Kiyoshi Bando

Generation of impulsive pressure wave by spark discharge in water and its propagation

Abstract An experimental investigation was performed to find a new method for diagnosing three-dimensional flows in which obstacle bodies or cavities are included by means of a pressure wave. In rectangular closed tanks 200 × 337 × 250 mm (acrylic resin) and 300 × 450 × 400 mm (brass) filled with water, an impulsive pressure wave was generated by an instantaneous small spark discharge. The pressure waveforms were measured at a point on the wall with a high-frequency pressure transducer, and the data were recorded with an A/D converter. The measured wave fluctuations differed depending on wall conditions of the tank and on whether there was a submerged body in the water. The size of the submerged body also affected the pressure fluctuation. When acrylic resin and brass were used as wall materials, both the phase and amplitude of the reflecting wave differed. When a stainless steel sphere of diameters of 50.8, 30.2, or 19.1 mm was submerged in the tank, two kinds of pressure waves were observed, one passing through the sphere and the other diffracted around it. These results suggest the possibility of identifying bodies of simple shape by interpreting the precisely measured output pressure wave signals.

A Panel Method for Design of Airfoils in Cascades

A design method for two-dimensional airfoils in cascades is presented. This is based on the panel method using piecewise constant vortices. Incompressible potential flow is assumed. Pressure distributions on the upper and lower surfaces are prescribed. The changes of the intensity of vorticity are calculated so as to make the difference of the pressure distributions detween prescribed and calculated equal zero, and the profile is modified in order that he changes of surface velocity induced by these vorticity variations satisfy the boundary condition. The design code gives satisfactory solution after several iterations. Three numerical results are shown. In each case the pressure distribution of Gostelows cascade is given as specified. Initial guess profiles are (1) Gostelows airfoil but partly flattened upper surface, (2) Gostelows airfoil but flat lower surface, and (3) NACA 0012 airfoil. The obtained profiles agree well with Gostelows airfoil.

Mechanical Characterization of APA Microcapsules by Parallel-Plate Compression

We produced microcapsules of alginate-poly(L)lysine-alginate (APA)with diameters on the order of 10 µm. To characterize their mechanical properties, we conducted an experiment on the parallel-plate compression of a microcapsule and modeled its deformation. In the modeling task, the microcapsule was assumed to be a spherical liquid-filled elastic membrane with negligible bending stiffness and permeability. The membrane thickness was estimated by applying Reissner’s linear elastic theory to the experimental force-displacement relationship during loading in the small displacement region. The initial stretch of the membrane was taken into account; it was mainly caused by the osmotic pressure difference across the membrane. The initial stretch of the microcapsule was determined by fitting the calculated and experimental force-displacement relationships during loading at small to medium displacements. At large displacements, the calculated force was smaller than the experimentally measured force because of fluid permeation across the APA membrane. The calculated and experimentally imaged shapes of the deformed microcapsule were compared. The effects of varying the membrane thickness on the force-displacement and transmural pressure-displacement curves were shown, and the limitations of applying the present deformation model were examined.

Mechanical Characterization of Microcapsules With Membrane Permeability by Using Indentation Analysis

Mechanical modeling of the deformation of a liquid-filled spherical microcapsule indented by a sharp truncated-cone indenter was proposed, in which membrane permeability was taken into account. The change in the internal volume of the microcapsule due to fluid permeation was calculated on the basis of Kedem and Katchalsky equations (1958, Thermodynamic Analysis of the Permeability of Biological Membranes to Non-electrolytes, Biochim. Biophys. Acta, 27, pp. 229-246). The membrane hydraulic permeability, membrane initial stretch, and effective osmotic pressure difference across the membrane of an alginate-poly(l)lysine-alginate (APA) microcapsule were identified by fitting calculated and measured force-displacement curves. The difference between deformed shapes with and without membrane permeability was shown, suggesting the spatial resolution of image analysis performed to measure the membrane permeability from the volume loss. The influences of changes in permeability, initial stretch, and a parameter β, used for determining the effective osmotic pressure difference, on the force-displacement relationship were examined, and mechanisms causing changes in the force-displacement relationship were discussed.

Analysis of Airway Narrowing Based on Dynamic Buckling Model

In order to elucidate the mechanism of airway narrowing in asthma, dynamic buckling analysis was performed for basement membrane. The basement membrane was treated as two-dimensional circular thin-walled viscoelastic shell of Voigt model and contraction of smooth muscle was replaced by inward transmural pressure applied to the basement membrane. Governing equations for the dynamic buckling was derived and wave number of buckling mode obtained were compared with numerical simulation results by non-linear FEM and with experimental results. The non-dimensional parameters are thickness radius ratio, non-dimensional increasing speed of inward transmural pressure, non-dimensional retardation time and Poisson ratio. Wave number of buckling mode is determined as the number having maximum amplification from initial imperfection mode. The wave number of buckling mode increases with increase in non-dimensional increasing speed of inward transmural pressure and it decreases with increase in non-dimensional retardation time. It has been known that wave number of buckling mode decreases due to thickening and hardening of basement membrane caused by the remodeling in asthma. This fact is originated from decrease in non-dimensional increasing speed of inward transmural pressure due to the remodeling. In the dynamic buckling analysis the damping effect of the basement membrane is necessary to take into consideration, because the primary component of the basement membrane is collagen having damping characteristics.

Numerical Simulation and Experiment of Pulsatile Flow in Modeled Aortic Arch

Velocity profiles of pulsatile flow in a tapered U-bend which is a model of aortic arch are visualized and measured by using a laser-induced fluorescence (LIF) method. Three-dimensional numerical simulation based on Navier-Stokes equation is carried out for the same boundary geometry and flow condition as those used in the experiment of LIF. Velocity profiles of the main flow between experimental data and calculation results are compared and cause of difference in velocity profile between them is discussed. In the numerical calculation for the tapered U-bend, change in secondary flow in the cross-section from inlet to outlet of the bend is shown and behavior of vortex pair is considered.

Numerical Simulation and Experimental Verification of Wave Propagation in a Collapsible Tube.

Propagation of solitary pressure wave through a thin-walled collapsible tube filled with a viscous incompressible fluid is calculated numerically. One-dimensional continuity equation, equation of motion including a wall friction term, and the tube law obtained experimentally are used as the basic equations. The pressure wave-forms at three locations along the collapsible tube calculated by the present method are compared with those obtained by the experiment. It is shown that the tube law obtained experimentally needs to be modified to make the slope discontinuous at an onset point of the locally two-dimensional buckling of the collapsible tube. The viscous effect is evaluated using an equivalent Womersley number a for the solitary wave. Incorporation of the wall friction term with high accuracy is necessary in the case of small a in one-dimensional flow calculation. The propagation velocity can be approximately calculated using the Moens-Korteweg velocity corresponding to a tube having circular cross-section when the disturbance velocity is small.

On the Structure of Near-Wall Turbulence.

It is intended in this report to discuss the structure of near-wall turbulence by drawing pictures of flow fields of specified concerns using three-dimensional computer graphics. The flow taken here as the material is a two-dimensional channel flow obtained by a large-scale computer simulation. The discussion is focused on the streaks which are observed in all kinds of near-wall turbulence as a marked feature. It turned out that impinging, which is the key phenomenon in high-speed streaks, plays a key role in the near-wall turbulence as well as the lift-up and break-up of low-speed streaks. Most of the important events take place in these sparsely distributed spots. Turbulent shear stress is found only sparsely where it is produced, and the whole process of shear stress mostly restricts itself to within a small confined area. It was confirmed that although the pressure diffusion and the redistribution of shear stress are important when considered separately, they almost cancel one another and as a result the splitting of the velocity-pressure gradient term into these two terms is not beneficial in turbulence modelling.

Generation and Propagation of Pressure Wave by Spark Discharge in Water.

Experimental basic research is performed for the indentification of cavitation bubbles or other bodies in liquid flow through ducts, valves, or impellers by using a pressure wave as a detector. In rectangular closed tanks of 200×337×250mm (made of acrylic resin) and 300×450×400mm (made of brass) filled with water, a pulse-shaped pressure wave is generated by an instantaneous small spark discharge. The pressure fluctuation due to the pressure wave is measured at a point on the wall by a high-frequency pressure transducer, and the data are recorded by A/D converter. The measured wave fluctuations differ from one another, depending on wall condition and the existence of and size of bodies in water. When we use acrylic resin and brass as wall material, both the phase and amplitude of the reflecting wave are changed due to the wall condition. When stainless steel spheres with diameters of 50.8, 30.2, and 19.1mm are set within the tank, the pressure wave passes through the sphere and diffracts around it. By interpreting the precisely measured output pressure wave signals, we can identify bodies of simple shape.

A three-dimensional inverse calculation of an axial-flow rotor by the finite-pitch actuator duct method.

A fully three-dimensional inverse solution to the axial-flow rotor of a constant hub to tip ratio by means of the finite-pitch actuator duct method for inviscid and incompressible flow is presented. The blade is expressed by a vortex sheet and a source sheet superposed on the mean surface, and the blade shape is determined to satisfy the specified thickness and loading distributions for free-vortex type flow. Two-dimensional numerical calculations are performed by modifying the present method in order to show the difference between the blade shape obtained by the two-dimensional inverse method and that obtained by the three-dimensional inverse method. Three-dimensional numerical calculations show the influences of the stacking position and the blade spanwise pressure distributions. The direct solutions for the designed two-dimensional and three-dimensional rotors are calculated in order to examine the numerical accuracy of the present inverse calculation.