Three-dimensional Velocity Field Measurements Research Articles

A Single-Camera-Based Three-Dimensional Velocity Field Measurement Method for Granular Media in Mass Finishing with Deep Learning.

Surface treatment processes such as mass finishing play a crucial role in enhancing the quality of machined parts across industries. However, accurate measurement of the velocity field of granular media in mass finishing presents significant challenges. Existing measurement methods suffer from issues such as complex and expensive equipment, limited to single-point measurements, interference with the flow field, and lack of universality in different scenarios. This study addresses these issues by proposing a single-camera-based method with deep learning to measure the three-dimensional velocity field of granular flow. We constructed a complete measurement system and analyzed the accuracy and performance of the proposed method by comparing the measurement results with those of the traditional DIC algorithm. The results show that the proposed method is very accurate in measuring spatial displacement, with an average error of less than 0.07 mm and a calculation speed that is 1291.67% of the traditional DIC algorithm under the same conditions. Additionally, experiments in a bowl-type vibratory finishing machine demonstrate the feasibility of the proposed method in capturing the three-dimensional flow of granular media. This research not only proposed a novel method for three-dimensional reconstruction and velocity field measurement using a single-color camera, but also demonstrated a way to combine deep learning with traditional optical techniques. It is of great significance to introduce deep learning to improve traditional optical techniques and apply them to practical engineering measurements.

Plenoptic Molecular Tagging Velocimetry For In-Situ Deployment In Water

We introduce a compact plenoptic imager to study wall-bounded turbulence along the surface of a 6:1 prolate spheroid, at a Reynolds number of 12 × 10 6 with molecular tagging velocimetry (MTV). This paper discusses the design of the imager and the technical solutions necessary to deploy the system in a large specimen. This includes using optical fiber laser delivery for UV and visible lasers. The end goal is the measurement of three-dimensional velocity fields near the wall, which is imperative for detailed turbulence analysis. We also stress the importance of understanding wall shear stress, a key factor in studying boundary layer dynamics in high-speed flows. Overcoming these challenges and refining our methods will result in an improved understanding of flow dynamics in high-turbulence regimes.

Aeroacoustics of sawtooth trailing-edge serrations under aerodynamic loading

The impact of aerodynamic loading on a serrated trailing edge is studied experimentally. Aerodynamic and acoustic measurements are conducted on a sawtooth-shaped trailing edge, retrofitted to a flat plate featuring a trailing-edge flap, and placed at incidence to the free-stream flow. The turbulent flow across the trailing edge is inspected by time-resolved three-dimensional velocity field measurements obtained from 4D-PIV, while the wall-pressure fluctuations are measured with surface-embedded microphones. Results discuss the relation between the velocity fluctuations over the serrations, the surface pressure fluctuations, and the far-field noise spectra. The aerodynamic analysis discusses the effect of counter-rotating vortex pairs, generated by the pressure imbalance across the edges of the serrations under loading. It is shown that the interaction of these vortices with the incoming turbulence affects the intensity of the wall-pressure spectrum at the outer rim of the serration surface. On the suction side, the intensity of the pressure fluctuations from the incoming boundary layer dominates over that induced by the vortex pairs. On the pressure side, instead, the velocity gradient prescribed by the vortex pairs produces a significant increase of the pressure fluctuations around the edges. The resulting spatial distribution of the wall-pressure fluctuations directly affects the far-field noise. Scattering predictions carried out with the wall-pressure fluctuations in the centre and root (on the suction side) exhibit good agreement with the measured noise in the low-frequency range, whereas using the surface pressure data at the tip of the serration (on the pressure side) yields a better prediction in the high-frequency range.

Experimental study of turbulent bubbly jet. Part 1. Simultaneous measurement of three-dimensional velocity fields of bubbles and water

This study proposes a method for simultaneous measurements of time-resolved three-dimensional velocity fields of the dispersed and continuous phases of a turbulent bubbly jet at a low void fraction using Lagrangian particle tracking (LPT) velocimetry with the Shake-The-Box algorithm. Four high-speed cameras are used to acquire time series of images that include both bubbles and fluid tracer particles. Bubbles are firstly tracked using intensity differences between tracer particles and bubbles, then the bubble images are removed from the camera images and all tracer particles are tracked using the residual images. Subsequently, FlowFit interpolation is applied to the LPT results obtained by phase separation to investigate flow characteristics of a bubbly jet. The bubbly jet was divided into two regions along the vertical direction: jet-like and plume-like regions. Streamwise vortex structures of continuous phase were generated mainly by the rising bubbles. The Gaussian and top-hat velocity profiles matched well with the ensemble-averaged fluid and bubble velocities, respectively. The measured slip velocity in the radial direction was not constant but linearly increased. The classical assumption of self-similarity with Gaussian profiles for fluid velocity and bubble concentration is experimentally verified. The fluid volume flux and entrainment coefficient are obtained as a function of the slip velocity, void fraction, plume and bubble width based on three-dimensional measurements. We found that the classical integral theory agrees well with experiments in the plume region.

Cylinder wakes in shallow oscillatory flow: the coastal island wake problem

Topographic complexity on continental shelves is the catalyst that transforms the barotropic tide into the secondary and residual circulations that dominate vertical and cross-shelf mixing processes. Island wakes are one such example that are observed to significantly influence the transport and distribution of biological and physical scalars. Despite the importance of island wakes, to date, no sufficient, mechanistic description of the physical processes governing their development exists for the general case of unsteady tidal forcing. Controlled laboratory experiments are necessary for the understanding of this complex flow phenomenon. Here, three-dimensional velocity field measurements of cylinder wakes in shallow-water oscillatory flow are conducted across a parameter space that is typical of tidal flow around shallow islands. The wake form in steady flows is typically described in terms of the stability parameter $S=c_{f}D/h$ (where $D$ is the island diameter, $h$ is the water depth and $c_{f}$ is the bottom boundary friction coefficient); in tidal flows, there is an additional dependence on the Keulegan–Carpenter number $KC=U_{0}T/D$ (where $U_{0}$ is the tidal velocity amplitude and $T$ is the tidal period). In this study we demonstrate that when the influence of bottom friction is confined to a Stokes boundary layer the stability parameter is given by $S=\unicode[STIX]{x1D6FF}^{+}/KC$ where $\unicode[STIX]{x1D6FF}^{+}$ is the ratio of the wavelength of the Stokes bottom boundary layer to the depth. Three classes of wake form are observed with decreasing wake stability: (i) steady bubble for $S\gtrsim 0.1$; (ii) unsteady bubble for $0.06\lesssim S\lesssim 0.1$; and (iii) vortex shedding for $S\lesssim 0.06$. Transitions in wake form and wake stability are shown to depend on the magnitude and temporal evolution of the wake return flow. Scaling laws are developed to allow upscaling of the laboratory results to island wakes. Vertical and lateral transport depend on three parameters: (i) the flow aspect ratio $h/D$; (ii) the amplitude of tidal motion relative to the island size, given by $KC$; and (iii) the relative influence of bottom friction to the flow depth, given by $\unicode[STIX]{x1D6FF}^{+}$. A model of wake upwelling based on Ekman pumping from the bottom boundary layer demonstrates that upwelling in the near-wake region of an island scales with $U_{0}(h/D)KC^{1/6}$ and is independent of the wake form. Finally, we demonstrate an intrinsic link between the dynamical eddy scales, predicted by the Ekman pumping model, and the island wake form and stability.

High-speed tomographic PIV and OH PLIF measurements in turbulent reactive flows

High-speed tomographic particle image velocimetry (TPIV) is demonstrated in turbulent reactive flows at acquisition rates ranging from 10 to 16 kHz. The 10-kHz TPIV measurements are combined with planar laser-induced fluorescence (PLIF) imaging of OH to mark the high-temperature reaction zone of the flame. Simultaneous TPIV/OH PLIF measurements are applied to the stabilization region of a weakly turbulent lifted dimethyl ether (DME)/air jet flame (Re D = 7,600) and the mixing layer of a turbulent partially premixed DME/air jet flame (Re D = 29,300). In the lifted jet flame, vortical structures exhibit time-dependent morphological changes and eventually dissipate as they approach the flame. In the near field of the turbulent jet flame, dynamics of localized extinction are captured as coherent structures with high compressive strain rates interact with the reaction zone and subsequently break apart. The principal axis of compressive strain has a strong preferential orientation at 45° with respect to the jet axis. The three-dimensional velocity field measurements are used to evaluate biases in two-dimensional (2D) measurements of compressive strain rates in a turbulent jet flame. The biases in the 2D measurements primarily stem from out-of-plane orientation of the principal axis of compressive strain. Comparisons with a constant density turbulent non-reactive jet (Re D = 22,600) show that the jet flame has larger coherent structures that are confined near the reaction zone. Data from the non-reactive jet are also used to evaluate effects of noise, bias, and spatial averaging on measurements of the velocity and velocity gradients.

1503 スキャニングステレオPIV による低フルード数浮力噴流の特異流入現象の3次元速度場計測(OS03-1 熱・流体の可視化と計測,オーガナイズドセッション 3:「熱・流体の可視化と計測」)

1503 スキャニングステレオPIV による低フルード数浮力噴流の特異流入現象の3次元速度場計測(OS03-1 熱・流体の可視化と計測,オーガナイズドセッション 3:「熱・流体の可視化と計測」)

Time-resolved scanning stereo PIV measurement of three-dimensional velocity field of highly buoyant jet

The time-resolved scanning stereo PIV system, which consists of a CW Nd:YAG laser, two high-speed CMOS cameras, a Galvano mirror and a pulse controller, is developed for time-sequential three-dimensional velocity field measurement of liquid flow. This experimental technique is validated by the measurement of a laminar non-buoyant jet, and is applied to the 3D velocity measurement of a highly buoyant jet at Froude number 0.3 and Reynolds number 200, which satisfy the inflow condition due to the unstable density gradient. The measurement of statistical properties of velocity field shows the growth of turbulence intensities near the nozzle exit, which indicates the presence of inflow motion near the nozzle exit due to the unstable density gradient. The vorticity contours about the horizontal axis shows the presence of counter-rotating vortices on both sides of the jet centerline, while the vorticity contour about the vertical axis indicates the presence of spiral growth of a pair of vortices along the jet centerline. The growth of the spiral structure along the jet centerline is recognized in the iso-vorticity contours obtained from the time-resolved measurement of 3D velocity field.

305 スキャニングステレオPIVによる浮力噴流の5次元速度場の同時計測(OS5-1熱流体の可視化と計測)

305 スキャニングステレオPIVによる浮力噴流の5次元速度場の同時計測(OS5-1熱流体の可視化と計測)

A304 噴霧燃焼器内部における三次元流れ場のPIV計測と誤差評価

This paper reports the measurement of three-dimensional velocity field in a spray combustion chamber with and without combustion using a combined use of planar PIV technique and with a rotary shutter mechanism. An uncertainty analysis has been carried out using artificial images, which include the influence of luminous noise generated by the spray combustion. The present results indicate that the flow pattern inside the combustion chamber is modified to strengthen the vertical flow motion relative to the horizontal one under the influence of combustion.

On the use of microjets to suppress turbulence in a Mach 0.9 axisymmetric jet

We have experimentally studied the effect of microjets on the flow field of a Mach 0.9 round jet. Planar and three-dimensional velocity field measurements using particle image velocimetry show a significant reduction in the near-field turbulent intensities with the activation of microjets. The axial and normal turbulence intensities are reduced by about 15% and 20%, respectively, and an even larger effect is found on the peak values of the turbulent shear stress with a reduction of up to 40%. The required mass flow rate of the microjets was about 1% of the primary jet mass flux. It appears that the microjets influence the mean velocity profiles such that the peak normalized vorticity in the shear layer is significantly reduced, thus inducing an overall stabilizing effect. Therefore, we seem to have exploited the fact that an alteration in the instability characteristics of the initial shear-layer can influence the whole jet exhaust including its noise field. We have found a reduction of about 2 dB in the near-field overall sound pressure level in the lateral direction with the use of microjets. This observation is qualitatively consistent with the measured reduced turbulence intensities.

Three-dimensional particle-streak tracking (PST) velocity measurements of a heat exchanger inlet flow

The particle-streak tracking system (PST) is a fast method for the measurement of three-dimensional velocity fields. The in-plane velocity components are measured with a single pulsed laser light sheet and one digital camera. The third velocity component is extracted from two continuous light sheets with a different wavelength than the pulsed light sheet, and an additional digital camera. Helium-filled bubbles are used to visualise the flow. A description of the set-up is given and the data evaluation process is explained. Measurements of a heat exchanger inlet flow and an analysis of the system limitations are presented.

Holographic Diffraction Image Velocimetry for Measurement of Three-Dimensional Velocity Fields

A new optical nonintrusive method for the gross-field measurement of three-dimensional (3-D) three-component (3-C) flows has been developed and tested. Termed Holographic Diffraction Image Velocimetry (HDIV), it is based on double-exposure dual-reference-beam holographic capture of particle-seeded flow fields and the subsequent processing of time-sequence image data obtained from a single observation direction. The technique uses variable-size transplacing-window cross-correlation (VS-TW-CC) together with an image cross-product (CP) method to extract inand out-of-plane particle displacements from the particle diffraction images. Preliminary experiments have shown that the method can resolve fine in-plane motions limited only by the finite pixel size of the image digitizer and the magnification of the imaging system used. For out-of-plane motions, resolutions measured with a relatively crude setup have been shown to be on the order of two tenths of the illumination wavelength divided by the square of the effective angular aperture of the system, which represents the image decorrelation distance. (Author)

Holographic diffraction image velocimetry for measurement of three-dimensional velocity fields

Holographic diffraction image velocimetry for measurement of three-dimensional velocity fields

Passage Flow Structure and Its Influence on Endwall Heat Transfer in a 90 deg Turning Duct: Mean Flow and High Resolution Endwall Heat Transfer Experiments

Three-dimensional measurements of the mean velocity field have been made in a square-cross-sectional, strongly curved, 90 deg turbulent duct flow. The mean radius to duct width ratio was 2.3. The study was performed as part of an overall investigation of the physics of endwall convective heat transfer. All three components of the velocity vector and the static and total pressure fields were measured using a five-hole probe at four duct cross sections: inlet, 0, 45, and 90 deg. Preliminary turbulence measurements using a single sensor hot wire at the inlet cross section were also obtained to provide streamwise fluctuation levels through the boundary layer. The endwall heat transfer coefficient distribution was determined using a steady-state measurement technique and liquid crystal thermography. A high-resolution heat transfer map of the endwall surface from far upstream of the curve through the 90 deg cross section is presented. The three-dimensional velocity field measurements indicate that a highly symmetric, strong secondary flow develops in the duct with a significant transfer of streamwise momentum to the transverse directions. The cross-stream vorticity components within the measurement plane were estimated using the five-hole probe data and an inviscid from of the incompressible momentum equation. The development of the total and static pressure fields, the three-dimensional mean velocity field, and all three components of the vorticity field are discussed. The endwall heat transfer distribution is interpreted with respect to the measured mean flow quantities.

Algorithms for fully automated three-dimensional particle tracking velocimetry

A three-dimensional Particle Tracking Velocimetry (3-D PTV) technique has been developed to provide time-resolved, three-dimensional velocity field measurements throughout a finite volume. This technique offers many advantages for fundamental research in turbulence and applied research in areas such as mixing and combustion. The data acquired in 3-D PTV is a time sequence of stereo images of flow tracer particles suspended in the fluid. In this paper, the implementation of the technique is discussed in detail, as well as the results of an extensive statistical investigation of the performance of the algorithms. The technique has been optimized to allow fully automatic processing of long sequences of image pairs in a computationally efficient manner, hereby providing a viable, practical tool for the study of complex flows.

An investigation of the near-field wake behind a full-scale test aircraft

Three-dimensional velocity field measurements were made on three transverse measurement planes located at 7.7,33.3, and 61.2 in. behind the inboard-wing trailing edge of an aircraft in flight. The test aircraft was an L-19 modified to incorporate a distributed suction boundary-layer control system. Test data were obtained at various lift coefficients and with both zero and full flap deflections. Flowfield measurements were made with a totalvector hot-film probe mounted to a boom and traversing mechanism attached to the rear fuselage of the test aircraft. The velocity measurements allowed computation of all three components of vorticity at the 7.7-in. plane and the normal (to the measurement plane) component of vorticity at the other two planes. The test results are presented as a series of contours of the various vorticity component values in the measurement planes. A typical set of axial velocity contours has also been provided. The plotted contours show a reproducible set of features, which are always associated with the formation of a concentrated core of axial vorticity. The test data are also compared to the predictions of a two-dimensional inviscid wake calculation based on measured wing loading for the L-19.