ratio, puffing frequency and turbulent structures resolution. In the second step, the flame above a 40×40 cm2 PMMA slab is simulated with the best numerical parameters found in the first step. The simulation of the flame is decoupled from pyrolysis aspects assuming by imposing the fuel mass flow rate observed at a particular stage of the experiment. The average temperature axial profile and the transverse profile of convective, radiative and total heat flux at the sample surface are compared to their experimental counterparts.It is shown that, at least for large scale pool fires such as the SANDIA methane flame, the increasing the mesh refinement permits to reach a good balance between the average velocity and the turbulent kinetic energy and to correctly recover the characteristic flame puffing frequency, whereas using non-dissipative centred schemes allows to catch a wider range of turbulent scales in the flowfield. Unfortunately, for smaller fuel sources such as the 40×40 cm2 PMMA slab, the present Large Eddy Simulations do not exhibit fully developed turbulence in most of the combustion zone, in spite of the use of centred schemes and of a fine grid. This uncertainty on the behaviour of the turbulence in such a configuration may be responsible for the observed anomalies, namely the overprediction on the average temperature and the radiative-to-convective heat flux ratio. Further experimental investigations would be useful to better understand the behaviour of turbulence on such mid-scale fires and prescribe relevant numerical model modifications.

3D-CFD Simulation of Liquid–Liquid Two-Phase Flow in A Pilot-Plant Scale Annular Pulsed Disc and Doughnut Column

ABSTRACTA three-dimensional (3D) computational fluid dynamics (CFD) simulation of liquid–liquid two-phase flow is performed on a pilot-plant scale annular pulsed disc and doughnut column (APDDC). Two-fluid Euler–Euler method augmented with k-ε model is used. The two-phase hydraulic performance are investigated and compared with experimental results under various operation conditions. Favorable agreements are obtained, corroborating the ability of the simulation model to predict hydrodynamic parameters of pilot-plant scale APDDC. As a novel result, it is discovered that circumferential fluctuations of continuous phase velocity and dispersed phase volume fraction exist in the pilot-plant scale APDDC, which might be due to the large-scale structure of turbulence. Effects of operation conditions on the hydrodynamic performance and flow profiles in APDDC are studied based on simulation results and correlated regarding to operation parameters. The studied hydrodynamic parameters include turbulent kinetic energy dissipation, swirling strength, and pressure drop.

Hydrodynamics of octagonal culture tanks with Cornell-type dual-drain system

Large culture tanks of several hundred or thousand m3 size are generally encouraged for economic advantages in Recirculating Aquaculture Systems (RAS). Out of numerous possibilities in designing the inlet and outlet configurations in octagonal culture tanks, the inlet pipes near the corner walls and the outlets at the tank’s center and/or on side wall are some of the widely-used configurations. The use of wall drain to achieve a controlled flow pattern in the tank, however, influences distinct flow features such as pressure, velocity, uniformity and turbulence in the tank, which are of theoretical interest as well as practical importance. A finite volume description of the flow in an octagonal culture tank at full-scale was therefore developed using Realizable turbulence model with second order accuracy in space and time. The tank was equipped with an inlet pipe near the corner wall and dual-drain outlet system of Cornell-type. The base case had a flow configuration of 45% of flow through central bottom drain, and the rest through the wall drain. Model verification was performed using grid convergence tests, and validation was conducted using Acoustic Doppler velocimetry (ADV) based velocity measurements. The effect of wall drain on the large-scale and small-scale turbulent structures was studied using the distribution of turbulent kinetic energy and vorticity respectively. The parametric study on the flow-split between the two outlets was analyzed using different flowfield indicators, such as flow velocity, uniformity, vorticity strength, maximum absolute vorticity and swirl number. Such an inclusive analysis not only explores the hydrodynamics in the commercial culture tanks with Cornell-type dual-drain but also recommends the farmers with the suitable flow-split between such outlet systems.

PIV test methods and mechanism on liquid turbulence modulation by solid-particles inside a centrifugal pump

As one of high energy consumption pumps, pump used for solid-liquid two-phase mixture transportation, such as slurry pump and mud pump, is extensively used in the hydraulic transportation of solid-liquid mixture through pipes in various fields. The erosion wear in slurry pumps has been identified as a critical issue during transportation of slurry as it affects the equipment performance and reduces its reliability and operation life, leading to the waste of energy. Many studies indicate that the performance and efficiency of solid-liquid two-phase centrifugal pump is controlled by the two-phase flow pattern inside the pump, so understanding flow characteristics and abrasion mechanism has important significance to improve the hydraulic design of the impeller for decreasing the abrasion and increasing the service life of the pump. In the present study, based on solid-liquid two-phase flow as object, an improved experimental facility without agitation was developed can improve the test precision by eliminating the influence of agitation on flow inside pump and improving particle-liquid two-phase flow circulation way. On the base of experimental studies, POD methods were applied to analysis the liquid turbulence modulation by solid-particles and the behavior of large eddy structures will be clearly understood. Thus, the theoretical system of the solid-liquid two-phase flow will be further improved. And a theoretical principle for the solid-liquid two-phase pump optimal design will be presented. The following conclusions are obtained: (ⅰ) a superior PIV two-phase test platform than that in the previous literature is designed and it can be very good to realize a stable solid-liquid two-phase flow measurement of centrifugal pump. Compared with the traditional platform, the results obtained by the novel solid-liquid two-phase centrifugal pump PIV test platform has a very high accuracy and it has a good reference value to understand flow mechanism of a centrifugal slurry pump. The two particle images with and without agitating are shown in Figure 5. As can be seen that a large number of bubbles are brought into the circulation line (Figure 5(a)), which is caused by a higher stirring speed for suspending solid particles, and thus the actual flow images shows a gas-liquid-solid three-phase flow. However, for the present test facility without stirring, there is no such problem, and the original image is very clear without bubbles. (ⅱ) The POD analyses show that the solid-particles injection has an important influence on the large scale turbulence structures which contain a large amount of energy. The modal energy distribution as a function of the POD mode number is displayed in Figure 10. The energy contribution of these large scale structures to the total energy becomes larger due to the injection of solid-particles, whereas the contribution of the small scale structures, which denotes the energy dissipation, becomes smaller. This is why the low solid-phase volume concentration has higher pump head and efficiency. The addition of solid-particle increases the friction loss, but reduces the flow separation loss and inhibits the development of small scale vortex. However, with the increase of solid-particle concentration, the friction loss increases is greater than the flow separation loss reduction, and thus pump head and efficiency decrease. The above phenomena show fully that the solid-particles addition has an important influence on the large scale energetic eddy structures. This is confirmed by the measurement results as shown in Figure 11.