The blog Fuck Yeah Fluid Dynamics posted some stills from this video recently. The images were fantastic, but I didn't totally understand what I was seeing. Thankfully, FYFD blogger (and aerospace engineering Ph.D. student) Nicole Sharp was kind enough to answer my questions.
What you're looking at is a rocket engine. The video shows what happens to airflow in the engine as it goes from subsonic to supersonic. In the video and the pictures, you can see a dark red line moving down the tunnel. That's the edge of the shockwave that marks the boundary between subsonic air and Mach 1. You should also pay attention to the little black vortices that whirl away from the edge of the engine wall. Those are pretty important.
The whole goal of an experiment like this, Sharp told me, is to learn more about shockwave/boundary layer interactions. The boundary layer is a very small region, right against the walls of the engine. It's the point where friction and viscosity matter to the air flow.
"Say I've got an airplane wing and air moving over it at 800 mph," Sharp said. "If I am a meter away from that wing the air doesn't care. It's not impacted by flow. But right at the surface of the wing you have friction, so the air can't just slide along surface. This is the region where the velocity of air changes from 0 to 800 miles per hour. It's millimeters or centimeters, but it's where you have a huge change in velocity."
It's important to study what happens in that boundary layer because this is where turbulence happens. In fact, those vortices you see are turbulence, generated when the impact of the shockwave hits the engine wall. That turbulence can cause pressure fluctuations, Sharp said. And those pressure fluctuations can have real, physical impacts on the structural integrity of the engine.
The Bank of England has unveiled its new £50 notes, which had been earmarked to honour a distinguished British scientist, and which will feature Alan Turing, the WWII hero who discovered many of the foundational insights to both modern computing and cryptography, and whose work with the codebreakers of Bletchley Park are widely believed to […]
The great science purge, they’ll call it one day. Donald Trump is closing science offices throughout the federal government. ‘As of June, around 85 percent of all scientific posts in the federal government, including an official scientific advisor to the President, were left unfilled,’ write the editors of I F***ing Love Science blog in an […]
Ed Hawkins, a climate scientist, created Show Your Stripes as a way to easily visualize the past century's climate change: give it a location and it will render a series of stripes representing a century's worth of average annual temperatures (above: global average temperature); as Kottke notes: "The warming patterns for particular regions are not […]
With the rising temperatures on tap this summer, the climate is going to be a frequent topic of conversation, and those conversations won’t be happy ones. Luckily, there’s a way to do a little climate change of your own – in a safe and sustainable way. When it comes to personal air conditioners, EvaPolar is […]
Whether you’re using them for next-level selfies or steady tracking shots, gimbals are a must for anyone who wants to maximize the potential of these powerful smartphone cameras we’re all carrying around. But those smartphones are also supposed to be portable, and let’s face it: Gimbals tend to offset that advantage. Weighing in at just […]
It’s too hot for yard sales, but hey: The internet is here for you. Here are the top ten deals on some of the Boing Boing Store’s best gear, just in time for summer. It’s everything from grills to security cameras to MacBook Pros, and they might be as low as they’re ever going to […]