Abstract
In the course of the most recent decades reduction of ship resistance and saving fuel consumption to accomplish higher speed with reduction of pollutants has been the significant subject for researchers. Micro bubble drag reduction technique is one of the most interesting thoughts in this field owing to its great advantages, such as considerable potential drag reduction, easy operations, environmental friendliness and low costs. In this study a 3-D numerical investigation into frictional drag reduction by air micro bubbles is applied on KRISO container ship model. The objective is to understand the mechanism of resistance reduction through micro bubbles injection under model ship at different Froude numbers, injection rate and of course volume fractions. The numerical simulations are performed using a commercial CFD code solving Reynolds averaged Navier–Stokes (RANS) equations. A large number of simulations has been performed to investigate the effect of injection of micro bubble under ship model hull to estimate the local coefficient of friction values along ship hull model. The results show that at all of the examined Froude’s numbers, frictional resistance reduction attained at different rates and a maximum drag reduction of 27.6% was obtained at 0.282 Froude number with 4.8% air volume fraction.
Highlights
These days ships are one of the most ordinary vehicles in worldwide business as it transports 90 % of the world cargo and it is commonly one of the most economical method contrasted with different method of transportation [1].Despite the fact that they are very productive as far as energy utilization per ton of and low emissions, their worldwide fuel consumption and environmental pollution are important parameters because of their broad use.[2]Marine engineers and maritime companies are striving to design and build ships with the lowest fuel consumption, in order to achieve the maximization of benefits and reduction of pollutants
Sudhir et al [22] conducted a numerical investigation for a flat plate in a 3D turbulent flow channel, and they studied the effect of micro bubbles on frictional drag reduction with varying flow speed, void fraction and geometry at the injection point, and they compared results with experimental study conducted by Moriguchi Y, Kato H [29] and found that numerical results are in good agreement with those of the model experiment
It can be seen that at all of examined Froude numbers, drag reduction attained but at different percentage and a maximum drag reduction of 27.6 % obtained at 0.282 Froude number with 4.8% air void fraction
Summary
These days ships are one of the most ordinary vehicles in worldwide business as it transports 90 % of the world cargo and it is commonly one of the most economical method contrasted with different method of transportation [1]. Researches in [28] have established a variety of experiment with the application of air lubrication method on a tanker model ship and they obtained a maximum drag reduction of 18.13% near the design speed 15 kts and they find that it was more effective to distribute the air injection at multiple locations than single injection. Sudhir et al [22] conducted a numerical investigation for a flat plate in a 3D turbulent flow channel, and they studied the effect of micro bubbles on frictional drag reduction with varying flow speed, void fraction and geometry at the injection point, and they compared results with experimental study conducted by Moriguchi Y, Kato H [29] and found that numerical results are in good agreement with those of the model experiment. In our study the model tests performed based on Froude similarity with a scale of 1/31.6, Table 1 gives the ship and model particulars.[32]
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