Numerical Experiments for Flow Around a Ducted Tip Hydrofoil

The performance and cavitation characteristics of marine propellers and hydrofoils are strongly affected by tip vortex behavior. A number of previous computational studies have been done on tip vortices, both in aerodynamic and marine applications. The focus, however, has primarily been on validating methods for prediction and advancing the understanding of tip-vortex formation in general, rather than showing effects of tip modifications on tip vortices. Studies of the most relevance to the current work include computational studies by Dacles-Mariani et al. (1995) and Hsiao and Pauley (1998, 1999). Daeles-Mariani et al. carried out interactively a computational and experimental study of the wingtip vortex in the near field using a full Navier-Stokes simulation, accompanied with the Baldwin-Barth turbulence model. Although they showed improvement over numerical results obtained by previous researchers, the tip vortex strength was underpredicted. Hsiao and Pauley (1998) studied the steady-state tip vortex flow over a finite-span hydrofoil, also using the Baldwin-Barth turbulence model. They were able to achieve good agreement in pressure distribution and oil flow pattern with experimental data and accurately predict vertical and axial velocities of the tip vortex core within the near-field region. Far downstream, however, the computed flow field was overly diffused within the tip vortex core. Hsiao and Pauley (1999) also carried out a computational study of the tip vortex flow generated by a marine propeller. The general characteristics of the flow were well predicted but the vortex core was again overly diffused.

Numerical Analysis of Air Convection in a Vertical Cylindrical Container With and Without a Gravitational Field Under a Gradient of a Magnetic Field

Two-dimensional numerical computations were carried out for natural convection of air in a vertical cylindrical container with and without a gravitational field under a gradient of a magnetic field. The magnetic field and the magnetizing force were induced in the cylinder area and the strength and the vectors of the magnetizing force were dependent on the axial location of the electric coil. Sample computations were carried out by changing the relative orientation of an electric coil and container. In a gravitational field, air in a cylindrical container was driven by both gravitational and magnetizing forces. On the other hand, the air flow was induced by the magnetizing force even in a non-gravitational field. Flow pattern and the heat transfer rate greatly depended on the axial position of the electric coil under both gravitational and non-gravitational fields.

Simulation of the Laminar Flow in a PRIMIX Static Mixer

The PRIMIX helical static mixer has been investigated using numerical simulations. The flow is in the laminar regime (Re = 1 to 1000). The simulations concentrate on the pressure drop and on the use of particle tracking for mixing studies. For the pressure drop, experimental validation is provided. It is found that the pressure drop can be simulated with high accuracy for Re < 350. For higher Re-values no grid independent solution could be obtained and the experimental results no longer agree with those of the simulations. The simulated pressure drop results scaled to the empty pipe pressure drop, can be well summarized as K = 4.99 + Re/31.4. Using Particle Tracking it has been possible to reproduce literature data. However, it has been shown that the obtained results are rather sensitive to the choice of the time step. This limits the direct use of particle tracking techniques for studying the mixing of static mixers in the laminar regime.

Numerical Study of the Two-Phase Air/Oil Flow Within an Aero-Engine Bearing Chamber Model Using a Coupled Lagrangian Droplet Tracking Method

Bearing chambers in an aero-engine are designed to provide specialised compartments where bearings may be supported to locate the shaft systems. The design of the bearing chambers, including sealing and oil system integration, is vital to the performance and reliability of aero-engines and hence it is of great significance to gain better understanding on the two-phase air/oil flow behaviour within the chambers. The physical phenomena occurring within the bearing chambers involve the interaction of turbulent airflow and oil in the form of jets, droplets and films. This paper reports two-way coupling CFD calculations for turbulent airflow and oil droplet motion in an aero-engine bearing chamber geometry in order to assess the influence of the interaction between airflow and oil droplets on the air flow and droplet impingement locations. In the CFD calculation the airflow is assumed to be incompressible and isothermal and the airflow motion is driven by rotating shafts and described by a standard k-ε turbulence model as implemented in the commercial CFD package CFX 4.2. The oil injected to the chamber is assumed to be in the form of discrete droplets and subsequent droplet motions are modelled using a Lagrangian tracking method. Turbulent dispersion and interaction between droplets are not included. The calculations are carried out at shaft speeds corresponding to a representative flight state with droplet diameters in the range of 1–500 microns. The CFD model of the bearing chamber used has a total cell number of 405,500 and the grid is constructed to ensure that the wall function formulation used at the boundaries for the turbulence model is valid. The boundary conditions within the chamber are specified by prescribing velocity conditions on chamber surfaces corresponding to the rotating components. The calculations are iterative; for the airflow, an additional source term, due to the drag forces from droplets, is added to the governing equations. The droplet trajectories are then simulated based on the updated airflow field. It is found that many major features of the airflow field obtained using the two-way coupling method are similar to those obtained using the simpler one-way coupling method. However, significant localised differences exist between the airflow fields obtained using the one-way and two-way coupling methods where the interaction of oil droplets with the airflow is more intense. There are localised regions in the vicinity of the oil injection where the oil droplet motion leads to an increased airflow speed. The motion of small droplets is differentially influenced by any change in airflow characteristics predicted using the two-way coupling method due to their small inertia and consequently the deposition characteristics of the small droplets are different. However, large droplets are less influenced by the modest change in the airflow and no significant difference is calculated in the deposition locations of oil droplets provided that droplet diameters larger than 100 microns are considered.

Development of Ultrasonic Temperature Sensors for Ultra-High Temperature Measurement in Nuclear Reactor Vessel

The temperature measurement of a very high temperature core melt is of importance in LAVA (lower-plenum Arrested Vessel Attack) experiment in which gap formation between core melt and the reactor lower head, and the effect of the gap on thermal behavior are to be measured. The existing temperature measurement techniques have some problems, where the thermocouple, one of the contact methods, is restricted to under 2000°C, and the infrared thermometry, one of the non-contact methods, is unable to measure an internal temperature and very sensitive to the interference from reacted gases. So, in order to solve these problems, the delay time of ultrasonic wavelets due to high temperature is suggested. One of the key initial conditions to be measured in LAVA is the initial corium melt temperature. To measure it, the LAVA measurement group has developed several kinds of UTS’s. As a first stage, a molten material temperature was measured up to 2314°C. Also, the optimization design of the UTS (ultrasonic temperature sensor) with persistence at the high temperature was suggested in this paper. And the utilization of the theory suggested in this paper and the efficiency of the developed system are certified by performing experiments.

Numerical Investigations of a Turbulence Mixing Process Related to Thermal Striping Phenomena at a T-Junction of Liquid Metal Fast Reactor Piping Systems

Fluid-structure thermal interaction phenomena characterized by stationary random temperature fluctuations, namely thermal striping are observed in the downstream region of a T-junction piping system of liquid metal fast reactor (LMFR). Therefore the piping walls located in the downstream region must be protected against the stationary random thermal process which might induced high-cycle fatigue. This paper describes the evaluation system based on numerical simulation methods for the thermal striping, and numerical results of the thermal striping at a T-junction piping system under the various parameters, i.e., velocity ratio and diameter ratio between both the pipes and Reynolds number. Then detailed turbulence mixing process at the T-junction piping region due to arched vortexes generating lower frequency fluctuations are evaluated through a separate numerical analysis of a fundamental water experiment.

Tools and Techniques for Modeling SOFC Fuel Cell Performance

Fuel cells have been utilized in certain specialized applications since the 1960’s, however the technology has recently been the focus of a broad research and development effort. The next 10 years will likely produce practical, affordable fuel cells that are applied in fixed power generation, automotive, and even powered bicycle applications. As the fuel cell becomes less of a research curiosity and more of an engineered commodity item, designers need tools to study and optimize the behavior of fuel cells. This paper discusses some of the questions that simulation can help fuel cell designers address.

Computational Modelling and Simulation of Proton-Exchange Membrane Fuel Cells (Keynote)

Fuel cells (FC’s) are electrochemical devices that convert directly into electricity the chemical energy of reaction of a fuel (usually hydrogen) with an oxidant (usually oxygen from ambient air). The only by-products in a hydrogen fuel cell are heat and water, making this emerging technology the leading candidate for quiet, zero emission energy production. Several types of fuel cell are currently undergoing intense research and development for applications ranging from portable electronics and appliances to residential power generation and transportation. The focus of this lecture is Proton-Exchange Membrane Fuel Cells (PEMFC’s). An electrolyte consisting of a “solid” polymer membrane, low operating temperatures (typically below 90 °C) and a relatively simple design combine to make PEMFC’s particularly well suited to automotive and portable applications. The operation of a fuel cell relies on electrochemical reactions and an array of coupled transport phenomena, including multi-component gas flow, two phase-flow, heat and mass transfer, phase change and transport of charged species. The transport processes take place in variety of media, including porous gas diffusion electrodes and polymer membranes. The fuel cell environment makes it impossible to measure in-situ the quantities of interest to understand and quantify these phenomena, and computational modelling and simulations are therefore poised to play a central role in the development and optimization of fuel cell technology. We provide an overview of the role of various transport phenomena in fuel cell operation and some of the physical and computational modelling challenges they present. The processes will be illustrated through examples of multi-dimensional numerical simulations of Proton-Exchange Membrane Fuel Cells. We close with a perspective on some of the many remaining challenges and future development opportunities.

Three-Dimensional Flow Analysis in VFP Type Artificial Heart by Unstructured Grid

To effectively design the vibrating flow pump (VFP) for left ventricular assist device, the numerical codes were developed for three-dimensional blood flow based on the finite volume method. The numerical codes were also developed based on the artificial compressibility method by the use of unstructured grid. Three-dimensional numerical computations and the visualizations were made for flow patterns in the casing of VFP, which were closely connected with hemolysis and blood coagulation. We examined the three different inlet conditions, i.e., radial flow, flow considering the 2nd vibration mode of the jellyfish valve motion, and the swirling flow, to explore the suitable condition for preventing the hemolysis and the blood coagulation. It was found that the swirling flow could effectively decrease hemolysis. The effect of rheology model of the blood flow was also studied in detail.

Density Distribution in Stagnation Region of Saffman Equation for Dusty Gas

We investigate the behaviour of flow field around an obstacle placed in uniform particle flow based on two-fluid Saffman equation. Particle density in the vicinity of the front stagnation point is, in particular, the primary interest in the present study. In the case of small Stokes number, in which particle impingement does not occur, there exists the exact solution of the flow field of particle phase is obtained. Perturbed solution is also obtained in the reciprocal of Stokes number when Stokes number is large enough. Comparison between numerical results and these solutions shows good agreement and the peak of particle density appears near the threshold of partide impingement to the body surface.