The new Mach number regulation at S1MA, sponsored by the European FP7-ESWIRP project, implements two complementary regulation components.
These components are the wind tunnel contra-rotating fans and in addition a dedicated variable air inlet located upstream of the fans.
A very precise identification of the various transfer functions affecting the Mach number drift has been established. An optimal trade-off between the fan speed and the air intake opening was implemented in the control algorithm. The Mach number drifts in polar process have consequently been drastically reduced.
These drifts are now in the same order of magnitude as the natural Mach number fluctuations of the wind tunnel in steady state conditions. Thus at Mach number 0.85, drift does not exceed ± 1.2/1000 that it is to say a reduction by a factor of 10 compared to the previous situation from 2006. The new regulation remains efficient up to Mach 0.97 where the drift does not exceed ± 5/1000.
The additional polars to a test matrix necessary to interpolate the load measurements are no longer needed. Productivity of the wind tunnel has been improved by 25 to 30% for the test phases. The data quality is also affected for data which cannot be interpolated: pressure distributions, acoustic measurements and various dynamic measurements. This new Mach number regulation system is now used as standard in S1MA, which reinforces the attractivity of this wind tunnel.