Abstract
The effect of wall constraint on rectangular-section prisms is investigated experimentally in a low-turbulence wind tunnel up to a blockage ratio of 0.25. The depth to width ratio ( d h ) of the sections varies from 0.5 to 5.0. It is shown that the effect of confinement on the mean surface pressure on the models is not uniform in the streamwise direction and therefore cannot be regarded as an increase in the effective dynamic pressure estimated from drag or base pressure measurements as assumed by some investigators. The current bluff-body blockage correction formulae are found to be inadequate for correcting the drag and base pressure for these sections, particularly at large blockage ratios. A new equation, which is a modification of Maskell's equation and includes a shape factor to allow for the depth of the rectangular section, yields satisfactorily corrected drag and base pressure. Due to the large depth of the sections in the stream direction, corrections to the pressure distribution around them for blockage using this equation, are not very satisfactory. The correction for the Strouhal number using the new equation is valid up to d h = 3.0 .
Published Version
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