Numerical realization for analysis of real flows by integrating computation and measurement

In this paper, we deal with a numerical realization, which is a numerical analysis methodology to reproduce real flows by integrating numerical simulation and measurement. It is difficult to measure or calculate field information of real three-dimensional unsteady flows due to the lack of an experimental field measurement method, as well as of a way to specify the exact boundary or initial conditions in computation. Based on the observer theory, numerical realization is achieved by a combination of numerical simulation, experimental measurement, and a feedback loop to the simulation from the output signals of both methods. The present paper focuses on the problem of how an inappropriate model or insufficient grid resolution influences the performance of the numerical realization in comparison with ordinary simulation. For a fundamental flow with the Karman vortex street behind a square cylinder, two-dimensional analysis is performed by means of numerical realization and ordinary simulation with three grid resolutions. Comparison of the results with those of the experiment proved that the feedback of the experimental measurement significantly reduces the error due to insufficient grid resolution and effectively reduces the error due to inappropriate model assuming two-dimensionality.