Low aspect-ratio triangular prisms in cross-flow: measurements of the wake fluctuating velocity field

摘要

An experimental investigation is carried out to study the characteristics of the fluctuating wake flow field of finite-length prismatic bodies in cross-flow, placed vertically on a plane and having isosceles triangular cross-section with 60° or 90° apex angle orientated in the down-stream direction. The wake flow field is studied with hot-wire anemometry for aspect ratios h/w = 1.0, 1.5, 2.0 and 3.0 at Re = wU/v approx= 1.2 * 10~5, and the velocity signals are analysed by means of procedures based on the wavelet transform. Velocity fluctuations with a clear dominating frequency are found immediately outside the wake along all the models, even if their magnitude decreases at a height corresponding to the free end of the bodies. The wavelet analysis of the phase difference between signals acquired at opposite sides of the wake shows that alternate vortex shedding occurs for all the models. An increase in the phase shift between the fluctuations on the same side of the wake with increasing vertical distance between the probes suggest that the shed vortices are curved. No evidence of symmetrical shedding or of the presence of arch-type vortices is found, even for the models with the smaller aspect ratios.