Newsletter 2021.11 Index
Theme : "Mechanical Engineering Congress, 2021 Japan (MECJ21)”
Workshop on Experimental Fluid Dynamics (EFD)

Integration method of measurement and simulation in flow analysis and its applications

Abstract
In order to obtain information on real flows, extensive studies have been carried out on methodology to integrate measurement and simulation, for example, the fourdimensional variational data assimilation method or the state estimator such as the Kalman filter or the state observer. Measurementintegrated (MI) simulation is a state observer in which a computational fluid dynamics scheme is used as a mathematical model of the physical system in state observers. In MI simulation the computational result of the model flows converges to the state of the real flow by the effect of the feedback signal or the artificial force to compensate the difference between the model and real flows. Figure 1 shows the hybrid wind tunnel by which the Kalman vortex in a wind tunnel is analyzed by the server in real time. As shown in Fig. 2 the flow structure is properly reproduced by MI simulation including the phase of the oscillation. Medical application of MI simulation is shown in Fig. 3. In twodimensional ultrasonicmeasurementintegrated (UMI) blood flow analysis system, blood flow simulation is performed by applying the feedback signal based on measurement of the Doppler velocity, velocity component of the blood flow along the ultrasound beam. As shown in Fig. 4 (b) complex blood flow in a carotid artery is properly reproduced in MI simulation while a simple Poiseuille flow was obtained by an ordinary simulation in Fig. 4 (a). By comparing the Doppler velocity measured values with the calculated values, the error of the Doppler velocity was reduced by about 1/3 compared with the ordinary simulation in the UMI simulation. These results show that complex blood flow fields can be reproduced with high accuracy by UMI simulation.
Key words
Computational Fluid dynamics, State observer, Measurementintegrated simulation, Karman Vortex, Blood Flow
Figures
Fig. 1 Realtime analysis of Karman vortices with a hybrid wind tunnel
Fig. 2 Streak lines obtained with (a) experiment and (b) MI simulation
Fig. 3 Twodimensional ultrasonicmeasurementintegrated (UMI) blood flow analysis system
Fig. 4 Analysis results of blood flow in a carotid artery with (a) ordinary simulation and (b) UMI simulation