Experimental Validation of a 1D Modelling Code for a Pipe Containing Gas of Varying Properties 950275

This paper reports on the experimental evaluation of certain aspects of the mathematical modelling by the GPB method of pressure wave propagation through finite systems, of unsteady gas flow in engine ducting. The aspects under examination are the propagation of pressure waves through a pipe which contains gases of dissimilar properties. In this case the gases are carbon dioxide and air.

The experimentation is conducted using the QUB SP (single pulse) pressure wave generator consisting of a cylinder, connected via a sliding valve to a long duct. The pressure waves it creates closely mimic those to be found in i.e. engines. The initial cylinder pressure may be set to simulate either an induction or an exhaust process, but the experiments reported here are of compression waves only. The duct attached to the pressure wave generator is a straight pipe. The cylinder and part of the pipe are filled with carbon dioxide and air. Pressure and temperature are recorded by transducers positioned at various locations in the apparatus and stored using a high speed data acquisition system. The duct is sufficiently long, and the pressure transducers so located strategically, that the pressure records show wave effects without confusion from superposition.

A computer simulation of the test apparatus has been written using the GPB modelling technique incorporating The Queen's University of Belfast (QUB) non-isentropic treatment of all boundary conditions. The accuracy of the predictive method is assessed by correlation with the experimental results. The GPB computer code produces good correlation for unsteady flow in a constant area duct containing the test gases which have very different properties. It is demonstrated that a computer code not capable of including variable gas properties within the solution will introduce very significant errors with respect to the measurements.

It has been shown in previous papers that the speed of computation of the GPB code closely rivals that of the Lax-Wendroff (LW+FCT) method. It has been reported that the computation time for the latter method can be 1.6 to 5 times slower when accurately calculating the inclusion of variable gas properties, whereas that for the GPB code is unchanged due to their automatic inclusion.