Shigeyuki Tomimatsu

Performance of a PIV System for a Combusting Flow and Its Application to a Spray Combustor Model

The performance of PIV system for combusting flow was evaluated by using artificial images generated from computer graphics and experimental data. The influences of shutter speed, filter, laser power and the PIV algorithms on the measurement uncertainty were studied for optimizing the performance of the PIV system. This system was applied to the spray combustor model for boiler, and the flow patterns with and without combustion were elucidated. Results showed that the burner flow generates complex three-dimensional flow pattern, which contributes to highly mixed fuel flow in the combustor. Although the flow pattern with and without combustion is similar, the growth of burner flow area and an increase in velocity magnitude are found in the flow field by the influence of chemical reactions in combustion.

Simultaneous measurement of droplet size and velocity field by an interferometric imaging technique in spray combustion

The present paper describes an experimental technique of droplet sizing and velocity measurement for application to a luminous flame in spray combustion. The size measurement of unburnt fuel droplets in combustion is carried out by using an interferometric imaging method, while the corresponding velocity field is measured by particle tracking velocimetry (PTV) in combination with the rotary shutter to avoid the high intensity noise of the luminous flame in spray combustion. The measurements are successfully applied to the spray flow from a gun-type burner with and without combustion. The experimental results in spray combustion indicate that the smaller size of fuel droplets are almost burnt in the centre of the flame and the unburnt droplets of larger size remain in the outer region of the burner flow. It was found that the mean droplet velocity measured by the present PTV technique in combustion is almost independent of the droplet size and agrees closely with the gas velocity. However, the velocity magnitude with combustion is increased in comparison with the case without combustion, which suggests the influence of gas expansion at high temperatures.

Measurement of Aerodynamic Noise and Unsteady Flow Field around a Symmetrical Airfoil

The purpose of this paper is to study the physics of aerodynamic noise generation from the symmetrical airfoil of NACA 0018 in a uniform flow. The relationship between the noise spectrum and the unsteady flow field around the airfoil is studied in an acoustic wind tunnel using flow visualization and PIV analysis. The discrete frequency noise was generated from the airfoil inclined at small angle of attack to the free stream. The flow visualization result indicates the presence of attached boundary layer over the suction side and the separated shear layer over the rear pressure side of the airfoil, when the discrete frequency noise is observed. It is found from the PIV analysis that a large magnitude of vorticity is generated periodically from the pressure side of the trailing edge and it develops into an asymmetrical vortex street in the wake of the airfoil. The periodicity of the shedding vortices was found to agree with that of the frequency of the generated noise.

PIV Measurement of Velocity Field in a Spray Combustor

AbsractThis paper reports a velocity measurement technique using PIV for application to a luminous flame in a spray combustor. The present system consists of a standard PIV system, a rotary shutter and a band-pass filter, the combination of which removes the influence of the high intensity of the luminous flame. The effectiveness of the rotary shutter is studied by changing the shutter speed from 2 ms to 37 ms. The simultaneous observation of the velocity field and the flame structure was carried out in the combustor model for a boiler. The measured velocity field indicates that the exit velocity from the burner is increased by chemical reactions, but the flow pattern inside the combustor is kept similar to that without combustion.

Prediction of flow field and aerodynamic noise of jet fan using large eddy simulation

To conduct a product development of turbomachinery continuously and developmentally, an approach using large eddy simulation (LES) should be one of the mainstream, because it is already essential to utilize computational fluid dynamics (CFD) using Reynolds averaged Navier–Stokes Simulation in industrial field. In recent years, the demand for a high-efficiency and low-noise jet fan, which is used for ventilation of a tunnel of a carriage way, is getting higher and higher. However, to conduct noise prediction of the jet fan with high accuracy, it needs the high-performance computing technique using a supercomputer. In this study, CFD of the jet fan is conducted using LES. Noise simulation is also conducted using the LES result. Moreover, the fine mesh model is generated by refining a coarse mesh, and LES is conducted using the Earth Simulator. The result of surface pressure using the fine mesh is clearer than the one using the coarse mesh.Graphical abstract

Study on Flow Condition around a Guide Vane Set in a Cuarved Circular Pipe

With respect to vibration problems of a guide vane, this vibration phenomenon seems to be generated by the fluid exciting force, which works on the guide vane in unsteady flow field. Thus, in order to understand the vibration mechanism of the guide vane, it is important to reveal unsteady flow field in the curved pipe with the guide vane. In this study, the difference of flow condition between a curved circular pipe and an elbow pipe fitting was inventigated by Computational Fluid Dynamics (CFD) using Reynolds Averaged Navier-Stokes Simulation (RANS). As a result of this study, there is no big difference between both flow conditions. Moreover, unsteady flow field in the curved circular pipe was investigated by Particle Image Velocimetry (PIV) measurements. This experiment was mainly carried out with focusing on unsteady flow field around the trailing edge of the guide vane. The results show that the vortex street is sometimes generated from the trailing edge of the guide vane.

Investigation of Air Entrainment Caused by Speedup in a Suction Sump

In order to reduce costs, speed-up in a suction sump is recently suggested. However, it is predicted that excess speedup causes air entrainment and performance of a pump goes down. In this paper, air entrainment caused by speedup in a suction sump is investigated. Recently, in order to speed up development time and reduce development cost, CFD technique is often used. So, investigation was carried out by using CFD analysis. The occurrence of air entrainment was checked by void fraction.

PIV Measurement of Flow Field inside a Combustion chamber under Spray Combustion

This paper reports a PIV measurement technique for application to the combusting flow with a luminous flame. The experiments are conducted on the velocity field and the flame structure of spray combustion in a combustion chamber model. The results with and without combustion indicate that the oncoming flow velocity from the burner is enhanced by the chemical reaction to promote the re-circulating flow inside the chamber model. The simultaneous visualization of flame structure showed the distribution of luminous flame, the unburned droplets, and the soot structure generated in a flame.