Energy scales & when air chemistry starts to matter

15:53complex. Yeah, it's very Yeah, it's very complex. All of a sudden, you you can't just rely on the Navier Stokes equation to like tell you everything, right? And now now it's it's no longer just viscosity and density and pressure. There's like molecular effects. You got to get down to the molecular level. And that's why it's hard, right? So, when it comes when it comes to like making something that wants to move at a hypersonic scale, there's two tyrants that you have to deal with. Okay? There's two types of drag. There's a pressure drag, which is basically my my plane is going through the air. There's higher pressure in the front because I'm piling up all the air and then I'm creating an effective vacuum behind me.

16:34>> Yes. >> Right. So, that's going to create a force >> because there's high pressure here, low pressure here. Just like a piston. >> Yes. >> There's going to be a force that's going to be like, "No, I don't want you to move that fast." >> That's the That's the pressure drag. >> Yes. Then there's also skin friction drag, which is the air is moving over my body. Yes. Right. And I'm I'm like tearing the air apart in some sense because the part that's stuck to my my vehicle, my flight >> is going to be moving with me, but the air away from me is stationary, right? So there's going to be that like velocity difference, right? And then there's another thing which is the heat. All of that energy that I'm imparting,

17:15if I'm going hypersonic, that heat is now changing the chemical structure of the air in front of me. >> Yes. >> And that heat load, that aerothermal load from the viscous dissipation is going to be something that I need to care about. Right. >> Right. So, there's all of these like little things. >> Yes. >> And the source of most of my problems comes from some something called the boundary layer. >> Okay. So, imagine you've got an air foil. It's like a wing. >> Yes. What I was saying earlier is there's a thin there's a thin layer where the velocity shears from zero relative to me. So I'm moving through the air. I'm moving through the air. >> All of the molecules that are near my

17:56that are stuck to my wing are moving with me. >> Yeah. >> But all of the molecules that are even a few millimeters away from me >> are far gone. Yes. >> Right. There's got to be some continuous way that I go from zero to my speed. >> Yes. >> Right. >> Yes. >> And that's that boundary layer. Okay. That boundary layer turns from laminer to turbulent. >> Okay. >> Okay. When it when it fully attacks when it fully attacks the air, it's laminer, meaning it's quite smooth. >> It's very smooth and it's very nice. Yes. >> Okay. There's a continuous sort of transformation from zero to whatever my velocity is. >> Yes. Later on that laminer flow is going

18:37to turn into turbulence. Yes. And the turbulence is going to be there's going to be these eddy currents. There's going to be like weird like like circulations happening in the back of my wing. And that transition from laminer to turbulent is a very poorly understood event. >> Gotcha. Okay. >> Okay. >> Yes. >> Like like like seeing where that happens in my wing, how that happens when I change the deflection of my wing. Yes. you know all of these things are are you know we've got models for it and we've got ways of understanding it but at the end of the day this is a extremely nonlinear phenomenon which means that you know there's not a simple nice >> like differential equation that I can

19:18just like solve and like and like I have like a solution that is like enclosed form okay th this makes sense and is it