ABSTRACT

Wells turbine has the cascade whose stagger angle is 90 degrees, namely the blades are perpendicular to the axial velocity. The good performance is required from 0 to 90 degrees of attack angle because the turbine is operated in the oscillating airflow produced with wave energy. Furthermore, very interesting and complex flows are experimentally observed by the oil film method in the large attack angle where the performance is strongly influenced, especially, the self-starting. This paper tries to analyze the mechanism of these three-dimensional flows around the turbine with the numerical analysis, focusing on the ofl:design condition.

INTRODUCTION

In the former time, a prototype trial ship of a wave power generator system, that is, KAIMEI (Ishii et. al., 1981) installed the general impulse turbine with a unidirectional rectifying air valve system in the type of an oscillating water column. It is found through this trial that the some valves in the system were broken down in the severe and frequent reciprocating airflow, which resulted in the fatal decrease of total efficiency. These experiences made them impress the necessity of simple and vane-less structured turbines such as Wells turbine. The Wells turbine is an axial flow turbine mainly used for wave energy devices of oscillating water column type, because the turbine has simple structure and can rotate in the same direction even if the air changes the direction of flow, which is called as a self-rectifying turbine. However, the turbine has efficiency of about 50% in the steady flow and about 40% in the irregular oscillating airflow produced by the swell of the sea. The reason why the efficiency is lower than the general turbines is that the turbine has the peculiar blade arrangement, which has stagger angle of 90 degrees as a cascade.

This content is only available via PDF.
You can access this article if you purchase or spend a download.