Theoretical and Numerical Study of a Preheated Ludwieg Tube with Adiabatic Compression

Abstract

This paper describes a novel hypersonic facility to reproduce the high stagnation pressures and temperatures necessary for the accurate simulation of hypersonic flows in the range Mach 5–7, while providing test times sufficiently long to study unsteady flow effects. The facility uses a preheated Ludwieg tube together with a piston-compression stage to generate reservoir temperatures difficult to achieve with electrical heating alone, but also avoiding the introduction of vitiation contaminants. The absence of shocks in the generating flow is expected to lead to increased flow quality while also providing longer test times compared with shock-driven facilities of comparable size. The operational concept is described and a condition for optimal operation is defined based on minimizing the dimensions of the heated section for a given set of desired flow conditions. A simple theoretical treatment shows that this condition constrains the ratio of the nozzle exit and Ludwieg tube diameters, assuming accurate simulation of flight conditions. A method-of-characteristics solver is used to determine the constrained facility parameters more accurately. Modeling of the unsteady adiabatic compression cycle is performed with quasi-one-dimensional finite volume computations, and various configurations are explored to minimize the pressure oscillations generated during compression.