On Wakes behind a Single Aerofoil and Cascade

Abstract

In an axial turbo-machinery, many cascades rotate in the downstream of the preceding cascade. The flow vector variation in the exit of the preceding cascade displays a marked variation of static pressure and flow pattern. It also brings about fatigue of cascade blades, generates noise and becomes a cause of losses. In order to predict and control losses in a cascade, it is necessary to analyse wake characteristics of a cascade and the performance of a cascade in non-steady flow. As a first step in the study of unsteady flow through or in a cascade, our experiment is concerned with wakes behind a two-dimensional single aerofoil and cascade. Experiments were made about wakes in transition and turbulent regions behind a single aerofoil and cascade of chord 30 mm and aspect ratio 3. The mean velocity and velocity fluctuation were measured by a Pitot tube and a hot-wire anemometer. In the transition region, it was shown that a Tollmien-wave interacts with the organ-type acoustic vibration of cascade, and considerable static pressure variation exists in the wake. In the turbulent region, the wake flow is self-preserving even in the immediate neighbourhood of the transition region.