Nao Ninomiya

Visualization and PIV Measurement of the Flow around and inside of a Falling Droplet

Although the phenomena related to the multiphase flow can be found in many kinds of industrial and engineering applications, the physical mechanism of the multiphase flow has not been investigated in detail. The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. Presently, the visualization and the PIV measurement have been carried out about the both phases of the liquid-liquid two-phase flow. The difference in the refractive indices makes the visualization in the vicinity of the boundary of the multiple phases very difficult. In this study, the refractive index of the aqueous phase has been equalized to that of the oil phase by adjusting the concentration of the aqueous solution. As for the surrounding fluid, silicon oil is chosen and as for the droplet, the aqueous solution of glycerol is prepared whose refractive index matches that of silicon oil. Both phases are seeded with neutrally buoyant particles. The droplet is slightly colored with Rhodamine B so that the position of the invisible droplet can be identified. The difference in the background brightness in both phases helps PIV algorithm in distinguishing the motions in each phases. The results show the details of the flow structures both around and inside of a falling droplet simultaneously.

3D velocity measurement by a single camera using Doppler phase-shifting holography

In order to understand the details of the flow field in micro- and nano-fluidic devices, it is necessary to measure the 3D velocities under a microscopy. Thus, there is a strong need for the development of a new measuring technique for 3D velocity by a single camera. One solution is the use of holography, but it is well known that the accuracy in the depth direction is very poor for the commonly used in-line holography. At present, the Doppler phase-shifting holography is used for the 3D measurement of an object. This method extracts the signal of a fixed frequency caused by the Doppler beat between the object light and the reference light. It can measure the 3D shape precisely. Here, the frequency of the Doppler beat is determined by the velocity difference between the object light and the reference light. This implies that the velocity of an object can be calculated by the Doppler frequency. In this study, a Japanese 5 yen coin was traversed at a constant speed and its holography has been observed by a high-speed camera. By extracting only the first order diffraction signal at the Doppler frequency, a precise measurement of the shape and the position of a 5 yen coin has been achieved. At the same time, the longitudinal velocity of a 5 yen coin can be measured by the Doppler frequency. Furthermore, the lateral velocities are obtained by particle image velocimetry (PIV) method. A 5 yen coin has been traversed at different angles and its shapes and the 3D velocities have been measured accurately. This method can be applied to the particle flows in the micro- or nano-devices, and the 3D velocities will be measured under microscopes.

Interaction between two falling droplets in the liquid–liquid two-phase flow

The interaction between two falling droplets in the liquid–liquid two-phase flow has been investigated in detail with the aids of the index matching technique and PIV. It has been almost impossible to measure or even visualize the multiple phases simultaneously. This is because of the difference in the refractive indices of each phase. In this study, the refractive index of the water phase has been equalized to that of the oil phase by adjusting the concentration of the aqueous solution of glycerol and thus the simultaneous visualization of both phases and also the PIV measurement have been carried out. Presently, the interaction between two falling droplets has been intensively investigated. The interaction between two solid particles has been well known by the name of drafting–kissing–tumbling (DKT) motion. Similar motion to DKT is also observed for the droplets, which are found not to really kiss. It is found that the flows inside of the droplets are also affected by the interaction between two droplets while one droplet overtakes the other. The conditions for the initial relative positions of the two droplets to overtake have been summarized. It has been made clear that the chasing droplet is pulled by the wake of the preceding droplet.Graphical abstract

Direct measurement of longitudinal velocity by Doppler phase-shifting holography

Graphical Abstract

Interaction Between Two Falling Droplets in the Liquid-Liquid Two Phase Flow

Although the phenomena related to the multiphase flow can be found in many kinds of industrial and engineering applications, the physical mechanism of the multiphase flow has not been investigated in detail. The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. The difference in the refractive indices makes the visualization in the vicinity of the boundary of the multiple phases almost impossible. In this study, the refractive index of the aqueous phase has been equalized to that of the oil phase by adjusting the concentration of aqueous solution. Presently, the simultaneous visualization and the PIV measurement have been carried out about the both phases of the liquid-liquid two-phase flow. The measurement has been carried out for the flow field around and inside of two falling droplets interacting each other while they travel.Copyright

Turbulence Measurement in a Free Jet by Spark Tracing Method with Color DP Matching

Although the spark tracing method is known as one of the most classical techniques of flow visualization, the measurement by this technique has been limited to a qualitative observation or to one-dimensional velocity measurement. Recently, the authors of this study have been succeeded in measuring the two- or three-dimensional velocity field by applying the DP (dynamic programming) matching technique, which has commonly been used in the voice recognition, to the images obtained by the spark tracing method with the aid of one or two high speed cameras. Presently, the distributions of the mean velocities, rms velocity fluctuations and the Reynolds stresses in an axisymmetric free jet have been compared with those of the previous study. In order to increase the accuracy of this technique, the powder of aluminum oxide, which shows the radiant trails while they are burned by sparks, has been introduced to the flow.

Interaction between Two Falling Droplets in Stationary Liquid

Although the phenomena related to the multiphase flow can be found in many kinds of industrial and engineering applications, the physical mechanism of the multiphase flow has not been investigated in detail. The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. Presently, the simultaneous visualization and the PIV measurement have been carried out about the both phases of the liquid-liquid two-phase flow. The difference in the refractive indices makes the visualization in the vicinity of the boundary of the multiple phases almost impossible. In this study, the refractive index of the aqueous phase has been equalized to that of the oil phase by adjusting the concentration of aqueous solution. The PIV measurement has been carried out for the flow field around and inside of two falling droplets interacting each other while they travel.

PIV Measurement of Falling Droplet near the Wall

Although the phenomena related to the multiphase flow can be found in many kinds of industrial and engineering applications, the physical mechanism of the multiphase flow has not been investigated in detail. The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. The difference in the refractive indices makes the visualization almost impossible. The authors of this study have developed the technique for the simultaneous visualization of the both phases of the liquid-liquid two-phase flow by adjusting the refractive indices of both phases. In this study, the PIV measurement has been carried out for a water droplet falling near the wall in the stationary oil. The results reveal the typical features of the effect of the wall on the convection around and inside of a droplet.

Measurement in a Two-Dimensional Jet by Three-Dimensional Three-Component PIV

Presently, a new measurement algorithm for PIV is proposed that enables us to obtain the three-dimensional velocity vectors at three-dimensional measuring points, i.e., 3-D 3-C PIV. According to the recent progress in PIV, the three-dimensional velocity vectors in a two-dimensional plane, i.e., 2-D 3-C PIV, are easily obtained and have revealed the many features in many kinds of applications. With the use of the cameras under the Scheimpflug condition, clear focus can be obtained for both cameras at different viewing angles and this stereoscopic arrangement enables the 2-D 3-C PIV. In order to obtain the third velocity component, three-dimensional camera calibration is necessary. This means that the three-dimensional position of a particle can also be calculated without implementing any additional devices to 2-D 3-C PIV. Presently, the 3-D 3-C PIV algorithm has been proposed and an actual 3-D 3-C measurement is carried out for a two-dimensional jet.

A Study about the Surface Temperature Measurement by LIF

A temperature sensitive particle, which can be utilized for the three-dimensional non-intrusive simultaneous measurement of velocity and temperature of water flow, had been developed by one of the author of this study. Presently, non-intrusive measurement of surface temperature has been carried out by developing a temperature sensitive paint and its thermo-optical characteristics are quantified. Even though the temperature sensitive particle can be formed by introducing a fluorescent substance into polystyrene, it cannot be used as a paint which elastically covers many kind of surface. Presently, several polymers have been investigated for the base material for the paint and the polyvinylbuthyral (PVB) is found to fit the condition very well. The thermo-optical characteristics of the temperature sensitive paint made from PVB has been intensively investigated. The optimal concentration of the fluorescent dye and the solvent has been quantified. The effect of the thickness of a paint and its unsteady response are also investigated.