Kazuyuki Toda

Development of Numerical Code to Predict Three-Dimensional Sand Erosion Phenomena

This paper presents a numerical procedure to predict a three-dimensional sand erosion phenomenon and the interaction between the flow field and the eroded surface. To simulate this phenomenon, the turbulent flow field, the particle trajectory and the amount of erosion on the eroded wall are calculated repeatedly. In computations of the flow field, compressible Navier-Stokes equations and low-Reynolds-number type k–e turbulence model are adopted. Assuming that the concentration of suspended particle is dilute, particle-particle collision and the influence of particle motions on the flow field are neglected. The Neilson-Gilchrist erosion model is used to estimate the weight loss due to erosion. To verify the developed code, two types of 90-degree bends are computed. The results show that the present procedure can reasonably reproduce the sand erosion process and the temporal change of both the flow field and the wall surface qualitatively.© 2003 ASME

Numerical Simulation of Sand Erosion Phenomena in a Particle Separator

Erosive actions of solid particles within a flow field are very important in a great number of engineering applications such as aircraft, ship, turbo-machinery and so on, which is referred to sand erosion. We have developed the numerical method to predict sand erosion phenomenon and the temporal change of the eroded surface. Performing iterative computations for the turbulent flow field, the particle trajectories, the mass removed from a wall, and the deformation of the wall, the behavior of sand erosion can be simulated numerically. In the present study, our numerical procedure is applied to the particle separator of a helicopter engine. Several kinds of particles with different diameter and combinations of wall and particle materials are selected to clear the sand erosion phenomena within the separator. Investigating the numerical results, the characteristics of particle motions, the temporal change of wall shape and the reason for the deterioration of separation efficiency are clarified.

Computation of Rotor/Stator Interaction With Hydrogen-Fuelled Combustion

For the next-generation aircraft, a new propulsion system using hydrogen fuel has been proposed. In the present system, hydrogen fuel injected from a stator surface combusts in the turbine passages, accordingly, the conventional combustor can be cut out. The advantage of this system is that we can design a lighter and smaller engine with low emission. We have demonstrated the realizability of this system by using the cycle analysis and the numerical simulations. Through the previous studies, it was confirmed that the rotor/stator interaction has to be investigated, because the hydrogen combustion phenomena within the stator passage is so complex, and thus it would highly affect the rotor performance. In this paper, we focus on the rotor/stator interaction for the detailed investigation of realizability of this system. The 2- and 3-dimensional numerical simulations are performed for a single stage turbine with hydrogen-fuelled combustion. In the 2-dimensional study, the effects of the injection position and injection rate on the flow structure, the static temperature over the blades, and the blade performance are investigated. Furthermore, 3-dimensional numerical simulation is performed. The general aspect of 3-dimensional flow field is demonstrated, and the effect of hydrogen combustion on the components of turbine, for example hub, tip and blade, are investigated.Copyright

Numerical Investigation on Wavy Streak Formation Due to Sand Erosion

It is well known that sand erosion is a typical multi-physic problem, that is, the interactions among flow field, particle motions and wall deformation are important. To simulate this phenomenon, turbulent flow field, particle trajectories and amount of erosion on an eroded wall are calculated repeatedly. In the computations of the flow field, compressible Navier-Stokes equations and low-Reynolds-number type k-e turbulence model are adopted. Assuming that the concentration of suspended particles is dilute, particle-particle collision and the influence of particle motions on the flow field are neglected. The Neilson-Gilchrist erosion model is used to estimate the weight loss due to erosion. Based on this numerical procedure, the gas-particle two-phase turbulent flow field in 90-degree bend with a square cross-section is simulated, in order to clarify erosion pattern formation by fluid/particle/wall interaction.Copyright

Numerical Investigation on Small-Scale Cyclone for SPM Removal

Recently, the fine particles have been of major interest, since they suspend in the ambient air for a long time and cause to a respiratory disease. This kind of fine particles is referred to Suspended Particulate Matter (SPM). The diameter is less than 10.0 μm, and the typical generation source is the exhausted gas from diesel engines. On the other hand, a cyclone separator is expected to be the promising equipment to remove the fine particles. It is one of the most widely used devices to remove the dust from gas. However, an existing cyclone is generally large in scale, and thus its scale-down is needed to mount on a diesel vehicle. Thus, the performance of such a small-scale cyclone has to be clarified. The purpose of this study is to numerically evaluate the collection efficiency of a small-scale cyclone for particles less than 5.0 μm, and provide the suggestions for the preferable design. Performing the computations under three different conditions of a diesel engine operation, with using the Eulerian-Lagrangian method, the particle trajectories and the collection efficiency are investigated.Copyright

Numerical Simulation of Sand Erosion in Steam/Water Separator

ABSTRACT This paper presents an investigation into a phenomenon Several wall and particle materials and also the combinthat happened on the wall surface of a Steam / Water Separator (SWS). It was reported that erosion caused from unknown solid particle took place on the SWS wall. In order to capture this sand erosion phenomenon numerically, the SWS flow field was solved, and then particle trajectory and wear quantity were calculated, based on the CFD results. Several wall and particle materials and also the combinations of them are assumed. Furthermore, the particle diameter was varied from 10 -6 to 10 -2 m. The numerical results insist that the particle, which could be the factor of the phenomenon, is limited in its diameter range and its material. The present study will be an aid to clarify the cause of sand erosion in a SWS. INTRODUCTION A Steam / Water Separator (below SWS) is today widely used in a power plant, for the purpose of separating steam and water of the two phase flow. In a SWS, the liquidized and gaseous components in the steam are separated, flow field can be reproducedmaking use of the difference of centrifugal force caused by the swirling motion, and finally the liquidized component is collected and removed. It was reported that a solid particle incidentally mixed into the steam caused the sand erosion to a dSWS. In the present study, sand erosion phenomenon in a SWS is investigated by simulating the turbulent flow field and the trajectory of a solid particle. To reproduce the strongly swirling turbulent flow in the SWS, Reynolds stress turbulence model (RSM) is employed. Using the Neilson-Gilchrist model, the wear quantity on the inner surface of the SWS is estimated.ations of them are assumed. Furthermore, the particle diameter was varied from 10

Modelling of Three-Phase Flow in Electro-Chemical Machining

Electro-Chemical Machining (ECM) is an advanced machining technology. It has been applied to highly specialized fields such as aerospace, aeronautics and medical industries. However, it still has some problems to be overcome. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are the typical issues. To solve such problems, CFD is considered to be a powerful tool in the near future. However, the numerical method that can satisfactorily predict the flow has not been established because of the complex flow natures. In the present study, we investigate the modelling of the three-phase flow (i.e. fluid, hydrogen bubble and metal sludge) in ECM process. First, the developed code is applied to the two-dimensional channel configuration. The interactions among three-phases and the dissolved wall are simulated, to verify the modelling and to determine the model parameters, Next, the sinusoidal channel is machined by our code. It is confirmed that hydrogen bubbles in the separation region suppress the dissolution of the wall, and make the final wall shape be wavy. Through this study, it is exhibited that our developed model and code are sound and useful for simulating ECM process.Copyright

Numerical Study on Thermal and Fluid Flow Around the New Type of Micro Flow Sensor

We design a new type of the micro flow sensor which can detect the wall shear stress and the flow direction. In the new type of the micro flow sensor configuration, the two sensing elements are arrayed on the silicon chip and also used as heater due to a self-heating of the elements for higher frequency response and miniaturization. The flow sensing elements are thermal sensitive thin film resistors fabricated on the silicon chip. The principle of the micro flow sensor is based on the convective heat transfer from the heated resistance to the surrounding fluid. The optimum spacing of the heaters is discussed by the numerical simulation of a two-dimensional low Reynolds number flow including the heat conduction within the chip. In the feasibility study the proposed micro flow sensor with 30% reduction in size is found to have higher sensitivity.Copyright

Computation of Turbulent Flow Around Blade With Local Surface Roughness

To improve aerodynamic performance of a blade and to maintain its designed performance, many study have been focused on this point. The factors for aerodynamic performances of a blade are its geometry and operating conditions, which are almost fixed during its lifetime. On the other hand, the factor such as surface roughness generated by impure sand grain or oil droplet is variable one. The surface roughness on the blade affects the flow past it by its aerodynamic nature. The blade design can be improved by revealing this change in aerodynamic performance due to surface roughness. In this study, three-dimensional computations are carried out on the blade root with local surface roughness to investigate how the roughness will change the aerodynamic performance. The locality of the surface roughness distribution is simulated with particle tracks in three-dimensional flow. The model replacing the effect of roughness elements with virtual force is used to simulate turbulent flow around blade with local surface roughness.Copyright

Numerical and Experimental Evaluation of Turbulent Flow in Volute

The performance of centrifugal fans is considerably influenced by the design of tongue at the re-circulation port. The flow in the volute of a centrifugal fan was studied both experimentally and numerically. In this experiment, flow angle, pressure and velocity profiles were measured at a large number of locations in the volute. The flow field in the volute passage was analyzed using Computational Fluid Dynamics. The flow was assumed to be three dimensional, turbulent and steady. The numerical simulation produced qualitatively good agreement with the experimental result. The results from experiment and numerical simulation indicated that the adoption of a re-circulating flow port improved fan performance for all flow conditions. In addition, the existence of strong secondary flow was apparent at the cross-section of the volute passage.Copyright