Run Silent, Run Very Fast

The Baltimore Sun

Russia has it. And reportedly, so does Iran. Now the United States is taking another look at supercavitation, a technology first honed in Maryland more than 50 years ago that would allow mini-submarines to travel beneath the ocean's surface at more than 100 miles an hour.

The Navy wants to build a vessel that could deliver SEAL commandos underwater to enemy shores undetected at high speed. If successful, the technology could one day be used commercially to transport cargo around the world faster, promising a huge impact on commerce.

The Defense Advanced Research Projects Agency (DARPA), the Defense Department's research and development arm, awarded Northrop Grumman Corp.'s Undersea Systems in Annapolis a $5.4 million grant in November to design a concept vessel called the Underwater Express that can attain speeds of 110 knots, or 127 miles per hour. By comparison, the government says a Virginia-class submarine's cruising speed is 25 knots (29 mph). General Dynamics Corp.'s Electric Boat subsidiary in Groton, Conn., also won a contract to come up with a competing concept.

Likely long, cylindrical and 8 feet in diameter, the sub would have a blunted nose that would cut through the water. At high speed, the nose deflects water away from the surfaces of the vessel. A gas bubble or cavity forms around it, from the nose to the stern, which nearly eliminates drag and allows it to go faster.

Funding pulled

The initial award is small by defense contract standards, but if one of the teams develops a successful prototype, the total contract could be worth as much as $46 million.

It won't be easy, said Marshall Tulin, who DARPA credits with being the father of the technology and whose Howard County company, Hydronautics Inc., tried to bring the technology to market during the 1960s and 1970s.

Back then, Tulin said, the Navy was intent on developing a supercavitating vehicle that would "skim" the water on a cushion of air, but Congress pulled the funding. Hydronautics turned its focus to supercavitating foils or fins and propellers, including one for the U.S. Maritime Administration's 50-knot Denison hydrofoil. Work on it was discontinued.

The company also tested propulsion systems for the Navy and NASA in its 300-foot model basin, then the largest privately owned test basin in the country. Tulin and a partner sold the company in 1982 to Austin, Texas-based Tracor Inc. along with patent rights to the technology, though much of their work was not patented, he said.

Now 80 and a professor emeritus at University of California, Santa Barbara, Tulin said the technology has long been promising, but Northrop Grumman must overcome two big challenges: control and noise. He believes the latter is a big reason why the Navy didn't explore a supercavitating sub before.

Quiet operation

"The Navy was always focused on quiet operation underwater, and really excelled in that area," said Tulin, who said he wrote his first scientific paper on the flow dynamics of supercavitation in 1953. At that time he worked at the Navy's David Taylor Model Basin, now part of the Naval Surface Warfare Center's Carderock Division headquarters in Bethesda.

Cavitation is the physical process by which liquid changes to vapor in the form of bubbles. Unlike with supercavitation, where a bubble grows and envelops the object, cavitating air bubbles grow to a certain point and then collapse violently. For example, when water boils in a pot, it is "cavitating," Tulin said. But cavitation doesn't require heat: An object cutting through water at high speed can create low pressure pockets, allowing bubbles to form.

Normally, ships and submarines want to avoid cavitation, said Kenneth M. Kalumuck, a senior staff member in the Oceanic, Atmospheric & Remote Sensing Sciences Group at the Johns Hopkins Applied Physics Laboratory in Laurel.

In the movie The Hunt for Red October, he said, the crew heard loud clanking when the submarine sped up - the speed of the propellers caused low pressure pockets to form, triggering the physical process in which the liquid molecules turned into air bubbles, which then collapsed against the propeller blades as they whirled through the water, emitting an audible noise.

In such a case, the noise would have not only disclosed the submarine's position to the enemy, he said, but the collapsing bubbles could have caused damage to the blades.

However, if supercavitation were to occur, a bubble would form somewhere on a propeller blade and extend behind it, Kalumuck said, making it more or less stable and allowing the vessel to go faster. Tulin's supercavitating propellers worked in this way.

Russian scientist

Tulin first called the phenomenon "supercavitation" based on his translation of similar work being done on propellers by a Russian scientist who dubbed it superkavitatzia. Tulin said he didn't know of the Russian's work until after he wrote his first few papers on supercavitation, but he credits the Russian - whom he knew only through scientific literature as Pozdunine - with being a pioneer in this field. Yet the Russians dismissed their countryman's work.

In contrast, Tulin said his second paper in 1955, which detailed how the Navy could develop supercavitating propellers, was classified for many years. The Navy later patented it under his name, and he said he was amused to hear that the Russians called supercavitating propeller blades "Tulin sections."

Likewise, Tulin was surprised to learn last year that the government was taking another look at the technology.

At more than 100 miles an hour, a supercavitating vehicle would be extremely hard to steer, Tulin said, which is why other countries have focused on torpedoes rather than vessels carrying people. Control is not as much of an issue for a torpedo because a large target like an aircraft carrier would not have enough time to move out of its way, Tulin said.

Over the past 30 years, the Russians have been developing a supercavitating torpedo called the Shkval that reportedly can travel at speeds topping 230 mph, more than four times faster than American torpedoes. While only a model has been displayed publicly, rumors that a test launch of the torpedo sank the submarine Kursk in 2000, and the arrest of an American businessman just months before who allegedly was seeking technical secrets about the Shkval from a Russian scientist, have buoyed claims that it is a legitimate threat.

Other nations

Last April, Iran said it tested a similar underwater missile called the Hoot, which Tulin and many others believe was acquired from the Russians, if it exists. The Germans also said they are working on a supercavitating torpedo, dubbed the Barracuda.

"Obviously, as other countries develop it, we're more interested in it," said Larry Lieberman, program manager for Northrop Grumman in Annapolis.

So far, the idea of underwater high-speed battle has been one of science fiction. Two brothers in Australia have written a screenplay called Dark Angel that envisions future wars being fought underwater, with vessels dogfighting like fighter jets. It would be an amazing feat, considering objects can travel 1,000 times faster in air than in water.

Several countries, including the United States and Russia, have tested supercavitating bullets with the aim of destroying underwater mines. In 1997, the Navy successfully fired a bullet underwater at Mach 1, the equivalent of breaking the sound barrier in air.

A high-speed underwater vessel would be a welcome alternative to the Navy's small, fast-moving ships and rigid inflatable boats used to deliver members of its SEAL combat units. In high seas, the boats are hampered by large waves and the bouncing can cause severe neck and back injuries among the SEALs and crew.

Stealth foremost

The Navy has a sub-like SEAL Delivery Vehicle, which docks with traditional submarines and can transport a handful of SEALs toward a target or enemy shore, but its top speed - which is classified - is thought to be only between 5 and 8 knots.

John E. Pike, director of GlobalSecurity.org, an Alexandria, Va.-based Web site that analyzes new defense technologies, wonders whether the Navy even needs a supercavitating vessel.

He explained that it's more important for SEALs to be stealthy than fast. And a supercavitating vessel traveling below the water's surface can be spotted because it leaves a triangular-shaped wake.

"It's fun to think about, and I don't begrudge them the effort," Pike said. "I just don't think they've thought it through carefully."

DARPA spokeswoman Jan Walker said the concept her agency is looking at is much more evolved than the one Tulin studied decades ago.

Today's sophisticated modeling and simulation software and computational fluid dynamics make it possible to build a supercavitating vessel without noise and control problems, Walker said.

"Those didn't exist when the earlier work was done," she said.

DARPA wants to develop a supercavitating vessel not only to transport people but also cargo for all the services.

Northrop Grumman and General Dynamics are expected to wrap up Phase I in September. If DARPA opts to continue on to Phase II, it said probably just one of the companies would be asked to produce a prototype.

To fulfill Phase III, the "Demonstration Super-fast Supercavitating Transport" vehicle would have to maintain a speed of 100 knots for 10 minutes. At that speed, the vessel could travel the 3,628 miles between New York and Paris in under 30 hours, much faster than regular cargo ships.

"Underwater cavitation vehicles are really the jet planes compared to the turboprops," said Eugene Cumm, business area director for Northrop Grumman.

Help from UM

Most of Northrop Grumman's work will be done in Annapolis and at Pennsylvania State University's Applied Research Laboratory in State College, Pa.

The team also includes the University of Maryland, College Park, the University of Minnesota, the Navy's Naval Undersea Warfare Center in Newport, R.I., and Cambridge, Mass.-based BBN Technologies.

Tulin said the United States could have developed supercavitation more fully than the Russians had Congress not canceled the program. Despite discovering the technology ahead of the Russians, he said the United States is now essentially starting from scratch because the knowledge has been lost.

"You need a long-range point of view," he said. "And you need faith."

allison.connolly@baltsun.com

Copyright © 2021, The Baltimore Sun, a Baltimore Sun Media Group publication | Place an Ad
54°