Test-Model-Induced Interference Effects in Expansion Tube Flows

A study is conducted to report observations of nonideal operation of expansion tubes that results in undesired properties in the test gas. The investigated interference effects result from the interaction of the initial unsteady flow with models located in the test section, and induces a significant increase in test gas pressure and temperature at the beginning of the test time. The study investigates the mechanism for the onset of such flow disturbance using a combined experimental, computational, and analytical approach. A series of experiments and computer simulations using ANSYS CFX have been carried out to gain insight on the cause of the pressure overshoots and reach the conclusions.