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To reveal the multiscale wake structures of a wall-mounted cube and the effects of a front inclined hole (FIH), a combination of wavelet multiresolution analysis and vortex identification techniques is applied to analyze time-resolved particle image velocimetry data. The cube model has a side length D = 50 mm and the Reynolds number ReD = 7800. The inlet of the FIH is located at a height 0.71D on the front surface of the cube, and the outlet is located at the center of the free end. Statistical analysis indicates that an FIH can reduce the recirculation zone around the cube, suppress downwash flow, and alter the development of free-end shear flow. The turbulence intensity and turbulent kinetic energy in the wake also decrease significantly in the presence of an FIH. The wavelet multiresolution analysis shows that the main structures of the flow field experience a transformation from small to intermediate and then large scales from the shear layer around the standard cube to its wake. However, in the presence of an FIH, the scale of the flow structure near the free end becomes smaller, the large-scale structure in the wake is weakened, and the transition from small to intermediate scales is no longer obvious. The wavelet vortex dynamics analysis reveals the evolutions of vortex structures with different scales. In the presence of an FIH, the trend of large- and intermediate-scale coherent structures moving to the bottom wall is weakened, while the streamwise extent of small-scale structures is greater. In the large-scale component of the wake, a transverse secondary vortex is observed, which is formed by the combined action of a shedding transverse vortex and downwash flow. [ABSTRACT FROM AUTHOR]

This paper describes an experimental investigation of flow control for the wake around a wall-mounted cube using horizontal control holes (HCHs) of different diameters drilled from the center of the front surface to the rear surface of the cube. The cube has side lengths of D = 50 mm, and HCHs with diameters of d = 10, 12, and 14 mm are considered. The instantaneous velocity fields are measured at a Reynolds number of 7800 based on time-resolved particle image velocimetry in a water tunnel. The HCHs suppress the recirculation zone, turbulence intensity, and Reynolds stress, and these control effects gradually increase with the hole diameter. The issuing flow from the large-diameter HCH completely obstructs the development of the downwash flow to the bottom wall and decomposes the near-wake arch-type vortex into a double arch-type structure. As the hole diameter increases, the dominant frequency of the spectrum in the HCH wake increases. Proper orthogonal decomposition analysis indicates that the large-scale spanwise vortices are suppressed by HCH. In the dynamic evolution process of the cube wake, the HCH issuing flow hinders the interaction of shear flow on both sides, and the issuing vortices attract the spanwise vortices and accelerate their shedding. [ABSTRACT FROM AUTHOR]

This paper proposes vehicle door mirrors with a tip shape and ditch to reduce the aerodynamic drag. The mean drag coefficients Cd of various mirror models were first measured using load cells within a 103–105 Reynolds number range in a wind tunnel. The Cd of controlled mirrors with different ditch widths remained constant at approximately 0.75 and was lower than that of conventional mirrors. Using a large eddy simulation (LES), the 3D flow structures around modified and conventional mirrors were numerically analyzed at a Reynolds number of 2.8 × 105. Based on a three-dimensional orthogonal wavelet multi-resolution technique, the instantaneous three-dimensional vorticity and velocity were decomposed into three wavelet levels or scales: large scale with a 62 mm central scale, intermediate scale with a 29 mm central scale, and small scale with a 16 mm central scale. This indicated that the length of the region of the vorticity iso-surfaces in an improved door mirror model as the tip ditch decreases. Because the tip ditch produced the more streamwise vortices, the large-scale spanwise vortices were suppressed. The streamwise vortices and spanwise vortices of the small- and intermediate-scale structures increased, which is mainly caused by the ditch in the tip. [ABSTRACT FROM AUTHOR]

Abstract The effect of self-excited soft fins on a pneumatic conveying with different vertical curved 90° bends was experimentally studied to reduce pressure drop, power consumption and conveying air velocity. The distributions of particle velocity and particle fluctuating velocity near and in the first bend were measured based on the high-speed PIV. The polyethylene particles with a diameter of 2.3 mm were used as conveying materials. The superficial air velocity was varied from 10 to 14 m/s, and the stable mass flow rate was fixed at 0.45 kg/s. Compared to the non-fin pneumatic conveying, the pressure drop, the minimum pressure drop (MPD) velocity, power consumption, and additional pressure drop can be reduced by using soft fins for two bends of different radii (R/D = 3.2 and 4.4) in lower air velocity range. The maximum reduction rates of the MPD velocity and power consumption by using soft fins is about 8.2% and 8%, respectively. At the upstream of the bend, the particle velocity of the soft fins is higher than that of the non-fin. The effect of soft fins on the particle velocity and its fluctuating energy remains in the bend. The particle velocity and fluctuating energy of particle velocity of the soft fins are higher than that of the non-fin in the first vertical bend. At the downstream of the bend, the fluctuating energy of particle velocity of the soft fins is higher than that of non-fin in the large radius bendon the top part of the pipe. Graphical abstract Unlabelled Image Highlights • A pneumatic conveying with vertical bends by using soft fins was studied. • The pressure drop, additional pressure drop and particle velocity were measured. • The pressure drop and conveying velocity were reduced by fins. • Particle velocity of fins was higher than that of non-fin near and in the bend. • Effect of fins on the particle velocity and fluctuating energy remains in the bend. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes an application of a rotation swirler to swirling flow pneumatic conveying for reducing the conveying velocity and pressure drop decrease. A comparison with the swirling flow pneumatic conveying generated by a non-rotation swirler and axial flow pneumatic conveying was made, the total pressure drop decrease, minimum conveying velocity, energy consumption, and additional pressure drop decrease were evaluated experimentally. In addition, the cross-section profiles of the particle velocity and particle fluctuation velocity along a pipeline near the minimum pressure drop decrease were measured by the PIV (Particle Image Velocimetry) technique. The pipeline was a 5-m-long horizontal straight acrylic pipe with an inside diameter of 80 mm. Polyethylene particles of diameter of 2.3 mm were used as the conveying materials. The initial swirl number was varied from 0 to 0.66. The solid mass flow rates of 0.1, 0.28, and 0.47 kg/s were applied, and the superficial air velocity was varied from 9 to 16 m/s. It is revealed that the total pressure drop decrease and power consumption of the swirling flow using the rotation swirler exhibit the smallest values among all cases in the region of low air velocity, and are almost the same as the axial flow in the high air velocity region. The particle velocity and particle fluctuation velocity of the swirling flow originated by the rotation swirler are almost the same as the axial flow in the acceleration regime, but become larger than that of the axial flow near the bottom of the pipeline in the fully developed regime. Graphical abstract Unlabelled Image Highlights • A rotation swirler was applied to swirling flow pneumatic conveying. • Pressure drop, minimum velocity and particle velocity were measured. • The rotation swirler pneumatic conveying exhibits the lowest pressure drop • High particle velocity and fluctuation velocity were observed near the bottom of pipe. [ABSTRACT FROM AUTHOR]

To further elucidate the mechanism of energy-conserving conveying in horizontal pneumatic conveying with the dune model, the high-speed particle image velocimetry is applied to measure particle fluctuation velocity near the minimum conveying velocity of the conventional pneumatic conveying. This study focuses on the effect of mounting dune models on the horizontal pneumatic conveying in terms of power spectrum, autocorrelation coefficients, two-point correlation coefficients, fluctuation intensity of particle velocity, skewness factor, and probability density function. It is found that the power spectrum peaks with the dune model are larger than those of the nondune system, suggesting the acceleration and suspending efficiency of the dune model, especially dune models mounted at the bottom of the pipe. Meanwhile, the profiles of particle fluctuation velocity intensity indicate that the large particle fluctuating energy is generated due to mounting the dune model so that the particles are more easily accelerated and suspended. This is one of the important reasons why the mounted dune model results in a low pressure drop and low minimum conveying velocity. Based on the distribution of skewness factor and probability density function, it is found that the particle fluctuation velocities of all cases follow the Gaussian distribution in the lower and middle parts of the pipe. The particle fluctuation velocities in the case of the dune models mounted at the bottom of the pipe obey the Gaussian-type fluctuation more. [ABSTRACT FROM AUTHOR]

Phase-average technique based on wavelet multi-resolution analysis and continuous wavelet transform are used to reveal the phase-averaged features of square cylinder wake measured by high-speed PIV. The one-dimensional orthogonal wavelet analysis is first applied to decompose the measured velocity fields into large-, intermediate- and small-scale structures. Then the phase information referenced with large- and intermediate-scale flow structures are clearly identified based on Morlet wavelet transform. Finally, the data ensembles are phase-sorted to give phase-averaged representations of measured flow field. The instantaneous multi-scale structures suggest that large-scale vortices are weakened and begin to transfer into intermediate-vortices at the downstream of separation region. The intermediate-scale vortex observed at the upper boundary of shear layer is considered to be associated with the secondary vortex movement. The phase-averaged intermediate-scale structures tend to convey downstream along streamwise direction, with the rotation sense varying from the first half period to the last half period. The peaks of phase-averaged large-scale Reynolds stress tend to move back and forth in the near-wake region. These findings suggest that the proposed phase-average technique is effective in revealing multi-scale fluid dynamics of wake flow structures. [ABSTRACT FROM AUTHOR]

In order to study the characters of particle fluctuation velocity at the minimum pressure drop (MPD) velocity in the acceleration and fully developed regimes of a horizontal pneumatic conveying, the particle fluctuation velocities measured by the high-speed particle image velocimetry (PIV) are first analyzed by time-averaged particle velocity, fluctuating energy, power spectrum and autocorrelation. Then the proper orthogonal decomposition (POD) and continuous wavelet transform are developed to reveal the particle fluctuation velocities in terms of the contributions to the particle fluctuation energy, time-frequency distribution, as well as probability density function from POD modes. The energy distributions of POD modes suggest that the first two POD modes are most energetic and dominate the particle motion, and the dominance increases from the acceleration regime to fully-developed regime. The time-frequency characteristics of POD modes reveal that small-scale particle fluctuations are suppressed in the fully-developed regime. It implies that the suppression of small-scale particle fluctuations may result in lower pressure drop at MPD velocity. The PDF distributions of POD modes exhibit that the particle fluctuation of first two POD modes follows the Gaussian distribution in the acceleration and fully developed regimes. However, the PDF distributions of POD modes gradually deviate from Gaussian distribution as increasing mode number. [ABSTRACT FROM AUTHOR]

11772035, 11721202, and 12072017) from Beihang university, Grant-in-Aid for Scientific Research (C) (Grant No. 20K04257) from JSPS, and a Grant-in-Aid for JSPS Fellows (Grant No. 19J20739)." Erratum: "Flow control of wake around a wall-mounted cube using a horizontal hole of different diameters" [Phys. REFERENCES 1 J. Li, X. Han, H. Rinoshika, W. Li, and A. Rinoshika, " Flow control of wake around a wall-mounted cube using a horizontal hole of different diameters", Phys. [Extracted from the article]

A horizontal dilute-phase pneumatic conveying system using vertically oscillating soft fins at the inlet of the gas–particle mixture was studied to reduce the power consumption and conveying velocity in the conveying process. The effect of different fin lengths on horizontal pneumatic conveying was studied in terms of the pressure drop, conveying velocity, power consumption, particle velocity, and intensity of particle fluctuation velocity for the case of a low solid mass flow rate. The conveying pipeline consisted of a horizontal smooth acrylic tube with an inner diameter of 80 mm and a length of approximately 5 m. Two types of polyethylene particles with diameters of 2.3 and 3.3 mm were used as conveying materials. The superficial air velocity was varied from 10 to 17 m/s, and the solid mass flow rates were 0.25 and 0.20 kg/s. Compared with conventional pneumatic conveying, the pressure drop, MPD (minimum pressure drop), critical velocities, and power consumption can be reduced by using soft fins in a lower air velocity range, and the efficiency of fins becomes more evident when increasing the length of fins or touching particles stream by the long fins. The maximum reduction rates of the MPD velocity and power consumption when using soft fins are approximately 15% and 26%, respectively. The magnitude of the vertical particle velocity for different lengths of fins is clearly lower than that of the vertical particle velocity for a non-fin conveying system near the bottom of the pipeline, indicating that the particles are easily suspended. The intensities of particle fluctuation velocity of using fins are larger than that of non-fin. The high particle fluctuation energy implies that particles are easily suspended and are easily conveyed and accelerated. [ABSTRACT FROM PUBLISHER]

This study focuses on the multi-scale turbulent structures of triangle cylinder wake flow measured by high-speed particle image velocimetry (PIV). The measured turbulent structures were spatially extracted into large-, intermediate-, relatively small-, and small-scale components using two-dimensional orthogonal wavelet analysis. Then the features of multi-scale turbulent structures were analyzed in terms of two-point auto correlation, power spectra, turbulent kinetic energy and Reynolds shear stress. It is found that the large-scale structure attributed to coherent motions in the wake flow makes largest contribution to the total fluctuating energy and maximum Reynolds shear stress, accounting for 84% and 92% respectively. The intermediate scale structures, which are unidentifiable by PIV measurement, are found to shed into the separated shear layer due to Kelvin-Helmholtz instability, and the central frequency of intermediate scale vortex is approximately twice of Kármán vortex shedding frequency. Besides, two symmetric regions of intensive velocity fluctuations having relatively small-scale are observed near the cylinder surface and the boundary of separation region, and they are not dominant. [ABSTRACT FROM AUTHOR]

The three-dimensional (3D) turbulent structure was simulated by large eddy simulation (LES), and then the numerical result was validated by PIV experiment. In order to give a detailed description of dune wake flow, the instantaneous velocity, vorticity, and pressure were decomposed into the large-, intermediate- and relatively small-scale components by 3D wavelet multi-resolution technique. To get a further understanding of coherent structure, the decomposed wavelet components were employed to calculate Q-criterion. It was found that the rollers and horse-shoe structures in the separation bubble were mainly contributed from large-scale structures and it made the most significance to the vorticity concentration. The observations of intermediate-scale horse-shoe structures indicated that the coherent structure was the combined effect of large- and intermediate-scale structures. Besides, from the visualization of 3D streamlines and pressure iso-surfaces, the separation bubble and pressure distribution are found to be dominated by large-scale structure. [ABSTRACT FROM AUTHOR]

Dynamic characteristic of ball screw feed system in a milling machine is studied numerically in this work. In order to avoid the difficulty in determining the stiffness of rolling joints theoretically, a dynamic modeling method for analyzing the feed system is discussed, and a stiffness calculation method of the rolling joints is proposed based on the Hertz contact theory. Taking a 3-axis computer numerical control (CNC) milling machine set ermined as a research object, the stiffness of its fixed joint between the column and the body together with the stiffness parameters of the rolling joints is evaluated according to the Takashi Yoshimura method. Then, a finite element (FE) model is established for the machine tool. The correctness of the FE model and the stiffness calculation method of the rolling joints are validated by theoretical and experimental modal analysis results of the machine tool’s workbench. Under the two modeling methods of joints incorporating the stiffness parameters and rigid connection, a theoretical modal analysis is conducted for the CNC milling machine. The natural frequencies and modal shapes reveal that the joints’ dynamic characteristic has an important influence on the dynamic performance of a whole machine tool, especially for the case with natural frequency and higher modes. [ABSTRACT FROM AUTHOR]

In order to reduce pressure drop and conveying air velocity, the paper studied the effect of the dune model and soft fins in horizontal pneumatic conveying involving a 90° bend. Experimental measurements were performed in terms of the pressure drop, conveying air velocity and additional pressure drop. The distributions of particle velocity near and in the curved 90° bend were measured by high-speed PIV. The test pipeline consisted of a 4.5m-long horizontal straight acrylic tube, a curved 90° acrylic bend (mean radius of curvature 250mm) and a 1.5m-long horizontal straight acrylic tube, having an inside diameter of 80mm. The polyethylene particles with diameter of 2.3mm were used as conveying materials. The superficial air velocity was varied from 10 to 14m/s, and the solid mass flow rate was fixed at 0.45kg/s. Comparing with the conventional pneumatic conveying, the pressure drop, the minimum pressure drop (MPD) velocity and additional pressure drop can be reduced by using soft fins in lower air velocity range. The reduction rates of the MPD velocity by using soft fins and dune model were about 4.1% and 8.3%, respectively. At the upstream of bend and in the bend, the particle velocity of using the dune model is evidently higher than that of the conventional pneumatic conveying and using soft fins. However, the effect of soft fins and dune model on the particle velocity is maintained downstream of the bend. [ABSTRACT FROM AUTHOR]

Abstract: In order to reveal the mechanism of the steady transport at the low conveying velocity by using soft fins, the high-speed particle image velocimetry (PIV) is used to measure and analyze particle fluctuation velocity near air conveying velocity of the minimum pressure drop (MPD) in a horizontal self-excited pneumatic conveying. The study focuses on the effect of the different fin's lengths on the horizontal pneumatic conveying in terms of the time-averaged particle concentration and velocity, power spectrum, auto-correlation coefficients, two-point correlation coefficients, fluctuation intensity of particle velocity, skewness factor and probability density function. It is found that the power spectra peaks of fins, especially the longer fins, are larger than that of non-fin even at lower air velocity, suggesting the accelerating efficiency of fins' vibration. Meanwhile, the profiles of particle fluctuation velocity intensity indicate that the fins' oscillation generates large particle fluctuating energy even at lower air velocity so that the particles are more easily accelerated and suspended. This is one of the important reasons why the fins' oscillation results in the low pressure drop and low MPD air velocity. From the distribution of the skewness factor and the probability density function, it is found that the particle fluctuation velocities of all cases follow the Gaussian distribution in the lower and middle parts of pipe, and departure from the Gaussian distribution in the upper part of the pipe. The particle fluctuation velocity of the most efficient Fin320 more obeys the Gaussian-type fluctuation. [Copyright &y& Elsevier]

A new pneumatic conveying system that applies soft fins mounted vertically on a center plane of pipe in the inlet of the gas-particle mixture is developed to reduce power consumption and conveying velocity. The effect of different fin's lengths on a horizontal pneumatic conveying is experimentally studied in terms of the pressure drop, conveying velocity, power consumption, particle flow pattern, and additional pressure drop. The test pipeline consisted of a horizontal smooth acrylic tube with an inside diameter of 80 mm and a length of about 5 m. Two kinds of polyethylene particles with diameters of 2.3 mm and 3.3 mm are used as conveying materials. The superficial air velocity is varied from 10 to 17 m/s, and the solid mass flow rate is from 0.20 to 0.45 kg/s. Compared with conventional pneumatic conveying, the pressure drop, minimum and critical velocities, power consumption, and additional pressure drop can be reduced by using soft fins in a lower air velocity range, and the efficiency of fins becomes more evident when increasing the length of the fins or touching particles stream by the long fins. The maximum reduction rates of the minimum velocity and power consumption by using soft fins are about 20% and 31.5%, respectively. The particle concentrations of using fins are lower than those of non-fin near the bottom of the pipe and are higher than those of non-fin in the upper part of the pipe in the acceleration region. Based on analyzing the frequency features of the fin's oscillation, the Strouhal number of more efficient fins is about St ≈ 0.75 in the air velocity range of lower than 13 m/s. [ABSTRACT FROM AUTHOR]

Abstract: In order to reduce power consumption and conveying velocity, a new pneumatic conveying system where soft fins are mounted in a horizontal plane through the pipe axis in the front of inlet is proposed in this paper. The experimental study focuses on the effect of the different fin''s lengths on the horizontal pneumatic conveying system in terms of frequency characteristics of fin''s oscillation, pressure drop, conveying velocity, particle flow pattern, power consumption and additional pressure drop. The test pipeline consisted of a horizontal smooth acrylic tube with an inside diameter of 80mm and a length of about 5m. The polyethylene spherical particles of density 978kg/m3 and 952kg/m3 with diameters of 2.3mm and 3.3mm are used as conveying materials. The mean air velocity is varied from 10 to 17m/s, and the solid mass flow rate is from 0.20 to 0.45kg/s. Comparing with the conventional pneumatic conveying, the pressure drop, minimum and critical velocities, power consumption and additional pressure drop can be reduced by using soft fins in lower air velocity range. The efficiency of fin is quite evident with increasing the length of fin. The maximum reduction rates of the minimum velocity and power consumption by using soft fins are about 14.8% and 25.5%, respectively. By analyzing the frequency characteristics of fin''s oscillation, Strouhal number of more efficient fins is about S t =0.65 in the range of low air velocity. [Copyright &y& Elsevier]

Abstract: The purpose of this study focuses on analyzing the particle velocity and concentration characteristics in a horizontal pneumatic conveying with dune model, so as to reveal the mechanism of the low conveying velocity and saving-energy conveying. The test pipeline consisted of a horizontal smooth acrylic tube with an inside diameter of 80mm and a length of about 5m. The polyethylene particles of density 978kg/m3 and 952kg/m3 with diameters of 2.3 and 3.3mm are used as conveying materials. High-speed PIV was first applied to measure the time-averaged particle velocity and was proven to be an efficient measurement technique in the pneumatic conveying. Then the particle velocity and concentration distributions of three locations were measured at mean air velocities of 12m/s and 13m/s and the solid mass flow rates of 0.45kg/s and 0.43kg/s. A comparison of the particle velocity and concentration profiles between dune model and non-dune model was performed. It is found that the particle concentration of using dune model becomes higher in the upper part of pipeline and becomes lower near the bottom of pipeline in the acceleration region. The particle velocities of using dune model are clearly higher than that of the conventional pneumatic conveying along pipeline and display a uniform profile at the downstream. It is also clear that the particles can be effectively accelerated by increasing air velocity and impacting the surface of dune model. The effect of dune model on the velocity profile of relatively small particles is larger than that of the larger particles and maintains to the downstream. [Copyright &y& Elsevier]

Abstract: In order to reduce power consumption and conveying velocity, a pneumatic conveying system where a dune model is mounted in a pipeline is proposed in this paper. The experimental study focuses on the effect of the mounted dune model in the horizontal pneumatic conveying system in terms of pressure drop, power consumption and conveying velocity. The test pipeline consisted of a horizontal smooth acrylic tube with an inside diameter of 80mm and a length of about 5m. Polyethylene spherical particles with a density of 952kg/m3 and diameters of 2.3 and 3.3mm are used as conveying materials. The mean air velocity is varied from 9 to 16m/s, and the solid mass flow rate is from 0.25 to 0.45kg/s. Firstly, the effect of the dune model location on pneumatic conveying is experimentally studied. It is found that in the lower air velocity range, the pressure drop of the pneumatic conveying with a mounted dune model is lower than that of a conventional pneumatic conveying system. A lower conveying velocity and energy-saving conveying can be realized by installing a dune model in the conveying pipe. Especially the case of fixing the dune model on the bottom of the pipe at the inlet of particle feed is more effective. The particle flow patterns also show that the dune model reduces the deposition of particles. Then, the effect of different surface materials of the dune model is examined. By using a surface material of the dune model with a large coefficient of restitution, the pressure drop of conveying large particles is the lowest. When conveying relatively small particles, however, the pressure drop becomes the lowest by a small coefficient of restitution. The maximum reduction rates of the minimum velocity and power consumption by the dune model are about 19% and 34%, respectively. [Copyright &y& Elsevier]

Wavelet multiresolution analysis has been applied to digital images of ethanol sprays injected into air at atmospheric pressure and at room temperature. The imaging was performed with laser-sheet imaging using the 308 nm light from a XeCl excimer laser. Image capturing was performed with a CCD camera. The importance of different scales in the turbulent structure of the sprays was easily recognized using wavelet multiresolution analysis. It was observed that the intermediate and small scale levels contained information of such important phenomena as the spray break-up. This was not easily recognized in the original images, due to averaging over all scales. [ABSTRACT FROM AUTHOR]

The flow feature of the jet issuing from the circular pipe with the rotating inclined section has been investigated by the methods of flow visualization and image processing. It has been found that the jet diffusion is affected by the inclined angle and the rotating speed. The coherent structure of the jet has also been studied by using wavelet multiresolution analysis. The multiscale turbulent structures were visualized and the core and edge of the vortex were identified at different broad scales. [ABSTRACT FROM AUTHOR]

This paper describes an application of the wavelet transform in in-line solder paste inspection. In the development of a three-dimensional (3D) automatic inspection device of solder paste, it is necessary to detect the characteristic positions in images. In this paper, on the basis of the property of local wavelet transform modulus maximum (WTMM) and the deference filter, a practical algorithm is proposed for the detection of the characteristic positions. The proposed algorithm is applied to more than 20 actual images obtained from the 3D automatic inspection device. The detected errors are smaller than the maximum permissible error of 5 pixels. Also, the proposed algorithm is verified in-line. The experimental results show that the quality of solder paste can be successfully judged in-line. The proposed algorithm is superior to other possible techniques reported so far because of its implementation in assembly lines. [ABSTRACT FROM AUTHOR]

Previous studies of the organized motion mostly focused on large-scale structures; investigations of other scales have been relatively scarce because of the difficulty of extracting the structures of these scales using conventional vortex-detection techniques. A wavelet multi-resolution technique based on an orthogonal wavelet transform has been applied to analysing the velocity data simultaneously obtained in two orthogonal planes in the turbulent near-wake of a circular cylinder. Using this technique, the flow is decomposed into a number of wavelet components based on their characteristic or central frequencies. The flow structure of each wavelet component is examined in terms of sectional streamlines and vorticity contours. The wavelet component at a central frequency of $f_{0}$, the same as the vortex-shedding frequency, exhibits the characteristics of the Kármán vortices, thus providing a validation of the analysis technique. The spanwise vorticity contours of the wavelet component at $f_{0}$ display a secondary spanwise structure near the saddle point, whose vorticity is opposite-signed to that of the Kármán vortices. This structure is observed for the first time and its occurrence is consistent with the streamwise decay in the vorticity strength of the spanwise structures. Two-point velocity correlations of wavelet components in the lateral and spanwise directions and the wavelet auto-correlation function indicate that the wavelet components of $f_{0}$ and 2$f_{0}$ are relatively large-scale and organized, displaying considerable two-dimensionality. The component of 4$f_{0}$ is significantly less organized and highly three-dimensional, as indicated by much smaller spanwise correlation coefficients. The components at frequencies of 8$f_{0}$ and higher have virtually zero correlation coefficients. [ABSTRACT FROM AUTHOR]

The opening of a gated community to expand the micro-road network in an urban traffic system is an importance research topic related to urban congestion. To satisfy the demands of opening an early choosing case, this paper proposes a comprehensive selection framework on qualified communities and their appropriate opening times by describing the traffic state at the boundary road network accurately. The traffic entropy model and fuzzy c-means (FCM) method are used in this paper. In the framework, a new opening evaluation entropy model is built using basic theory of the thermodynamic traffic entropy method. The traffic state entropy values of the boundary road network and entropy production are calculated to determinate the opening time. In addition, a specific fuzzy range evaluation standard at a preset gated community is drawn with an FCM algorithm to verify the opening determination. A case study based on the traffic information in a simulated gated community in Shanghai is evaluated and proves that the findings of opening evaluation are in accordance with the actual situation. It is found that the micro-inter-road network of a gated community should be opened as the entropy value reaches 2.5. As the travel time is less than 20 s, the correlation between the opening entropy value and the journey delay time exhibits a good linear correlation, which indicates smooth traffic flow. [ABSTRACT FROM AUTHOR]

Highlights • The three-dimensional dune wake are investigated by PIV. • The large-scale structure is responsible for the formation of separation region. • The intermediate-scale structure is more active near the separation region. • The intermediate-scale structure makes more contribution to Reynolds stresses. • The small-scale vortical structures decay quickly at the downstream. Abstract The three-dimensional wake structures behind a barchan dune model are investigated by the high-speed particle image velocimetry (PIV) at the Reynolds number of 5530. The measured velocity fields are first evaluated by time-averaged flow patterns and power spectra analysis. Then the one-dimensional orthogonal wavelet analysis is applied to reveal multi-scale turbulent structures and their corresponding second order statistics in the dune wake. The instantaneous multi-scale structures suggest that the large-scale structure is responsible for the formation of separation region. The intermediate-scale structure tends to be more active at the boundary of separation region, which may be due to the secondary vortex movement caused by the interactions between the wake and main flow. The appearance of small-scale vortices at the downstream of separation region indicates the breakdown process of large-scale vortices. The Reynolds stress and kinetic energy distribution suggest that the large-scale structures dominate the generation of turbulence in the dune wake. The lower kinetic energy contained in intermediate- and small- scale structures is considered to be related to smaller-scale interactions that reflect energy cascading phenomenon. The Reynolds shear stresses distributions suggest that the intermediate-scale structures also make significance in the separated boundary layer. As for small-scale structure, it is worthy to note that a region of high Reynolds shear stresses with an opposite sign is observed around the dune crest. The cross-correlation function of multi-scale structures suggest the quasi-periodicity of large-scale structure. The intermediate-scale structures also show a certain periodicity, however, such structures tend to be more unstable and the strength of them reduces as they travel downstream. When decreasing to small-scale, the vortical structures decays quickly at the downstream with larger convective velocity. This may indicate the breakdown process of large-scale vortices and the quick dissipation of small-scale vortices. [ABSTRACT FROM AUTHOR]

A preface for the 2006 issue of the "International Journal of Wavelets, Multiresolution and Information Processing" is presented.

• Front inclined hole is used for passive flow control of a wall-mounted cube wake. • Jet injected from hole suppress separation flow above free-end significantly. • Flow structures and statistic characteristics in near-wake are influenced. • Wake vortical shedding becomes more regular and is accelerated near the free-end. • POD analysis indicates that alternating spanwise vortices are suppressed. To control the wake flow around a wall-mounted cube, passive control is performed by drilling a front inclined hole (FIH) from the front surface to the free end of the cube. To study the control features and mechanism, controlled and uncontrolled cubes are experimentally investigated. A circulation water tunnel is used to perform PIV measurements, where the Reynolds number is Re D = 11550 based on the cube side length of D = 70 mm, and the thickness of the boundary layer on the tunnel bottom is δ/D = 0.25. To study the effect of the hole position, three FIHs with inlet heights of 20, 35, or 50 mm are investigated. The time-averaged flow fields show that the velocity of the FIH jet increases with the FIH inlet height. Comparing with the flow structures around standard cube, it is found that the reverse zone and shear layer above free-end are obviously suppressed due to the FIH jet. In addition, the scale of the reverse zone and arch-type vortex in the near-wake is reduced by the FIH jets. Because the FIH jets disrupt the development of wake vortices, the Reynolds shear stress and turbulent kinetic energy in the near-wake decrease. The control effect is most apparent for the cube with an FIH at a spanwise height of 50 mm (the FIH50 cube). In this case the effect of the free-end downwash flow on the wake is weaker, and the shedding frequency of the wake vortices near the free-end increases. Proper orthogonal decomposition analysis indicates that the FIH50 suppresses the alternately arranged flow features and enhances the symmetrically arranged features. [ABSTRACT FROM AUTHOR]

A hybrid two-dimensional orthogonal wavelet multiresolution and proper orthogonal decomposition technique is developed to analyze the wake flow behind a semi cylinder. The two-dimensional orthogonal wavelet analysis is first applied to decompose the measured velocity fields into four wavelet components based on their spatial scales. Then the extracted multi-scale structures are further investigated based on proper orthogonal decomposition. The modal energy distributions of multi-scale flow structures suggest that the dominance of first two POD modes is reduced and the relative energy becomes more distributed as the flow structure changes from large-scale to small-scale. The first two POD modes of intermediate-scale structure also appear in a mode pair and they are related to secondary resonance accompanied with large-scale flow oscillation. The POD mode 3 of intermediate-scale structure suggest the existence of symmetric vortex shedding pattern. The first two POD modes of small-scale structure also display a symmetrically distributed vortex pair and the distance between adjacent vortices is about half of the case of mode 3 of intermediate-scale structure. The PSD distributions of POD modes of multi-scale structures suggest that the bandwidth of PSD becomes less concentrated as the flow structure varies from large-scale to small-scale. Distinctive flow patterns associated with first and second order harmonics of fundamental flow oscillation can be successfully extracted from the dominating POD modes of intermediate-scale and small-scale structures. The proposed hybrid technique provides a tool for relate the most energetic flow events over a period of time with multi-scale structures cascaded in the turbulence flow. • A hybrid 2D orthogonal wavelet multiresolution and proper orthogonal decomposition technique is developed. • The multi-scale structures of semi cylinder wake are decomposed by 2D orthogonal wavelet analysis. • The decomposed multi-scale structures are further analyzed by POD. • Distinctive flow patterns are extracted from the dominating POD modes of intermediate-scale and small-scale structures. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) flow structures around a wall-mounted short cylinder of height-to-diameter ratio 1 were instantaneously measured by a high-resolution tomographic particle image velocimetry (Tomo-PIV) at Reynolds number of 10 720 in a water tunnel. 3D velocity fields, 3D vorticity, the Q criterion, the rear separation region, and the characteristic of arch type vortex and tip vortices were first discussed. We found a strong 3D W-type arch vortex behind the short cylinder, which was originated by the interaction between upwash and downwash flows. This W-type arch vortex was reshaped to the M-shaped arch vortex downstream. It indicated that the head shape of the arch vortex structure depended on the aspect ratio of the cylinder. The large-scale streamwise vortices were originated by the downwash and upwash flows near the center location of W-type arch vortex. Then the 3D orthogonal wavelet multiresolution technique was developed to analyze instantaneous 3D velocity fields of Tomo-PIV in order to clarify 3D multiscale wake flow structures. The W-type shape arch vortex was extracted in the time-averaged intermediate-scale structure, while an M-shaped arch vortex was identified in the time-averaged large-scale structure. The tip vortices distributed in the time-averaged large- and intermediate-scale structures. The instantaneous intermediate-scale upwash vortices played an essential role in producing W-type head of arch structure. It was also observed that strong small-scale vortices appeared in the shear layer or near the bottom plate and most of them were contained in the intermediate-scale structures.

The turbulent boundary layer flow measured by two-dimensional time-resolved particle image velocimetry is analyzed using the discrete orthogonal wavelet method. The Reynolds number of the turbulent boundary layer based on the friction velocity is Re_{τ}=235. The flow field is decomposed into a number of wavelet levels which have different characteristic scales. The velocity statistics and coherent structures at different wavelet levels are investigated. It is found that the fluctuation intensities and their peak locations differ for varying scales. The proper orthogonal decomposition (POD) of different wavelet components reveals a cascade of scales of coherent structures, especially the small-scale ones that are usually difficult to be identified in POD modes of the undecomposed flow field. The interactions among the scales are investigated in terms of large-scale amplitude modulations of the small-scale structures. In previous studies the velocity fluctuations are separated into two parts, the large scale and the small scale, divided usually by the boundary layer thickness. In the present study, however, the scales smaller than the boundary layer thickness are further separated. Therefore, the modulation analysis is a refined investigation that differentiates the modulation effects on separated small scales. The results reveal that the modulation effects vary among the small scales.

The effect of the Reynolds number on the wavelet-decomposed turbulent structures in a self-preserving plane wake has been investigated for Re_{theta} (based on the free-stream velocity and momentum thickness, theta, of the wake) =1350 and 4600. Measurements were made at x/theta (x is the streamwise distance downstream of the cylinder) =580 for the circular cylinder using two orthogonal arrays of 16 X wires, eight in the (x,y) plane, and eight in the (x,z) plane. A wavelet multiresolution technique is used to analyze the measured hot-wire data. This technique decomposes turbulence structures into a number of components based on their central frequencies, which are linked with the turbulence scales. Sectional streamlines and vorticity contours at the same central frequency, i.e., the comparable scales of turbulent structures, are examined and compared between the two Reynolds numbers. Discernible differences are observed in the turbulent structures of relatively large to intermediate scales. The differences are further quantified in terms of contributions from the turbulent structures of different scales to the Reynolds stresses, vorticity variance, and probability density functions of the fluctuating velocities. The large-scale structure contributes most to the Reynolds stresses and this contribution drops for the higher Re_{theta}.

The effect of initial conditions on the turbulent structures of various scales in a near-wake has been investigated for two wake generators, i.e., a circular cylinder and screen of 50% solidity, of the same characteristic dimension. Velocity data were obtained at x/h (x and h are the stream-wise distance downstream and the height of the wake generators, respectively) =20 using 16 X wires, eight aligned in the plane of mean shear and eight in the plane parallel to both the cylinder axis and the flow direction. A wavelet multi-resolution technique was used to decompose the velocity data into a number of wavelet components based on the central frequencies, which correspond to the scales of turbulent structures. It was found that the behaviors of intermediate- as well as large-scale structures depend on the initial conditions. In the circular cylinder wake, the large- and intermediate-scale structures make the largest (and comparable) contribution to Reynolds stresses, but in the screen wake there is a significant difference in the contribution between the two types of structures. The two-dimensionality of the wavelet component is also examined.