Mixing of Thermally Stratified Gas in Horizontal Tube Using Shock Waves Research Methodology

Mixing of Thermally Stratified Gas in Horizontal Tube Using Shock Waves Research Methodology

A Ludwieg tube can be equipped with a heating system to enable higher Mach number hypersonic wind tunnel tests. However, if axial nonuniformities are present in the temperature distribution, buoyancy effects cause nonuniform temperature distribution in the radial direction making the test conditions suboptimal. To mitigate the problem, it is proposed that the test gas can be pre-mixed by shock waves generated by oscillating a free piston inside the barrel. Two piston oscillation cases were simulated: (1) harmonic oscillation at 10 Hz; and (2) an oscillation in which the stroke is completed in 24 ms, but is repeated only once every second. CFD simulations of pistons oscillating with peak speeds approaching 20 m/s have shown that the shock waves are slightly oblique and have capacity to initiate mixing. Simulations demonstrate that the majority of the mixing occurs within just the first few seconds, although, significant temperature gradients may persist near the walls due to convective heat transfer. Nevertheless, the mixing method has shown promising simulation results and physical experiments are now being planned to assess the practical viability of the method.