Hull efficiency is defined as:ηH=(1 –t) / (1 –wT), see Equation (16.2) wherewTis wake fraction andtthe thrust deduction factor.
8.11.1 Submarine and AUV Wake
In the absence of aft control planes or a propeller, the wake contours would be con- centric circles around the propeller axis. This would be ideal from the point of view of the propeller operating in a uniform flow. With rudders and control planes present, there are wake shadows from these upstream appendages and the wake contours tend to be distorted as shown in Figure 8.18. The propeller now works in a non- uniform flow as it rotates. This leads to a fluctuating loading, which is not desirable from a blade strength point of view or for predicting the onset of cavitation and noise.
Wake values for propulsor design purposes are shown in Figure 8.19, which were derived using data from [8.29]. Tailcone angle is defined in Figure 8.20. It is noted that wTdecreases as Dp/Dh increases, with less of the propulsor in the boundary layer.
Hence the expected improvement inηO, henceηD, with an increase in propulsor diameter will be reduced due to the decrease inwTandηH.
Mean
P S
Centreline Thrust
forces
Torque forces
Figure 8.17. Thrust and torque forces due to tangential wake.
Figure 8.18. Submarine circumferential wake variation.
0.1 0.2 0.3 0.4 0.5 0.6
10 20 30 40 50 60 70
Tailcone angle (deg.)
Wake Fraction Dp/Dh = 0.40
Dp/Dh = 0.50 Dp/Dh = 0.60 Dp/Dh = 0.70
Dp = Prop Dia Dh = Hull Dia
Figure 8.19. Submarine mean wake fraction values. (Note: these are model values and suit- able for AUVs. Full-scale values for submarines are about 10% lower.)
Figure 8.20. Definition of tailcone angle.
0.00 0.05 0.10 0.15 0.20 0.25
10 20 30 40 50 60 70
Tailcone angle (deg.)
Thrust deduction factor
Dp/Dh = 0.40 Dp/Dh = 0.50 Dp/Dh = 0.60 Dp/Dh = 0.70
Dp = Prop Dia Dh = Hull Dia
Figure 8.21. Submarine and AUV thrust deduction factor values.
8.11.2 Submarine and AUV Thrust Deduction
Figure 8.21 shows values of thrust deduction factor (t) for design purposes. The values were derived using data from [8.29].t reduces with increase in Dp/Dh, but not as much aswT, and the net overall effect is a decrease inηH.
8.11.3 Submarine and AUV Relative Rotative Efficiency Take, say, 1.03 as a working value [8.29], or 1.05 [8.30].
REFERENCES (CHAPTER 8)
8.1 Harvald, S.A. Potential and frictional wake of ships.Transactions of the Royal Institution of Naval Architects, Vol. 115, 1973, pp. 315–325.
8.2 Harvald, S.A.Resistance and Propulsion of Ships. Wiley Interscience, New York, 1983.
8.3 Van Manen, J.D. Fundamentals of ship resistance and propulsion. Part B Propulsion. Publication No. 129a of NSMB, Wageningen. Reprinted inInter- national Shipbuilding Progress.
8.4 Harvald, S.A. Wake distributions and wake measurements.Transactions of the Royal Institution of Naval Architects, Vol. 123, 1981, pp. 265–286.
8.5 Van Manen, J.D. and Kamps, J. The effect of shape of afterbody on propulsion.
Transactions of the Society of Naval Architects and Marine Engineers, Vol. 67, 1959, pp. 253–289.
8.6 ITTC. Report of the specialist committee on wake fields.Proceedings of 25th ITTC, Vol. II, Fukuoka, 2008.
8.7 Di Felice, F., Di Florio, D., Felli, M. and Romano, G.P. Experimental investi- gation of the propeller wake at different loading conditions by particle image velocimetry.Journal of Ship Research, Vol. 48, No. 2, 2004, pp. 168–190.
8.8 Felli, M. and Di Fellice, F. Propeller wake analysis in non uniform flow by LDV phase sampling techniques.Journal of Marine Science and Technology, Vol. 10, 2005.
8.9 Visonneau, M., Deng, D.B. and Queutey, P. Computation of model and full scale flows around fully-appended ships with an unstructured RANSE solver.
26th Symposium on Naval Hydrodynamics, Rome, 2005.
8.10 Starke, B., Windt, J. and Raven, H. Validation of viscous flow and wake field predictions for ships at full scale.26th Symposium on Naval Hydrodynamics, Rome, 2005.
8.11 ITTC. Recommended procedure for the propulsion test. Procedure 7.5-02-03- 01.1. Revision 01, 2002.
8.12 Dyne, G. On the scale effect of thrust deduction.Transactions of the Royal Institution of Naval Architects, Vol. 115, 1973, pp. 187–199.
8.13 Lübke, L. Calculation of the wake field in model and full scale.Proceedings of International Conference on Ship and Shipping Research, NAV’2003, Palermo, Italy, June 2003.
8.14 Taylor, D.W.The Speed and Power of Ships. Government Printing Office, Washington, DC, 1943.
8.15 Lackenby, H. and Parker, M.N. The BSRA methodical series – An overall presentation: variation of resistance with breadth-draught ratio and length- displacement ratio.Transactions of the Royal Institution of Naval Architects, Vol. 108, 1966, pp. 363–388.
8.16 Pattullo, R.N.M. and Wright, B.D.W. Methodical series experiments on single- screw ocean-going merchant ship forms. Extended and revised overall analy- sis. BSRA Report NS333, 1971.
8.17 Holtrop J. A statistical re-analysis of resistance and propulsion data.Interna- tional Shipbuilding Progress, Vol. 31, 1984, pp. 272–276.
8.18 Parker, M.N. and Dawson, J. Tug propulsion investigation. The effect of a but- tock flow stern on bollard pull, towing and free-running performance.Trans- actions of the Royal Institution of Naval Architects, Vol. 104, 1962, pp. 237–279.
8.19 Moor, D.I. An investigation of tug propulsion.Transactions of the Royal Insti- tution of Naval Architects, Vol. 105, 1963, pp. 107–152.
8.20 Pattulo, R.N.M. and Thomson, G.R. The BSRA Trawler Series (Part I). Beam- draught and length-displacement ratio series, resistance and propulsion tests.
Transactions of the Royal Institution of Naval Architects, Vol. 107, 1965, pp. 215–241.
8.21 Pattulo, R.N.M. The BSRA Trawler Series (Part II). Block coefficient and longitudinal centre of buoyancy series, resistance and propulsion tests.
Transactions of the Royal Institution of Naval Architects, Vol. 110, 1968, pp. 151–183.
8.22 Thomson, G.R. and Pattulo, R.N.M. The BSRA Trawler Series (Part III).
Resistance and propulsion tests with bow and stern variations.Transactions of the Royal Institution of Naval Architects, Vol. 111, 1969, pp. 317–342.
8.23 Flikkema, M.B., Holtrop, J. and Van Terwisga, T.J.C. A parametric power pre- diction model for tractor pods.Proceedings of Second International Confer- ence on Advances in Podded Propulsion, T-POD. University of Brest, France, October 2006.
8.24 Bailey, D. A statistical analysis of propulsion data obtained from models of high speed round bilge hulls.Symposium on Small Fast Warships and Security Vessels. RINA, London, 1982.
8.25 Gamulin, A. A displacement series of ships. International Shipbuilding Progress, Vol. 43, No. 434, 1996, pp. 93–107.
8.26 Moor, D.I. and O’Connor, F.R.C. Resistance and propulsion factors of some single-screw ships at fractional draught.Transactions of the North East Coast Institution of Engineers and Shipbuilders. Vol. 80, 1963–1964, pp. 185–202.
8.27 Harvald, A.A. Wake and thrust deduction at extreme propeller loadings for a ship running in shallow water.Transactions of the Royal Institution of Naval Architects. Vol. 119, 1977, pp. 213–236.
8.28 Blount, D.L.Performance by Design: Hydrodynamics for High-Speed Vessels.
Published by the author, Virginia Beach, USA, 2014.
8.29 Burcher, R.K. and Rydill, L.J.Concepts in Submarine Design. Cambridge Ocean Technology Series, Cambridge University Press, Cambridge, UK, 1994.
8.30 Renilson, M. Submarine Hydrodynamics. Springer Science and Business Media, London, 2015.
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