FORCE ON A CIRCULAR-CYLINDER IN AN ELLIPTIC ORBITAL FLOW AT LOW KEULEGAN-CARPENTER NUMBERS

The flow structure and force acting on a horizontal circular cylinder exposed to uniform orbital flows of varying ellipticity have been dete rmined by a finite-difference solution of the two-dimensional problem using vorticity/stream-function variables. The Keulegan-Carpenter numb er (KC) for the analysis is two or less with frequency parameter (beta ) values of 483 and 2300. For a uniform circular orbital flow, the cal culated results are compared to previous analytical and computational results with excellent agreement in most respects. For a uniform ellip tical orbital flow, a series of calculations was done for three sets o f parameter values, letting only the orbital ellipticity vary from cir cular to rectilinear. No change in the maximum total force occurred at KC = 0.1 for increasing values of ellipticity, but, for KC of 1 and 1 .02, the maximum total force decreased with increasing values of ellip ticity (E) at a given value of beta and E has a strong influence on th e rate of decrease. The maximum total force also decreased at a given value of E as beta increased for constant KC; this decrease in force m ay be explained by the difference in flow patterns between the two val ues of beta. The formation of a small separation and reattachment regi on is observed for E greater than or equal to 0.8 when KC = 1.02 and b eta = 2300; this how feature is evident from the spikes present in the force curve and from the surface vorticity distribution. (C) 1995 Aca demic Press Limited