PTV Measurements Research Articles

1007 風波界面近傍のPTV計測(2)(OS10-2 大気海洋の流体現象と環境流体,OS10 大気海洋の流体現象と環境流体,オーガナイズドセッション)

1007 風波界面近傍のPTV計測(2)(OS10-2 大気海洋の流体現象と環境流体,OS10 大気海洋の流体現象と環境流体,オーガナイズドセッション)

1007 風波界面近傍のPTV計測(1)(OS10-2 大気海洋の流体現象と環境流体,OS10 大気海洋の流体現象と環境流体,オーガナイズドセッション)

1007 風波界面近傍のPTV計測(1)(OS10-2 大気海洋の流体現象と環境流体,OS10 大気海洋の流体現象と環境流体,オーガナイズドセッション)

Design of a set-up for high-accuracy 3D PTV measurements in turbulent pipe flow

Turbulent flows are often encountered in common practice, usually at high Reynolds number. The development of Lagrangian stochastic models of these flows requires knowledge of Lagrangian statistics. To study the Lagrangian statistics of turbulent pipe flow, a dedicated 3D particle tracking velocimetry set-up has been designed. In this paper, design parameters, selection criteria and solutions are discussed. The measurement accuracies are studied in detail. Typical 3D particle tracking velocimetry results for turbulent pipe flow are compared and found to be in good agreement with direct numerical simulations.

Numerical Simulation of a Droplet taking the Effect of Surfactant Transport on the Interface by Front-tracking Method

In this paper, a front-tracking (FT) method combined with a solver of interfacial transport of surfactant was proposed in order to resolve interfacial flows affected by contamination. In the FT method, because the interfaces are presented explicitly, advection-diffusion equation on the interface can be easily treated and can be solved highly accurately. In this study, a scheme which conserves the total mass completely was constructed and proposed. Numerical simulations of a water drop sinking in silicone oil were performed taking the Marangoni effect into account. The effects of three parameters, damping coefficient of interfacial tension, diffusion coefficient and total mass, were evaluated. Calculated results were compared with PTV measurements and were in very good agreement with them in the points of stagnant cap size, flow separation point, peak of shear stress and so on. So, we can expect that our simulations can estimate the conditions of surfactant on the interfaces, which is very difficult to be measured.

Experimental Investigation to Study Convective Mixing, Spatial Uniformity, and Cycle-to-Cycle Variation During the Intake Stroke in an IC Engine

The work described in this paper focuses on experiments to quantify the initial fuel mixing and gross fuel distribution in the cylinder during the intake stroke and its relationship to the large-scale convective flow field. The experiments were carried out in a water analog engine simulation rig, and, hence, limited to the intake stroke. The same engine head configuration was used for the three-dimensional PTV flow field and the PLIF fuel concentration measurements. High-speed CCD cameras were used to record the time evolution of the dye convection and mixing with a 1/4 deg of crank angle resolution (and were also used for the three-dimensional PTV measurements). The captured sequences of images were digitally processed to correct for background light non-uniformity and other spurious effects. The results are finely resolved evolution of the dye concentration maps in the center tumble plane. The three-dimensional PTV measurements show that the flow is characterized by a strong tumble, as well as pairs of cross-tumble, counter-rotating eddies. The results clearly show the advection of a fuel-rich zone along the wall opposite to the intake valves and later along the piston crown. It also shows that strong out-of-plane motions further contribute to the cross-stream mixing to result in a relatively uniform concentration at BDC, albeit slightly stratified by the lean fluid entering the cylinder later in the intake stroke. In addition to obtaining phase-averaged concentration maps at various crank angles throughout the intake stroke, the same data set is processed for a large number of cycle to extract spatial statistics of the cycle-to-cycle variability and spatial non-uniformity of the concentration maps. The combination of the three-dimensional PTV and PLIF measurements provides a very detailed understanding of the advective mixing properties of the intake-generated flow field. [S0742-4795(00)00103-4]

Direct numerical simulation of an impinging jet into parallel disks

A direct numerical simulation code with cylindrical geometry has been developed. A direct numerical simulation (DNS) of an impinging round jet into parallel disks is performed for a Reynolds number of 10,000 based on the nozzle exit velocity and the nozzle diameter (D). Mean flow variables, turbulent intensity, pressure distribution and turbulent kinetic energy budgets are obtained at various radial locations. The present DNS results are in fairly good agreement with the two‐dimensional PTV measurements by Nishino and co‐workers in 1996. Some flow features of this impinging round jet regarding a turbulent transition process are discussed.

The investigation of an unstable convective flow using optical methods

The convective flow field in a vessel is investigated by laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV, namely Particle Tracking Velocimetry—PTV). The vessel is heated from below along a linear element at a temperature higher than that of the fluid. Hot fluid raises up and generates two counterrotating vortices. For a given aspect ratio, the two vortices become unstable and start to oscillate on a vertical plane (orthogonal to the heating element). This regime is investigated for increasing Rayleigh numbers to analyze the transition from regular to irregular conditions. The main transition mechanism is observed to be mostly connected to type II intermittency, a mechanism not frequently observed in experiments. However, at some Rayleigh numbers the present data does not definitely rule out type III intermittency. The phenomenon is analyzed by looking at the main frequencies in the spectrum of the horizontal velocity component and their changes with the Rayleigh number at a point above the heating element. Modifications in the local energy spectrum are analyzed by using the Wavelet Transform (WT) tool. Data obtained by PTV measurements make it possible to point out the spatial configuration of the flow and to determine the two velocity components on the measurement plane. These data are used to clarify the fundamental mechanisms of the transition. Instabilities are observed as sudden changes between two regimes of oscillations of the two counterrotating vortices: the first is characterized by oscillations centered on the vertical axis and the second by nonsymmetrical oscillations.

Measurement of Cycle-to-Cycle Variations and Cycle-Resolved Turbulencein an IC Engine Using a 3-D Particle Tracking Velocimetry.

Measurements of the instantaneous in-cylinder flow fields were carried out in a water analog engine simulation rig using a state of the art 3-D Particle Tracking Velocimetry(3-D PTV).Raw images for the 3-D PTV measurements were acquired at the end of intake stroke (Bottom Dead Center, BDC) for a simulated idle condition using a pair of high speed video cameras. Efforts were made to maximize the particle seeding density(and the resulting number of 3-D velocity vectors)to yield approximately 500 to 600 instantaneous vectors at each cycle. Using an appropriately designed spatial filter, large scale(low pass filtered) 3-D instantaneous velocity fields were reconstucted for each cycle as well as the ensemble averaged flow fields over large number of cycles. Based on these cycle-resolved(low pass filtered)flow fields and the ensemble averaged flow field, cycle-to-cycle variations were computed. Furthermore, the deviations of the instantaneous flow fields from the corresponding cycle-resolved large scale motions were computed to estimate the root mean square(rms)levels of the "in-cycle"turbulence. This paper presents the unique application of the 3-D PTV and the water analog engine simulation approach not only to measure the ensemble averaged mean 3-D flow patterns, but also to study the cycle-to-cycle stability of such flow patterns and ultimately to gain a better understanding of the combustion stability characteristics.

Flow Analysis in a Pump Diffuser—Part 1: LDA and PTV Measurements of the Unsteady Flow

This paper describes experimental research aimed at improving our understanding of the complex unsteady three-dimensional flow field associated with the interaction between a pump impeller and its vaned diffuser. The paper provides the results of experiments carried out using Laser Particle Tracking Velocimetry (LPTV) and Laser Doppler Anemometry (LDA), in which time-resolved details of the unsteady flow field in a vaned diffuser of a medium specific speed pump have been obtained as a function of the local position of the pump impeller blades. Detailed flow field measurements have been carried out at several measurement positions in the diffuser and at a number of operating points along the pump characteristic. The measurement results have been analyzed to elucidate some interesting flow features observed in this typical pump diffuser. These include three-dimensional flow at the impeller outlet, flow separation in the diffuser channel, unsteady recirculation of the flow from the diffuser into the impeller, the passage of vorticity in the impeller blade wakes through the diffuser, and periodic unsteadiness and turbulence in the diffuser flow channel. The relevance of these flow features to the stability of the pump characteristic is discussed.

DIGITAL PTV MEASUREMENTS OF A SEPARATED AIR FLOW BEHIND A BACKWARD-FACING STEP

DIGITAL PTV MEASUREMENTS OF A SEPARATED AIR FLOW BEHIND A BACKWARD-FACING STEP

Statistics of numerically generated turbulence

This paper considers numerically generated turbulence obtained by integrating the complete time-dependent three-dimensional Navier-Stokes equations. The simulated unidirectional turbulent flow, bounded by two parallel planes, is strongly inhomogeneous in the direction normal to the planes but homogeneous in the parallel directions. The resulting flow field, which is considered a numerical realization of fully developed turbulent channel flow, contains detailed information on spatial coherent flow structures as well as on the time-dependency and statistics of the three-dimensional velocity and pressure fields. Focussing here on the statistics of the numerically generated turbulence, second-moments and higher-moments are presented and compared with the most recent PTV and LDV laboratory measurements. It is concluded that direct numerical simulations are an invaluable approach to turbulence which complements field studies and laboratory investigations. Numerical experiments are now becoming a principal source of detailed and reliable information, which play a key role in the deepening of our understanding of turbulent flow phenomena.