Noboru Koike

Flow Visualization and Numerical Calculation in a Curved Diffuser. Effects of Existence of a Guide Vane.

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.

An Experimental Investigation of the Flow in a Curved Diffuser. Effects of the Position of the Leading Edge of a Guide Vane Interposed in a Diffuser with Uniform Inlet Velocity Distribution.

This paper deals with an experimental study of the flow in a logarithmic spiral curved diffuser with uniform inlet velocity distribution. In this study, the effects of the variation in the interposed position of the guide vane in a diffuser and the position of its leading edge on the pressure distributions along both diffuser walls, velocity and vector distributions, and the diffuser efficiency are clarified. The results obtained from this study are summarized as follows : In the case where the ratio, bn/B1, of the distance bn between the convex wall and the interposed position of the guide vane at the diffuser inlet to the diffuser inlet breadth B1 is in the region of about 0.25∼0.375, the diffuser efficiency indicates the most desirable value. When the leading edge of the guide vane is placed upstream, superior diffuser efficiency can be obtained, in every interposed position of a guide vane.

Flow Visualization and Numerical Calculation in a Curved Diffuser

In this study, the effects of the variation in the logarithmic spiral angle of the curved diffuser profile and the existence of a guide vane in the curved diffuser on the flow pattern are clarified by the flow visualization using the dye-streak method and the condensed-milk method colored by green dyes, and their results are compared with the numerical solutions obtained by the finite element method.As the results of this study, it was found that the separation point in the flow pattern obtained from the flow visualization using condensed-milk method agreed comparatively with numerical results, and the performance of the curved diffuser was affected considerably by the logarithmic spiral angle and the existence of a guide vane, especially, the flow pattern indicated the most desirable result, when the spiral angle β was 22.5°.