# Rocket propulsion and vortexes

1. Jun 28, 2008

### curiouschris

rocket propulsion and "vortexes"

Hi

I have been reading a little about vortexes of late. ie hurricane shaped formations. and I wondered if such vortexes were deliberately designed into rocket propulsion systems.

I have seen no examples of such in standard rockets whether they be powered by a fuel/oxygen mix or black powder, but of course my research is relatively limited and most diagrams do not go into great detail for simplicity.

I was wondering if by forcing the expelled gases of a rocket engine whether it be a space shuttle, ICBM or fireworks into a vortex would create better lift.

Of course for something like the space shuttle you would require counter opposing spins on its engines to prevent a very dizzy ride for its occupants.

If this is not a current practice of rocket design would it help?

My thoughts are this, As the gases exit the engine it is rapidly moving away from the craft and as such propels the craft forward. ie equal and opposing reactions.

But at the same time the gases are expanding in other directions, surely then through the same equal and opposite reaction rule a lot of energy must be lost in vectors which are not used to propel the object forward (although they may have a stabilising effect).

By creating a vortex couldn't the resultant force be better controlled?

Does this seem reasonable ?

2. Jun 28, 2008

### FredGarvin

Re: rocket propulsion and "vortexes"

How you have tied vorticies into this line of thinking is a question I have.

To somewhat answer your question, there really is no such thing as lift in a rocket. It is pure thrust. Granted there are aerodynamic surfaces that control the ascent of the vehicle but that's not what you are asking about.

Great care is taken in designing a smooth flow from a nozzle. Boundary layer separation in a nozzle is a very bad thing. There are many engineering tradeoffs that get balanced. Vorticity is not in the equation anywhere that I can think of. How would one force the expelled gases into a vortex? That would imply that there was some sort of vortex constantly following the vehicle.

You do state a fact when you mention expansion in directions other than in the axial direction of the nozzle. The term that describes the extent of the exit exhaust that is not in line with the intended direction in the nozzle divergence angle. In a conical nozzle, the optimal divergence angle is about 18°. In a bell shaped nozzle it is around 10°. These angles involve tradeoffs between having the largest amount of exhaust momentum in line with the axis of the engine and the length of the nozzle required to create the proper exhaust direction.

I think you'll have to explain a little bit your idea of the whole vortex thing. I'm not quite getting how you would see this actually happening.

3. Jun 29, 2008

### curiouschris

Re: rocket propulsion and "vortexes"

To create the vortex one would rotate the high speed exhaust gases as they exit the exhaust ports using fins or some arrangement that would have the same effect. but as you say the divergence angle has been optimised so it may well be that changing the angular momentum of the exiting gases would provide sub optimal operation.

Then again as the gases strike the fins and change direction they must impart some of their energy onto the fins thus potentially providing greater momentum to the rocket.

Sort of in the same way a propeller screws through the air. except in this case the propeller remains stationary and the air screws around it.

But that wasn't my original musing more that it just seemed to me that a tight column of gases exiting the rocket would provide greater momentum than a diverging column of gases as it flares out of the rocket exhaust.