Aerodynamic Design of the Hyperloop Concept

1 Aerodynamic Design of the Hyperloop ConceptMax M. J. Opgenoord and Philip C. Caplan Massachusetts Institute of Technology, Cambridge, MA, 02139 The Hyperloop is a ground-based transportation system Concept slated to drasticallyreduce travel times over medium range distances, for example between San Francisco andLos Angeles. This paper discusses Aerodynamic Design considerations for the Hyperlooppod. A Hyperloop capsule travels in an unconventional flow regime very low Reynoldsnumbers with high Mach numbers which brings with it unique challenges.

2 This workfocuses on the Aerodynamic Design of the MIT Hyperloop pod. For this Design , it is crucialto delay separation over the pod as much as possible by forcing the boundary layer totransition further upstream, resulting in a droplet shape for the Aerodynamic shell. Theperformance of this Design is investigated for nominal flow conditions, as well as for flowconditions close to the Kantrowitz limit. The overall Design of this team s Hyperloop podwon the Design competition of the spacex Hyperloop competition in January areaApodFrontal area of podAtubeCross-sectional area of tubeCDDrag coefficientCpPressure coefficientHShape parameterKnKnudsen numberMextExternal Mach numberM Freestream Mach numberNcritLaminar instability amplitude expo-nent at which transition occursPMomentum defectReReynolds numberRe Reynolds number based on momen-tum thicknessV Freestream velocitylReference

3 LengthptubeTube ambient pressuretTime tNon-dimensional timeueVelocity at edge of boundary layery+Dimensionless wall distanceSymbols Lam e parameter Free stream density eDensity at edge of boundary layerI. IntroductionTheHyperloop is a Concept for high speed ground transportation, where passenger pods travel at transonicspeeds in a partially evacuated tube. The Concept was originally proposed in a white paper publishedby spacex in 2013 [1] as an alternative to the high-speed rail system currently being developed between LosAngeles and San Francisco, which was deemed too expensive and Hyperloop Concept could fill a growing need for an alternative transportation mode for short-haultravel.

4 For short routes, such as Los Angeles San Francisco, or Boston New York, the time spent traveling byaircraft at cruise speed is quite low compared to overall end-to-end travel time due to inescapable inefficenciesin air travel (runway taxiing, climb, descent, holding patterns, etc.). The high-frequency throughput ofHyperloop pods could alleviate some of these inefficiencies. Recently, KPMG published a preliminary studycommissioned by Hyperloop One one of the companies commercializing the Hyperloop Concept on the Graduate student, Department of Aeronautics and Astronautics, Team Lead & Aero/Structures Lead, MIT HyperloopTeam, Student Member AIAA Graduate student, Department of Aeronautics and Astronautics, Aero/Structures Engineer.

5 MIT Hyperloop Student Member AIAA1 of 18 American Institute of Aeronautics and AstronauticsHelsinki Stockholm corridor where they found that the Hyperloop could cut down end-to-end travel timeby 75% to 28 minutes [2].Momentum is growing in the Hyperloop movement, with a number of newly founded companies attempt-ing to commercialize it. In addition, spacex is sponsoring a student competition to encourage innovationand to help accelerate the development of a working prototype, starting June 1,000 teamssubmitted their intent to compete, and over 100 teams made it to Design Weekend in January 2016.

6 Thestudent team from the Massachusetts Institute of Technology the MIT Hyperloop Teamb won first placeoverall in that Design weekend [3]. The Aerodynamic Design of that team s prototype is the subject of research into the Hyperloop Concept has focused mostly on system integration. A conceptualsizing tool using the OpenMDAO framework [4] focuses primarily on the Aerodynamic and thermodynamicinteractions between the pod and tube, with recent work focusing on the energy consumption of the system[5]. The pods for the spacex Hyperloop competition were the first physical prototypes of the Hyperloopconcept.

7 Recently, one team reported on their Aerodynamic Design [6]. For that Design , a low-fidelityaerodynamic model was used to optimize the outer mold line, which was subsequently analyzed using athree-dimensional RANS solution with a turbulence paper describes the Design approach for the Aerodynamic shell used by the MIT Hyperloop Team. Forrapid Design iterations, we use an axisymmetric viscous/inviscid coupled boundary layer method to accuratelypredict flow separation and transition.

8 The final Design is then analyzed using a three-dimensional CFDsolver, which is also used to characterize the aerodynamics at higher velocities to investigate the potentialissues related to Hyperloop pods traveling through a partially evacuated tube at transonic II discusses historic background of the Hyperloop Concept , as well as the spacex Hyperloopcompetition. Section III explains the Design philosophy chosen by the MIT Hyperloop team, as well as abrief overview of the overall pod Design .

9 Section IV then describes the Aerodynamic Design V focuses on the final Aerodynamic Design and its performance for different flow BackgroundThe Hyperloop Alpha white paper [1] combined several historic concepts for magnetically-levitating trains[7 9] and spurred a great deal of public interest in the Concept , something the earlier ideas were somewhatlacking. This white paper discusses a Hyperloop pod that travels at 1220km/hin a partially evacuated tube(1/1000th of atmospheric pressure) levitating using air bearings.

10 The use of wheels at these high speedswould be quite problematic because of the massive centripetal forces on them. Air bearings are proposedas a more efficient mechanism, where the pod floats on a thin film of compressed air. In the HyperloopAlpha Concept , this compressed air is supplied by an onboard compressor. Propulsion is provided by a linearinduction motor. The benefit of this is that the heavy components are built track-side and the pod only hasto carry a rotor which makes the propulsion quite efficient.