Mechanical Design of a Contra-Rotating Propeller Assembly ...
Design and Analysis of Contra-Rotating Propeller Blade PPT
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Transcript of Design and Analysis of Contra-Rotating Propeller Blade PPT
Design and Analysis of Contra-Rotating Propeller Blade
Contra rotating propellers are the two propellers rotating in opposite directions with respect to each other.
This type of propulsive system has the hydrodynamic advantage of recovering the slip stream energy, thus maximizing the thrust power and the propulsive efficiency.
The main aim is to analyze the contra-rotating propeller blade.
This involves modeling of blade in CATIA, Meshing in HYPERMESH, Static analysis in ANSYS. Theoretically by applying Bernoulli’s principle and Newton’s second law on the flow of water through the blade, its performance is analysed.
Abstract
The Contra rotating propeller (CRP) is a type of propulsion system which consists of two propellers on the same line of shaft, spaced a short axial distance apart and rotating in opposite directions.
contra rotating propellers can be classified broadly by virtue of its location for installation in a marine vehicle into two of its kinds
Single end CRP – Both propellers placed at single end of marine vehicle.
Dual end CRP-propellers placed at both exterme ends of the vehicle.
Contra-rotating propeller
Focus on Single end CRP Single end CRP is considered where the
rotational slip stream energy of front propeller is utilized by the aft propeller thus increasing thrust force.
Rotational speed- The aft propeller is directly installed on main engine shaft, its RPM and optimum diameter are determined. The front propeller RPM is reduced and its rotating direction is reversed by the gearing system.
Distance between propellers – To effectively utilize the slip stream energy, the propellers are placed at closest distance.
Propeller diameter-The diameter of aft propeller is reduced by a few mm since the slip stream get contracted leaving the front propeller.
Design Characteristics of CRP
The material that is considered for the analysis is forged alluminium AL-24345.
It is high corrosive resistant, light in weight and easy to maintain.
Propeller material
Property Value
Density (gm/cm3) 2710
Young’s modulus (N/mm2) 7.00*104
Poisson’s Ratio 0.33
Before modeling the blade, the data is considered for modeling.
Modeling of CRP blade
Sections r/R LLE (m) LTE (m)Pitch angle (Deg)
82.0 0.4439 0.0537 -0.0392 46.583.1 0.45 0.0541 -0.0393 46.892.4 0.5 0.0571 -0.0408 47.9
101.6 0.55 0.0589 -0.0427 48.1110.8 0.6 0.0593 -0.0452 47.6120.1 0.65 0.0579 -0.049 46.5129.3 0.7 0.0551 -0.0522 45.1138.5 0.75 0.0513 -0.0544 43.4147.8 0.8 0.0463 -0.0562 41.3157.0 0.85 0.0396 -0.0568 39.2166.2 0.9 0.0313 -0.0562 36.5170.8 0.925 0.0267 -0.054 35175.5 0.95 0.02 -0.0496 33.2180.1 0.975 0.0104 -0.0386 31.5184.7 1 -0.0019 -0.0256 29.2
Open CATIA icon. Start – shape-Generative shape design. Open macro file (Excel file) options-enable
this content and then go to view option- Macros-Click.
Select a plane and offset plane to blade radius
Plane type : offset from plane Reference plane : XY plane Offset distance : blade radius
Procedure of modeling
Select that offset plane and then go to sketcher Project all points by using project 3D element Select spline and join all the projected points Join the corner with the line after that draw the
tri tangent circle for radius of the trailing edge Trim the circle and spline to get a shape
Draw a line beside the blade section and give constraint of distance between Leading edge and generator line.
Select all the splines, curves and click on translate and drag the selected lines to the point of intersection taking origin as base.
Select the translated section and rotated it with respect to origin (click rotate and click on origin and give pitch angle)
Select circle center-support (ZX plane)-radius (take circle center as (0,0and 0))
Click on extrude-profile: circle. Direction: Y- axis and then click ok.
Click on develop-Wire to develop: profile Hide all except develop Then disassemble the developed profile in to 4 curves Repeat the process for all the sections Select spline and join all the sections. Select all the lower sections and guide curves after
clicking multi section. And repeat it for upper sections and corners
After that double click on any plane or surface and go to GSD then the four multi sections should be extrapolated.
After that all extrapolated surfaces are to be joined by using join command. Once they joined the unnecessary part is eliminating by using split command.
After the splitting the split surface is filled by using fill option.
Once they are joined, by using close surface command, the blade is to be made solid
Blade is imported to HYPERMESH Environment Select the import sub panel on the files panel. Select the Geom option. Select the appropriate file format to be imported from
the pop-up menu.
Importing of Blade to Mesh
Select the solid map panel on the 3-D page. Select the volume tetra sub-panel. With the surf selector active, select one of the surfaces in the
model. The rest of the connected surfaces are selected automatically. Set 2D: to trias and 3D: to tetras and specify element size. Click mesh to create the hexa mesh.
Meshing
The propeller blade is assumed as radial vane and the water is assumed to flow tangentially at the inlet of blade.
From Bernoulli’s theorem, for an incompressible fluid like water, the total
energy at any point is constant P1/ρg + v1
2/2g + z1 = P2/ρg + v22/2g + z2
P1, v1, z1 - initial conditions of water before striking the propeller
P2, v2, z2 – final conditions of water after striking the propeller
Theoretical calculations
P1/ρg – P2/ρg = v22/2g
Power required to accelerate the water Power (P) = w*Q*H P = w*Q*(P1/ρg – P2/ρg) P = ρ*A*v2
3/2 Since the blade is assumed as radial vane, its
velocity triangle is as shown
To calculate the thrust force, the data consideration is as shown
Single
Propeller
Contra rotating
Propeller
Front Propeller Aft Propeller
Engine Power(hp) 20,000 10,000 10,000
Engine Speed(rpm) 800
550
800
Propeller
diameter (m)
1
1
0.74
PropellePitch (inches)
27 28
20
Angleof
deflection(degrees)
120
120
120
The blade angle is calculated by treating the propeller as screw
Tan α = Pitch / 2πr Considering the angle of deflection as 1200
From the velocity triangles, Thrust force Fx = ρav1 (vw1 – vw2) Thrust power = Fx x V ( where v is the
average velocity of ship i.e., 15 knots)
Propulsive efficiency η p = T.P / P
From the procedure, the obtained results for both single propeller and contra rotating propellers is as shown
Single
Propeller
Thrust
Force (KN)
1174.298
Thrust
Power (KW)
8861.056
Propulsive
Efficiency (%)
59
Contra Rotating
Propellers
Front
Propeller
Aft
PropellerThrust Force
(KN)
617.87 646.944
Thrust Power
(KW)
9544.05
Propulsive
Efficiency
(%)
65
Static analysis is performed to determine deflection and stresses experienced by the CRP blade.
From the theoretical calculations, the force acting on CRP is assumed to be uniformly distributed at all sections.
Meshed blade is imported to ANSYS for analysis as shown
Static Analysis
One end is fixed and loads are applied at every section from the load data shown
SECTIONSIN Z Direction
SECTION LOAD (THRUST) (N)
SECTION LOAD (TORQUE) (N)
FX FY
82.103 - -
83.25 16.58 12.33
92.5 16.58 12.33
101.75 16.58 12.33
111 16.58 12.33
120.25 16.58 12.33
129.5 16.58 12.33
138.75 16.58 12.33
148 16.58 12.33
157.25 16.58 12.33
166.5 16.58 12.33
171.125 16.58 12.33
175.75 16.58 12.33
180.375 16.58 12.33
185 0 0
TOTAL 646.42 480.29
The displacement vector sum and von-mises stress are as shown
Maximum deflection is 0.641mm Maximum stress is 103.264N/mm2
Prototype
More power can be transmitted for a given propeller radius.
The propeller efficiency is increased by recovering energy from the tangential (rotational) flow from the leading propeller.
The mechanical installation of coaxial contra-rotating shafts is complicated, expensive and requires more maintenance.
Suitable for Tankers, Cargo vessels, LNG carriers, Ferries, Cruise vessels and various types of Naval vessels.
Suitable for wind turbine and tidal turbine for ocean energy utilisation.
Advantages, Disadvantages and Applications
The results show the contra rotating propeller found to be as expected superior to the traditional single propeller.
The propulsive efficiency of the contra rotating propeller at the design point of view is about 6% higher than the single propeller design (65% and 59% respectively).
The Ansys results proves that the obtained deflections and stresses induced in the after propeller are within permissible limits.
Conclusion
Single
propeller
Contra Rotating
Propellers Front Propeller After Propeller
Thrust force
(KN)
1174.298 617.87 646.944
Thrust Power
(KW) 8861.056 9544.07
Propulsive
Efficiency
(%)
59 65
USUM U X UY UZ
0.641 0. 456 0. 451 0. 031