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“air multiplying” jet engine (Dyson Fan + AeroSpike Engine)

Every curious engineer has wondered how to use the principles developed in the Dyson “Air Multiplyer” fan for propulsion.  There may be a way to do this.

Take a gander at this diagram of fluid flow rate through and around the Dyson fan.  The air jets that slide along the inner surface of the airfoil ring flow at a rate of 50mph as reference.

You can see that the film of high-speed air is introduced on the surface of the ring early on, very close to the forward plane of the fan.  You can also see the green zone emanating outward perpendicular to the 50 mph flow stream.  This effect is what must be responsible for recruiting air from in front of the ring by creating a low pressure region.  This is classic Bernoulli effect stuff.

It is interesting to note that all of the recruited air seems to merge with the high-speed flow and exits the ring as a conical flow with an area of ‘dead space’ in the center of the cone.

Now, in order to begin thinking about creating an engine out of this design we need to evaluate the power consumption issue.  In the case of the Dyson fan almost no thrust is generated but despite that, a very powerful motor and robust inductor is required to form adequate pressure.  It seems implausible that even a large turbine would be able to induce high enough flow rates while being light enough to leave the ground.  In addition, such a scaled-up version of the Dyson fan would be very complex and costly.

This line of thinking leads to the idea of getting rid of the impeller and replacing it with a rocket system.  This new concept would reduce the complexity and cost of the system while permitting the highest possible nozzle velocities and maximum thrust.

One particular type of rocket nozzle suggests that a rocket-powered air multiplying ‘jet engine’ is actually possible.  This nozzle is called an AeroSpike engine.  The geometry of an AeroSpike rocket engine is the inverse of a traditional bell-shaped nozzle that we are all familiar with.  The principle of operation for AeroSpike engines is that the pressure of the atmosphere forces the flow being ejected along the surface of the spike and provides uniform thrust in this way.  AeroSpikes were developed because they are less influenced by air pressure and have been considered as thrusters on the next space shuttle.

Here are some pictures of AreoSpike engines:

If it is possible to combine the AeroSpike operating principles with those of the Dyson fan the resulting technology would be a very elegant propulsion system with few moving parts and better efficiency over conventional rockets.  Further analysis is required to divine weather the flow in such an engine would remain laminar or if it would become a jumbled turbulent mess.  It is also not clear at this point what the fuel efficiency of such a system would be and if it would be applicable to UAVs or (more importantly) to general aviation propulsion.

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