As has been addressed before, the Trent/777 does just fine in Suction only regime.
So did the UA 767 referred to in my link:
http://www.pprune.org/forums/showpost.php?p=4000971&postcount=1101
The engines on the 767 performed just fine in suction all the way from sea level to 41,000 ft.
What they could NOT handle was a cessation of boost pressure during the climb.
The engines spooled down 14 seconds after the boost pumps were turned off.
Exposed leaky pipes and seals were not involved because the tanks were full.
This seems a clear indication to me that the boost pumps were doing something which the HP pump could deal with so long as boost pressure continued.
But when boost pressure was discontinued, the engines spooled down after a delay of 14 seconds.
That something which boost pumps were doing could have been bringing air out of solution.
Which was OK with boost pressure on, but not OK when the boost ceased.
Air bubbles in the fuel do not cause cavitation damage. The air cushions the collapse of the air bubble, so the bubble does not disappear when pressure is restored, and there is no damaging shock wave.
Also, prior post (recent) explains that a non uniform Fuel supply (eg entrained air) would prevent cavitation, not cause it.
In the case of BA038, does it really matter whether air bubbles did or did not cause cavitation damage?
The AAIB says although there was cavitation damage, it was not sufficient to prevent the fuel being pumped. The damage was not significant wrt pumping capacity.
What matters is - why did the fuel stop advancing through the system?
More than 30 years ago a Royal Aircraft Establishment repot by WGS Lester, “Temperature and Fluid Effects on Cavitation in Aircraft Fuel Pumps” showed that air coming out of solution could cause the volume output of centrifugal type boost pumps to fall markedly.
He was not concerned about cavitation damage, only about whether the pump continued to deliver fuel.
With air dissolved in the fuel, his test pump didn’t stop pumping, but the output volume fell.
Sound familiar?
And the fall off in performance was greater when the fluid was cold.
Sound familiar?
In fact the pump output was greater when the test liquid was boiling (no dissolved air) than when it was cold (with dissolved air).
Some of his test results are shown in:
http://www.pprune.org/forums/showpos...postcount=1102
Fuel saturated at room temperature becomes highly supersaturated when cooled.
It typically remains supersaturated for many hours in aircraft fuel tanks at altitude.
This was mentioned by Lester, and confirmed decades later in Boeing test flights.
Bottom line The difficulty in finding the restriction to fuel flow maybe because there was no restriction to flow, just a fall-off in boost pumping capacity due to air coming out of solution from cold fuel, and a mixture of air bubbles and fuel delivered to the HP pump.
Just my 2cents. Maybe 1 cent.
