Computational fluid dynamics(CFD) modeling and experiments have both advantages and disadvantages. Doing both can be complementary, and we can expect more effective understanding of the phenomenon. Although CFD has more advantages than experiments for the prediction where experiments are difficult to carry out, generally when compared with experimental results, it is difficult to obtain reliable results for a large domain by using CFD. However, it is possible to obtain useful CFD results based on verification by the experimental results. Moreover, experiments cannot deliver correct results for any arbitrary condition due to limitations to experimental equipment, measurement errors and problems with measurement systems. Utilizing CFD can complement very fundamental experimental results. In this paper, a wind turbine is used as an example to discuss the verification of experimental results by using CFD.

抄録全体を表示

One-dimensional stability analysis of a hydraulic system composed of a penstock, a runner and a draft tube was carried out to determine the cause of the full load draft tube surge. It is assumed that the cavity volume at the runner exit is a function of the pressure at the vortex core evaluated from the instantaneous local pressure at the runner exit and an additional pressure decrease due to the centrifugal force on the swirling flow. It was found that the diffuser effect of the draft tube has a destabilizing effect over all flow rates while the swirl effects stabilize / destabilize the system at larger / smaller flow rates than the swirl free flow rate. Explanations of the destabilizing mechanism are given for the diffuser and swirl flow effects.

抄録全体を表示

Leak detection for leaks at two points was done using the inverse transient method and genetic algorithm. The locations and discharges of each leak were selected as GA parameters for leaks at two points in pipeline. The steady pressures and leak discharges at all nodes were calculated using Newton iteration method. Calculations under assumption of two leaks points were done for not only leaks at two points but also leak at one point in pipeline. Furthermore, the effect of noise in pressure data was discussed, and the leak locations and leak discharges can be predicted precisely even in the case of noisy data.

抄録全体を表示

Flow field around an entire stage of an axial cooling fan is analyzed using the three-dimensional unsteady Reynolds-averaged Navier-Stokes (RANS) equations with Shear Stress Transport (SST) turbulence model, aiming at the investigation of the cooling performance of the fan. The main focus in this study is on the effect of the distance between the cooling fan and the surface to be cooled. Detailed flow measurement is also executed using a slant hot-wire probe to clarify time-resolved flow structure as well as turbulent flow characteristics contained in the downstream flow of the fan. The numerical results are compared with the experimental data as well as the flow field in the vicinity of the fan blades. This study reveals the important role of the fan-surface distance in terms of flow rate and cooling performance.

抄録全体を表示