Time-dependent flows around cylinders with circular and noncircular (D-cylinder) cross sections were studied by using a numerical approach based on a low-order panel method. The method was previously used successfully for several applications, such as calculation of the added mass and damping coefficients, and prediction of hydrodynamic coefficients for underwater vehicles. In simulating the viscous time-dependent flow around the cylinder, time dependent wake feature of the code is utilized. The results agree well with the experiments and the theoretical values, when available.
Impulsively started flow around cylinders is a fundamental problem for which some analytical and numerical solutions are available for small times and relatively large Reynolds numbers. Examples with engineering relevance for flows around circular and noncircular cylinders include offshore structures, loading response of underwater vehicles, and flow around appendages. In most cases, the knowledge of the location of separation point is not readily available from the analysis, and this information is typically obtained from the experiments (Sarpkaya, 1966, Sarpkaya and Kline, 1982, Okamato and Sunabashiri, 1992). The numerical solutions in the literature for this problem are typically based on finiteelement or finite-difference techniques (Cebeci, 1979, Tuann and Olson, 1976), and some form of discrete vortex methods (Shoaff and Franks, 1981). In this study we employed PMARC (Ashby, Dudley, and Iguchi, 1988), a low-order panel method based on constant strength source and dipoles on each surface panel. It was modified successfully to calculate the added mass and moment coefficients of several two and three-dimensional bodies (Sahin, Crane and Watson, 1993). The code is based on ideal flow theory and, therefore, it is limited in applications where the viscosity plays a dominant role. However, the "time dependent wake" feature of the code works well in simulating many real fluid phenomena, such as vortex roll-up.
