Ekman Layer Scrubbing and Shroud Heat Transfer in Centrifugal Buoyancy-Driven Convection
2020
This paper presents large-eddy and direct numerical simulations
of buoyancy-driven convection in sealed and open rapidly
rotating cavities for Rayleigh numbers in the range 107–109, and
axial throughflow Reynolds numbers 2000 and 5600. Viscous
heating due to the Ekman layer scrubbing effect, which has previously
been found responsible for the difference in sealed cavity
shroud Nusselt number predictions between a compressible N-S
solver and an incompressible counterpart using the Boussinesq
approximation, is discussed and scaled up to engine conditions.
For the open cavity with an axial throughflow, laminar Ekman
layer behaviour of the mean flow statistics is confirmed up to
the highest condition in this paper. The Buoyancy number Bo
is found useful to indicate the influence of an axial throughflow.
For the conditions studied the mean velocities are subject to Ra,
while the velocity fluctuations are affected by Bo. A correlation,
Nu' = 0.169(Ra')0.318, obtained with both the sealed and open
cavity shroud heat transfer solutions, agrees with that for free
gravitational convection between horizontal plates within 16%
for the range of Ra' considered.
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