The influence of corner radius on the forces experienced by cylindrical bluff bodies in oscillatory flow

Measurements are presented of the effects of corner radius on the hydrodynamic forces experienced by cylindrical bluff bodies in oscillatory flow over the Keulegan Carpenter number range from 1 to 100. The range of Reynolds number covered is from 200 to 2 × 10⁴ and two basic cross-sectional shapes, namely a square and a diamond, were used in the investigation. Drag coefficients in oscillatory flow are found to be more sensitive to corner radius than in steady flow. At a fixed Keulegan Carpenter number the drag coefficient of a diamond section decreases with increasing corner radius and the reduction is more marked at low Keulegan Carpenter numbers. The drag of a square section does not follow a consistent trend with corner radius and for high Keulegan Carpenter numbers the rounded square with a corner radius of 0.265D (where D is the width of the model normal to the flow) can have a drag coefficient equal to half the value for a circular cylinder.