Experimental and Numerical Research on the Influence of Stern Flap Mounting Angle on Double-Stepped Planing Hull Hydrodynamic Performance

Abstract

In the current hydrodynamic research relating to planing hulls, the stern flap and steps are generally considered to be two independent resistance reduction measures. Limited research has focused on the coupled effects of flaps and steps. Therefore, experimental and numerical simulation methods are carried out in this paper to explore the influence of the flap mounting angle coupled with the steps. A series of model towing tests were implemented for a double-stepped planing hull with 2°, 3° and 4.5° flap angles. The test results show that, as the mounting angle increased, the low speed resistance performance was improved and the porpoising critical speed was delayed, with a slight resistance cost. Based on the tests, a numerical simulation method was established with volume Froude numbers ranging from 0.88 to 5.20. The simulated hull flow field showed good agreement with the testing data. The simulation results suggest a cavity induces the negative pressure after the steps; the cavity core region is the air phase, and this expands with the air–water mixture flow. The cavity also causes wetted surface reduction and pressure distribution changes. Finally, comparisons of cavities after-steps and load coefficients of different planing surfaces among models were considered. Numerical results analysis gave distinct interpretations for the experimental phenomenon of porpoising critical speed increasing with a slight resistance increment.

Influence on Stern Flaps in Resistance Performance of a Caterpillar Track Amphibious Vehicle

“…Fr = V 0 / gL WL (16) where R t is the total drag resistance, S is the wetted area of the vehicle in the steady state. Table 4 listed four levels of grids (G1, G2, G3 and G4) generated with the refinement ratio r = 1.2, and the C t results calculated by them are noted as S 1 , S 2 , S 3 , and S 4 respectively.…”

“…The bow flat was not considered because it was hard to be installed on this vehicle. Previous analogous researches have been carried out on deep-vee ship, with a drag-reduction rate of less than 10% [15], [16]. That could not meet our requirement.…”

Experimental Study on Motion Behavior and Longitudinal Stability Assessment of a Trimaran Planing Hull Model in Calm Water

“…As shown in Figure 4, the hydroflap was mounted in the tunnel, located at 1/8 L from the transom in the longitudinal direction, and a pair of flat stern flaps were introduced and mounted on the main hull aft close to the chine. The stern flaps were mounted in a fixed form along with the main hull planing surface, and an extra angle of 2 • was considered [7]. The main dimensions of the stern flap were as follows: width 100 mm × length 75 mm.…”

“…The aerodynamic effect is poorer than in the planing catam mentioned above [5]. Therefore, the navigation mechanism of a trimaran is still simil a conventional planing hull, especially in the high-speed region; i.e., the hull in the h speed region is confronted with greater resistance and weaker stability [6][7][8]. Several experimental and numerical studies have been conducted focusing on performance of tunneled planing hulls.…”

“…Zeng et al and Liu et al introduced the mathematical motion equations of a trimaran, then introduced a T-foil and a flap and discussed the effects on vertical stabilization control [19,20]. Lu et al studied the coupling action of a stern flap and step on a monoplaning hull, both experimentally and numerically [7]. Sajedi and Ghadimi assumed the wetted surface area as a step height and location function, and by experimental and numerical investigation, the optimal layout and configuration of the step were discussed and extracted with the aim of minimizing the resistance [21].…”