Flow physics could help forecasters predict extreme events

Flow physics could help forecasters predict extreme events
Brian Elbing (left) holds a microphone with storm chaser Val Castor (right) in front of his storm chasing truck, in which the researchers mounted an infrasound sensor for monitoring tornadoes. Credit: Brian Elbing

About 1,000 tornadoes strike the United States each year, causing billions of dollars in damage and killing about 60 people on average. Tracking data show that they’re becoming increasingly common in the southeast, and less frequent in “Tornado Alley,” which stretches across the Great Plains. Scientists lack a clear understanding of how tornadoes form, but a more urgent challenge is to develop more accurate prediction and warning systems. It requires a fine balance: Without warnings, people can’t shelter, but if they experience too many false alarms, they’ll become inured.

One way to improve tornado prediction tools might be to listen better, according to mechanical engineer Brian Elbing at Oklahoma State University in Stillwater, in the heart of Tornado Alley. He doesn’t mean any sounds audible to human ears, though. As long ago as the 1960s, researchers reported evidence that tornadoes emit signature sounds at frequencies that fall outside the range of human hearing. People can hear down to about 20 Hertz—which sounds like a low rumble—but a tornado’s song likely falls somewhere between 1 and 10 Hertz.

Brandon White, a graduate student in Elbing’s lab, discussed their recent analyses of the infrasound signature of tornadoes at the 73rd Annual Meeting of the American Physical Society’s Division of Fluid Dynamics.

Elbing said these infrasound signatures had seemed like a promising avenue of research, at least until radar emerged as a frontrunner technology for warning systems. Acoustic-based approaches took a back seat for decades. “Now we’ve made a lot of advances with radar systems and monitoring, but there are still limitations. Radar requires line of sight measurements.” But line of sight can be tricky in hilly places like the Southeast, where the majority of tornado deaths occur.

Maybe it’s time to revisit those acoustic approaches, said Elbing. In 2017, his research group recorded infrasound bursts from a supercell that produced a small tornado near Perkins, Oklahoma. When they analyzed the data, they found that the vibrations began before the tornado formed.

Researchers still know little about the fluid dynamics of tornadoes. “To date there have been eight trusted measurements of pressure inside a tornado, and no classical theory predicts them,” said Elbing. He doesn’t know how the sound is produced, either, but knowing the cause isn’t required for an alarm system. The idea of an acoustics-based system is straightforward.

“If I dropped a glass behind you and it shattered, you don’t need to turn around to know what happened,” said Elbing. “That sound gives you a good sense of your immediate environment.” Infrasound vibrations can travel over long distances quickly, and through different media. “We could detect tornadoes from 100 miles away.”

Members of Elbing’s research group also described a sensor array for detecting tornadoes via acoustics and presented findings from studies on how infrasound vibrations travel through the

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Why Vanadium Flow Batteries May Be The Future Of Utility-Scale Energy Storage

Earlier this year, the California Energy Commission (CEC) published a $20 million solicitation to fund research projects for the deployment of long-duration energy storage. The objective was to develop a clear understanding of the role that long-duration energy storage (10 hours or greater) can play in helping to meet the state’s mandates to decarbonize the electricity sector by 2045. Lithium-ion batteries were excluded from the solicitation.

The CEC selected four energy storage projects incorporating vanadium flow batteries (“VFBs”) from North America and UK-based Invinity Energy Systems plc. The four sites are all commercial or industrial facilities that want to self-generate power (like solar) and in some cases have the ability to operate off-grid. Invinity’s total scope is 7.8 megawatt-hours (MWh) of batteries across the four projects. Part of the objective is to be able to take those facilities off-grid for an extended period of time, to avoid interruptions to their power supply during grid outages. 

What is a VFB, and how does it differ from the more ubiquitous lithium-ion battery? To answer these questions and learn more about Invinity Energy Systems, this week I spoke with Invinity’s Chief Commercial Officer and co-founder, Matt Harper and Joe Worthington, the company’s Communications Director.

Matt is a mechanical engineer by training, and he explained that he has been building clean energy technology for 25 years. For the past 15 years, he has been developing flow batteries.

Vanadium is an element that can commonly exist in four different oxidation states. That just means that it can exist as an ion with different charges. For example, a vanadium ion that is missing three electrons would have a charge of V3+. If you add an electron to it, it converts to a V2+ ion. This transfer of electrons back and forth is what makes VFBs charge and discharge, as the vanadium ions in the battery swing from V2+ to V5+.

This differs from lithium-ion batteries in that every time lithium charges and discharges it is plating and deplating lithium metal on the cathode. Although this reaction is almost completely reversible, it will lead to degradation after a few thousand cycles and performance will decrease.

A VFB consists of two tanks of electrolyte dissolved in water and separated by a proton exchange membrane. Both electrolytes are vanadium-based. As the batteries are charged and discharged, vanadium ions are simply moved between oxidation states. According to Matt, this can be done tens of thousands of times over a time period measured in decades, with no degradation in the ability of the vanadium solutions to hold charge.

They estimate that every 10-20 years, the membrane that the ionic species crosses over will require a replacement. Again, this is unlike a lithium-ion battery where the entire battery would need to be replaced. They compared this to maintenance on a car. Matt indicated they have

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