Direct numerical simulation of turbulent flow and heat transfer within a spanwise-rotating elliptical pipe
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Date
2021-05-03
Authors
Hurtado Rosas, Rafael
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Abstract
In this thesis, the effects of spanwise system rotation on turbulent flow and heat
transfer in an elliptical pipe are investigated using direct numerical simulation (DNS).
To study the effects of system rotation on the heat and fluid flows, seven rotation
numbers have been tested for 0.25 ≤ Ro τ ≤ 24.0. The results of these rotating
flow cases are compared with those of the non-rotating flow case (Ro τ = 0). The
pipe length has been extended to L z = 20πb to ensure that the most energetic eddy
motions are well captured on the axial direction in the DNS. The results show that
large counter-rotating vortical structures appear in the cross-stream plane in response
to system rotation, which have profound influence on the turbulence statistics. It is
further observed that laminarization occurs on the suction side of the pipe and spreads
towards its pressure side with an increasing rotation number. At a moderate rotation
number (Ro τ = 8.0), the Coriolis term of the transport equation of Reynolds stresses
dominates turbulence kinetic energy transfer from axial to the wall-normal Reynolds
stress components. Similarly, the Coriolis term in the transport equation of turbulence
heat fluxes transfers turbulent scalar energy from <w'θ'> to <v'θ'>, and dominates the turbulent production term at a moderate rotation number. The influences of the
Coriolis force on the turbulent transport of momentum and thermal energy have
been analyzed in both physical and spectral spaces through analyses of the first- and
second-order statistical moments, including the mean velocities and temperatures,
Reynolds shear stresses, turbulent heat fluxes, pre-multiplied spectra of the velocity
and temperature fluctuations, and coherent flow and thermal structures.
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Keywords
Turbulence, Rotating flow, Elliptical pipe flow, Turbulent heat transfer