Papers by Keyword: Particle Image Velocimetry (PIV)

Abstract: In recent years, minimum quantity lubrication (MQL) machining is regarded as a promising method for reducing machining cost and cutting fluid, while improving cutting performance. However the effectiveness and the working principle of MQL are still questionable with very few explanations provided. The aim of this study is to determine the optimum distance between the nozzle and tool tip and appropriate flow pattern of the mist flow for minimum quantity lubricant using Particle Image Velocimetry (PIV) and Computer Fluid Dynamic (CFD) for optimizing the spraying conditions thus reducing the lubricant consumption. The spray from the nozzle with outlet diameter of 2.5mm is analysed using Particle Image Velocimetry (PIV) to measure the mist flow velocity and identify the flow pattern. The input pressure of 0.2, 0.3 and 0.4MPa will be discharged throughout the experiment. Higher pressure produce more mass flow rate which helps in reducing the cutting force and cutting temperature efficiently and prolong tool life. Thus the appropriate distance can reduce lubricant consumption and increase the cooling and lubricating ability with best nozzle position. The applied distance increases the efficiencies of MQL applied during machining process.

Abstract: Various diffuser types characterized by the geometry are introduced in the flow line to recover the energy. A 3-D turning diffuser is a type of diffuser that its cross-section diffuses in all 3 directions of axes, i.e. x, y and z. In terms of applicability, a 3-D turning diffuser offers compactness and more outlet-inlet configurations over a 2-D turning diffuser. However, the flow within a 3-D turning diffuser is expected to be more complex which susceptible to excessive losses. As yet there is no established guideline that can be referred to choose a 3-D turning diffuser with an optimum performance. This paper aims to investigate the effects of varying inflow Reynolds number (Re_in) on the performance of 3-D turning diffuser with 90^o angle of turn. The outlet pressure recovery (C_p) and flow uniformity (σ_u) of 3-D turning diffuser with an area ratio (AR = 2.16) and outlet-inlet configurations (W₂/W₁ = 1.44, X₂/X₁ = 1.5), operated at inflow Reynolds number of Re_in = 5.786E+04 - 1.775E+05 have been experimentally tested. The experimental rig was developed by incorporating several features of low subsonic wind tunnel. This was mainly to produce a perfect fully developed and uniform flow entering diffuser. Particle image velocimetry (PIV) was used to examine the flow quality, and a digital manometer was used to measure the average static pressure of the inlet and outlet of turning diffuser. There is a promising improvement in terms of flow uniformity when a 3-D turning diffuser is used instead of a 2-D turning diffuser with the same AR. An unexpected trend found with a drop of pressure recovery at maximum operating condition of Re_in = 1.775E+05 shall require further investigations. The results obtained from this study will be in future used to validate the numerical codes. Upon successful validation, several other configurations will be numerically tested in order to establish the guidelines in the form of mathematical models.

Abstract: The purpose of this investigation is to research and develop a new type water turbine, which is appropriate for low-head open channel, in order to effectively utilize the unexploited hydropower energy of small river or agricultural waterway. The application of placing cross-flow runner into open channel as an undershot water turbine has been under consideration. As a result, a significant simplification was realized by removing the casings. However, flow field in the undershot cross-flow water turbine are complex movements with free surface. This means that the water depth around the runner changes with the variation in the rotation speed, and the flow field itself is complex and changing with time. Thus it is necessary to make clear the flow field around the water turbine with free surface, in order to improve the performance of this type turbine. In this research, the performance of the developed water turbine was determined and the flow field was visualized using particle image velocimetry (PIV) technique. The experimental results show that, the water depth between the outer and inner circumferences of the runner decreases as the rotation speed increases. In addition, the fixed-point velocities with different angles at the inlet and outlet regions of the first and second stages were extracted.

Abstract: In this paper, an improved PIV algorithm is proposed for the velocity field of oil-water two-phase dispersed flow in horizontal pipe. In the proposed PIV algorithm, interrogation windows are overlapped by 50% in all iterations other than just overlapped in the final iteration. And what’s still different is that the interrogation window can also be a rectangular window just as [64 64; 64 64; 32 32; 32 32; 32 16;]. What’s more, if any element of the final interrogation window is different from the penultimate iteration, there is going to be another interrogation with the last interrogation window size, which can reduce the false vectors. Experimental results show that velocity measurements of oil-water two-phase flow can be realized by this advanced PIV algorithm with high accuracy. At the same time, it provides the basis for further studying the application of PIV in velocity measurements of oil-water two-phase flow.

Abstract: The research studies the characteristics of the vertical flow past a finite-length horizontal cylinder at low Reynolds numbers (Re_D) from 250 to 1080. The experiments were performed in a vertical closed-loop water tunnel. Flow fields were observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake was observed and the size of the vortex increased as the observed section was away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake was observed. The characteristics of vortex formation also change with increasing Reynolds numbers. At X/D = -3, a pair of vortices was observed in the wake for Re_D = 250, but as the Re_D increases the vortex street was observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow affects the vortex shedding frequency even to 5 diameters of the cylinder from its tip. The interaction between the downwash flow and the Von Kármán vortex street in the wake of the cylinder is presented in this paper.

Abstract: A turning diffuser is often introduced in the flow line to recover the energy losses by converting the kinetic energy to pressure energy. There are two types of turning diffusers, i.e. a 2-D and 3-D diffuser that are commonly defined by their expansion direction. This study aims to investigate the performance of a 2-D and a 3-D turning diffuser with 90^o angle of turn and an area ratio, AR=2.16 by means of varying operating conditions. The geometry configurations applied for a 2-D turning diffuser are outlet-inlet configurations, W₂/W_12-D=2.160, X₂/X_12-D =1.000 and an inner wall length to an inlet throat width ratio, L_in/W_12-D=4.370, whereas for a 3-D turning diffuser, they are W₂/W_13-D=1.440, X₂/X_13-D =1.500 and L_in/W_13-D=3.970. The operating conditions represented by inflow Reynolds numbers, Re_in are varied from 5.786E+04 to 1.775E+05. Particle image velocimetry (PIV) is used to examine the flow quality, and a digital manometer provides the average static pressure at the inlet and outlet of the turning diffuser. A compromise between the maximum permissible pressure recovery and flow uniformity is determined based upon the need. Whenever the flow uniformity being the need it is promising to apply a 3-D turning diffuser for Re_in=1.027E+05 - 1.775E+05 and a 2-D turning diffuser for Re_in=5.786E+04-6.382E+04. On the other hand, it is viable to opt for a 3-D turning diffuser for Re_in=5.786E+04-6.382E+04 and a 2-D turning diffuser for Re_in=1.027E+05-1.775E+05 in the case of the outlet pressure recovery being the need. The secondary flow separation takes place prior at 1/2L_in/W₁ for a 2-D turning diffuser, whereas approximately at 3/4L_in/W₁ for a 3-D turning diffuser.

Abstract: In this paper, a new particle matching algorithm for 3D-PIV is proposed based on Delaunay triangulation and projective invariants. In the proposed algorithm, fuzzy similarity is first computed for the triangulation in the matching particle images and rough matching is executed. Then, error matching in the results of rough matching is removed based on projective invariants. Experiment results further demonstrate the effectiveness of the proposed method.

Abstract: Travelling wave thermoacoustic heat engines have been reported to have a higher efficiency than the standing wave ones. The former are generally large systems which consist of toroidal shape resonators. While standing wave heat engines are inherently smaller, a reduction in size could be considered which may involve curvatures as compared to the straight tube conventional systems. However, as with the streaming losses in the travelling wave resonators, losses due to the curvature may be generated. This study involves preliminary experimental measurements using the Particle Image Velocimetry (PIV) method to analyze the velocity profiles in a standing wave resonator before and after a ninety degree curvature. This design can reduce the space generally occupied by the straight standing wave resonator. The overall length of the resonator fits a quarter wavelength wave based on the straight closed-end tube type. The working gas is air at 1 atmospheric pressure. Results have shown that the velocity profiles after the stack but before the curvature exhibit clear straight paths up just as reported elsewhere. Signs of disordered motion could be observed just before the bend and the pattern continues until after the curvature. The results are obtained before one periodic cycle and before the acoustic wave front hit the tube end. The trend is expected to affect the overall thermoacoustic performance of the engine as returning gas particles interact with the oncoming particles that pass by the curvature.

Abstract: The flow structure inside a water basin that, serves as a water tank of a modeled washer system with an immersed coiled heater and air supply nozzle is investigated experimentally. To obtain the flow velocity field, particle image velocimetry is employed, and different view-point sections are analyzed. A large-scale vertical flow structure, which is attributed to the strong air jet flow enhancement, causes the development of a 3D mixing layer in the entire flow regime. Although a coiled heater can provide buoyancy to the working fluid, the bubbly flow structure significantly dominates this stage by supplying air from the bottom nozzles.

Abstract: Internal flow field of water-sediment two phase flow was hardly observed by PIV system, due to poor light transmittance. To improve this situation, the glass particle was used in experiment instead of sediment particle. According to the experiment results, the light transmittance of the mixture of glass beads and water was better than the mixture of sediment and water; so the relatively clear internal image of the two-phase flow could be obtained by PIV system. According to the experiment, the glass beads movement was similar to sediment in water.