Numerical and experimental studies of bluff bodies in tandem in presence of rotating cylinder flow control
Student thesis: Doctoral Thesis
The rotating cylinders flow control method was applied to several two-dimensional two-body model sets by using high speed spinning cylinders as momentum injecting devices. In all cases, two bluff bodies in various dimensions were arranged in tandem and each side edge of the downstream body was replaced by a rotating cylinder. The effects of width ratios, spacing ratios and cylinder rotation ratios on control effectiveness were extensively studied by numerical simulations and wind-tunnel tests. Computational fluid dynamics (CFD) simulation was developed to simulate bluff body fluid dynamics in the presence of rotating cylinders. Sensitivity tests for simulations were performed to determine the least minimum length of grid edge for computational domain and the choice of time step in simulations. After comparing simulation results from RNG (Re-Normalization Group) k-Ɛ with LES and several other turbulence models, the RNG k-Ɛ turbulence model was chosen for the present CFD simulations. A series of two-dimensional CFD simulations with RNG k-Ɛ turbulence model and finite volume meshes with an adequate number of grid points were performed and extensive wind-tunnel investigations were carried out to examine the characteristics of the wake flow in the presence of rotating cylinders. Data were obtained for two Reynolds numbers of 1.67×104 and 2.52×104. Two values of width ratio (1.0H1 and 1.5H1), three values of spacing ratio (0.5H1, 1.0H1 and 1.5H1) for each width ratio and six values of cylinder rotation ratio (from Uc/U∞ = 0 to 5.0) for each spacing ratio, amounting up to a total thirty-six cases were considered for numerical simulations and experimental tests, respectively. Comparison of numerical and wind-tunnel velocity results showed narrowing of the wake and suppression of vortex shedding with increase of rotor speed. Computed results and profile changing trends compared were in good agreement with measurement results. The pattern changes in distributions of surface pressure on the two bodies, simulated base pressures and drag coefficients of the rear body, the computed velocity profiles in the vicinity of the upper rotor, as well as the Strouhal number indicated the dependence of the flow control effect on the two-body system on width ratio, spacing between the pair of obstacles and cylinder spinning speed. From results mentioned above, it could be concluded that the effectiveness of the rotating cylinder flow control method stands confirmed.
- Fluid dynamics, Data processing