DRAG REDUCTION THROUGH AIR LUBRICATION

JAY PRAKASH JHA2015AMX155509

FLASHBACK:1. Background of the project2. Frictional Drag: Review3. Ways for reduction of FDR4. Advantages of ALS 5. Techniques of ALS6. Future projects7. Outcomes 8. Timeline9. References

WAY AHEAD:1. Flat plate experiment method2. Conclusions and results3. Boundary mixture model4. Conclusions and results5. Gambit modelling6. Workbench modelling7. Simulation results

1. CFD ANALYSIS

CFD STUDY OF DRAG REDUCTION IN AXISYMMETRIC UNDERWATER VEHICLES USING AIR JETS1. AXISYMMETRIC BODY2. MULTIPHASE FLOW3. STEADY FLOW4. SST k-€ model

GAMBIT MODELLING:

WORKBENCH MODELLING:

2. BOUNDARY LAYER MODEL:

The air volume fraction Cv is defined as the ratio of the injected air flow rate divided by the summation of the air flow rate and the water flow rate within the boundary layer,

*H. Schlichting, Boundary-Layer Theory,

BOUNDARY LAYER MODEL:Reistance coefficient of flat plate

frictional resistance of a flat plate with a water-bubble mixture boundary layer

DRAG REDUCTION RATIO DR PREDICTED BY THE BOUNDARY LAYERMIXTURE MODEL *H. Schlichting, Boundary-Layer Theory,

CONCLUSIONS:

Cv ρb/ρw Rebl^(0.2)/Rel^(0.2) Cfb/Cf DR0 1 1 1 00.1 0.9 1 0.9 0.10.2 0.8 1.001 0.801 0.1990.3 0.7 1.001 0.701 0.2990.4 0.6 1.002 0.602 0.3980.5 0.501 1.003 0.502 0.4980.6 0.401 1.004 0.402 0.5980.7 0.301 1.006 0.303 0.7970.8 0.201 1.011 0.203 0.8970.9 0.101 1.024 0.103 0.9970.99 0.011 1.174 0.013 0.987

CONCLUSIONS:

0 0.2 0.4 0.6 0.8 1 1.20

0.2

0.4

0.6

0.8

1

1.2

0

0.1

0.199

0.299

0.398

0.498

0.598

0.797

0.897

0.997 0.987

DR

DR

CONCLUSIONS:

0 0.2 0.4 0.6 0.8 1 1.20

0.2

0.4

0.6

0.8

1

1.2

0

0.1

0.199

0.299

0.398

0.498

0.598

0.797

0.897

0.9970.987

DR

CONCLUSION:

The effect of the Reynolds number is very small when compared with the effect of density of the mixture.

The density of the bubble mixture becomes the key parameter for the microbubble drag reduction technique.

The ratio of the frictional resistance of the water-bubble mixture boundary layer to the water boundary layer is almost directly proportional to the density ratio.

2. FLAT PLATE EXPERIMENT MODEL

• The power savings resulting in the reduction of friction drag are compared to the air pumping costs for flow on the flat bottom of a ship hull. • The effect of speed, length, and draft are considered. • These calculations represent the best-case conditions for an ideal, two-dimensional flow.

FLAT PLATE EXPERIMENT MODEL

We consider the flow beneath a horizontal flat surface.

Gas is injected near the leading edge of a horizontal flat surface of length L and width b. The free-stream flow beneath the surface has velocity U, and the depth (i.e. draft) of the surface is d.

.

FORMULAE INVOLVED:

The baseline power needed to move the fluid across the surface of the plate is

The power needed to inject a given quantity of air beneath the surface of the hull is given by

Friction drag coefficient

qA = gas volume flux per unit width pA = atmospheric pressureηA = the pumping efficiency.

Ceccio, S.L. “Friction Drag Reduction

FORMULAE INVOLVED:To create an air layer on a smooth surface

producing an average %DR =80%, the required minimum flux is: qALS = 0.0002U^ 2 + 0.0063U − 0.0234

To create an air layer on a rough surface producing an average of %DR = 80%, the required minimum flux is qALR = 0.0004U ^ 2 + 0.0058U − 0.0003

Power saved is given by ELBING ET AL(2008)

CONCLUSIONS: The relationships presented above suggest that the air flux

required to form air layers increases as ~ U^2, while the propulsive power increases as U^3.

Also, the required pumping power will increase as ~ d^2.

Therefore, with 100% drag reduction, and negligible air pumping power, the savings would be 100%.

The required gas fluxes will most likely increase when the

unsteadiness and three dimensionality of a ship hull is present.

1.) Given rectangular plate dimensions: using ITTC FORMULA, power required to move the plate (without ALS) P1 = 711.816 watts 2.) using ALS, power required to move to plate is given by So, P2 = 377.735 watts also, for 80% drag reduction, power required to pump the air is given by P3 = 0.667 watts

REDUCTION IN POWER VALUE= 46.8 %

CALCULATION:

LENGTH: 20 MBREADTH: 5MSPEED OF ADVANCE:10M/S

1. Ceccio, S.L., Perlin, M. and Elbing, B.R., “A cost-benefit analysis for air layer drag reduction” Proc. Int. Conf. On Ship Drag Reduction- SMOOTH-SHIPS, Istanbul, Turkey. 2010

2. Gokcay, S., Insel, M., and Odabasi, A.Y. “Revisiting artificial air cavity concept for high speed craft.” Ocean Engineering, 31

3. Hoang, C. L., Toda, Y., and Sanada, Y. “Full scale experiment for frictional resistance reduction using air lubrication method,” Proc. of the Nineteenth International Offshore and Polar Engineering Conference, 812-817, 2009

4. Kodama, Y., Kakugawa, A., Takahashi, T., and Kawashima, H. “Experimental study on microbubbles and their applicability to ships for skin friction reduction.” International Journal of Heat Fluid Flow, 21:582–88. 2000

5. Latorre, R., “Ship hull drag reduction using bottom air injection.” Ocean Engineering, 24(2),. 1997

6. Mizokami, S., Kawakita, C., Kodan, Y., Takano, S., Higasa, S., & Shigenaga, R. "Experimental Study of Air Lubrication Method and Verification of Effects on Actual Hull by Means of Sea Trial." Mitsubishi Heavy Industries Technical Review, 47(3), 41-47, 2010.

REFERENCES