Heat on heat shield. Friction or compression?

[thenewmans]

I always thought of a reentry vehicle compressing the air in front of it. And that would cause a lot of heat kind of like filling my tires. But I keep hearing friction even from NASA heat shield experts. OK, I guess maybe 10% of the heat is friction. I always assumed they said that to make the concept easier. But I’ve heard it so much recently that I’m starting to think I’m wrong. Or maybe they’re the same thing in a way that I hadn’t understood yet. Can you straiten me out?

 

[Doug Huffman]

The jargon is atmospheric heating, and its explanation is

When fluid flow slows down its kinetic energyis converted to heat; in high speed flows, tremendous energy is represented by the mean motion of the flow. As the flow is slowed to near zero speed, its temperature increases, the gradient in the speed in a direction normal to the surface allows small scale mass transport effects to dissipate the temperature in the outward direction and thus the temperature at the surface is less than the stagnation temperature; the actual temperature is referred to as the recovery temperature. [ ... ]

I am a sustaining contributor to The Wikimedia Foundation

 

[boneh3ad]

Both are contributors. The heat is mostly generated through the compression but there is some that comes from viscous dissipation as well (or what you might call "friction"). The "friction" plays a great role in transferring that heat to the surface, however.

 

[thenewmans]

That's what I love about PF. Thanks guys. I did found some good stuff on "viscous dissipation"