Date of this Version
Center for Turbulence Research Annual Research Briefs 2012.
1. Motivation and objectives
The Electric Arc Shock Tube (EAST) facility at NASA Ames Research Center is used to generate high-enthalpy gas tests for studying high-speed atmospheric entry physics. The facility is composed of a long tube and a chamber. In the chamber, which contains a driver gas, an electrical discharge takes place, giving rise to a sudden increase of the gas temperature and pressure. The chamber’s geometry can be approximated as a 10- cm cylindrical tube though its real geometry is more complex and not axisymmetric. An aluminum diaphragm separates the driver from the driven gas. At the high pressure generated by the discharge, the diaphragm bursts, forming a shock wave that travels at high speed through a long cylindrical tube, 10 cm in diameter. As the shock propagates downstream, the shock-heated gas radiates, and in a test section emission spectroscopy is used to determine the radiative signature and thereby the thermo-chemical and radiative properties of the medium.
The experiments being simulated here make use of helium as a driver gas and synthetic air (N2 + O2) as a test gas (or driven gas). The shock velocities obtained in EAST experiments range between 9 and 16 km/sec. The distance between the diaphragm and the test section is 7.0 m. At the test section the spectrally and spatially resolved shocklayer radiance is analyzed by taking a snapshot of the shock wave and the following gas as they pass in front of an optical access window.
It is important to note that optically probing the shocked gas does not provide any information about the radial structure of the flow in the shock tube. The experiments only provide integrated measurements that include all the absorption and emission across the tube. Experimental data processing currently conducted at NASA Ames takes the flow to be one-dimensional, and any boundary layer effects are neglected. In reality, however, viscous effects may significantly impact the interpretation of the tests. To make better use of the flow radiation measurements one needs to know the radiative properties within the boundary layer, which can be estimated by numerical simulations.