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 actual construction of the control panel for the expansion tube was an adventure from drilling the frame with a handheld drill to cutting out the front panel with the water jet cutter. Our team met challenges in bending pipe and wiring the pressure gages. While it isn't quite done yet, the control panel is becoming a well designed piece of equipment that will be used by students for years to come.
An expansion tube is an impulse flow device for studying supersonic flow. The applications of supersonic flow research are primarily in the field of aeronautical engineering for military jets, space shuttles, and rockets; however, supersonic conditions also occur in some turbines.
I designed the control panel for the expansion tube over the summer. I tried to match the layout of the control panel to the layout of the tube. The panel includes almost all of the valves for controlling gasses in the tube, power wiring for vacuum pumps, and displays for the pressure gages.
The viewing section for the expansion tube needed to be designed to let us study supersonic flow over a test object. It was designed with fused silica windows, half inch thick welded stainless steel sides, and a removable side. Because cubes are not typical ASME pressure vessels, much work was put into developing a safe viewing section, even though it will typically never see positive pressures.