Drag analysis of proposed submarine hull designs.

• AIM OF THE PROJECT

Aim of this project is to examine using CFD analysis, the bare hull form of submarines for minimizing the drag resistance under water. There are several parameters involved in determining the submarine hull design out of which the most important parameter is drag. Water drag resistance is a lot more of a concern than other minimal effects..All operational characteristics of submarines are related to the drag resistance, like required power and underwater speed and range.

• SCOPE OF THE PROJECT

Submarine shape design strictly depends on the hydrodynamic characteristics. In submerged navigation, submarines posses only a limited amount of energy, hence any resistance to its motion should be minimised in order to navigate effectively and efficiently. Based on this fact, it is important for the submarine design to offer as much low resistance as possible. This project thus focuses on design and dnalysis of various submarine hull shapes for minimum drag resistance and establishing a base design for further research.

• METHODOLOGY

The standard submarine dimensions of a typhoon class submarine are 175m length to 23-25m wide. These were scaled down by a factor of 25.The dimensions of all the prototypes were kept similar for easier comparison. The prototypes had a length of 7m and a width/diameter of 1m.The CAD models of the submarine hulls were created using SolidWorks .These models were meshed using the Ansys mechanical mesher with close to a 100000 nodes for each model. The flow analysis was performed using Ansys fluent. The velocity of the submarine was taken to be 40knots(20m/s).The solutions converged at about 200-500 iterations. A k-omega SST turbulence model was used for this analysis.

• PROPOSED DESIGNS

1)

The first design is more sleek as compared to other designs.This design has a complete taper from head to tail with the head having fine contours to reduce the drag as much as possible.The manouvering fins dimensions are smaller for this design as compared to others to create as less frontal are as possible.

2)

The second design has a tapering section at the head of the submarine with all the the manouvering fins at the tail side.The mid section of the submarine is a straight cylinder.The manouvering fins for this design are larger as compared to the other designs to observe its impact on the drag force.

3)

The third design has the tapering section at the tail.The mid section is a straight cylinder which continues to the head.It is to be noted that this design has the maximum frontal area as compared to the other three desings.The manouvering fins are placed at the tail with reduced dimensions.

• PRESSURE AND VELOCITY CONTOURS

Pressure contours Velocity contours

• DRAG FORCE RESULTS

• CONCLUSIONS

1)The three designs proposed consisted of different design pecularities with varying cross sections.

2)From the velocity and perssure contours the stagnations points can be observed for the three designs.

3)The pressure distributuion is better for design 1 and hence is more structurally safe.

4)The larger manouvering fins in design 2 contribute to a larger drag force due to increase in frontal area.

5)The comprehensive analysis results show that drag coefficient of the touchstone (Subhull_1) model is 2.06, at a velocity of 20m/s(40 knots) underwater at the depth of 100m(standard submarine operating conditions).

6)The resultant drag force observed is 58.78N and total force on the hull observed was 58.78N which is the least among all the proposed designs.Hence this design is recommended for further analysis.