Impulsively started steady flow about sharp-edged rectangular prisms has been investigated experimentally and numerically. The forces acting on the bodies have been determined at a Reynolds number of about 20,000 for various angles of incidence as a function of the relative displacement of the fluid. The results have shown that the shedding of the first few vortices has profound effects on both the lift and drag coefficients, often resulting in a large initial rise in drag. The surface-vorticity-distribution version of the discrete vortex model has shown that the strength of the vortex clusters varies from 80 to 90 percent of the vorticity generated in the shear layers. The Strouhal number is correctly predicted but the calculated forces are somewhat larger than those measured experimentally.

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