A STUDY OF STEAM AND SMOKE
STEVE RAPLEY, GENERAL STEAM NAVIGATION LOCOMOTIVE RESTORATION SOCIETY CME
ONE COULD be forgiven for thinking the Covid-19 pandemic would slow down progress on No. 35011 General Steam Navigation. In truth, progress has gone from strength to strength in the past year.
The boiler was lifted from the frames in October 2020, and the trailing truck was also removed ahead of its restoration this year. Behind the scenes, a lot of research has been undertaken, with support from the University of Birmingham, the Bulleid Pacific Locomotive Association and Andrew Marshall (35006 Locomotive Company Limited), on the design and materials for the replacement crank axle.
As part of the GSNLRS’ efforts to engage the next generation of engineers, as well as to use modern analysis techniques to understand the problems with the original ‘Merchant Navy’ design, Computational Fluid Dynamic (CFD) studies were undertaken in conjunction with Loughborough University.
The original design was known to suffer considerably from drifting exhaust, and while modifications were made that cured the problem somewhat, in crosswinds it still exists. The CFD studies looked at the existing design, highlighting how the exhaust can be drawn into the low pressure region alongside the locomotive, obscuring the driver’s vision. Modifications to the length of the smoke deflectors showed that the 1948 design was fairly optimal, extending them further back having no significant improvement on the obscuration.
Adjusting the ducting around and behind the chimney, in line with sketches John Click (Bulleid’s assistant), produced showed some improvement. The ‘Light Pacifics’ 34064 and 34092 both highlighted the benefits a Giesl ejector can have on exhaust clearance; the CFD studies suggests fitting either an oblong or round diffuser, both of shallower angle than the original Bulleid-Lemaître design, could have significant benefits in exhaust clearance.
Bulleid ‘Pacifics’ are excellent steamers, yet the evidence from 34064 and 34092, as well as the tests conducted in 35022 in Rugby, suggest more power and efficiency could be drawn from these magnificent machines. We have started a series of CFD studies of the flows in the smokebox of a ‘Merchant Navy’, to understand the inefficiencies in the design and work towards design improvements. The tests conducted on 35022 showed no discernible front-end limit, with significant untapped potential in the locomotive. The CFD study highlights potential inefficiencies in the exhaust owing to it being too short, the steam nozzles are too far from the base of the chimney, and the potential that more modern exhaust designs could have if applied to 35011. These could make 35011 more efficient or potentially more powerful.
Returning 35011 to original design condition is a major undertaking, with significant work ahead of us. For more details on the unique project to restore 35011 General Steam Navigation back to her near original condition, find us at www.35011gsn.co.uk
STUDIES SUGGEST FITTING EITHER AN OBLONG OR ROUND DIFFUSER