A numerical investigation of the wake of an axisymmetric body with appendages

Abstract

We report wall-resolved large-eddy simulations of an axisymmetric body of revolution with appendages. The geometry is that of the DARPA SUBOFF body at 0 yaw angle and a Reynolds number equal to Re L = 1.2 × 10 6 (based on the free-stream velocity and the length of the body). The computational grid, composed of approximately 3 billion nodes, is designed to capture all essential flow features, including the turbulent boundary layers on the surface of the body. Our results are in good agreement with measurements available in the literature. It is shown that the wake of the body is affected mainly by the shear layer from the trailing edge of the fins and the turbulent boundary layer growing along the stern, while the influence of the wake of the sail is minimal. In agreement with the reference experiments, a bimodal behaviour for the turbulent stresses is observed in the wake. This is due to the displacement of the maximum of turbulent kinetic energy away from the wall along the surface of the stern, where the boundary layer is subjected to strong adverse pressure gradients. The junction flows, produced by the interaction of the boundary layer with the leading edge of the fins, enhance this bimodal pattern, feeding additional turbulence in the boundary layer and the downstream wake. The evolution of the wake towards selfsimilarity is also investigated up to nine diameters downstream of the tail. We found the mean flow approaches this condition, while its development is delayed by the wake of the appendages, especially by the flow coming from the tip of the fins. However, the width of the wake and its maximum momentum deficit follow the expected powerlaw behaviour on the side away from the sail. The second-order statistics, on the other hand, are still far from self-similarity, which is consistent with experimental observations in the literature.

Active and passive in-plane wall fluctuations in turbulent channel flows

“…The pressure Poisson equation is solved directly using fast Fourier transforms in the periodic directions (x 1 and x 3 ) and a tridiagonal matrix algorithm in the wall-normal direction (x 2 ). Beratlis, Balaras & Kiger (2007) and Posa & Balaras (2016) used the same solver with an immersed boundary formulation for treating complex geometries. A description of the numerical scheme along with a detailed validation can be found in Balaras (2004).…”

Wall-modeling for large-eddy simulation of flows around an axisymmetric body using the diffuse-interface immersed boundary method

“…The mean velocity profiles of the current simulation are in good agreement with the similarity law and the results in Refs. [25] and [27]. Fig.…”

“…(25) are algebraic, and the wall shear stress can be reconstructed by the numerical integration of Eq. (25) under the boundary condition provided by the probe point in each time step.…”

“…3). The hull has a maximum diameter D and a total length [25] . The uniform upstream flow is specified at the inlet, and the free-convection boundary condition is set at the outlet.…”

“…We have calculated the pressure coefficient with different wall models. Figure 8 shows the pressure coefficient predicted by using the WW, EB, and NEB models, respectively, where the numerical results obtained by Posa and and Balaras [25] are wall-resolved LES with full appendages while the results obtained by Posa and and Balaras [25] and Jimenez et al [27] are obtained from the side opposite to the sail. The distributions of the pressure coefficient are not sensitive to different wall models for most locations except in the trailing edge, where the pressure coefficient obtained by the NEB model is higher and agrees better with the data of Jemenez et al [27] and Huang et al [26] .…”