2022
Yin, Tingyun; Pavesi, Giorgio; Pei, Ji; Yuan, Shouqi
Numerical investigation on the inhibition mechanisms of unsteady cavitating flow around stepped hydrofoils Journal Article
In: Ocean Engineering, vol. 265, iss. August, 2022, ISSN: 00298018.
Abstract | Links | BibTeX | Tags: Backward finite-time Lyapunov exponents, Partial cavity oscillation, Passive suppression, Proper orthogonal decomposition, Spatial–temporal behaviors
@article{YinPavesi2022-02,
title = {Numerical investigation on the inhibition mechanisms of unsteady cavitating flow around stepped hydrofoils},
author = {Tingyun Yin and Giorgio Pavesi and Ji Pei and Shouqi Yuan},
doi = {10.1016/j.oceaneng.2022.112540},
issn = {00298018},
year = {2022},
date = {2022-01-01},
journal = {Ocean Engineering},
volume = {265},
issue = {August},
publisher = {Elsevier Ltd},
abstract = {In this work, the influence of obstacles on the control of unsteady cavitating flows is investigated numerically within the framework of homogeneous flow. The predicted Strouhal number of the cavity shedding around the smooth hydrofoil is close to the experimental value, indicating the accuracy of the numerical simulation. Four installation sites are examined, including 10%, 20%, 30%, and 40% of the chord length from the leading edge. The instantaneous and time-averaged hydrodynamics in conjunction with the unsteady cavity behaviors are discussed in detail. The results indicate that all cases display similar flow patterns within one shedding cycle, including the development of the attached sheet cavity, sheet/cloud transformation, and cloud cavity collapse. The hydraulic lift is governed by the partial cavity oscillation but could be significantly modified by the trailing wake vortices, especially after installing the obstacle. The recommended optimal position of the obstacle is X/L=0.4, and the corresponding pressure fluctuations and lift-to-drag ratio achieve the best performance. However, the mean vapor volume is significantly reduced when the obstacle is located at X/L=0.3, indicating the minimum risk of cavitation erosion. Installing the obstacle at different locations along the suction surface will provide different effects on oscillation based on the analyses of the Lagrangian coherent structures. The corresponding primary frequency varies in a narrow range between 106.67 Hz ∼ 121.33 Hz. Proper orthogonal decomposition (POD) analyses of the vapor fraction reveal the contribution of flow morphology to the partial cavity oscillation. Installing the obstacle could significantly limit the size of each pattern, especially for X/L=0.4.},
keywords = {Backward finite-time Lyapunov exponents, Partial cavity oscillation, Passive suppression, Proper orthogonal decomposition, Spatial–temporal behaviors},
pubstate = {published},
tppubtype = {article}
}
In this work, the influence of obstacles on the control of unsteady cavitating flows is investigated numerically within the framework of homogeneous flow. The predicted Strouhal number of the cavity shedding around the smooth hydrofoil is close to the experimental value, indicating the accuracy of the numerical simulation. Four installation sites are examined, including 10%, 20%, 30%, and 40% of the chord length from the leading edge. The instantaneous and time-averaged hydrodynamics in conjunction with the unsteady cavity behaviors are discussed in detail. The results indicate that all cases display similar flow patterns within one shedding cycle, including the development of the attached sheet cavity, sheet/cloud transformation, and cloud cavity collapse. The hydraulic lift is governed by the partial cavity oscillation but could be significantly modified by the trailing wake vortices, especially after installing the obstacle. The recommended optimal position of the obstacle is X/L=0.4, and the corresponding pressure fluctuations and lift-to-drag ratio achieve the best performance. However, the mean vapor volume is significantly reduced when the obstacle is located at X/L=0.3, indicating the minimum risk of cavitation erosion. Installing the obstacle at different locations along the suction surface will provide different effects on oscillation based on the analyses of the Lagrangian coherent structures. The corresponding primary frequency varies in a narrow range between 106.67 Hz ∼ 121.33 Hz. Proper orthogonal decomposition (POD) analyses of the vapor fraction reveal the contribution of flow morphology to the partial cavity oscillation. Installing the obstacle could significantly limit the size of each pattern, especially for X/L=0.4.
2021
Yin, Tingyun; Pavesi, Giorgio; Pei, Ji; Yuan, Shouqi
Numerical investigation of unsteady cavitation around a twisted hydrofoil Journal Article
In: International Journal of Multiphase Flow, vol. 135, pp. 103506, 2021, ISSN: 03019322.
Abstract | Links | BibTeX | Tags: Dynamical behaviors, Proper orthogonal decomposition, Spectrum Analysis, Temporal/spatial analysis, Unsteady Cavitating Flow
@article{Yin2021,
title = {Numerical investigation of unsteady cavitation around a twisted hydrofoil},
author = {Tingyun Yin and Giorgio Pavesi and Ji Pei and Shouqi Yuan},
url = {https://doi.org/10.1016/j.ijmultiphaseflow.2020.103506 https://www.sciencedirect.com/science/article/pii/S0301932220306170},
doi = {10.1016/j.ijmultiphaseflow.2020.103506},
issn = {03019322},
year = {2021},
date = {2021-01-01},
journal = {International Journal of Multiphase Flow},
volume = {135},
pages = {103506},
publisher = {Elsevier Ltd},
abstract = {In this paper, the unsteady cavitating flow around a symmetrical twisted hydrofoil is investigated numerically. Cavitating flow characteristics are analyzed in terms of dynamical behaviors and temporal/spatial fluctuations of the cavities along the hydrofoil. At the midsection of the foil, sheet cavity firstly grows with nearly constant speed until the occurrence of the reverse flow at the closure line. During the reverse phase the flow moves upstream, and the sheet cavity keeps growing turbulently with low vapor content at the closure area. Fast Fourier Transform (FFT), Bispecturm and Dynamic Mode Decomposition (DMD) analyses show the existence of harmonics of the shedding frequency, of which the double and triple frequency are captured but only the fundamental frequency dominates the cavitating field. Pressure fluctuations around the hydrofoil and force coefficients are governed by the acceleration of vapor cavity. Application of Proper Orthogonal Decomposition (POD) displays the large-scale coherent structures among cavity shedding evolution. The sheet cavity growth, the main cavity shrinking and developing into a pair of root-like cavity structure and the sector cavity structure are captured by the first mode.},
keywords = {Dynamical behaviors, Proper orthogonal decomposition, Spectrum Analysis, Temporal/spatial analysis, Unsteady Cavitating Flow},
pubstate = {published},
tppubtype = {article}
}
In this paper, the unsteady cavitating flow around a symmetrical twisted hydrofoil is investigated numerically. Cavitating flow characteristics are analyzed in terms of dynamical behaviors and temporal/spatial fluctuations of the cavities along the hydrofoil. At the midsection of the foil, sheet cavity firstly grows with nearly constant speed until the occurrence of the reverse flow at the closure line. During the reverse phase the flow moves upstream, and the sheet cavity keeps growing turbulently with low vapor content at the closure area. Fast Fourier Transform (FFT), Bispecturm and Dynamic Mode Decomposition (DMD) analyses show the existence of harmonics of the shedding frequency, of which the double and triple frequency are captured but only the fundamental frequency dominates the cavitating field. Pressure fluctuations around the hydrofoil and force coefficients are governed by the acceleration of vapor cavity. Application of Proper Orthogonal Decomposition (POD) displays the large-scale coherent structures among cavity shedding evolution. The sheet cavity growth, the main cavity shrinking and developing into a pair of root-like cavity structure and the sector cavity structure are captured by the first mode.
