Fully-resolved LES of weakly separated flows

A high-accuracy large eddy simulation (LES) is applied to flows over a sphere and an underwater vehicle. Both objects have relatively weak separated stern flows that may depend upon the accurate resolution of turbulence structures in the attached flow regions upstream of the separation point. For the sphere we compute flows over a range of Reynolds numbers from sub- to super-critical (Re = 1×10⁴ to Re = 1:14×10⁶, respectively) for which we obtain decent agreement for the separation location, pressure distributions and integrated forces. Long time series data shows evidence of low-frequency shedding phenomena. We perform LES on the Advanced SEAL Delivery System (ASDS), an underwater vehicle with a rounded-rectangular cross section and stern slope that promotes weak flow separations. We compute the fully resolved flow over the ASDS for length-based Reynolds numbers 128 × 10³, 256 × 10³ and 512 × 10³. We show that the mean flow fields over the attached flow region are reasonable in that the boundary layer profiles, shape factors and skin friction agree with other examples of developing turbulent boundary layer flows. The instantaneous flow fields exhibit near-wall turbulence structures with the correct length scales and dynamics as compared with the wall-bounded turbulent flow literature. The separation point moves aft and the extent of the separation region decreases markedly as the Reynolds number increases.