PIV expands its function from fluid velocity measurement to estimation of pressure, incorporating governing equations of flow. In this article, basic principle and applied algorithm of pressure field estimation from PIV data is explained. Since PIV has poor velocity resolution, use of differential equation encounters severe errors amplified. Several velocity-data filtering techniques are elaborated to overcome the error propagation in pressure field. As its applications, various type of pressure fields of a flow around a body are presented, including airfoil with surface jet, a Darrieus turbine blade, hydrofoil close to a free surface, and Savonius turbines.
This review paper provides particle measurements using holography as a guide for the beginner. Especially, phase retrieval holography with two high-speed cameras is explained by comparing with conventional Gabor holography. Additionally, we introduce a graphic processing unit (GPU) acceleration to reconstruct holograms. Conventional holography has two problems: the twin image problem and reconstructed particle elongation. The first problem causes blurred and low contrast particles due to the lack of phase information. Phase retrieval holography can resolve this problem with several holograms recorded at different positions. The particle elongation is that a spherical particle is elongated in the optical axis in the reconstructed process. The elongation is proportional to the relationship between particle diameter and the wavelength of recording hologram. This relationship can precisely measure the microparticle diameter more than the measured diameter in the recorded plane with low resolution. This review paper demonstrates the observation of the three-dimensional trajectory of microdroplet and measurement of droplet diameter with the elongation using phase retrieval holography.
Recently, various studies of Micro Air Vehicle (MAV) and Unmanned Air Vehicle (UAV) have been reported from wide range points of view. The aim of this study is to research the aerodynamic improvement of delta wing in low Reynolds number region to develop an applicative these air vehicles. As an attractive tool in delta wing, leading edge flap (LEF) is employed to directly modify the strength and structure of vortices originating from the separation point along the leading edge. Various configurations of LEF such as drooping apex flap and upward deflected flap are used in combination to enhance the aerodynamic characteristics in the delta wing. In this study, the numerical simulations are performed based on the model in which different shaped leading edge flaps are assembled in the delta wing at various mounting angle. Additionally, the fluid force measurement by six component load cell and PIV analysis are performed in the wind tunnel experiments. The relations between the aerodynamic superiority and the vortex behavior around the models are clarified.
Velocity measurement of electric field driven microbubbles is attempted by PTV. Cationic surfactant are dissolved to add positive electric charge to the microbubbles. These electrified microbubbles are placed in artificially applied electric field. Direction of the microbubble movement is limited only in horizontal direction to avoid influence of gravity. The microbubbles are moved toward the negative electrode by Coulomb force in the electric field. Diameter and velocity of each microbubble are measured by digital image processing. It is found that the velocity of microbubble is increased with increase of the electric field strength (voltage between positive and negative electrodes). It is also revealed that the velocity increases with increase of diameter of the microbubble. This trend is remarkably observed in large electric field strength condition. From the above, it is confirmed that the velocity of microbubble is able to be modified by electric field strength and diameter of the microbubble.
The surface polishing method is required for post processing of three-dimensional (3-D) shape mechanical parts with the progress of new fabrication process. Buffing and magnetic polishing are often performed, however, there are no reports for comparing these polishing characteristics under same conditions. With the above background, the purpose of this study is to investigate the relationship among pressure distribution, tool deformation behavior and tool followability on the polished surface. In this paper, the various observation tests between tool and workpiece were conducted by using buffing and magnetic polishing. As a result, it was revealed that the compression modulus of buffing tool is one of the main cause of tool followability. When polishing the grooved surface, comparison of buffing and magnetic polishing suggests that the magnetic clusters in magnetic polishing can reach the corner of groove.
In our previous study the method adding prestress before cyclic loading were suggested to improve the degradation in cyclic fatigue life-time of partially stabilized zirconia. The test results indicated that the method could make the lifetime appreciably increase in cycling fatigue with a low applied stress. In this study, in order to examine more effective pre-loading conditions for the fatigue life increase the cyclic fatigue tests changing prestresses by two types pre-loading methods were conducted. Furthermore, SEM observations, X-ray diffraction, and ultrasonic measurements were also used for the examination. As a result, it was found that adding the prestress close to transformation stress was more effective for fatigue life increase, because the prestress promoted the occurrences of microcracks in the neighborhood of main crack extended during cyclic loading.
Magnesium alloy generally has plastic anisotropy in mechanical properties due to hexagonal close-packed lattice structure and large differences among critical resolved shear stress of slip and twin systems. This study aimed to change the mechanical properties in a selected area of AZ31 Mg alloy thin-walled circular tube to meet the demands of products. First, the uniaxial tension-compression tests and compression-tension tests were conducted to investigate the influence of load reversal on the mechanical responses concerning the twin deformation. It was found that the strain hardening phenomenon in the deformation after the load reversal was strongly influenced by the pre-straining. Next, the localized bulging deformation was applied to the selected area to activate the extension twinning. The bulged area was then restored to its original profile by press forming in the radial direction of the circular tube. The activation of twinning in the bulged area was confirmed by the electron backscatter diffraction (EBSD) analysis. The change in the mechanical properties in the bulged area was investigated by the uniaxial tensile test and micro Vickers hardness test. The obtained results revealed that the bulged area exhibited better ductility as well as the higher flow stress than the initial state, with the aid of mechanical twinning.