A computational fluid dynamics approach to study drag reduction of axisymmetric underwater bodies by air jet injection in the boundary layer is presented. The well-known ‘mixture’ model is used to capture the multiphase flow and the SST k-ω (shear stress transport) turbulence closure model has been used in the computations. Well-studied Afterbody1 (Huang et al., 1978) which has a tapered and smooth stern profile is considered. A companion shape of Afterbody1, which has a blunt stern profile, is also studied. The numerical study is carried out with different air jet velocity to body velocity ratios, various angles of air jet and various angles of attack of the body. Effects of these parameters on drag reduction are reported. The effect of tapered vs. blunt aft shape of Afterbody1 has been found to have significant effect on drag reduction performance. © 2013 Taylor and Francis Group LLC.

S. Vengadesan

Department of Applied Mechanics

S. K. Bhattacharyya

Department of Ocean Engineering

S. G. Shereena

V. G. Idichandy

Fulltext

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IIT Madras

CFD Study of Drag Reduction in Axisymmetric Underwater Vehicles using Air Jets

Engineering Applications of Computational Fluid Mechanics

The increase in fuel costs and looming restrictions on carbon dioxide emissions are driving the shipowner into reducing the ship’s resistance and required installed power. It was earlier reported that, merchant vessels operating at lower speeds, the frictional drag accounts of almost 70–80% of the total drag; thus, there is a strong demand for the reduction in the fluid frictional drag, especially in the marine transportation business. The use of air as a lubricant, by injecting below the plate or the body, which is famously known as microbubble drag reduction (MBDR) in order to reduce that frictional drag is an active research topic. Latest developments in this field suggests that there is a potential reduction of 80% in frictional drag in case of flat plates and about 30% reduction in case of ships, which encourages researchers to investigate further. In this study, 3D numerical investigations into frictional drag reduction by microbubbles were carried out in Star CCM+ on a channel for different flow velocities, different void fractions and different cross sections of flow at the injection point. This study is the first of its kind in which variation of coefficient of friction both in longitudinal and transverse directions was studied along with actual localized variation of void fraction at these points. The numerical framework consists of the Reynolds-averaged Navier–Stokes (RANS) equations and the standard k−ε turbulence model with standard wall function treatment, which is validated in both conditions of with and without microbubbles with the existing experimental data. The design exploration study was carried out for various flow speeds, injector flow rates, cross sections of the channel/heights of channels and of course void fractions. Coefficient of friction and void fraction values are measured at 12 longitudinal positions, and at each longitudinal position, 11 in number transverse and 10 in number depthwise positions were studied. In all, for one simulation, data at more than 1000 positions were collected. More than 60 simulations were carried out to understand the effect. From the study, it is concluded that since it is a channel flow and as the flow is restricted in confined region, effect of air injection is limited to smaller area in transverse direction as bubbles were not escaping in transverse direction. © Springer Nature Singapore Pte Ltd. 2019.

Lecture Notes in Civil Engineering

Numerical investigation of influence of microbubble injection, distribution, void fraction and flow speed on frictional drag reduction

This paper adopts Genetic Algorithm (GA) -driven optimisation framework to solve the design optimisation problem of an autonomous underwater vehicle that aims to minimise the delivered power under the constraints on the geometric parameters that define the hull shape. The GA and computational fluid dynamics (CFD) solvers are seamlessly integrated into a single code so that it becomes an effective computational tool for optimisation. Adopting a hull and a ducted propeller, for which some experimental data are available for CFD validation, the optimisation is done for the shape of the hull for a single velocity, leading to significant reduction in delivered power. The hull shape is described by a 5-parameter axisymmetric form. Delivered power minimisation problem is compared with the corresponding drag minimisation problem of the chosen hull. © 2017 Informa UK Limited, trading as Taylor &amp; Francis Group.

Ships and Offshore Structures

Shape optimisation of an AUV with ducted propeller using GA integrated with CFD

Science China Physics, Mechanics and Astronomy

Numerical investigation of turbulent bubbly wakes created by the ventilated partial cavity

Ocean Engineering

Numerical simulation of micro-bubble drag reduction using population balance model

Robust design of microbubble drag reduction in a channel flow using the Taguchi method

International Journal of Heat and Fluid Flow

Drag reduction by gas injection into turbulent boundary layer: Density ratio effect

International Communications in Heat and Mass Transfer

Temporal correlation modification by microbubbles injection in a channel flow

CFD study of drag reduction in axisymmetric underwater vehicles using air jets

Journal	Engineering Applications of Computational Fluid Mechanics
Open Access	No