The Influence of Pebble Placement on the Wake of Tandem Pebbles in a Free Stream

Abstract

The effect, the pebble spacing has, on the fluid flow past two spheres in a free stream, was investigated by utilizing Direct Numerical Simulation (DNS), a Spectral Element Method (SEM) and NEK5000. There was seen that for a spacing of 2 pebble diameters (D), between the centroids, the turbulence statistics were asymmetric. For this study four different pebble spacings were investigated: 1.5D, 2.0D, 2.5LD, 3.0D. For all the cases the inlet flow, (U0) was selected that the Reynolds number, (Re) equalled 1000. The flow was allowed to develop for 200 Convective Units (CU = D/U0) before tests were conducted to ensure compliance to DNS. With the Kolmogorov scales captured and adequate Y+ values, time averaging was done for 800 CU to calculate the turbulence statistics. Calculated parameters include turbulence statists for selected line profiles and turbulent kinetic energy (TKE) budget terms. The generated statistics will be compared for each spacing selection.