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Force measurements on bluff cylinders and aeroelastic galloping of a rectangular cylinder Santosham, Thomas V.


Dynamic wind tunnel tests were made on plunging rectangular 2:1 and 1/2:1 cylinders and the results were compared with predictions of a quasi-steady theory. The velocity-amplitude and time-amplitude curves for those cylinders which oscillated were recorded. Dynamic tests were also performed on a 2:1 rectangular cylinder with a 10" splitter plate mounted on the wake centerline to prevent the vortex excitation. Direct static force measurements for the Reynolds number range 2 x 10⁴<R(N)<7 x 10⁴ were made for the rectangular 2:1 and 1/2:1 cylinders and the "D" section, using an Aerolab pyramidal strain gauge balance system. The quasi-steady theory used assumes that the instantaneous aerodynamic forces acting on the oscillating cylinder may be approximated by the static forces on the cylinder at an angle of attack equal to the apparent angle of attack of the oscillating cylinder at that instant. The above theory was also extended by including an expression for the vortex excitation. The rectangular 2:1 cylinder for values of critical reduced wind speed U₀ greater than 10 oscillated in agreement with the predictions of the quasi-steady approach. The rectangular 1/2:1 cylinder was found to be a "hard" oscillator as predicted by the quasi-steady theory. By the solution given by the quasi-steady theory the rectangular 2:1 cylinder which exhibits the galloping phenomenon in air flow will not gallop under similar conditions in water flow. In the Reynolds number range considered the static forces on the "D" Section were extremely Reynolds number dependent in the range of the angle of attack 36°<∝<60°.

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