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Control of Cloud Cavitation Pattern over a Hydrofoil Using Surface Microstructures

Velayati, Vahid | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58534 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Javadi, Khodayar
  7. Abstract:
  8. Cloud cavitation is one of the major challenges faced by hydrodynamic systems, occurring unsteadily around submerged and moving components such as propellers and rudders. This phenomenon, observed in various industries—including marine propulsion, turbomachinery, and hydrodynamic systems—can cause shock waves, erosion, undesirable vibrations, and efficiency losses, particularly due to the collapse of vapor bubbles near solid surfaces. In this research, to control and mitigate the effects of cloud cavitation, the influence of semi-spherical surface microstructures on a three-dimensional Clark-Y hydrofoil was investigated through both numerical simulations and experimental studies. The numerical simulations were performed using ANSYS Fluent, employing the Large Eddy Simulation (LES) approach in combination with the Schnerr–Sauer cavitation model to analyze the effects of the position and geometric arrangement of the microstructures on the dynamic characteristics of cloud cavitation. The experimental tests were conducted in a cavitation tunnel to validate the numerical results and further develop the proposed method. The experiments were designed to examine the influence of microstructure diameter, height, and installation position on the dynamic behavior of cloud cavitation, using a high-speed camera and pressure sensors. In both numerical and experimental parts, the hydrodynamic conditions were kept constant with a cavitation number of 0.8, a Reynolds number of 7 × 10⁵, and an angle of attack of 8°. The numerical results revealed that the location of the microstructures on the hydrofoil had distinct effects. Placement near the leading edge reduced the frequency of cloud cavitation oscillations and increased the length of the attached sheet cavity, but simultaneously caused a decrease in the lift-to-drag ratio. In contrast, arranging the structures near the trailing edge led to the breakup of large cavities into smaller bubbles, an increase in oscillation frequency, and improved hydrodynamic efficiency. Arrangements in the mid-chord region also showed different outcomes by influencing the pressure field and preventing the upstream motion of the re-entrant jet. The experimental results confirmed the numerical findings and showed that increasing the diameter of the surface microstructures installed near the trailing edge from 1 mm to 2 mm reduced the cavity length by about 8% and increased the cavitation shedding frequency by approximately 6% and 13%, depending on the protrusion configuration. Furthermore, analysis of the experimental data indicated that increasing the height of the surface microstructures from 0.25 mm to 1 mm, when installed near the trailing edge, reduced the effectiveness of the proposed passive control method. Among all tested configurations, the simultaneous installation of surface microstructures near both the leading and trailing edges proved to be the most effective arrangement due to its combined influence on the upstream flow field and cavity closure region. In this configuration, with equal microstructure diameter and height, the alteration of the pressure field and disruption of re-entrant jet formation resulted in a 53% reduction in cloud cavity length compared with the smooth hydrofoil
  9. Keywords:
  10. Cloud Cavitation ; Passive Control ; Experimental Studies ; Numerical Simulation ; Hydrofoil ; Clark-Y Hydrofoil

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