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Holographic PIV (HPIV) is the most promising candidate for the next generation full-field velocimetry that can measure high spatial resolution instantaneous three-dimensional (3D) velocity fields. To explore the maximum performanc...
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Holographic PIV (HPIV) is the most promising candidate for the next generation full-field velocimetry that can measure high spatial resolution instantaneous three-dimensional (3D) velocity fields. To explore the maximum performance capabilities of HPIV including spatial resolution, off-axis holography based HPIV has become a major direction of development. A fully automated off-axis HPIV system based on an injection-seeded dual-pulsed YAG laser and 3D data processing software has been implemented in the laser flow diagnostics lab (LFD). In our system, 90-degree particle scattering, dual reference beams, in situ reconstruction/data processing, and 3D velocity extraction based on a fast "concise cross correlation" (CCC) algorithm are utilized. The off-axis HPIV system is tested for an acoustically excited air jet and the wake of a surface-mounted tab in a water channel flow giving instantaneous 3D velocity fields for both flows. Experimental data of instantaneously measured 3D flow structures using this technique show great promise. [References: 37]
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Эффективность управления вентиляцией угольных шахт во многом определяется точностью анемометрических измерений. Перспекти...
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Эффективность управления вентиляцией угольных шахт во многом определяется точностью анемометрических измерений. Перспективным направлением обеспечения безо- . пасности горных работявляется разработка устройств пространственного интегрального анемометрического контроля.В данной работе получено общее выражение для траектории акустического луча в анемометрическом канале. Проведена оценка степени отклонения этой траектории от прямолинейной для случаев ламинарного и турбулентного потока воздуха и выведены соответствующие аналитические зависимости. Полученные уравнения отклонений траекторий акустического пучка в аэродинамическом поле от прямолинейных позволяют устранить соответствующие погрешности измерений и вычислений при разработке аппаратуры интегральной акустической анемометрии.
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We introduce in this work a concept of rough driver that somehow provides a rough path-like analogue of an enriched object associated with time-dependent vector fields. We use the machinery of approximate flows to build the integr...
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We introduce in this work a concept of rough driver that somehow provides a rough path-like analogue of an enriched object associated with time-dependent vector fields. We use the machinery of approximate flows to build the integration theory of rough drivers and prove well-posedness results for rough differential equations on flows and continuity of the solution flow as a function of the generating rough driver. We show that the theory of semimartingale stochastic flows developed in the 80's and early 90's fits nicely in this framework, and obtain as a consequence some strong approximation results for general semimartingale flows and provide a fresh look at large deviation theorems for 'Gaussian' stochastic flows.
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Fluid dynamics has the purpose of understanding the movement of liquids and gases by functions that describe the distribution of velocities. Some natural phenomena that present these functions are hurricanes, generated by pressure...
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Fluid dynamics has the purpose of understanding the movement of liquids and gases by functions that describe the distribution of velocities. Some natural phenomena that present these functions are hurricanes, generated by pressure differences; cyclones, developed by the horizontal temperature gradient; and eddies, associated with a hydrostatic pressure gradient. In the particular case of eddies, they generate the so-called secondary velocities, which are flows formed by the presence of unequal forces between a hydrostatic pressure gradient and centrifugal forces, or by shear stresses at the joining of two flows. In addition, this phenomenon is observed in tornados, where the centrifugal force is greater in the upper layer and decreases towards the bottom, whereas the pressure gradient moves from a high to a low pressure; while in rivers it is detected particularly in bends or joins. Understanding the development of secondary currents is important for the reason that flow behavior is a function of the magnitude of these currents; hence their characterization is fundamental. The objective of this study was to obtain the secondary velocities developed as an effect of the union of two water currents, based on data acquired from Doppler acoustic recorders. A second objective was to draw the secondary velocities and to show the rotation flow effect, a kind of results that are difficult to obtain in any other way. The flow mechanisms are related with erosion and sedimentation processes; therefore, understanding them might help to evaluate and predict morphological changes in rivers.
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We consider the transport of dynamically passive quantities in the Batchelor regime of a smooth in space velocity field. For the case of arbitrary temporal correlations of the velocity, we formulate the statistics of relevant char...
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We consider the transport of dynamically passive quantities in the Batchelor regime of a smooth in space velocity field. For the case of arbitrary temporal correlations of the velocity, we formulate the statistics of relevant characteristics of Lagrangian motion. This allows us to generalize many results obtained previously for strain delta correlated in time, thus answering a question about the universality of these results. [S1063-651X(99)12810-1]. [References: 21]
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Local and temporal temperature mapping of the liquid phase around boiling bubbles and above the heat-transfer surface reveals that convective heat transfer plays a significant role in boiling heat transfer. To investigate this, we...
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Local and temporal temperature mapping of the liquid phase around boiling bubbles and above the heat-transfer surface reveals that convective heat transfer plays a significant role in boiling heat transfer. To investigate this, we employ one of the most accurate methods for detecting temperature: the laser-induced fluorescence (LIF) technique. Previously, ratiometric LIF has been conducted mainly at temperatures well below 70 degrees C, which is too low for our purposes. We used Rhodamine B (RhB) and Rhodamine 110 (Rh110) as fluorescent dye pairs. We found that Rh110 excited by a 532-nm laser (rather than the blue laser used in some earlier studies) exhibited a temperature dependence: the combination of RhB and Rh110 could be used as a temperature indicator up to 88 degrees C. The calibration curve was extended beyond the superheating temperature range, permitting liquid-phase temperature visualization of boiling. A thin film heater sandwiched between two transparent plates was used to gain optical access to the liquid-vapor structure. This method successfully captured characteristic phenomena such as superheated liquid layer formation and thermal plumes beneath the rising boiling bubbles.
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In this paper, measurements of velocity and stress fields in rigid pipes are performed by means of planar particle image velocimetry (PIV). The attention is focused onto the effect of Reynolds number and of continuous or pulsating...
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In this paper, measurements of velocity and stress fields in rigid pipes are performed by means of planar particle image velocimetry (PIV). The attention is focused onto the effect of Reynolds number and of continuous or pulsating flows by investigating pipe geometries ranging from the straight pipe to the reduced section and bifurcated ones. The obtained results show that, in the tested range, the effect of Reynolds number is limited for straight and reduced section pipes, while significant for the bifurcated one. Independently of Reynolds number, different geometries and forcing (continuous or pulsed) produce strong variations in intensity and spatial distribution of velocity and stress fields. Considering the latter, the contribution of viscous and turbulent stresses are measured separately and compared. Indeed turbulent stresses are always larger than the viscous ones, but the relative intensity is highly variable as also the spatial distribution of maxima and minima. Specifically, in the pulsating flows, this distribution is phase-dependent reflecting the oscillations of regions of flow separation which form especially in reduced section and bifurcated pipes. These results are useful for all engineering applications in which turbulent pipe flows are involved.
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Electromagnetic flow meters have succesfully been used in many industries to measure the mean flow velocity of conductive liquids. This technology works reliably in single phase flows with axisymmetric flow profiles but can be ina...
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Electromagnetic flow meters have succesfully been used in many industries to measure the mean flow velocity of conductive liquids. This technology works reliably in single phase flows with axisymmetric flow profiles but can be inaccurate with asymmetric flows, which are encountered, for example, in multiphase flows, pipe elbows and T-junctions. Some computational techniques and measurement devices with multiple excitation coils and measurement electrodes have recently been proposed to be used in cases of asymmetric flows. In earlier studies, we proposed a computational approach for electromagnetic flow tomography (EMFT) for estimating velocity fields utilizing several excitation coils and a set of measurement electrodes attached to the surface of the pipe. This approach has been shown to work well with simulated data but has not been tested extensively with real measurements. In this paper, an EMFT system with four excitation coils and 16 measurement electrodes is introduced. The system is capable of using both square wave and sinusoidal coil current excitations and all the coils can be excited individually, also enabling parallel excitations with multiple frequencies. The studies undertaken in the paper demonstrate that the proposed EMFT system, together with the earlier introduced velocity field reconstruction approach, is capable of producing reliable velocify field estimates in a laboratory environment with both axisymmetric and asymmetric single phase flows.
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This paper is concerned with the motion of small gas bubbles, equivalent diameter about 1.0 mm, in isotropic turbulent flows. Data on the mean velocity of rise and the dispersion of the bubbles have been obtained numerically by si...
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This paper is concerned with the motion of small gas bubbles, equivalent diameter about 1.0 mm, in isotropic turbulent flows. Data on the mean velocity of rise and the dispersion of the bubbles have been obtained numerically by simulating the turbulence as a slim of Fourier modes with random phases and amplitudes determined by the Kraichnan and the von Karman-Pao energy-spectrum functions, and by calculating the bubble trajectories from a reasonably well-established equation of motion. The data cover the range beta less than or equal to 1, where beta is the ratio between the turbulence intensity and the velocity of rise of the bubbles in still fluid. An approximate analysis based on the assumption that beta is small yields results that compare favourably with the numerical data, and clarifies the important role played by the lift forces exerted by the fluid. [References: 29]
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A study is undertaken to ascertain non-Newtonian effects in steady flows of elastic fluids along circular cylinders when there is extraction across the boundary surfaces. Exact representations for the velocity and stress fields ar...
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A study is undertaken to ascertain non-Newtonian effects in steady flows of elastic fluids along circular cylinders when there is extraction across the boundary surfaces. Exact representations for the velocity and stress fields are derived when the fluid prototypes are generalized Maxwell prototypes (exhibiting stress relaxation). Whilst the scheme of study has physical importance, it is the nature of the solution which is of foremost interest here, it being shown that the presence of elasticity (of the type considered) has a marked effect on the transport velocity.
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