Where is the LX S80?

On Sunday, 2 November 2014 21:03:39 UTC+2, Andy Blackburn wrote:
I'm curious what your running the numbers looks like. I admit I don't have a good mental model for how thermals work from a thermodynamic and aerodynamic perspective. I thought it had something to do with the fact that warm air was less dense and therefore buoyant. How that buoyancy accelerates a volume of air until some form of resistance at the edges progressively resists the acceleration and a steady rate of upward velocity is reached is beyond my understanding at a level detailed enough to relate thermal strength to temperature differences.

As to the temperature gradient across the thermal - I'm not sure it's linear from the edge to the center. Imagine a volume of air rising at 500 FPM. Presumably you have some mixing at the edges but the rest of the heat transfer would mostly be conductive over a period of 10 minutes before the thermal reaches, say, 5000'. I'm not sure what all the coefficients are, but it isn't 100% obvious to me that you'd end up with a linear temperature gradient all the way to the center of the thermal since there is so much new warm air being introduced continuously from the bottom, there isn't much time for heat to transfer to the outside air and air isn't that great a heat conductor in the first place. Have there been studies done?

9B

I can't quote any sources but I bet digging into Google Scholar would result studies (boundary layer physics would be good place to start). I know that warm air in thermal bubble or column is little bit warmer (numbers quoted earlier are realistic) than surround. That temperature difference is maintained with altitude (per hydrostatic equation), and thermal is surprisingly "closed" system, mixing at the edge of ascending air is quite small compared to thermal volume. It's true that average temperature gradient is not realistic figure, the gradient is probable decade higher at edge of thermal than figure I threw out of my sleeve.

I think running constant temp difference analysis would be quite easy with simple and cheap linux computer, temp signals going through DA conversion to digital domain. Sensors could be calibrated over time to match each other, so small differences could be readable, even if absolute accuracy is something like 0,1 degrees. If this has been done in 80's, technology probably was analog electronics. Nowadays it would be more software project.