Describing function analysis of density wave oscillations

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1984

OSTI ID:5225650

Lee, S C

Density-wave oscillation (DWO) is a form of low-frequency flow instability that can occur in all the two-phase flow systems satisfying a constant pressure-drop boundary condition. In this thesis, DWOs are investigated using the describing function (DF) method, which extends the linear frequency-domain analysis to nonlinear systems, yielding information on the frequency and magnitude of periodic oscillations, or limit-cycles, that can occur in nonlinear systems. The proposed nonlinear model for the DWO considers only those nonlinearities that enter the calculation of the pressure drops in terms of flow velocity and density variations, in the implementation of constant pressure-drop boundary conditions. The model was applied to the interpretation of the experiments by Takitani et al., in which the two-phase flow system is linearly stable but yet displays periodic density wave oscillations. It is found that the period of these oscillations can be reproduced by the DF method if the nonlinear terms in the model are multiplied by a factor of the order of 2 or 3. It is also found that the DF method with the proposed nonlinearity satisfactorily reproduces, without any modifications, the period of DWO in two-phase flow systems that are linearly unstable, such as the cases in the Sandia 5-tube test and the ANL sodium-heated steam generator test.

• Research Organization: Michigan Univ., Ann Arbor (USA)
• OSTI ID: 5225650
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
420400* -- Engineering-- Heat Transfer & Fluid Flow
BOILERS
BOUNDARY CONDITIONS
FLUID FLOW
INSTABILITY
NONLINEAR PROBLEMS
PRESSURE DROP
STEAM GENERATORS
TWO-PHASE FLOW
VAPOR GENERATORS