Condensation shock topologies in carbon dioxide and a non-condensable gas mixture in supersonic nozzles

Abstract

Condensation shock waves may occur in many flow expansion devices such as turbomachinery, gas ejectors, micro thrust-nozzles, and supersonic gas flow separators. However, their experimental analysis has been barely addressed as condensation shocks comprise complex phenomena such as compressible flow behavior, a shock-like phase transition, and a two-phase flow expansion. This work characterizes experimentally some condensation shock topologies of a mixture of carbon dioxide and dry air at several compositions in a Laval nozzle. Experiments were carried out in a test-rig instrumented with high-response pressure transducers installed along the Laval nozzle wall along with a Schlieren setup equipped with a high-speed video camera imaging the flow behavior within the nozzle. The nozzle wall profile was built by using the method of characteristics developed from a real equation-of-state suited for the testing mixture. Results revealed the influence of the nozzle wall profile on the condensation shock location and topology. Moreover, there types of flow behavior were captured and named as conventional, transition, and Mach wave condensation shocks. The transition from one topology to another occurred due to the interaction between cancelation waves originated from the nozzle wall and the phase-change phenomenon, giving rise to two distinct regions characterized by certain observable droplet population density. The current investigation presents an in-depth phenomenological discussion of the three types of condensation shock topologies as such assessment has not been previously developed.