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is bring it to the forefront of the public interest. Just as the Tesla roadster breathed new life into the largely stagnant electric car industry, and the inexpensive and reusable rockets of SpaceX forced established launch companies to reconsider their design philosophies, the Elon Musk stamp of approval has allowed evacuated tube transportation to quickly progress from a collection of disparate engineering concepts to a coherent segment of academic research and industrial innovation. With the creation of the MIT Hyperloop team, almost 200 other university teams, and two successful startups, the Hyperloop concept is rapidly transitioning from idea to reality.

AERODYNAMIC CHALLENGES AND ANALYSIS The overall concept of the Hyperloop raises several interesting scientific challenges capable of endlessly tickling the curiosity of engineers. As a team, we needed to determine which of these challenges were relevant to the competition put forth by SpaceX. For example, the full-scale Hyperloop would need to overcome the so-called “Kantrowitz limit.” This limit is reached when the flow around the pod reaches the speed of sound. No additional air would be able to pass over the pod (a concept called “choking”) and the aerodynamic drag would increase dramatically as the pod continued to accumulate the air ahead of it. In other words, air would be trapped in front of the pod and, over time, it would be pushing an entire column of air in front of it, instead of floating through it. Some back-of-the-envelope calculations for the tube geometry and of our preliminary design revealed we were safe from the Kantrowitz limit for this competition. On the topic of aerodynamic drag, we also needed to tweak our design over the course of the competition due to changes in the minimum tube pressure SpaceX could provide. Initially at 130 Pascals, we were confident that the aerodynamic drag was insignificant relative to the levitation drag induced by the magnetic skis. The change to a minimum tube pressure of 860 Pascals meant the flow regime over the pod would be a combination of both laminar and turbulent flow. As astute students of AeroAstro Professor Mark Drela’s course on viscous fluids, we turned to his software MTFLOW to model various axisymmetric profiles and determine which geometry would reduce the flow separation behind the pod and avoid excessive laminar separation bubbles, known to negatively impact drag. We also used MTFLOW to model the effects of “boundary layer tripping,” which essentially keeps the boundary layer attached to the pod as long as possible, thereby minimizing the drag induced by flow separation. This is the same concept behind the dimples you see

SPECIAL SECTION

Student Projects: tiny rocket drones, hyper-speed transport, a composite rocket, and a lunar orbit competitor

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MIT AeroAstro annual magazine 2015-2016Aeroastro 2015 16  

Annual magazine review of MIT Aeronautics and Astronautics Department research and educational initiatives.

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