Counter-directional vortex cover for underwater propellers
The contra-rotating propeller also known as counter rotating propeller cancels out the rotational air flow, pushing a maximum amount of air uniformly through the propeller disk, resulting in high performance and low induced energy loss.
The concept for the project involves contra-rotating propeller but with different functionality. The two propellers of contra-rotating propeller will be called as main propeller and tail propeller. The diameter of main propeller will be less than that of tail propeller. The function of main propeller is to form the primary vortex which is responsible for the thrust generation where as the tail propeller is responsible for the generation of secondary counter-directional vortex to narrow down the diverging primary vortex. This will result in unidirectional non-cancellable rotation of air flow. As the vortex of main propeller is converge, the thrust will increase significantly.
The rotational motion of propeller cause reaction force known as thrust. As a result, the plane and boat gains linear acceleration. The diameter of vortex form by propeller goes on increasing along the downstream, which result in decrease of thrust generated proportionally with each other. The basic idea to increase the thrust is to converge the diameter of primary vortex with the help of additional secondary counter-directional vortex formation over it.
Concept:
Increasing the performance of the propeller by decreasing the downstream divergent vortex and ultimately increasing the thrust with the help of contra-rotating propeller.
Design:
Shaft diameter of main propeller = D
Shaft length of main propeller = D
Blade diameter of main propeller = 3D
Shaft diameter of tail propeller = 3D
Shaft length of tail propeller = D
Blade diamter of tail propeller = 5D
The shaft diameter is hollow and the blades are mounted on the circumference of it. The postioning of tail propeller is first along the downstream as a result the counter-directional vortex cover is form before the formation of primary vortex.
An enclosure is created around each of the propeller and also a fluid flow region is created through which the flow of water will be simulated.
The project is divided into 3 cases as per the rotating speeds of main rotor and tail rotor.
For the analysis of this model, K-epsilon turbulence model with scallable wall functions is used in order to capture the turbulence and flow of water around the blades of the propeller.
Boundary conditions:
Mesh element size = 30mm
Velocity of water at inlet = 2 m/s
Case 1:
Rotational speed of main rotor = -10000 rad/s
Rotational speed of tail rotor = 5000 rad/s
Velocity contour:
Velocity vectors:
Case 2:
Rotational speed of main rotor = -10000 rad/s
Roatational speed of tail rotor = 10000 rad/s
Velocity contour:
Velocity vectors:
Conclusion:
According to the results obtained from the simulations above, it can be concluded that as the rotational velocity of the tail rotor increases, the counter-directional vortex cover generated by the tail rotor also increases its effect on the divergence characteristic of the vortex formed by the main rotor.
Implementation of counter-directional vortex cover will not only increase the thrust of existing propeller but also make the downstream vortex controllable. It will make two speed jets to ride closely with each other without worrying the water current generated by them.