Outline

  • Abstract
  • Keywords
  • 1. Introduction
  • 2. Experiment Set-Up
  • 2.1. Circular Cylinder Model
  • 2.2. Suction Flow Control System and Studied Cases
  • 3. Cylinder Model Response
  • 3.1. No Control
  • 3.2. Suction Control
  • 4. Pressure Coefficients of the Cylinder Model
  • 4.1. No Control
  • 4.2. Suction Control
  • 5. Aerodynamic Coefficients of the Cylinder Model
  • 5.1. No Control
  • 5.2. Suction Control
  • 6. Discussion
  • 7. Conclusion
  • Acknowledgments
  • References

رئوس مطالب

  • چکیده
  • 1. مقدمه
  • 2. دستگاه آزمایشگاهی
  • 2.1. مدل استوانه دایروی
  • 1.1 2.2. سیستم کنترل جریان مکش و حالات بررسی شده
  • 3.پاسخ مدل استوانه
  • 3.1 بدون کنترل
  • 3.2. کنترل مکش
  • 4. ضرایب فشار مدل استوانه
  • 4.1 بدون کنترل
  • 4.2 کنترل مکش
  • 5.ضرایب آیرودینامیکی مدل استوانه
  • 5.1 بدون کنترل
  • 5.2 کنترل مکش
  • 6. تشریح مطالب
  • 7. نتیجه گیری

Abstract

In the present study, a flow control method is employed to mitigate vortex-induced vibration (VIV) of a circular cylinder by using a suction flow method. The VIV of a circular cylinder was first reproduced in a wind tunnel by using a spring–mass system. The time evolution of the cylinder oscillation and the time histograms of the surface pressures of 119 taps in four sections of the circular cylinder model were measured during the wind tunnel experiments. Four steady suction flow rates were used to investigate the effectiveness of the suction control method to suppress VIV of the circular cylinder. The vibration responses, the mean and fluctuating pressure coefficients, and the resultant aerodynamic force coefficients of the circular cylinder under the suction flow control are analyzed. The measurement results indicate clearly that the steady suction flow control method exhibits excellent control effectiveness and can distinctly suppress the VIV by dramatically reducing the amplitudes of cylinder vibrations, fluctuating pressure coefficients and lift coefficients of the circular cylinder model. By comparing the test cases with different suction flow rates, it is found that there exists an optimal suction flow rate for the maximum VIV control. The cases with higher suction flow rates do not necessarily behave better than those with lower suction flow rates. With the experimental setting used in the present study, the suction flow control method is found to behave better for VIV suppression when the ratio of the suction flow velocity to the oncoming flow velocity is less than one.

Keywords: - - - -

Conclusions

In the present study, an experimental investigation was conducted to control/suppress the VIV of a circular cylinder by using a suction flow control method. The experimental study was conducted in a wind tunnel with a circular cylinder test model as a spring–mass system. The VIV of the test model with and without such flow control are quantified in the terms of the dynamics of the vibration responses, the mean and fluctuating pressure coefficients, and the aerodynamic force coefficients acting on the test model. Important flow parameters, such as the reduced velocity of the oncoming flow and the suction flow rate, on the effectiveness of the suction control method to suppress VIV of the test model are assessed quantitatively.

The measurement results indicate clearly that the suction flow control method exhibits excellent control performance to suppress the VIV of the test model by substantially reducing the amplitude of the VIV oscillation, fluctuating surface pressure, and the unsteady aerodynamic forces acting on the test model. By comparing the test cases with different suction flow rates, it is found that there exists an optimal suction flow rate for the best VIV control. The cases with higher suction flow rates do not necessarily behave better than those with lower suction flow rates. The suction flow control method is found to have the best control effectiveness for VIV suppression when the velocity ratio of the suction flow velocity to the oncoming free stream flow velocity to start the VIV of the test model is less than one.

It should be noted that, as the first report of an ongoing multi-year research project, the major objective of the present study is to demonstrate the effectiveness of using suction flow method to control/suppress VIV phenomena. While the time- resolved measurement results reported in the present study, in the terms of the dynamics of the vibration responses, the mean and fluctuating pressure coefficients, and the resultant aerodynamic force coefficients acting on the test model, are very useful and essential to reveal many interesting features and important global characteristics of the VIV phenomena with and without suction flow control. It is highly desirable to obtain the quantitative information about the corresponding flow field around the test model in order to elucidate the underlying physics of the VIV phenomena more clearly. With this goal in mind, we are conducting detailed flow field measurements by using a high-resolution Particle Image Velocimetry (PIV) system to quantify the time evolution of the unsteady vortex and wake flow structures around the test model with and without suction flow control. The detailed flow field measurement results will be reported in our future papers.

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