richard_leeds wrote:speedsense wrote:richard_leeds wrote:
I’d appreciate it is an aero person could explain how the temperature of the exhaust contributes to the enhanced flow compared to cold air.
F(thrust) ~ Area(air stream) * Density(air) * Average Velocityair2
That formula shows that the heat reduces the force, hot air is less dense.
My question is because comments on this topic often refer to the heat, not just the velocity.
Is the heat beneficial because less dense air helps with reducing pressure at the DDD exit?
With regard to a generated vortex, a heated vortex would contain higher velocity, thus having more effect than one that is below ambient temp (non heated vortex). "Controlled" vortices are vital to increasing performance of the diffuser. For example, the slats in the diffuser, create counter rotating vortices at each 90 of the slat. One slat creates two vortices counter rotating, one on each surface of the slat. Any intensity increase in these vortices (heated) results in preventing higher pressures at the end (exit) of the diffuser by way of less expansion of the exiting air.
The question of the RB's use of exhaust gas around the outside of the diffuser and some inside, the vortices would be more intense and of higher velocities.
Personally, I don't believe that "thrust" is the result, except if the thrust is an acceleration of the vortex itself. IMHO
"Driving a car as fast as possible (in a race) is all about maintaining the highest possible acceleration level in the appropriate direction." Peter Wright,Techical Director, Team Lotus