Effect of the Reynolds number on the aerodynamic forces and galloping instability of a cylinder with semi-elliptical cross sections

• The aerodynamic forces on semi-elliptical cylinders in Re=34k–175k are obtained.
• The aerodynamic forces strongly vary with the angle of attack in the critical regime.
• The critical flow is responsible for translational and 3-DOF galloping instabilities.

The effects of the Reynolds number on the aerodynamic forces and galloping instability of a semi-elliptical cross-section, which are used to simulate the shape of the iced conductors, have not been fully studied. Simultaneous multi-pressure wind tunnel experiments were conducted to explore the aerodynamic forces on cylinder with semi-elliptical cross-sections; the Reynolds number was in the sub-critical and critical regimes. A unified single-degree-of-freedom (SDOF) approach and a three-degree-of-freedom (3-DOF) model were used to analyze the galloping instability with the Reynolds number in the following regime: Re=34k–175k. The variation in the aerodynamic force with the angle of attack is sensitive at the critical Reynolds number; at this critical regime, the sudden decrease in the lift coefficient value with an increasing angle of attack is sufficient to create negative aerodynamic damping. The galloping instability analysis shows that the occurrence of negative aerodynamic damping strongly depends on the critical flow state. In all cases considered in the present work, the critical Reynolds number effects are shown to include aerodynamic forces that could well be responsible for the whole range of translational galloping instabilities and part range of torsional flutter and 3-DOF galloping instabilities for semi-elliptical cylinders.

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