Experimental Parametric Investigation to Reduce Drag of a Scaled Model of Bulk Carrier Using BDR/ALS Technique

Abstract

The shipping business expects to develop energy-saving and drag-reducing techniques addressing the cost of shipping and environmental problems. It has been reported that for slow-moving vessels, frictional resistance accounts for up to 80% of the total resistance, needing urgent attention to reduce the same. To reduce frictional resistance, the air has been used as lubricant, which is injected below the moving body known as Bubble Drag Reduction or the Air Lubrication System. In this article, results obtained from experimental investigations into drag reduction of a 1:23 scaled model of an 8000-ton deadweight bulk carrier by injecting air bubbles below it are presented. Investigations were carried out for a speed range of 6-10 knots, and for each speed, the effect of six injection flow rates of .5-3.0 CFM were investigated. To investigate the effect of different sizes of injection holes, two types of injector units have been used: one with injection holes of 1 mm diameter and the other with injection holes of 2 mm diameter. The study carried out has many practical implications because it is easier to create bigger size holes which will reduce the power required to inject air, thereby increasing the efficiency of the entire technique. 1. Introduction It is projected that crude oil prices will continue to increase in the future, forcing marine businesses to rely on researchers to develop energy-saving devices (ESD) and drag-reducing technologies. It has been reported that for slow-moving vessels such tankers, bulk carriers, very large crude carrier (VLCC), and ultra large crude carrier (ULCC), frictional resistance accounts for up to 80% of the total resistance, needing urgent attention to reduce the same (Lewis n.d.; Larsson & Raven 2010). Numerous technologies have been studied and applied in reducing the frictional drag (Brostow 2008; Abdulbari et al. 2013; Luo et al. 2015; Mohammad & Mousavi 2015; Sindagi et al. 2016). Based on further studies Sindagi et al. (2018a, 2018b, 2018c, 2018d) and Sindagi and Vijayakumar (2020), it is concluded that air lubrication has additional advantages over other technologies, such as it is environmentally friendly, the operation is quite easy, and it results in low operating costs and high energy savings. Moreover, with air lubrication, an 80% reduction in the drag of the flat plate was achieved by Merkle et al. (1983) and Madavan et al. (1984, 1985).

Micro/Bubble Drag Reduction Focused on New Applications

“…On the other hand, according to the authors, the size of the bubble was a dominant parameter for the MBDR region, with the finding that the smaller the size, the better the DR. However, this is in contrast to the previous results of Sindagi et al [60]. On the other hand, speed was also found to be relevant, as it affected the size of the bubbles, with a higher DR for a higher Fr.…”

“…From the search of publications conducted, only seven of them referred to microbubble drag reduction experiments conducted in towing tank facilities. In most of them, ship models were tested, with the most common type of ships tested being the barge [57,58] and the bulk carrier [59,60]. The length of the models ranged from 0.2 m in Ref.…”

“…The size of the bubbles generated is not usually provided, but instead either the flow rate or the injection flow coefficient is usually used. The flow rate is generally measured by means of flowmeters [60,61]. In this way, the injection coefficient is defined as [57,58,62]:…”

“…In 2021, Sindagi et al [60] performed an experimental study on a scale model of a bulk carrier in a towing tank facility at different speeds (6-10 knots), with two series of different sizes of injection holes (2 mm and 1 mm) at different air injection rates. Acrylic sheets were used to replace the bottom to visualize the flow and the migration of the bubbles.…”