Shouichiro Iio

Computational Fluid Dynamics Study of a Noncontact Handling Device Using Air-Swirling Flow

The vortex gripper is a recently developed pneumatic noncontact handling device that takes advantage of air-swirling flow to cause upward lifting force and that thereby can pick up and hold a work piece placed underneath without any contact. It is applicable where, e.g., in the semiconductor wafer manufacturing process, contact should be avoided during handling and moving in order to minimize damage to a work piece. For the purpose of a full understanding of the mechanism of the vortex gripper, a computational fluid dynamics (CFD) study was conducted in this paper, and at the same time, experimental work was carried out to measure the pressure distribution on the upper surface of the work piece. First, three turbulence models were used for simulation and verified by comparison with the experimental pressure distribution. It is known that the Reynolds stress transport model (RSTM) can reproduce the real distribution better. Then, on the basis of the experimental and numerical result of RSTM, an insight into the vortex gripper and its flow phenomena, including flow structure, spatial velocity, and pressure distributions, and an investigation into the influence of clearance variation was given.

Performance of a non-contact handling device using swirling flow with various gap height

Vortex levitation can achieve non-contact handling by blowing air into a vortex cup through a tangential nozzle to generate a swirling flow. In this paper, we focused on the relationship between the sucking pressure and the flow dynamics when gap distance from the cup to a work piece changes. Then simultaneous measurement of a pressure and a flow field in the cup was performed. As a result, the mean pressure changes and the pressure fluctuation inside the cup enhances with increasing gap height. Especially, periodic pressure perturbation is observed with wide gap height and it synchronizes with an eccentric rotation of the swirling flow. It is also found that the rotation axis of swirling flow steadily inclines against the central axis of the cup for appropriate gap height.Graphical Abstract

Enhancement of Impinging Jet Heat Transfer Using Two Parallel Confining Plates Mounted near Rectangular Nozzle Exit

Impinging jet heat transfer on a target plate was enhanced by using two parallel confining plates mounted between a rectangular nozzle end plate and a jet target plate. The target plate was set equal to 2, 3, 4, and 5 times the jet exit width, , and the gap ratio of two parallel confining plates, , were changed from 2.7 to 8.0 only by impinging length and from 2.7 to 6.7 by . Two confining parallel plates mounted near the jet exit produced swing-type flow under some conditions. As a result, the maximum Nusselt number attained around the stagnation point was augmented by about 50% compared to the one for normal impinging jet without the two parallel plates and then spatial mean Nusselt number was increased by about 40%.

Flow Visualization of Vortex Structure in a Pulsed Rectangular Jet

Pulsating jet is visualized using hydrogen bubble method to clarify the vortex nature in the near field of the jet. This study focused on the development in space and time of vortex structures evolution in low aspect-ratio rectangular jet with pulsation. Pulsation means large-amplitude, low-frequency excitation which is expected to increase the mixing and spreading of the jet and to accelerate its transition from a rectangular form to an axisymmetric form. It was deemed appropriate to investigate whether jet characteristics of a pulsating, submerged jet flow can be altered by including pulsations. The difference of the vortex deformation process is discussed in relation to pulsating conditions. Consequently, the pulsation leads to the formation of vortices at regular intervals, which are larger than those occurring in a steady jet. The results show that the streamwise interaction, between leading vortex and trailing vortex rolled up at nozzle lips, strengthens with increasing pulsating frequency. The spanwise drift of the vortex becomes strongly apparent at large amplitude and high frequency conditions. The drifting start position does not change regardless of pulsating condition. The convection velocity of vortex increases at lower frequency and larger amplitude.

Numerical Simulation of Water Flow through a Nano-Hydraulic Turbine of Waterfall-Type by Particle Method

This study simulates the flow through an impulse-type small-scale hydraulic turbine utilizing a waterfall of extra-low head. The two-dimensional Moving Particle Semi-implicit (MPS) method is employed for the simulation. The fluid is discretized by particles, and the flow is computed by the Lagrangian calculation for the particle motion. When the distance between the particles discretizing the waterfall of a width , , is set at , the flow can be simulated with the sufficiently high spatial resolution, and the rotor performance can also be favorably predicted. The present simulation also successfully analyzes the effect of the rotational speed of rotor on the flow and the turbine performance.

Study on Open Cross-Flow Runner for Environmentally Friendly Nano-Hydraulic Turbine Utilizing Waterfall (Influence of Waterfall Thickness on the Runner Performance)

The aim of this investigation is to develop an open type cross-flow runner for environmentally friendly nano-hydraulic turbine utilizing extremely low head waterfalls. The waterfall condition is strongly affected by weather, so flow rate changes frequently. It causes a decrease in runner performance because it does not have any flow adjusting mechanisms. It is, therefore, important to evaluate the runner performance against the change of flow condition for stable power generation. This study focused on the influence of waterfall flowing position and its thickness on the runner performance. An open type cross-flow runner was applied for waterfall generation. As a result, we found that the runner characteristic varied with the waterfall condition. In particular, the waterfall thickness has great influence on the runner performance. The value of CPmax reaches the highest value of 0.61 at Q = 3.0×10−3 m3 /s.Copyright

Numerical study on the flow and performance of an open cross-flow mini-hydraulic turbine

This study simulates the flow through a small-scale open cross-flow hydraulic turbine and analyzes the turbine’s performance. The simulation employs a two-dimensional particle method that was used for the simulation of a small-scale impulse-type hydraulic turbine in a prior study. Flow in the turbine is successfully simulated, with the simulated turbine performance showing good agreement with experimental measurements. The simulations also clarify that the deterioration in performance with increasing water flow rate is caused by the degeneration of the radially outward flow between the rotor blades.

Investigation of Blade Angle of an Open Cross-Flow Runner

Abstract The aim of this study was to develop a nano-hydraulic turbine utilizing drop structure in irrigation channels or industrial waterways. This study was focused on an open-type cross-flow turbine without any attached equipment for cost reduction and easy maintenance. In this study, the authors used an artificial indoor waterfall as lab model. Test runner which is a simple structure of 20 circular arc-shaped blades sandwiched by two circular plates was used The optimum inlet blade angle and the relationship between the power performance and the flow rate approaching theoretically and experimentally were investigated. As a result, the optimum inlet blade angle due to the flow rate was changed. Additionally, allocation rate of power output in 1st stage and 2nd stage is changed by the blade inlet angle.

Experimental and Theoretical Analysis of Active Charge Accumulator for Water Hydraulics System

The active charge accumulator (ACA) is a pressure converter device in a water-hydraulic system that is able to increase and decrease pressure without using a pressure-regulating valve. The basic characteristics of ACAs, however, have not yet been sufficiently revealed. In this paper, we experimentally examined the basic characteristics of ACAs with focus placed on how ACAs reduce pressure. This examination has revealed that the piston stroke of ACAs depends on the load flow rate as well as the valve switching timing. We theoretically analyzed these phenomena using a mathematical model. With an analytic model built taking into consideration the compressibility of the working fluid, valve performance level, and other elements, we made a comparison between the analytic and experimental results to verify the validity of our analysis. This comparison revealed that the pressure waveforms in the low-pressure and pressure-conversion sections obtained through the analysis agreed with those obtained through the experiments, indicating that the analytic model was valid.