Observation and Scaling of Tip Vortex Cavitation on Elliptical Hydrofoils

Experimental study on tip vortex cavitation (TVC) was carried out for elliptical hydrofoils with various chord lengths. The purpose of the experiment was to clarify the influences of Reynolds number and water quality on tip vortex cavitation. Experiments were made in a large cavitation tunnel of the Naval Systems Research Center, TRDI/Ministry of Defense Japan. The elliptical hydrofoils tested were NACA 0012 cross section with chord lengths of 500mm, 250mm and 50mm. Reynolds number based on hydrofoil chord length was 2×105 < ReC < 7.4×106. Water quality of the tunnel was characterized by air content and nuclei distribution. Air content of the tunnel was varied between 30% and 80%. Nuclei distribution was measured by a cavitation susceptibility meter (CSM) with center-body venturi. Cavitation inception was determined from high speed video observation. A standard formula, (σL/σS) = (ReL/ReS)n, was applied for the scaling. In the present study, exponent of the scaling law n was found to be 0.2 < n < 0.4. High speed video observation showed that the process of the TVC inception strongly depends on water quality. In the experiments, unsteady behaviors of TVC were also investigated. Strong interactions between sheet cavitation and TVC were observed.

PIV Measurements of Propeller Flow Field in a Large Cavitation Tunnel

Flow field around a marine propeller was measured by means of PIV technique in a large cavitation tunnel of the Naval Systems Research Center, TRDI/Ministry of Defense, Japan. Test section of the tunnel is 2m(W) × 2m(H) × 10m(L) and it contains 2000m3 of water. 2-dimensional PIV (2-D PIV) and stereo PIV (SPIV) measurements were made for a five-bladed highly skewed marine propeller. In the case of 2-D PIV measurements, high spatial resolution measurements were possible by seeding relatively small amount of tracer particles. Phase-averaged flow fields showed details on evolution of tip vortices. In the case of SPIV measurements, much larger amounts of tracer particles were required, and it was difficult to perform high resolution measurements. Phase averaged velocity profiles from SPIV measurements showed good agreement with 2-D PIV-measured results. PIV-measured results were compared with results of LDV measurements. Although PIV-measured velocity profiles showed fairly good agreements with LDV-measured results, some discrepancies were found at the blade tip region.

The Development of Extremely-Compact Static Pressure Probe for the Simultaneous Measurement of Pressure and Velocity in the Turbulent Flows

A new static pressure probe was developed to improve the space resolution and the measurement accuracy of the combined probe for the simultaneous measurement of the static pressure and the velocity in turbulent flows. The external diameter of the static pressure tube is 0.3 mm and its internal diameter is 0.2 mm. There are 8 static pressure holes on the wall of the static pressure tube and their diameters are 0.1 mm. The MEMS microphone is used as the pressure sensor and embedded inside the flare of the static pressure tube. The diameter of the MEMS microphone is 2.54 mm and has the wide range flat frequency response. The measurement results by the new static pressure probe in the two-dimensional turbulent jet show that the measurement accuracy of the static pressure probe is sufficient and the seven-thirds power law is clearly observed in the power spectra of the fluctuating pressure measured at the position of a half width of the mean velocity distribution in the cross-streamwise direction apart from the jet center line. In addition, the yaw angle characteristics of this new pressure probe shows that the measurement accuracy of the static pressure has less dependency on the yaw angle of the probe to the flow direction than the one of the previous static pressure tube (its external diameter is 0.5 mm). From these results, it is found that the new static pressure probe is effective for the measurement of static pressure in turbulent flows and useful to improve the space resolution and the measurement accuracy of the combined probe for the simultaneous measurement of the velocity and the static pressure. By using this static pressure tube, the space resolution of the combined probe is reduced approximately 40%. Further, by combing two X-type hot-wire probes with the new pressure probe, the simultaneous measurement of three velocity components and static pressure is realized.

An Investigation of Cavitation and Suction Vortices Behavior in Pump Sump

A numerical and an experimental investigation on a suction vortices including cavitation, free vortices and subsurface vortices behavior in the model sump system with multi-intakes is performed at several flow rates and water levels. A test model sump and piping system were designed based on Froude similitude for the prototype of the recommended structure layout by HI-9.8 American National Standard for Pump Intake Design of the Hydraulic Institute. An experiment is performed according to the sump model test procedure of Hyosung Goodsprings, Inc. A numerical analysis of three dimensional multiphase flows through the model sump is performed by using the finite volume method of the CFX code with multi-block structured grid systems. A k-ω Shear Stress Transport turbulence model and the Rayleigh-Plesset cavitation model are used for solving turbulence cavitating flow. Several types of free surface and submerged vortex which occurs with each different water level are identified through the experimental investigation. From the numerical analysis, the vortices are reproduced and their formation, growing, shedding and detailed vortex structures are investigated. To reduce abnormal vortices, an anti-vortex device is considered and its effect is investigated and discussed.

Flow Characteristics of Fluid Droplet Obtained From Air Assisted Atomizer

Air assisted atomizer system was designed and developed for fuel injection. The present purpose is to utilize a low pressure in supplying of atomized fuel. Distilled water was used as test liquid on the experiments for the system of atomization. The results revealed air assisted atomizer had a capability to inject the test liquid in the range of the rates of 0.0019–0.00426 kg/s, with the use of air pressure supplied from 68.9 to 689 kPa. In this research, the test liquid supply pressure was kept constant and the air flow rate through the atomizer was varied over a range of air supply pressure to obtain the variation in air liquid mass flow ratio (ALR). The spray solidity was studied by taking pictures of the spray at different liquid air supply pressures. The experimental investigations suggest that spray cone angle tends to increase with increasing in air liquid mass flow ratio because the kinetic energy of the flow keeps on increasing. The solid cone spray has a pattern of penetration depth between 408–446 mm. and cone angle between 14.5–23.6°. It was observed that spray formed the solid cone at all the operating conditions.

Micro-PIV Measurement on Transient Flows in Pneumatic MEMS Device for Cell Trapping

This paper presents a micro-PIV measurement for investigation of flow characteristics in a micro chamber for trapping of a live cell. The micro cell chip consisting of pneumatic vibrator arrays and a trap chamber was fabricated through a replica molding technology with a SU-8 mold and Polydimethylsiloxane (PDMS) polymer. The single cell in the trap chamber was manipulated and trapped in the equilibrium region by exploiting the geometrical symmetry of the vibrators. The x-axial velocity of the viscous fluid induced by the deformation of the flexible diaphragms was eliminated or minimized at the center of vibrators. From the measurement results, the proper operational conditions of the vibrators were determined and it is also verified that the particle can be actively manipulated and trapped as desired.

Size-Exclusion Surface Plasmon Resonance Sensing With a Microslit Array Chip

In this study, we propose a novel surface plasmon resonance (SPR) chip on which the microslit array was fabricated. The microslit excludes micrometer-size objects that are larger than its slit size from sensing field, so that it acts as a filter. In order to confirm the filtereffect, we demonstrated the sensing of microparticles of different diameters using the SPR chip. As the demonstration of the biotechnology application, we performed the discrimination of aggregation of bio-molecules using SGNP (Sugar chain imobilized Gold Nano Particle) as a model sample.

Development of Polydiacetylene-Embedded Microfibers Using 3-D Hydrodynamic Focusing Technique

Polydiacetylene (PDA), conjugated polymer, is an attractive sensor material that has a unique optical property to transform its color from visible blue to fluorescent red upon environmental perturbations like heat, pH, specific metal ions, and etc. In this study, we propose a novel method to detect metal ions by using polydiacetylene (PDA)-embedded sensor microfibers fabricated with a 3-D hydrodynamic focusing technique using alginate and calcium solutions. Moreover, by changing the head groups of PDA, we successfully detected Al3+ and Zn2+ ions up to 1mM using PDA micro fibers.

An Estimation of Thermodynamic and Transport Properties of Cryogenic Hydrogen Using Classical Molecular Simulation

In this paper, we estimated the thermodynamic and transport properties of cryogenic hydrogen using classical molecular simulation to clarify the limit of classical method on the estimation of those properties of cryogenic hydrogen. Three empirical potentials, the Lennard-Jones (LJ) potential, two-center Lennard-Jones (2CLJ) potential, and modified Buckingham (exp-6) potential, and an ab initio potential model derived by the molecular orbital (MO) calculation were applied. Molecular dynamics (MD) simulations were performed across a wide density-temperature range. Using these data, the equation of state (EOS) was obtained by Kataoka’s method, and these were compared with NIST (National Institute of Standards and Technology) data according to the principle of corresponding states. Moreover, we investigated transport coefficients (viscosity coefficient, diffusion coefficient and thermal conductivity) using time correlation function. As a result, it was confirmed that the potential model has a large effect on the estimated thermodynamic and transport properties of cryogenic hydrogen. On the other hand, from the viewpoint of the principle of corresponding states, we obtained the same results from the empirical potential models as from the ab initio potential, showing that the potential model has only a small effect on the reduced EOS: the classical MD results could not reproduce the NIST data in the high-density region. This difference is thought to arise from the quantum effect in actual liquid hydrogen.

Digitalization of High Accuracy Thermo-Anemometer for Heat Flux Measurement in Stratified Flow

In this study, the high-accuracy thermo-anemometer was developed to execute simultaneous measurement of temperature and velocity by employing Field Programmable Gate Array (FPGA) devices. A cold-wire temperature sensor has first-order lags due to thermal time constants, that means that a phase compensation is essential to measure temperature fluctuations with high frequency. The digital filter comprised the exact first-order lead characteristics was realized by the bilinear s-z transformation. It was verified that the temperature signals were appropriately compensated with an uncertainty of less than ±3.9% in frequency up to 10 kHz. For velocity measurements, a temperature compensation is indispensable owing to velocity and temperature dependence of response of a hot-wire anemometer in thermally stratified flow fields. The accuracy of the velocity measurements at high temperature was improved with the strict algorithm of the temperature compensation calculation incorporating the temperature dependence of the thermal properties of the air. The high-accuracy velocity measurement was realized within the accuracy of ±1.6% in the temperature range of 1.5 times as wide as that of the previous analog based system. The simultaneous measurement system for temperature and velocity was applicable to measure heat flux in thermally stratified flows.