This paper investigates the influence of the propeller on the drag of twin self-propelled AUVs, firstly, to examine the fleet performance for various propulsive conditions of leading and following AUV and, secondly, to study the parametric influence of transverse separations and longitudinal offsets on the fleet's drag. A series of CFD RANS-SST simulations have been performed at the Reynolds Number 3.2 × 10 6 with a commercial code ANSYS CFX 12.1. Mesh convergence is tested and validated with experimental and empirical results. The RANS-HO and RANS-UT propeller models are selected to estimate the time averaged thrust and torque of the propeller. The results show that the self-propelled vehicles experience an additional drag which is dominated by the thrust distribution of the propeller rather than torque. The drag of the following AUV is increased due to the upstream propeller, defined as a propeller race deduction. For the parametric studies, the results show that increasing the spacing results in a lower drag. The two sources of self-propelled drag increment are the viscous interaction and a direct result of proximity to the propeller race upstream. The result highlights the importance of considering both thrust deduction and any propeller race deductions when calculating the propulsive power consumption.

This paper investigates the influence of the propeller race on upstream and downstream self-propelled AUVs. Initially simulations of a self-propelled hull are performed at the Reynolds Number 3.2 × 10 6 with the commercial RANS code ANSYS CFX 12.1, utilising a body force model to replicate the impact of the propeller utilising momentum source terms. This is then extended to consider a fleet of two self-propelled vehicles operating at a range of longitudinal offset and transverse separations. The results highlight that operation in close proximity to another self-propelled vessel has a significant impact of both the flow around the hull and drag experienced by the vehicle. A propeller race deduction is proposed to account for the increase in vehicle drag due to the propulsors of other vehicles. The propeller race deduction is dependent upon both longitudinal and transverse separation. From a vehicle or mission design perspective, it is important to correctly understand the true propulsive energy budget of the vehicle and its impact on both range and endurance. This study highlights the importance of considering both thrust deduction and any propeller race deductions when calculating the propulsive power consumption of an individual or fleet of vehicles.

The purpose of this paper is to provide guidance for operators on suitable spacings for multiple vehicle missions. This paper then investigates the combined drag of a pair of towed prolate spheroids for the lengthReynolds Number of 3.2 × 10 6 . The model has a lengthdiameter ratio of 6:1. A series of configuration of a pair of spheroids is simulated by varying both longitudinal and transverse spacing. Three-dimensional simulations are performed using a commercial Reynolds Averaged Navier Stokes (RANS) Computational Fluid Dynamics code ANSYS CFX 12.1 with the SST turbulence closure model. In each case, the fluid domain has a mesh size of approximately nine million cells including inflated prism layers to capture the boundary layer. Mesh convergence is tested and then validated with wind tunnel test results. The drag of each spheroid is compared against the benchmark drag of a single hull.The results show that the transverse separations and longitudinal offsets determine the interaction drag between both hulls. Increasing of spacing results in lower the interference drag. Five zones have been suggested based on the characteristics of the combined drag and individual drags. These are Parallel Region, Echelon Region, Low Interaction Region, Push Region and Drafting Region. Based on the results, operators can determine the optimal configurations based on energy considerations.

Recent studies have demonstrated that periodic spanwise modifications of the Trailing Edge of an airfoil can significantly reduce the noise produced and can also increase its aerodynamic performances. This study aims to analyse the effects of such modifications on the aerodynamic performances of a profile by numerical simulation, with a particular emphasis on low Reynolds numbers typical of Unmanned Aerial Vehicles, Micro Aerial Vehicle, and/or small wind turbines. In the range of Re numbers considered here, the flow presents laminar separation eventually followed by transition and reattachment (depending on Reynolds number, Angle of Attack and Free Stream Turbulence). As the standard for industrial applications is still the RANS approach, thanks to its moderate computational cost, this approach is considered here and a first step consists in evaluating the ability of recently proposed transition models (Menter, 2015; Ge, 2014; Kubacki, 2016) to predict the characteristics of the flow for such geometries. A baseline NACA0012 profile is considered, together with modified Trailing Edges (blunt and serrated). Simulations are performed using Code_Saturne (2nd order finite volume), and the influence of the Free Stream Turbulence, Angle of Attack, and Reynolds number on the aerodynamics performances is examined. The results are compared with data from the literature.

The influence of the cut-in sinusoidal trailing edge shape with different wavelengths on the aerodynamics characteristic has been parametrically investigated by numerical unsteady RANS simulation, open-source code; Code_Saturne. The results were compared with the benchmark baseline and blunt profile trailing edge shape. The geometry of NACA0012, NACA4412 and NACA4415 airfoil with a small modification to obtain a zero thickness trailing edge are selected as a baseline profile. The blunt trailing edge is a cut-offs at the trailing edge for 10% of the chord. Three wavelengths of sinusoidal trailing edge shape at 0.25c, 0.50c and 0.75c with 0.05c amplitude are selected, where c is the airfoil chord length. The flow is studied at high Reynolds numbers (Re) 106 for the angle of attack 5 degrees. The results show the change in lift and drag characteristics with changing of NACA profiles and the modified trailing edges.