COMPARATIVE NUMERICAL ANALYSIS OF PASSIVE CONTROL TECHNIQUES FOR CAVITATION MITIGATION ON CAMBERED MODIFIED TRAILING EDGE HYDROFOIL

The present study investigates the transient 3D numerical prediction of the significance of passive control techniques, using triangular and rectangular span-wise pimples, placed at cambered section at the location 32% chord length from of the nose of the hydrofoil, and combined with a modified finite trailing edge radius on the cambered NACA4412 hydrofoil. These hydrofoils are termed as Rt and Rr for this study. The analysis is conducted at an angle of attack of 8° and cavitation numbers of 0.65 and 0.78, covering sheet cavitation regimes. The realizable k-ε turbulence model and Zwart-Gerber-Belamri (ZGB) cavitation model are employed for simulations, with validation against experimental data from Akcabay and Leroux. The outcomes demonstrate that both triangular and rectangular pimples are effective in delaying cavitation onset and reducing the extent of vapor formation. At σ = 0.65, the pimpled Rr hydrofoil reduces the time-averaged vapor volume by 66%, while the pimpled Rt reduces it by 48%. Both pimpled configurations achieve almost negligible cavity lengths at both cavitation numbers. In terms of drag reduction, pimpled Rt and pimpled Rr show a decrease in the drag coefficient of 39% and 19% at σ = 0.65, and 45% and 48% at σ = 0.78, respectively. However, this drag reduction comes with a trade-off in lift; the lift coefficient decreases by approximately 20% and 10% for pimpled Rt and pimpled Rr at σ = 0.65, and by 31% and 39% at σ = 0.78. The lift-to-drag ratio improves significantly, with increases of about 30% and 25% for pimpled Rt and pimpled Rr at σ = 0.65, and 13% and 18% at σ = 0.78. These results demonstrate that while both pimpled hydrofoils improve cavitation control and reduce drag, they also result in reduced lift, particularly at lower cavitation numbers.