Ocean Systems Engineering

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Effect of flap angle on transom stern flow of a High speed displacement Surface combatant

  • Hemanth Kumar, Y. (Department of Ocean Engineering, Indian Institute of Technology) ;
  • Vijayakumar, R. (Department of Ocean Engineering, Indian Institute of Technology)
  • Received : 2019.03.18
  • Accepted : 2019.11.15
  • Published : 2020.03.25
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Abstract

Hydrodynamic Drag of Surface combatants pose significant challenges with regard to fuel efficiency and exhaust emissions. Stern flaps have been used widely as an energy saving device, particularly by the US Navy (Hemanth et al. 2018a, Hemanth Kumar and Vijayakumar 2018b). In the present investigation the effect of flap turning angle on drag reduction is numerically and experimentally studied for a high-speed displacement surface combatant fitted with a stern flap in the Froude number range of 0.17-0.48. Parametric investigations are undertaken for constant chord length & span and varying turning angles of 5° 10° & 15°. Experimental resistance values in towing tank tests were validated with CFD. Investigations revealed that pressure increased as the flow velocity decreased with an increase in flap turning angle which was due to the centrifugal action of the flow caused by the induced concave curvature under the flap. There was no significant change in stern wave height but there was a gradual increase in the stern wave steepness with flap angle. Effective length of the vessel increased by lengthening of transom hollow. In low Froude number regime, flow was not influenced by flap curvature effects and pressure recovery was marginal. In the intermediate and high Froude number regimes pressure recovery increased with the flap turning angle and flow velocity.

Keywords

Acknowledgement

Authors thankfully acknowledge the technical support provided by the Department of Ocean Engineering, Indian Institute of Technology Madras in providing High-speed computing facilities, Towing tank and Instrumentation for undertaking simulations and conducting the experiments. We are also, indebted to Prof. Anantha Subramanian, Professor, Department of Ocean Engineering, for all the support rendered towards successfully completing research investigations.

References

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