Theory, Design, Construction, and Testing of an Expansion Tube
The Lafayette College Expansion Tube is a two-stage dynamic flow expansion device that was designed and built during 2014 and 2015 at Lafayette College to study supersonic flow. Supersonic flow is studied to achieve more efficient or faster flight for jets and spacecraft, and advances in combustion of scramjet engines have the potential to drastically reduce the cost of spaceflight. Expansion tubes are used to study combustible hypersonic flow because they are able to generate higher Mach numbers than shock tubes and do not push the fluid through stagnation conditions as a supersonic wind tunnel would.
The expansion tube is a long tube similar to a shock tube with four sections: the driver, double diaphragm, driven, and expansion sections. The sections are initially separated by plastic diaphragms and pressurized separately. The diaphragms are ruptured to create a unsteady expansion and compression waves, which travel down the tube into a viewing section.
The tube was designed to generate high enthalpy flows at Mach numbers between 2 and 8. Predicted test times are 100µs to 800µs with shorter test times for faster flows. The tube has been designed to maximize test times for conditions of interest. Conditions in the tube will be measured using high-speed pressure sensors, infrared sensors, and Schlieren imaging.
The tube has been designed and manufactured, but assembly of the tube and surrounding piping and instrumentation is still in progress. Test procedures are planned for calibrating models to the tube by determining whether the flow appears to be inviscid, laminar or turbulent in various conditions.