NPS student operational insight and faculty collaboration advances hypersonics applied research

ByMatthewSchehl Naval Postgraduate School

In a small area 4 inches by 4 inches to beprecise inaNavalPostgraduateSchool (NPS)researchlaboratory,auniquely-capablefacilityissupportingfoundationalhypersonics research and preparing U.S. Navy and MarineCorps officers toadvance, integrate,andemploytheseaservices’emerging hypersoniccapabilities

Under the leadership of NPS’ Mechanical and Aerospace Engineering (MAE) department and with sponsorship by the Office of Naval Research, recent improvements in the NPS Supersonic Wind Tunnel (SSWT) laboratory have made the facility fully capable of conducting long duration high supersonic testing and experimentation, advancing NPS’ support to the Navy’s ForceDesignimperatives asoutlinedinthe Chief of Naval Operations’ (CNO) NavigationPlan(NAVPLAN)2022.

“Hypersonicsystemsprovideacombination of speed, maneuverability and altitude that enable highly survivable, long-range, rapid defeat of time-critical, heavily-defended and high-value targets,” CNO Adm. Mike Gilday commented during an early 2022 visit to industry partners developing hypersonictechnologies “Deliveringhypersonic weapons continues to be one of the Navy’shighestpriorities,whichtheNavigationPlanmakesclear.”

“Ourresearchcapabilityisuniqueamong academic institutions in the United States,” said Dr. Garth Hobson, MAE professor and PrincipalInvestigatorfortheSSWT “You’d have to go to NASA or the big Air Force research laboratories to match these capabilities Wecanrunthewindtunnelforhalf an hour at a time at Mach 4 and that allows ustodoverymeaningfulexperimentation.

Thiscapability,combinedwithNPS’abilitytoconducthighly-classifiedresearchand the intellectual and operational capital of its faculty and officers, positions NPS to be a critical enabler in meeting future force requirementsintherealmofhypersonics

In recognition of its role in educating mid-career officers in warfighting applications and applied hypersonics research, on Dec 8, 2022, NPS was officially welcomed intotheUniversityConsortiumforApplied Hypersonics (UCAH), a collaborative network of more than 100 universities and 150 industry partners actively working in thefield.MembershipinUCAHhasalready bornefruit,withcollaborativeeffortsunderwaybetweenNPS theUniversityofArizona and North Carolina State University initiatedthroughthisengagement

“Membership in UCAH opens up a wide spectrumofopportunitiesforNPStoengage in basic and applied research essential to helping the United States remain competitivewithouradversariesinthischallenging discipline,” stressed Dr Kevin Smith, NPS ViceProvostforResearch

“The national effort in hypersonics will undoubtedly generate advances in many existing and new technologies with applicationsthatcanhelpsolveoperationalproblems of warfighting,” he continued. “NPS participation in UCAH can help accelerate thetransitionofthesetechnologiestooperationalapplications.”

Supersonic vs Hypersonic

A Mach number is generally understood as the ratioofairspeedtothe local speedof sound: “Mach 2” refers to twice the speed ofsound;“Mach3”isthreetimes,andsoon

The speed of sound, however, is not a constant. The “local” speed of sound depends on a variety of factors including thealtitude temperatureanddensityofthe surrounding air For example, the speed of sound at sea level at 59 degrees Fahrenheit is 761 miles per hour. At a height of 20,000 meters and minus 70 degrees Fahrenheit, it’s 660 miles per hour. The term “supersonic” refers simply to a speed higher than thespeedofsound. At high speeds around Mach 5, however, thingsgetratherpeculiar Thesurrounding air molecules break apart and turn into an electrically-chargedplasmawiththekinetic energyoftheaircraftchangingtoheat,yieldingintensevariationsinairdensityandpressure that materialize through a series of shockwavesandexpansions

Thisishypersonicspeed

“Something becomes hypersonic when it’s in air that can no longer be treated as ‘perfect. Thingsstarttoreactandyoustartto worry about how hot things get, explained Ben Nikaido, a computational fluid dynamics expert with NASA’s Ames Research Center who is working on his doctorate at NPSwiththeSSWTteam.

“There really is no absolute line in the sandthatsayseverythingbeyondthisspeed is hypersonic and below it is supersonic It’s a large gray area with a lot of overlap,” Nikaido explained. “For example the air is so thick at sea level that even when you’re flyingsomethingatMach2or3,youcanstill gethypersoniceffects.”

Mitigating such extreme forces and temperatures for air-breathing aircraft or missiles, let alone maintaining command andcontrol,isnosmallfeat.However,breakingthroughtothehypersonicsidepresents a host of tactical and strategic advantages namelythroughunmatchedspeedanddifficultytodetectanddefend.

“While the U.S. Navy currently uses the Aegis Combat System on Arleigh Burke and Ticonderoga-class cruisers to defend ships at sea, high-energy lasers are becomingmoreimportanttoourlayereddefensive against rapidly evolving threats,” said Navy Lt Cmdr Brian Curran, a Ph.D. candidate in laser physics and executive director of the Meyer Scholar program. “To lead effectively and fight decisively, NPS is working to develop officers who are technologically competentandconfidentintheemployment ofadvancednavalwarfaresystems.”

A Mighty Wind Thankstoathree-yeargrantbytheOffice of Naval Research (ONR) Code 35 Naval Air Warfare and Weapons, ONR’s innovative naval prototypes division, Hobson and his team have spent the last year renovating,reconstitutingandrecalibratingvarious componentsofthewindtunnel.

Thecomplex adecommissionedengine test cell which dates back to 1956 now consists of three massive pressure vessels of compressed air at several hundred psi. Operation is powered by a powerful electric motor and multiple compressors that pump the high-pressure air into air dryers before converging in a plenum chamber, from which it blasts at Mach 4 into the 4 inch-by-4 inch test section at temperatures nearminus300degreesFahrenheit

Additionally, with a grant provided by the NPS Foundation, the installation of a specialized air heater allows air speeds to beincreasedthroughMach5.

Over the next year the team will focus on modeling and investigating the elemental physics of hypersonics, Hobson says Drawing extensively on Xerox’s first liquid metalprinterandasmallpowderbedmetal printer,NPSengineersareabletofabricatea widevarietyofcomponentsoutofdifferent metals including aluminum and titanium, predict their performance using computational fluid dynamics and see how they performunderhypersonicconditions.

Crucialtothisprocesshasbeenthework of NPS Aerospace Engineering student U.S. Navy Ensign G. Forrest Dawe, who has developed a method to measure internal conditions to further streamline the newly-upgradedwindtunnel

The newly-commissioned ensign is attending NPS as a Shoemaker Scholar meaning he’s on a fast track to earning his master’s degree right after his undergraduate degree at Boston University and before attending Navy flight training in Pensacola, Fla. He aims to become a test pilot, so not onlyisheintimatelyinvolvedinthescience ofhypersonics,hecouldbeapractitionerof hypersonicflightaswell.

“During the course of the supersonic wind tunnel upgrade our team ran simulationsonitandpredictedthattherewould be vortex conditions along the sidewall, he explained. “So my thesis involved using a probe to measure velocity and pressure alongthewindtunnel.”

All of this initial research is in preparation for the third year of the ONR grant for experimentingwithhypersonicpropulsion. Specifically,theteamwilldevelopandmodel asolutiontoavexingprobleminhypersonic research anengine“unstart,”whichisthe violentbreakdownofengineinletairflowat hypersonicspeeds

“In other words, an ‘unstart’ is when a supersonicinletreversessupersonicairflow within a nanosecond,” Nikaido explained. Onthebestofdays,thisresultsinpowerloss oftheaircraftandasuddenifnotviolentyaw.

“We do the research to generate novel ways of preventing this from occurring all the while learning a lot about the physical underpinning of supersonic airflow. Hobson said. “There are many challenges associated with hypersonic speeds The value of our research is not only to develop solutionstoimprovinghypersonicflight,but todoitalongsideourmilitarystudentswho contribute operational insight while they gain technical understanding to develop effectiveconceptsofoperation.”

Such aircraft, and the leaders ready to employ them, are on the horizon with NPS and its SSWT laboratory playing a critical roleinhypersonicsinnovationthroughgraduateeducationandresearch.