Cavity Rotation Research Articles

Experimental study of unsteady thermal characteristics and rotation induced stabilization of air convection in a bottom heated rotating vertical cylinder

Flow stabilization by cavity rotation in convection of air ( Pr = 0.7) in a vertical circular cylinder heated from below is studied experimentally. The cylinder is rotated at a constant speed about its own axis. In the experiment the time variations of the air temperature at selected locations in the cylinder are measured. Results are obtained for a cylinder with diameter D = 5 cm, height H = 10 cm, imposed temperature difference Δ T = 5°C to 15°C and rotation rate Ω from 0 to 346.1 rpm. The experimental data clearly show the stabilization of the thermal buoyancy driven irregular flow by the cavity rotation when the rotation rate is in certain ranges. For a given Δ T two different ranges of Ω exist for the flow to be stabilized. Outside these ranges the flow oscillates periodically or quasi-periodically in time. At given Δ T and Ω the temperature oscillation at various locations exhibits some change in amplitude but negligible change in frequency. However, change of the oscillation frequency with the rotation rate is nonmonotonic and is rather significant at high rotation rates. But this frequency change with the imposed temperature difference is small.

Time-averaged and reverse transition in oscillatory air convection in a differentially heated rotating cubic cavity

An experimental study was carried out to investigate the time-averaged and unsteady thermal characteristics in an inclined cubic air cavity, subject to differential heating across a pair of side walls and subject to rotation about an axis which is normal to the insulated bottom wall and through the geometric center of the cavity. Specifically, the air temperature in the cavity at selected locations was measured for both steady and unsteady flows. Results were obtained for the cavity height H = 10 and 15 cm, temperature difference ΔT ranging from 2 to 10°C, rotation rate Ω from 0 to 452.9 rpm and inclined angle φ from 0 to 90° (heated from below). Time records of the air temperature showed the presence of the flow re-stabilization in two different ranges of the rotation rates. Thus, the transient oscillatory flow can be stabilized by increasing the cavity rotation when the rotation rate is in these ranges. This flow restabilization is more pronounced for a higher inclined angle. Moreover, a power spectrum density analysis of the time records indicated that at low rotation rates the amplitudes of the temperature oscillation are location dependent, but the oscillation frequencies at various locations for a given set of ΔT, Ω and φ are the same.

A combined numerical and experimental study of air convection in a differentially heated rotating cubic cavity

A combined numerical and experimental study was carried out to investigate the steady convective flow structure and the flow stability in an inclined cubic air cavity subject to differential heating across a pair of side walls and subject to rotation about an axis which is normal to the insulated bottom wall and through the geometric center of the cavity. In the numerical simulation the three-dimensional Navier-Stokes and energy equations were directly solved by the projection method for the vertical cavity (φ = 0°). While in the experimental study the air temperature in the cavity at selected locations was detected for both steady and unsteady flows. Results were obtained for ΔT = 10°C and 4.6°C, ω from 0 rpm to 453 rpm and φ from 0° to 75°. The numerical results clearly revealed the complex multicellular flow structure in a vertical cavity at low rotation rates in which the mutual interactions of the thermal buoyancy, Coriolis force and rotational buoyancy are important. The experimental data suggested that the air flow can be stabilized by the cavity rotation when the rotation rate is low. But at high rotating speed the cavity rotation produced destabilizing effects.

Deterministic solution to the inhomogeneously broadened bidirectional ring laser equations with backscattering, asymmetry, and cavity rotation

The third order equations of motion for a rotating, bidirectional, inhomogeneously broadened ring laser at line center with backscattering and asymmetry are solved exactly when the additive noise terms are negligible. The resulting solution for the relative phase of the two counterpropagating modes may exhibit steady state or transient oscillations. For certain initial conditions and operating parameters the phase solution is unstable. This gives rise to deterministic phase jumps in both the transient and steady state behavior. A series of phase jumps occurs if the system repeatedly crosses its unstable boundary. The jumps are multiples of π radians in magnitude, except for the case in which the phase discontinuity is caused by slowly varying operating parameters. Conditions are derived under which the frequency difference between the two modes (i) exhibits the well-known frequency lock-in effect at low rotation rates, or (ii) remains sensitive to cavity rotation regardless of rotation rate (lock-in suppression). Difficulties in achieving the latter result in a practical device are discussed.

Conservation Laws and Energy-Release Rates

New path-independent integrals recently discovered by Knowles and Sternberg are related to energy-release rates associated with cavity or crack rotation and expansion. Complex-variable forms are presented for the conservation laws in the cases of linear, isotropic, plane elasticity. A special point concerning plastic stress distributions around cracks is discussed briefly.