# Engineering Mechanics

Proceedings Vol. 32 (2026)

ENGINEERING MECHANICS 2026

Copyright © 2026 Institute of Thermomechanics of the Czech Academy of Sciences, Prague

 

Šnábl P., Procházka P., Skála V.
pages 129 - 132, full text

This paper presents a calibration methodology for an Eiffel-type wind tunnel equipped with a bypass flow system designed for aeroelastic investigations of a blade cascade subjected to a radial flow component. Since flutter onset is highly sensitive to incoming flow conditions, precise and repeatable setting of flow ve- locities in both the main and bypass tunnels is essential. The main tunnel velocity is determined from static pressure differences across the contraction section using Bernoulli’s equation. The bypass tunnel velocity, which cannot be measured directly due to spatial and geometric constraints, is evaluated using particle image velocimetry near the blowing orifice. Velocities are measured across 30 combinations of variable-frequency drive settings of both tunnel fans. A third-order polynomial surface is fitted to the measured data using a least- square minimisation with outlier rejection. To avoid the need for numerical inversion of the fitted surfaces, dense lookup tables with linear interpolation are constructed, and iso-velocity contour diagrams are produced. The resulting calibration tool allows straightforward and reliable identification of fan frequency combinations corresponding to any desired pair of main and bypass tunnel velocities.

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All papers were reviewed by members of the scientific committee.