At that size, between Reynolds number losses and tip losses, why stick with
turbines? Tip path to outlet ratios become enormous, and ratio between tip
clearance area (with reverse flow) and driven area gets uglier and uglier and
that size.
Positive displacement pumps such as gear and Roots pumps seem to exist at this
size and look easier to engineer.
On Sep 6, 2018, at 1:47 PM, Peter Fairbrother <zenadsl6186@xxxxxxxxx> wrote:
On 04/09/18 08:17, Wyatt Rehder wrote:
Also at 400N I'm not sure a turbopump would be the most efficient
choice. Far as I knew they don't scale down to sizes that small that
well.
They do not, which is why I have been working on exotic materials for blisks.
However if you don't want RD-170 (or BE-4) numbers something like below can
be done.
With a turbine inlet temperature of only 600C and a tip speed of 275m/s, the
turbine material requirement isn't too ridiculous, and the overall turbopump
efficiency requirement is only 10.0%.
However ... that 10% efficiency is not easily obtained.
Pump specific speeds are about 150-600 (US units) - Barske pumps can deliver
about 15-40% efficiency in that range, if well designed and built. Turbine
efficiencies of about 60% are also attainable, and 80% plus mechanical
linkages are possible.
However you have to match the turbine and the pumps for torque and speed,
which is not easy, an even then - 15% x 60% x 80% = 7.25% = fail.
But do I think it is doable :)
Peter Fairbrother
400N rocket engine v2.0
LOX-rich staged combustion
Pumps:
LOX - 107 g/s @ 1.142 kg/l = 93.7 ml/s
kero - 45 g/s @ 0.78 kg/l = 57.7 ml/s
total = 152 g/s = 151.4 ml/s
O/F = 2.38
output pressure 12 MPa
delivered power LOX 1125W (93.7 ml/s x 12MPa)
delivered power RP1 693W (57.7 ml/s x 12MPa)
delivered power total 1818W
at 100,000 rpm-
LOX head= 1050m 93.7 ml/s specific speed = 166 (= 291 US units)
kero head= 1538m 57.7 ml/s specific speed = 97 (= 163 US units)
at 200,000 rpm-
LOX head= 1050m specific speed = 332 (= 582 US units)
kero head= 1538m specific speed = 194 (= 326 US units)
Preburner:
11.6 MPa -> 6MPa exit
LOX/RP1 O/F 36:1
Ae/At 1.0046
Te 613C, 886K
Ve 573 m/s mach 1.07 26.1 kg/m^3
110 g/s flow rate
Turbine:
Gas stream kinetic power 18.06kW
Pumps delivered power 1818W
Turbopump overall efficiency required 10.0%
20 degree Turbine tip optimum velocity 275 m/s
Main Chamber:
Pc 6MPa Pe 1 atm
LOX/RP1 2.38
Ae/At 9.09
ISP: 295s 321s(vac)