Accession Number : ADA189500

Title :   Application of a Flux Vector Splitting Methodology towards the Solution of Unsteady Transonic Flows, with Future Emphasis on the Blade Flutter Problem.

Descriptive Note : Final rept. Aug 86-Aug 87,

Corporate Author : NAVAL POSTGRADUATE SCHOOL MONTEREY CA

Personal Author(s) : Fransson, Torsten H

PDF Url : ADA189500

Report Date : Jul 1987

Pagination or Media Count : 256

Abstract : This study presents a method, based on the flux vector splitting approach, to the problem of unsteady two dimensional inviscid transonic flows, with emphasis on the numerical determination of the shock position, through nozzles with varying back pressure. The method, governed by Euler equations, is first explained for one and two dimensional steady state applications, and the accuracy of the results is validated by comparison with exact (one dimension and numerical (two dimensions) solutions. The model is then applied to the problem of fluctuating back pressure in quasi one dimensional and two dimensional flows. The one dimensional results are validated by comparison with a small perturbation analytical unsteady solution, whereafter sample cases are performed with the objective to understand fundamental aspects of unsteady flows. It is concluded that both the amplitude and frequency of the imposed fluctuating exit pressure are important parameters for location of the unsteady shock. It is also shown that the average unsteady shock position is not identical with the steady state position, and that the unsteady shock may, under certain circumstances, propagate upstream into the subsonic flow domain. The pressure jump over the shock, as well as the unsteady post-shock pressure, is different for identical shock-positions during the cycle of fluctuation, which implies that an unsteady shock movement, imposed by oscillating back pressure, may introduce a significant unsteady lift and moment. This may be of importance for flutter predictions.

Descriptors :   *TRANSONIC FLOW, *UNSTEADY FLOW, *VECTOR ANALYSIS, *NOZZLE GAS FLOW, *INVISCID FLOW, ACCURACY, BACK PRESSURE, BLADES, COMPARISON, CYCLES, DIFFERENTIAL EQUATIONS, EXITS, FLUTTER, FLUX(RATE), METHODOLOGY, NOZZLES, ONE DIMENSIONAL FLOW, OSCILLATION, POSITION(LOCATION), PREDICTIONS, PRESSURE, SHOCK, SPLITTING, STEADY STATE, SUBSONIC FLOW, VALIDATION, VARIATIONS, COMPRESSIBLE FLOW, TWO DIMENSIONAL FLOW, COMPUTATIONS, FLUID DYNAMICS

Subject Categories : Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE