Investigation of expansion cooling in throttled flow

Abstract

The main objective of this thesis is the presentation of joint numerical and experimental data for the flow field and heat transfer in a supersonic expanding Argon gas jet confined within a rectangular pipe, driven by a pressure ratio of 120. The numerical part of the study has been carried out via a single phase large-eddy simulation(LES) employing a fully-coupled, pressure-based finite volumes compressible flow solver. This solver is based on a novel framework starting from an existing pressure-based and fully-coupled finite-volumes formulation for incompressible Navier-Stokes equations. Additional implementation of pressure-density-energy coupling as well as shock-capturing leads to a framework capable of efficiently solving flow problems at all Mach numbers. The proposed numerical methodology features an implicit coupling of pressure and velocity, which improves the numerical stability in the presence of complex sources and equations of state, as well as an energy equation discretised in conservative form that ensures numerical stability and an accurate prediction of temperature and Mach number across strong flow gradients. This newly developed framework is extensively validated by a large number of test cases, demonstrating the accurate simulation of steady-state and transient flows in a vast range of flow speed regimes on complex geometries. It is then applied to carry out the numerical study for the expansion cooling problem of an expanding Argon gas jet.

The numerical data for the confined Argon jet are compared with experimental measurements of fluid velocity and temperature taken under the same physical conditions. Since the compressed gas is placed at extremely high total pressure of over 100 bars, real gas phenomena such as the Joule-Thomson effect are to be expected during the expansion process and are accounted for in the numerical model via the use of a cubic real gas equation of state. The experimental data consists of Schlieren imaging and fluid measurements which are obtained using thermographic particle image velocimetry(PIV) technique permitting the simultaneous determination of fluid velocity and temperature values. First and second order flow statistics from the experimental measurements and numerical simulations are presented; and by using the available data, an one-dimensional analysis is carried out to study wall-fluid heat transfer. The methods presented in this thesis have led to a detailed understanding about the aerodynamics and thermodynamics of an extremely challenging real gas flow configuration.