Publications

Dependence of calculated postshock thermodynamic variables on vibrational equilibrium and input uncertainty

Campbell, Matthew F.; Owen, Kyle G.; Davidson, David F.; Hanson, Ronald K.

The purpose of this article is to explore the dependence of calculated postshock thermodynamic properties in shock tube experiments upon the vibrational state of the test gas and upon the uncertainties inherent to calculation inputs. This paper first offers a comparison between state variables calculated according to a Rankine-Hugoniot-equationbased algorithm, known as FROSH, and those derived from shock tube experiments on vibrationally nonequilibrated gases. It is shown that incorrect vibrational relaxation assumptions could lead to errors in temperature as large as8% for 25% oxygen/argon mixtures at 3500 K. Following this demonstration, this article employs the algorithm to show the importance of correct vibrational equilibration assumptions, noting, for instance, that errors in temperature of up to about 2% at 3500 K may be generated for 10% nitrogen/argon mixtures if vibrational relaxation is not treated properly. Finally, this article presents an extensive uncertainty analysis, showing that postshock temperatures can be calculated with root-of-sum-of-square errors of better than ± 1% given sufficiently accurate experimentally measured input parameters.