In the present study experimental efforts have been conducted in order to reveal the detailed flow structure of the dynamic stall in low speed flows. In the present experiments, a low speed wind tunnel, whose diameter is 2m, is used. A special device for oscillating the airfoil in pitch sinusoidally is developed by using a special mechanical link system. The flow fields are visualized by smoke-wire method and smoke lines (streak line) are recorded with a conventional camera and a video camera. The mean angle of attack of the airfoil is changed variously and the effect of mean angle of attack on the characteristics of the dynamic stall are investigated carefully. The results show that the dynamic stall characteristics in low speed flow are significantly influenced by the mean angle of attack.
This experimental research simulates that tidal waves which are higher than coastal pine forests strike against the forests. Canopy models of coastal forests are presented as groups of circular cylinders with steel wool placed perpendicularly on a ground plane. The circular cylinders and the steel wool present trunks and crowns of trees, respectively. The effect of canopy models on flow fields is studied with flow visualization and image processing. Two patterns of canopy models are used; one is a continuous pattern and the other a gap-toothed pattern. With flow visualization, crowns of these models dam up tidal waves, and the waves rise up to about twice the height of trees at the frontal part of canopy models. Velocity fields of the flows are measured by image processing of the correlation method. Then, the velocity fields are revised under constraint of the equation of continuity. Velocity fields in the downstream regions of the plant canopies are evidently different between two patterns of models.
To create the comfortable room ventilation with a low speed air flow has been investigated. The paper focuses on a quantitative flow analysis of a low speed air flow, which is based on the flow visualization and the digital image processing. The ventilation air flow in a room model and the natural convection induced by a human body were visualized by a smoke method and a technique of laser light sheet. The quantitative velocity data were obtained from the flow visualization image by a simplified density correlation method. The results indicated that the ventilation air supplied from the ceiling was circulated in the whole region of the room, and that the influence of strong upward natural convection due to the presence of the human body was an important factor in the design of the room ventilation.
In our previous experiments using a wind tunnnel, the flow in a two-dimensional curved diffuser with logarithmic spiral angle was clarified quantitatively about the variation of spiral angle and the existence of a guide vane. The wind tunnel method however requires much time for preparation of the experimental system and for the main experimental procedure. We have recently devised a new experimental method for identifying optimum diffuser forms in less time than that required by the conventional technique. This new method involves visualization of flow (using dye streaks and condensed milk) and numerical calculation using the finite element method. The results obtained with this new method were compared with those obtained with the wind tunnel method to assess its usefulness. The results of numerical calculation approximately agreed with the findings from flow visualization. The analysis using this method showed that the flow in the diffuser was improved by the existence of a guide vane, although some differences were observed depending on the magnitude of the logarithmic spiral angle. These findings are consistent with those obtained in our previous wind tunnel experiments. This method involving flow visualization and calculation is therefore expected to provide a simple and useful means of determining ideal forms of curved diffusers.