Fluctuation characteristics of hull surface force of a four-screw vessel in oblique flow

Abstract

To study the influence of oblique flow on propeller fluctuation pressure characteristic of a four-screw ship, the wake field and self-propulsion performance are calculated and analyzed utilizing Computational Fluid Dynamics (CFD) simulations. The characteristics of the wake field and propeller fluctuation pressure under different drift angle consist of 0{degree sign}, {plus minus}10{degree sign} and {plus minus}20{degree sign} are compared and discussed in detail. The results show that the negative drift angle affected the wake field of inside propeller more severely due to the generation of bilge vortex. The mean values of inside propeller fluctuation pressure are about 30% larger than those of outside one, while the amplitudes of fluctuation pressure are reversed. The mean values of propeller fluctuation pressure experience a gradual decrease within β=-20º to β=20º with exception of inside propeller at β=-20º condition. The fluctuation amplitude of outside propeller is more affected by oblique flow due to the effect of oblique flow on flow separation point.

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

“…In addition, as shown in Figure 10 shows the internal flow field distribution and the shape of the vortex rope inside the draft tube. Under high-load conditions, the vortex rope inside the draft tube exhibits a spindle shape [33,34]. Just as stated in Kumar's paper [35], under rated conditions, the inlet flow at the draft tube is nearly identical to the normal outflow; however, as the flow rate increases, the strong swirl flow is directed contrary to the runner's rotation, and eventually, a cavitation vortex rope shaped like torch forms.…”