Influence of Propulsion Type on the Stratified Near Wake of an Axisymmetric Self-Propelled Body

Abstract

To better understand the influence of swirl on the thermally-stratified near wake of a self-propelled axisymmetric vehicle, three propulsor schemes were considered: a single propeller, contra-rotating propellers (CRP), and a zero-swirl, uniform-velocity jet. The propellers were modeled using an Actuator-Line model in an unsteady Reynolds-Averaged Navier-Stokes simulation, where the Reynolds number is Re L = 3.1 × 10 8 using the freestream velocity and body length. The authors previously showed good comparison to experimental data with this approach. Visualization of vortical structures shows the helical paths of blade-tip vortices from the single propeller as well as the complicated vortical interaction between contra-rotating blades. Comparison of instantaneous and time-averaged fields shows that temporally stationary fields emerge by half of a body length downstream. Circumferentially-averaged axial velocity profiles show similarities between the single propeller and CRP in contrast to the jet configuration. Swirl velocity of the CRP, however, was attenuated in comparison to that of the single propeller case. Mixed-patch contour maps illustrate the unique temperature distribution of each configuration as a consequence of their respective swirl profiles. Finally, kinetic and potential energy is integrated along downstream axial planes to reveal key differences between the configurations. The CRP configuration creates less potential energy by reducing swirl that would otherwise persist in the near wake of a single-propeller wake.

Modelling a Moving Propeller System in a Stratified Fluid Using OpenFOAM

“…This is visualised by the warped contours in the centre of Figure 2. Similar temperature profiles have been observed in propeller studies involving actuator line models [11,12]. The temperature of the patch was not perfectly uniform as a result of this continuous entrainment from the undisturbed regions of the stratification.…”

“…Numerical approaches to modelling the action of propeller motion on fluids include actuator line and actuator disk models [9][10][11][12]; blade element momentum theory [13][14][15][16]; and models in which the propeller blades are fully resolved by the computational mesh and dynamically rotated [17][18][19]. The latter approach was considered by Colley [17], for example, who modelled a 5-blade KCD-32 series propeller using OpenFOAM; an open-source fluid dynamics modelling framework [20][21][22].…”

Computational hydroacoustic analysis of the BB2 submarine using the advective Ffowcs Williams and Hawkings equation with Wall-Modeled LES

“…For this reason in the close future we plan to address further investigations about BB2 submarine acoustic signature, taking into account also the effect of the ocean stratification. In fact, it is well known (Pal et al, 2016;Jones & Paterson, 2018;Armenio & Sarkar, 2002) that stratification strongly influences the distributions of Reynolds stresses in the wake and, as a consequence of this, it could affect the resulting noise. To make the model even more realistic, the marine propeller should be then considered.…”

Formation of the Vorticity Field of a Stratified Fluid Near a Wedge

“…The molecular flow interruption at the impermeable boundaries of arbitrary shape generates induced diffusion flows. A stable stratification enables transport of dissolved substances and self-displacement of neutral buoyancy solids in even in the absence of evident external mechanical influences [1,2].…”

“…The set of equation (1)(2)(3)(4) with the initial and boundary conditions (5, 6) is characterized by a number of characteristic scales including time scale, T b , velocity scales (…”