We analyze the effect of large-scale coherent structures on the deposition of low-inertia
particles in a turbulent pipe flow using extended proper orthogonal decomposition (EPOD)
and spectral analysis. We perform direct numerical simulations (DNSs) at two the Reynolds
numbers 5300 and 10 300 (based on bulk parameters) with the particles released at the pipe
inlet. The equilibrium Eulerian model is employed for calculating particle velocity, and
the analysis is limited to particles with Stokes number (based on wall units) less than 1.
Increasing the Stokes number increases the energy at small streamwise wavelengths (due
to inertial clustering), and the spectral energy peak moves from λ+
z ≈ 1000 to λ+
z ≈ 150.
The spectral peak in the (λ+
z , y+) plane, where y+ is the wall-normal distance, moves
from the buffer layer to the logarithmic region. Gravity has a substantial effect on the
POD mode shapes. For the downward flow, a second peak appears closer to the center.
A new Fukagata-Iwamoto-Kasagi (FIK) identity is derived for the wall deposition rate
coefficient (Sherwood number, Sh) and employed to quantify the contributions of the mean
and fluctuating velocity and particle concentration fields for different Stokes, Froude, and
Reynolds numbers. Modes with azimuthal wave numbers kθ equal to three or four are found
to contribute most to deposition. Application of the developed methodology to higher
Reynolds number can elucidate the role of large- and very-large-scale flow structures on
particle deposition to the wall. It is well known these structures leave their footprint at the
wall but their contribution to deposition is not well understood.