Theoretical validation and experimental calibration of a variable Mach number tunnel with continuous wave-elimination

Abstract

The increasing demand for wide-range aircraft techniques drives the development of variable Mach number test facilities. Existing tunnels can provide uniform flow at design case, but the imperfect wave-elimination at non-design cases leads to insufficient flow uniformity, limited variation range, and complex operation. By applying flowfield inverse design and elasticity inverse design, this paper designs a continuous wave-elimination variable Mach number nozzle. The nozzle is validated by the perfect nozzle theory. By a single jack, the nozzle can deform to the perfect nozzles with different Mach numbers, eliminating the Mach waves continuously and achieving the high-quality test flow. The numerical evaluation validates the design and supports the fabrication of continuous wave-elimination variable Mach number tunnel for the National University of Defense Technology. The flow visualizations by Schlieren and nanoparticle-tracer based planar laser scattering technique indicate no vortices or waves induced by imperfect nozzle geometry. The Mach number calibrations show that the maximum deviations are less than 0.6%, and the standard deviations meet the national advanced standards. These results show that the tunnel eliminates the Mach waves at different Mach numbers through simple operation, providing a wider variable Mach range and a higher flow quality.