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Title: Computation of unsteady flow by time-marching methods
Author: James, M. N.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1982
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Finite amplitude wave motion in an inviscid, subsonic, perfect gas medium is analysed by explicit finite-difference methods. A series of one-dimensional problems are used to examine the accuracy of the algorithms when applied to unsteady flow regimes. Computations are carried out in two space dimensions using a two-step, Lax-Wendroff algorithm. The computed flow field has similarities with that which occurs in the vicinity of an isolated rotor in an axial-flow compressor stage. The rotor effect is simulated by prescribing either a velocity or a pressure disturbance along a single row of grid points normal to the stream direction and results in 'forced' outflow boundary. Particular emphasis is placed on devising a simple non-reflecting, far-field inflow boundary treatment. This is achieved by using a streamwise expanding grid to place the inflow boundary at a large distance from outflow in a position where wave amplitudes are negligible. The side boundaries are spatially periodic. The computed solutions are compared with analytical, small-perturbation solutions; higher-order effects arising from non-linearities are revealed by Fourier analysis. Solutions which closely approached a periodic state were obtained. The two-step Lax-Wendroff method combined with the expanding grid is shown to be accurate and stable. The use of the computational procedures for the accurate resolution of unsteady flow through a turbo-machinery cascade is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available