As per our last post we ended up with some kind of mysterious power gain. Having few ideas we’ve been able to rule out all at the point when Richard clearly stated that it is the Venturi effect!
So what’s the Venturi effect again?
The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe. The Venturi effect is named after its discoverer, the 18th-century Italian physicist Giovanni Battista Venturi.Wikipedia
I think that following picture tells even more.
As you can see, it pretty much correlates with what we are experiencing. Input velocity is same, but output one is higher. Well, now how to test this. Richard stated that there is no way to gain whatever energy out of nowhere so with higher velocities we should be also seen higher power demand. And the easiest way to do so is to monitor the input Wattage.
Local Jaycar luckily offers their Mains Power Meter with extendable LCD Display which does exactly that for shabby $34.95.
So we grabbed one!
Then we rebuilt our testing setup, plugging our new power meter in front of our 2kW PSU. Running on idle power meter clearly indicated constant consumption ~8W.
Oli and Sam helped with testing where they were checking on highest measured value. I prepared everything to repeat our tests on EDF only, 1m PU tube and our new 6m CF tube. Also received new set of propellers from Chris and I was hoping to duplicate same test on those, but hit some problems there so I don’t have video of guys measuring and following form is just half-filled, waiting for another opportunity.
Measurements above clearly shows that with higher speeds power consumption was clearly growing. Where we were getting very much 20% gain on the wind speed (17.26m/s -> 20.65m/2), our power requirements were also growing – making it 14% higher power input.
I suppose that this concludes it for now, mystery solved a now to back to building our airship again! 🙂