Laminar vortex shedding from a trapezoidal cylinder with different height ratios

The Strouhal number from trapezoidal cylinders depends on the Reynolds number as well as the height ratio, which is the ratio of the height of the rear face to that of the front face. For Re=100 and 150, distributions of the Strouhal numbers show their minimum values at a height ratio of 0.7 and 0.85, respectively. However, for Re=200, the variation of Strouhal number increases as the height ratio from a square section decreases. After showing the maximum value at a height ratio of 0.7, it decreases as the height ratio decreases. It then increases again for the smaller height ratios. Movement of the flow separation point from the rear to front corners and change of secondary vortex strength are important factors in determining the shedding structure for Re=100 and 150. However, for Re=200, flow separation always occurs at the front corners. The change of secondary vortex strength and the interaction between the primary and secondary vortices influence the variation of shedding. (C) 2000 American Institute of Physics. [S1070-6631(00)02705-7].