Timeline for Contra-rotating coaxial shrouded fans: design guidelines
Current License: CC BY-SA 4.0
6 events
| when toggle format | what | by | license | comment | |
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| Dec 14, 2021 at 9:06 | comment | added | Buk | The size limitation is fixed, unchangable. I cannot double it. I also want the duct. For the safety of totally enclosed rotor(s) amongst other reasons. (Thanks for your attempt to help, but I'd really like soome help to do what I described in teh OP; not do it your way.! I'll stop wasting our time now. | |
| Dec 13, 2021 at 8:52 | comment | added | Robin Bennett | The power requirement is absolutely not fixed. If you double the rotor disk area, you halve the downwash speed required for the same lift. The mass flow is the same but the speed term in the energy equation is squared, so the power is halved. That power makes air move, and as that moving air mixes with stationary air its energy gets turned into noise and heat. Ducts and multiple blades can change the character of the noise, but reducing power addresses the root of the problem. | |
| Dec 12, 2021 at 0:50 | comment | added | Buk | "noise is mainly related to power and air speed"; Could you elaborate on that a little please? Starting with a given mass -- say 500g -- and the need to hover that. Steady state. The power requirement is essentially fixed; but there are several (a continuum) of ways to achieve that delivery. (Many) small diameter at high speed. One large at (much) lower speed. Lower speed tends to produce less noise. Wrap it in a shroud, and less noise still is radiated. Size limited+plus yaw control requirement suggests 2, contra rotating props. More blades; lower speed (but more torque). | |
| Dec 10, 2021 at 9:08 | comment | added | Robin Bennett | Sure, the above process doesn't tell you anything about the number of blades, only their total area. You can run the numbers and split that area any way you want, although it may result in very thin blades. You should note that noise is mainly related to power and air speed, and the best way to reduce them is to increase the disk diameter. HBR turbofans are only quiet when compared to the supersonic exhaust of a turbojet. Lots of people have build drones that use EDF units, and they're always loud. | |
| Dec 8, 2021 at 20:35 | comment | added | Buk | You'll probably find that you don't need anything like 13 blades and a coaxial rotor. Can I turn that on its head, and say its what I want to use and configure the motor KV to suit? I need two contra-rotating, because that the basis of yaw control. I want two different, prime numbered blade counts to reduce/eliminate harmonic 'beats'. (My primary goal is "quiet".) | |
| Dec 8, 2021 at 12:52 | history | answered | Robin Bennett | CC BY-SA 4.0 |