Teaching sessions week 40

Transcription

1 Teaching sessions week 40 Monday 28 September Lecture: Introduction to propulsion. Momentum theory of propeller action. Friday 2 October Lecture: Screw propeller Introduction of Marine Hydrodynamics 1

2 Propellers and propulsion Kul Introduction of Marine Hydrodynamics Introduction of Marine Hydrodynamics 2

3 Content of the course Resistance Propulsion (Week 40) Introduction, Momentum theory on propeller action (Week 40) Screw propeller (Week 40) Propeller-hull interaction Early design of a propeller Propeller main engine interaction Stopping, accelerating and backing properties Propeller cavitation Special types of propulsors Afterbody form of a ship Ship dynamics Introduction of Marine Hydrodynamics 3

4 Topic, learning outcomes, literature Topic General on propulsion On the development of the propulsors Momentum theory of propeller action After this part you can describe features of a good propulsor. describe the historical development of propulsors. explain the action of a propeller using the momentum theory of propeller action. Additional reading Matusiak J (2010) Laivan propulsio. M-176. Chapters 1-2 Matusiak J (2008) Short introduction to Ship Resistance and Propulsion. Sections Lewis E.V., editor (1988) Principles of Naval Architecture, Second revision. Volume II, parts of Chapter 6. SNAME. Available in Knovel. Introduction of Marine Hydrodynamics Aalto University 4

5 Outline: Introduction to propulsion General Development of the propulsors Momentum theory of propeller action Summary Introduction of Marine Hydrodynamics 5

6 On the hydrodynamic design of a ship Ideal conditions Still water Constant speed No drift angle Forces acting on a ship Weight of a ship Environmental forces acting on a hull acting on a propulsor Introduction of Marine Hydrodynamics 6

7 Forces acting on a ship Introduction of Marine Hydrodynamics 7

8 Forces acting on a propulsor Integration of the stress q over the surface A of the propulsor gives the force F p and the moment M p of the propulsor x z G V Thrust T: The force component that acts on the propeller in the direction of the ship. F x = R T + R P = T p n r M p da F p T Introduction of Marine Hydrodynamics 8

9 On propulsors Propulsion means development of a thrusting force which balances ship resistance and inertia force associated with ship acceleration. Explaining the action of a propulsor: Momentum theory The propulsor accelerates water backwards. The generated reaction force push the ship forwards. Features of a good propulsor Steady thrust, Good efficiency, Reliability Thrust is easily controlled and directed (good acceleration and stopping qualities) Propulsion is well suited to hull and vice versa Small investment and operational costs Does not cause vibration nor noise Operates well in a variety of conditions (ice, shallow water, etc.) Introduction of Marine Hydrodynamics 9

10 Outline: Introduction to propulsion General Development of the propulsors Momentum theory of propeller action Summary Introduction of Marine Hydrodynamics 10

11 Development of ship propulsion Rowing Fastest and most reliable propulsion used from ancient times till 14th century Ancient Rome rowing galley could reach speed of 6 knots Sail propulsion Introduction of artillery and guns meant giving up rowing propulsion and substituting it with sails in the 14th century. Introduction of Marine Hydrodynamics 11

12 Development of ship propulsion Jet type propulsion Earliest propulsive device to use mechanics power Jet type propulsor that used a prime-mover and a pump 1661: patent to Toogood and Hayes in Great Britain 1852: Jet propulsion patent to Alexandre Hediard. Sucks water from the vessel s bottom, accelerated it and discharged through nozzle located at stern. Water-jet does not operate well at low speeds (low efficiency). Particularly good in shallow water. Q Introduction of Marine Hydrodynamics 12

13 Development of ship propulsion Paddle wheel (Siipirataspropulsio) Known already in ancient China First, propelled by human and animal (bulls) forces s Paddle wheel period of ship propulsion 1807: Cleremont vessel with a steam engine (L = 40 m, V max = 5 kn) Good in river boats Does not perform well in waves Introduction of Marine Hydrodynamics 13

14 Development of ship propulsion Screw propeller 1/2 Ancestor: Archimedean screw, Archimedean ( BC) 1840s Introduction to merchant and naval vessels The projected area of those propellers resembles present-day propellers Hydrofoil section (profile) was far from optimum Introduction of Marine Hydrodynamics 14

15 Development of ship propulsion Screw propeller 2/2 Limiting factor for the usage: steam engine 1897 Sir Charles Parsonin s Turbinia (L = 30 m) Achieved the speed of 34 kn 3 bladed tandem propellers rotated by 3 shafts Total power of the steam engines: 2000 hp Introduction of Marine Hydrodynamics 15

16 Development of ship propulsion Ducted propeller 1936: patent to Ludwig Kort in USA. Produces extra thrust, especially at low speeds. Duct length is similar to the radius of a propeller. Propeller locates in the middle of the duct Introduction of Marine Hydrodynamics 16

17 Development of ship propulsion CRP 1825: Jacob Perkins patent to contra-rotating propellers Mechanical problems prevented it to get popular. Nowadays: Popularity increases steadily (z-drive units). n U Q0 T0 Introduction of Marine Hydrodynamics 17

18 Development of ship propulsion Air-screw propulsion 18 th century: The idea was presented in France. Purpose: substitute sails. Used in hovercrafts ie air cushion vehicles Introduction of Marine Hydrodynamics 18

19 Outline: Introduction to propulsion General Development of the propulsors Momentum theory of propeller action Summary Introduction of Marine Hydrodynamics 19

20 On the momentum Principle Propellers derive their propulsive thrust by accelerating the fluid in which they work. This is in accordance with Newton s law of motion: Force is required to alter the existing state of motion of any material body in magnitude or direction. The action of any two bodies upon one another is equal and opposite. Introduction of Marine Hydrodynamics 21

21 Momentum theory of propeller action What do we learn by using this theory? Understanding and estimating the propeller action How does the efficiency depend on the loading of the propeller? Universal theory The propulsor does not need to be a screw propeller. Ideal conception of the propeller The propeller is regarded as a disk or a mechanism that imparts a sudden increase of pressure to the fluid that passes through it. The actual method by which it does so is ignored. Introduction of Marine Hydrodynamics 22

22 Momentum theory of propeller action Assumptions The propeller imparts a uniform acceleration to all the fluid passing through it. Thrust generated is uniformly distributed over the disk. Flow is frictionless and irrotational. Unlimited inflow to the propeller. Downstream Upstream Plane 3 Plane 2 Plane 1 Introduction of Marine Hydrodynamics 23

23 Momentum theory of propeller action An example of the propeller flow in reality Planar velocity Axial velocity Measurement Particle Image Velocimetry Introduction of Marine Hydrodynamics 24

24 Momentum theory of propeller action On the thrust T T = p A 0 p: Apply Bernoulli s equation p ρv2 = constant Streamline fore of the propeller plane Streamline aft of the propeller plane Introduction of Marine Hydrodynamics 25

25 Momentum theory of propeller action On the thrust T T = p A 0 p: Apply Bernoulli s equation p ρv A 2 = p ρ V A + U A 2 p ρ V A + U A0 2 = p ρ V A + U A 2 p = p p = 1 2 ρu A0 U A0 + 2V A T = pa 0 = ρu A0 V A U A0 A 0 Introduction of Marine Hydrodynamics 26

26 Momentum theory of propeller action On the thrust T Mass flow of water through the disk m = ρa 0 V A + U A Downstream Upstream Change of momentum must equal to the thrust T on the disk T = m V A + U A0 V A = m U A0 Plane 3 Plane 2 Plane 1 Introduction of Marine Hydrodynamics 27

27 Momentum theory of propeller action On the induced velocities U A and U A0 Two definitions of T T = mu A0 = ρa 0 V A + U A U A0 T = pa 0 = ρu A0 V A U A0 A 0 U A = 1 2 U A0 Introduction of Marine Hydrodynamics 28

28 Momentum theory of propeller action Efficiency of the propeller η I = useful work obtained work expended η I = P T P D Work done by the propeller in time unit (power) P T = TV A = ρa 0 U A0 V A U A0 V A Lost of the kinetic energy of the water passing through the disk P D = 1 2 m V A + U A mv A 2 = 1 2 ρa 0 V A + U A V A + U A0 2 V A 2 Introduction of Marine Hydrodynamics 29

29 Momentum theory of propeller action Efficiency of the propeller η I = useful work obtained work expended η I = P T P D η I = P T P D = V A V A U A0 = U A0 V A Introduction of Marine Hydrodynamics 30

30 Momentum theory of propeller action Efficiency of the propeller It is practical to express the efficiency as a function of the thrust loading coefficient T C T = 1 2 ρa 2 0V A T = pa 0 = ρu A0 V A U A0 A 0 C T = ρu A0 V A U A0 A 0 1 = U A0 2 ρa 2 0V A 2 V A U A0 V A U A0 V A = C T Screw propeller Paddle wheel Vertical axis propeller ruuvipotkuri vertikaaliakselipotkuri siipiratas vertical axis propeller - VAP Introduction of Marine Hydrodynamics 31

31 Momentum theory of propeller action Efficiency of the propeller It is practical to express the efficiency as a function of the thrust loading coefficient η I = P T P D = V A V A U A0 = U A0 V A U A0 V A = C T 1 η I = C T h I C T 100 Introduction of Marine Hydrodynamics 32

32 Outline: Introduction to propulsion General Forces acting on a ship Development of the propulsors Momentum theory of propeller action On the momentum theory On the propeller action Summary Introduction of Marine Hydrodynamics 33

33 Summary Describe the development of ship propulsion What features does a good propeller have? Explain the action of a propeller using the momentum theory of propeller action. When does a propeller has good efficiency? Introduction of Marine Hydrodynamics Aalto University 34

34 References Matusiak J (2010) Laivan kulkuvastus. M-289. Available in Noppa Lewis E.V., editor (1988) Principles of Naval Architecture, Second revision. Volume II. SNAME. Available in Knovel Introduction of Marine Hydrodynamics 35

35 Example on the prediction of the resistance Introduction of Marine Hydrodynamics Aalto University 36

36 On the resistance Introduction of Marine Hydrodynamics 37

37 On the resistance Introduction of Marine Hydrodynamics 38

38 Resistance Calculate the resistance and the effective power of a ship using Guldhammer-Harvald s method. ship speed: 19.5kn length L WL =96.62 m breadth B=10.66 m depth T=4.26 m longitudinal prismatic coefficient C P =φ=0.650 midship section coefficient C M =0.920 Assume that the resistance consists of frictional resistance, residual resistance (see diagrams in appendices 1 and 2) and model-ship correlation allowance. Calculate frictional resistance coefficient with ITTC-57-method. Model-ship correlation allowance is in this exercise C A = Wetted surface of ship hull can be approximated with S=2.65. The density of sea water is =1026kg/m 3. The kinematic viscosity of sea water: m 2 /s. More information: Guldhammer, H.E., Harvald, S.A.: Resistance and Propulsion of Ships (Kirjasto) Guldhammer, H.E., Harvald, S.A., (1974):"Ship Resistance, Effect of Form and Principal Dimensions, Revised". Akademisk Forlag, Copenhagen. Introduction of Marine Hydrodynamics 39