Completion of Bethel's Shock Tunnel

For the past few years, the Bethel Physics department has had many students collaborating towards the goal of a shock tunnel with airflow speeds of up to mach 3.5. The purpose of the tunnel is ultimately to analyze supersonic airflow around objects of research interest. Through the efforts of students and faculty, the tunnel has gone from an idea, to a design, to fabricated parts, to a fully operational research tool.

During the spring semester of 2007, some students in Dr. Stein's fluids class worked on the design of the shock tunnel as a lab project. Matthew Freeland continued working on the specifics of the design including the nozzle specifications utilizing in depth computational modeling and analysis over the summer of 2007. Using Freeland's suggested dimensions, Tim Johnson worked on the early assembly of the shock tunnel, fabricating some parts himself and contracting a local company to machine the more intricate components (i.e. the nozzle) during the 2007-2008 school year. At the end of the 2008 spring semester, the shock tunnel resided in the Carlson Analysis Center as an open-ended tube.

The summer of 2008 marked the final assembly of the shock tunnel. Justin Knapp and Jack Houlton worked on the installation of sensitive pressure sensors along the length of the tube. A local fabricator was employed to finish the construction of the nozzle, test section, and dump tank. Finally, the shock tunnel was assembled, ridded of leaks, and ready for full operation. Being joined by Brandon Peplinski and David Swenson the summer research team worked on imaging the shock wave produced by the open-ended tunnel using thorough shadowgraph testing and simple Schlieren techniques.

The tunnel consists of the following five major components: driver, driven section, nozzle, test section, and dump tank. A diaphragm and gaskets isolate the driver and driven sections so that a pressure difference can be established between the two sections. When the diaphragm ruptures, the air masses travel down the driven section towards the dump tank as a shock wave. This apparatus sustains supersonic flow conditions for several milliseconds.

Over the 2008-2009 school year, the now constructed shock tunnel was available for use in senior research projects. Andrew Rice and Jonathan Dallmann were the first to carry out senior research on the assembled tunnel. Andrew was able to perfect shock wave detection and timing while Jonathan used shadowgraph imaging to reveal how the shock wave enters the test section. This summer Jack Houlton and Nathan Youngblood are experimenting how the shock wave interacts with blunt objects in the test section. Eventually the shock tunnel will be used to see how different models behave in supersonic environments and will be available as a teaching tool for future fluids classes and as a subject of research.

--Jack Houlton and Nathan Youngblood