An investigation on the wake of a cylinder with rotational oscillations

Author

Jia-Da Mo

Date of Award

5-1989

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Aerospace Engineering

Major Professor

J. M. Wu

Committee Members

T. H. Moulden, K. C. Reddy, A. D. Vakili, R. L. Young

Abstract

Analytical, numerical and experimental studies on a rotationally oscillating cylinder with or without a uniform flow have been performed. The analytical solutions were obtained for no on-coming stream. A Stokes layer and the curvature effect of the cylinder on the vorticity generation and diffusion were discussed. In the limit, the solution reduces to the classical oscillatory flat plat flow. For steady or oscillating cylinders in a uniform stream, the flow was numerically solved by taking the Navier-Stokes equation in the form of vorticity and stream function. Shedding of vorticies with or without external excitation of oscillation were discussed. Hydrodynamic forces were computed by integrating vorticity and its normal derivative over the cylinder surface. The results showed that forces acting on the cylinder strongly depend on the oscillation frequency and to a lesser degree with the amplitude. Flow visualization was conducted in a water tunnel for the above conditions. When the forcing frequency was near the natural vortex shedding frequency, the shed vortex in the waive became more organized which qualitatively agreed with the numerical prediction.

This study has proven that a rotational oscillation applied to a cylinder can significantly change the wake flow' structure. A "resonant" flow state is reached when the forced frequency is that of the natural vortex shedding frequency. Both the unsteady lift and drag components reach their maximums when this resonance occur. The time averaged drag is also a maximum at such a state. Results indicated that no additional vorticity is created by the body but the vorticity distribution is altered due to the oscillation. The significant change to the wake flow and the mean values are attributed to the nonlinearity of convection in the waive flow.

Recommended Citation

Mo, Jia-Da, "An investigation on the wake of a cylinder with rotational oscillations. " PhD diss., University of Tennessee, 1989.
https://trace.tennessee.edu/utk_graddiss/11725